Background: In a series of experiments, we have shown that the doxapram HCl inhibited the cardiac conduction system under urethane anesthesia in the adult Wister rats. The purpose of the present study is to evaluate the effect of doxapram HCl on the cardiac conduction system under sevoflurane anesthesia which has been clinically used. Materials and Methods: ECG and respiratory movements were recorded by Biopac MP-35 system with a sampling frequency of 1000 Hz. The doxapram HCl (0.3-10 mg/kg) was repeatedly injected into the right femoral vein with an appropriate interval in each animal. The effect of the drug was evaluated by measuring RR, PQ and QT intervals of ECG at 3 min after administration of the drug. Results: 1) RR interval was dose-dependently prolonged with administration of the doxapram HCl. Administration of 10 mg/kg of the drug showed significant prolongation (0.168±0.012 sec) as compared with the control (0.159±0.011 sec). 2) PQ interval showed no change in any dose of the doxapram HCl. 3) QTc value was significantly prolonged by administration of the drug (0.147±0.015 sec with 3.0 mg/kg and 0.154±0.018 sec with 10 mg/kg) as compared with the control (0.138±0.011 sec). Conclusion: We should carefully pay an attention to QT prolongation when we use the doxapram HCl for an accelerant of respiration under the sevoflurane anesthesia. [J Physiol Sci. 2008;58 Suppl:S178]

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Cooling of myocardial tissue destabilizes spiral wave reentry through a prolongation of the action potential and a decrease in conduction velocity. We have recently demonstrated that moderate regional myocardial cooling (by ∼5°C) causes a significant decrease in the intensity of DC shocks required to terminate spiral wave reentry in the rabbit ventricle (Heart Rhythm 2006). In this study, we have investigated its underlying mechanisms in 2-dimensional rabbit ventricular myocardium by using high-resolution optical mapping. Application of high-intensity shocks caused an immediate termination of spiral wave reentry through a phase-resetting mechanism (mode-1 termination) regardless of absence or presence of regional cooling. Moderate-intensity DC shocks created multiple phase singularities and interactions of these shock-induced singularities with the stationary spiral wave (rotor) often resulted in delayed termination of reentry through unpinning of the rotor (mode-2 termination). In the presence of regional cooling, the mode-2 termination of spiral waves occurred with lower-intensity DC shocks. These results suggest that appropriate regional myocardial cooling facilitates DC shock-induced termination of spiral wave reentry through unpinning of rotors in the ventricular myocardium. [J Physiol Sci. 2008;58 Suppl:S178]

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A time- or frequency-domain analysis of RR interval variability has been generally used as an indirect estimate of cardiac autonomic activity to the sinoatrial node of the heart. The basic assumption for this analysis is that the variability of RR interval would be always coincident with the variability of PP interval. However, we have recently found that the variability of RR interval becomes much smaller during dynamic exercise than that of PP interval, despite the same shortened average interval. Thus, we hypothesized that a high frequency component (HF at 0.15-0.40 Hz) of PP interval variability, not RR interval variability, was a better estimate of cardiac vagal outflow. To test this hypothesis, the HF components of the power spectrums of PP and RR interval variability during dynamic exercise were assessed using a Wavelet transform. Nine athletes and six sedentary subjects performed ergometer exercise to increase heart rate (HR) to 160 beats/min from the baseline. During resting, HF of RR interval variability was coincident with that of PP interval variability. In contrast, although HF of RR interval variability decreased to nearly zero at 160 beats/min during exercise, HF of PP interval was considerably present. We conclude that cardiac vagal outflow to the sinoatrial node is better estimated by HF of PP interval variability. The conclusion leads to an idea that substantial cardiac parasympathetic activity exists at a higher HR during dynamic exercise. [J Physiol Sci. 2008;58 Suppl:S179]

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Heart rate (HR) during exercise is controlled by increases in cardiac sympathetic discharge and plasma catecholamines, and a decrease in cardiac parasympathetic discharge. However, their relative contribution remained little known. To examine their contribution to the exercise-induced tachycardia in conscious rats by adrenalectomy and autonomic blockades, we measured HR during treadmill exercise (20 m/min for 30 min) in conscious rats. HR was 365 bpm before and increased to 455 bpm during exercise in 4 intact rats. The baseline HR was increased to 423 bpm by atropine and decreased to 333 bpm by atenolol. The exercise-induced tachycardia was decreased by either atropine or atenolol, suggesting that cardiac sympathetic activation and adrenal secretion of catecholamines play a role in producing the exercise-induced tachycardia. To identify the relative contribution of adrenal catecholamines, we examined the effects of atenolol and atropine on the exercised-induced tachycardia in 2 adrenalectomized rats. The baseline HR and the exercise-induced increase in HR in adrenalectomized rats was the same as those in intact rats. The effect of atropine on the exercise-induced tachycardia was also similar with and without adrenalectomy, although atenolol more blunted the tachycardia by 65 bpm in adrenalectomized rats. The present results suggest that stimulation of cardiac sympathetic discharge plays a more important role in increasing HR during dynamic exercise rather than adrenal secretion of catecholamines. [J Physiol Sci. 2008;58 Suppl:S179]

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Positive chronotropy induced by β1-adrenergic stimulation is achieved by multiple interactions of ion channels and transporters in pacemaker cells. In order to investigate roles of the ion channels and transporters and their interactions in the chronotropy quantitatively, we updated our SA node cell model developed in 2003 and incorporated β1-adrenergic signaling cascade. Firstly, the validity of the model was reviewed by comparing behavior and parameters of the model with experimental data. Secondly, the response to β1-adrenergic stimulation was analyzed by isoprenaline (ISO) application, which enhanced multiple currents and increased firing frequency. From the analysis of enhanced currents during the stimulation, it was concluded that the L-type Ca²⁺ current (I_CaL), the sustained inward current (I_st) and the hyperpolarization-activated cation current (I_ha) played major roles in increasing the inward current during slow diastolic potential and thus increasing the firing rate. On the other hand, I_Ks was important to counterbalance increased inward currents especially in repolarizing phase of action potentials. The alteration of Ca²⁺ dynamics during the stimulation was also calculated in the model. It was suggested that the Ca²⁺ release from sarcoplasmic reticulum (SR) played a minor role in inducing chronotropic effect in our model. [J Physiol Sci. 2008;58 Suppl:S179]

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Sarcoplasmic reticulum (SR) functions (Ca²⁺ uptake, content, release and leakage) are modulated by β-adrenoceptor stimulation (ARS) through phosphorylation of phospholamban and/or ryanodine receptor. In this study, we investigated the effect of β-ARS on SR functions using saponin-treated mouse myocardium. Thin trabeculae obtained from mice hearts were skinned with saponin (50 μg/ml) after treatment with isoproterenol (Iso) (1 μM, 30 min) or without Iso as control preparations. For the estimation of each SR function, Ca²⁺ remaining in SR after various maneuvers was released by caffeine (50 mM) and measured with fluo-3 (30 μM). Ca²⁺ uptake was estimated by measuring Ca²⁺ in SR after Ca²⁺ was loaded into SR by applying the solution containing ATP (4 mM) at various Ca²⁺ concentrations (pCa 8-5.6) for different periods (10-120 sec). Ca²⁺ leakage was estimated by measuring the remaining Ca²⁺ in SR after washing SR with the solution containing EGTA for various durations (15-300 sec) after Ca²⁺ loading (pCa 6.2, 120 sec). Iso-treatment increased Ca²⁺ uptake rate but did not alter maximal Ca²⁺ content. On the other hand, Ca²⁺ leakage was accelerated after Iso-treatment. These effects of β-ARS on SR were blocked by protein kinase A (PKA) inhibitor H-89 (2 μM). Thus, the PKA-dependent phosphorylation of phospholamban and ryanodine receptor in SR accelerates the turnover of Ca²⁺ in the myoplasm. [J Physiol Sci. 2008;58 Suppl:S179]

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Introduction: The sympathetic nervous system modulates cardiac L-type Ca²⁺ channels through α₁- and β-adrenoceptors (ARs). We previously showed that α₁-AR stimulation alone potentiates L-type Ca²⁺ current (I_Ca) through α_1A-AR-Gq-PLC-PKC-CaMKII pathway (O-Uchi J. et al., PNAS, 2005 and J. Physiol. Sci., 2006 (Suppl)). However, the interaction of α₁- and β-AR signalings on I_Ca was not fully clarified. In the present study, we investigated the effect of α₁-AR stimulation on I_Ca in the presence of β-AR stimulation. Methods: Perforated patch was employed for recording I_Ca from isolated adult rat ventricular myocytes. Cells were at first superfused with 100 nM isoproterenol (Iso) for β-AR stimulation and then α₁-AR agonists were applied in the continuous presence of Iso. Results: The Iso-stimulated I_Ca was markedly inhibited by an α₁-AR agonist, 100 μM phenylephrine (Phe) (19.6±7.6%) (n=7). This effect was abolished by the application of an α₁-AR antagonist, 1 μM prazosin. The α_1A-AR selective antagonist, 2 μM WB4101 or 100 nM 5-methylurapidil also blocked this inhibitory effect, but an α_1B-AR selective antagonist, 100 nM L-765,314 did not. The α_1A-AR selective agonist, 100 nM A61603 showed 18.3±6.7% inhibition of Iso-stimulated I_Ca (n=7) as in the case of Phe, confirming that α_1A-AR is involved in this mechanism. Conclusion: α_1A-AR stimulation inhibits I_Ca in the presence of β-AR stimulation, which is opposite to the effect observed in the absence of β-AR stimulation. [J Physiol Sci. 2008;58 Suppl:S180]

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Although α-adrenergic receptors are distributed throughout the nucleus tractus solitarii (NTS) but the functional significance of the receptors in regulating cardiovascular system is not fully understood. In this study, the cardiovascular effects of α-1 adrenergic receptor agonist (phenylephrine) microinjected into the two different sites of the NTS were evaluated in urethane anesthetized rats. Phenylephrine injected bilaterally into the rostral part of the NTS, wherein injection of L-glutamate causes typical depressor responses, elevated mean arterial blood pressure (MAP) and heart rate (HR) but opposing responses such as decreased MAP and HR were observed when injected into the caudal commissural NTS. The elevation or depression of MAP and HR by phenylephrine was dose dependent (0,6,12, and 24 nmol) and remained for more than 15 min. Pretreatment with α-adrenergic receptor antagonist, phentolamine (1 nmol) into the NTS abolished the phenylephrine induced elevation and depression of MAP and HR. These results suggest that the pressor or depressor effects of phenylephrine injected into the NTS may be site specific. [J Physiol Sci. 2008;58 Suppl:S180]

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Objective: Autonomic nervous activity is altered under microgravity. Cardiac response to autonomic regulation is mostly determined by β-adrenergic receptors/cAMP signal that is regulated by adenylyl cyclase (AC). We thus examined the role of a major cardiac AC isoform, type 5 AC (AC5), in the autonomic regulation of the heart under microgravity induced by parabolic flights. Methods: We used transgenic mice with either disrupted (AC5KO) or overexpressed AC5 in the heart (AC5TG), and analyzed heart rate variability during parabolic flight. Results: The standard deviation of normal R-R intervals, a marker of total autonomic variability, was significantly greater under microgravity in AC5KO while no significant changes in WT and AC5TG. LF (low frequency)/HF (high frequency), a marker of sympathetic activity, became significantly lower under microgravity in WT and AC5TG while there was no such a decrease in AC5KO. Normalized HF, a marker of parasympathetic activity, became significantly greater in WT under microgravity, and became even greater in AC5TG, while no such increase in AC5KO. Conclusions: Putting together, changes in autonomic indexes in response to microgravity were augmented in AC5TG while attenuated in AC5KO, suggesting that AC5 plays a major role in determining the magnitude of cardiac responses to autonomic regulation under microgravity. [J Physiol Sci. 2008;58 Suppl:S180]

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The muscarinic potassium (K_ACh) channels mediate a rapid heart rate (HR) change and contribute to the steady-state HR reduction during vagal stimulation (VS). The present study aimed at elucidating the effects of background sympathetic tone on the negative chronotropic effect mediated by the K_ACh channels. In anesthetized rabbits (n=6) with sinoaortic denervation and vagotomy, we estimated dynamic and static characteristics of the HR response by using random binary VS (0-10 Hz) and stepwise VS (5, 10, 15 and 20 Hz). In the dynamic characteristics, a selective K_ACh channel blocker tertiapin decreased the dynamic gain (from 4.8±1.3 to 2.1±0.8 bpm Hz⁻¹, P<0.01, mean±SD) and the corner frequency (from 0.24±0.03 to 0.06±0.01 Hz, P<0.01). Under a concomitant cardiac sympathetic stimulation (5 Hz), tertiapin also decreased the dynamic gain (from 7.4±1.2 to 3.5±1.0 bpm Hz⁻¹, P<0.01) and the corner frequency (from 0.23±0.06 to 0.06±0.02 Hz, P<0.01). In the static characteristics, tertiapin attenuated the magnitude of steady-state HR reduction during 20-Hz VS by 60±24 bpm (from 91±16 to 30±12 bpm, P<0.01). Under the concomitant sympathetic stimulation, tertiapin also decreased the magnitude of steady-state HR reduction during 20-Hz VS by 63±17 bpm (from 130±27 to 67±13bpm, P<0.01). In conclusion, the K_ACh channels significantly contribute to the dynamic and static heart rate responses to VS regardless of background sympathetic tone. [J Physiol Sci. 2008;58 Suppl:S180]

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Central command activates brain stem circuits controlling cardiovascular function during exercise. Although sympathetic outflows to the heart and the kidneys increased immediately at the onset of dynamic exercise in conscious cats, it was unknown how central command regulated catecholamine secretion from the adrenal medulla. We, therefore, examined the effect of electrical stimulation of the subthalamic locomotor region (SLR) on adrenal pre- and postganglionic nerve activity (AdSNA) and the secretion of catecholamines from the adrenal medulla in urethane and α-chloralose anesthetized rats. Renal sympathetic nerve activity (RSNA), mean arterial blood pressure (MAP), heart rate (HR), adrenal venous blood flow, and muscle blood flow were also measured. Stimulation of SLR is known to evoke locomotion in decerebrate animals. Stimulation of SLR for 30 s at a 100 µA current intensity evoked vasodilatation in the triceps surae muscle as well as increases in MAP and HR. SLR stimulation abruptly increased pre- and postganglionic AdSNA and RSNA. A rapid increase in adrenal epinephrine and norepinephrine output was observed during the stimulation, but adrenal venous blood flow did not change during the stimulation. Interestingly, the secretion level of epinephrine returned to the baseline levels within 30 s from the end of stimulation. In conclusion, stimulation of SLR immediately activates preganglionic AdSNA, which in turn causes an abrupt secretion of catecholamines from the adrenal medulla. [J Physiol Sci. 2008;58 Suppl:S181]

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"Alternans" is an arrhythmia exhibiting alternating amplitude or interval from beat to beat on the electrocardiogram and was first described in 1872 by Traube. Recently alternans was finally recognized as the harbinger of a cardiac disease when an ischemic heart exhibited alternans. In animal models we detected alternans at various experimental conditions, including the heart with injury, the heart under emotional stress and the heart of a dying specimen. We have tested the detrended fluctuation analysis (DFA) on alternans and revealed that in both, animal models and humans, alternans rhythm lowers the scaling exponent that was computed by the DFA. We concluded that the scaling exponent can reflect a risk for the "failing" heart, especially when the low scaling exponent and alternans are concurrently present. [J Physiol Sci. 2008;58 Suppl:S181]

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To elucidate the postnatal development of aortic baroreflex afferents, we examine the cross sections of the left aortic nerves (ANs) in rat neonates with light- and electron-microscopy. We took the pictures of transverse cross sections of left ANs and made these montages (approx. x13K at final magnification) after the observation of semi-thin sections for light microscopy. The number of unmyelinated fibers of left ANs was 258, 594, 454 or 841 in the 9 days old group (n=4), and that in the 25 days old group (n=5) was 87,187, 212, 407 or 424, respectively. These results show that there is a lot of unmyelinated fiber in the ANs in the early stage of postnatal growth, suggesting that these fibers seem to be eliminated partly in accordance with the functional development of baroreflex in the rat. [J Physiol Sci. 2008;58 Suppl:S181]

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We have recently reported that mechanical stretch of skeletal muscle in cats is capable of evoking the reflex cardiovascular responses, which are suppressed in the conscious condition but exaggerated by anesthesia. To test the hypothesis that the reflex cardiovascular changes during passive limb movement in humans are also suppressed in the awake condition, the cardiovascular responses to supine passive leg cycling were compared between the awake and sleep conditions in nine subjects. In the awake condition, heart rate (HR), stroke volume (SV), cardiac output (CO) increased slightly in response to passive cycling for 30s at 60 rpm and total peripheral resistance (TPR) decreased slightly. Mean arterial blood pressure (MAP) did not change during passive cycling. On the other hand, the increases in HR and CO and the decrease in TPR during passive cycling were largely enhanced during sleep in the daytime. When the HR response to passive cycling were examined at non-REM and REM sleep overnight, the increase in HR was augmented during non-REM sleep, depending on the sleep depth. It was interesting that the increase in HR during passive cycling was peaked during REM sleep. It is concluded that a muscle mechanoreflex induced during passive cycling is suppressed in the awake condition but exaggerated by non-REM and REM sleep in humans. [J Physiol Sci. 2008;58 Suppl:S181]

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We examined the effect of 17β-estradiol replacement on the blood pressure regulatory response to central and systemic adminsistration of angiotensin II (ANGII) in ovariectmized rats. Seven-week-old female rats were ovariectomized and were assigned into estradiol (E2)- and choresterol (vehicle)-treated groups. Two weeks after the ovariectomy, we measured arterial pressure and heart rate response to icv injection of ANGII (5 ng) and to systemic injection of ANGII (50, 100, and 150 ng/kg) under urethan-chloralose anesthesia. We also examined the blood pressure response to iv injection of phenylephrin (PE). The peak increase in mean arterial pressure (MAP) in response to icv ANGII was not different between E2- and Vehicle-treated rats. MAP returned to preinfusion level within 10 min in E2-treated rats, but MAP remained increased for 30 min in vehicle-treated rats, while heart rate response was similar between two groups. The MAP response to iv ANGII was not affected by E2 replacement, while the decrease in heart rate induced by iv ANGII was significantly attenuated by E2 replacement, suggesting that vasoconstrictor response and baroreflex response controlling heart rate are attenuated by E2 replacement. MAP and heart rate responses to systemic PE was not different between two groups. These results suggest that E2 specifically affects ANGII-associated blood pressure regulation. [J Physiol Sci. 2008;58 Suppl:S182]

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At rest, respiratory-induced changes in the partial pressure of arterial carbon dioxide (PaCO₂) play a major role in the regulation of cerebral blood flow (CBF). Changes in CBF affect stability of the ventilatory (V_E) responsiveness to CO₂ via alterations in the degree of washout in central chemoreceptor hydrogen [H⁺] . No data, however, is available on the comparison of the CBF and V_E responsiveness to PaCO₂ at rest and during exercise. To describe the CBF and V_E reactivity to PaCO₂, we measured the blood velocity in the middle cerebral artery (MCAV) in six males under various V_E conditions by controlling ventilation for 12 min at rest (V_E = 9 to 38 L/min) and during 40 W ergometer cycling (V_E = 12 to 68 L/min). The MCAV and V_E reactivity to PaCO₂ at rest was similar to that during exercise (-0.9 ± 0.3 cm/s/mmHg vs. -1.0 ± 0.5 cm/s/mmHg, respectively, P>0.05; mean ± SEM). The intercept of MCAV with PaCO₂ tended to be greater during exercise than at rest (83 ± 11 vs. 66 ± 9 cm/s when V_E = 0 L/min: P=0.1); this finding indicates that the upward shift of MCAV reactivity to V_E may have a role in washing out CO₂ from the brain, potentially due to the greater amount of CO₂ production during exercise. [J Physiol Sci. 2008;58 Suppl:S182]

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The hemodynamic mechanism for anaphylactic shock is not fully clarified. We determined the change in peripheral vascular resistances during anaphylactic hypotension in anesthetized rats. We measured the mean circulatory filling pressure (Pmcf) using the mechanical occlusion method of inflation of the right atrial balloon, along with systemic arterial pressure (Psa), central venous pressure (Pcv) and portal venous pressure (Ppv). Cardiac output (CO) was also measured with the thermodilution method. From these hemodynamic variables we calculated the total peripheral (Rt) and venous (Rv) resistances during anaphylactic hypotension in anesthetized rats. These hemodynamic variables were compared with those in the hemorrhagic shock. After an intravenous injection of antigen ovalbumin 0.6mg in sensitized rats, Psa decreased from 119±4 to 43±2 mmHg, CO decreased from 84.5±5.7 to 37.8±2.1 ml min⁻¹, Pcv decreased from 0.9±0.1 to 0.1±0.1 mmHg, and Pmcf also decreased from 6.0±0.2 to 5.2±.3 mmHg. Thus, the venous resistance (Rv) increased from 0.06±0.05 to 0.15±0.02 mmHg ml⁻¹ min, but Rt did not significantly change. Ppv also increased from 5.6±0.5 to 21.5±0.9 mmHg. During hemorrhagic shock Psa decreased in the manner similar to anaphylactic shock; however, Rv did not significantly change and Ppv decreased. In conclusion, in rat anaphylactic shock, a substantial increase in Rv presumably due to hepatic venoconstriction may decrease venous return, resulting in systemic hypotension. [J Physiol Sci. 2008;58 Suppl:S182]

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We investigated the roles of nitric oxide (NO) and isozymes of NO synthase in rat anaphylactic hypotension. Effects of inhibitors of endothelial NOS (eNOS), inducible NOS (iNOS) and neuronal NOS (nNOS), using N^G-nitro-L-arginine methyl ester (L-NAME; 10 mg/kg), aminoguanidine (100 mg/kg), and 7-nitroindazole (7-NI; 50mg/kg), respectively, were determined on the antigen-induced hypotension and portal hypertension in conscious SD rats sensitized with the ovalbumin antigen. Systemic arterial pressure (Psa) and portal venous pressure (Ppv) were directly and simultaneously measured. The control rats injected with antigen showed a decrease in Psa along with an increase in Ppv, but did not die within 24 hrs after antigen injection. In rats pretreatment with L-NAME, anaphylactic hypotension was attenuated only at the early stage of 10 min after antigen, but portal hypertension was augmented, resulting in fatal outcome within 12 hr after antigen. In contrast, the pretreatment with a nNOS inhibitor, 7-NI, substantially attenuated anaphylactic hypotension over 20 min after antigen, while iNOS inhibitor of aminoguanidine did not affect it. In conclusion, NO derived from eNOS and nNOS, but not iNOS, is involved in anaphylactic hypotension, but inhibition of eNOS is lethal in conscious rats. [J Physiol Sci. 2008;58 Suppl:S182]

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It is still unclear to what extent augmentation index (AIx) of peripheral pressure waves reflects that of central pressure waves in response to change in blood pressure level in the presence of atherosclerosis. We investigated subservient relationship between AIxs from central and peripheral pressure waves in the normal and Kurosawa and Kusanagi-hypercholesterolemic (KHC) rabbits aged 12 months. Changes in pressure waves in response to intravenous infusion of angiotensin II (Ang II) and sodium nitroprusside (NTP) were simultaneously recorded at the ascending aorta (AA) and distal end of the right brachial artery (Br) using two catheter-tip transducers under pentobarbital anesthesia. AIx at Br changed in parallel with that at AA during pressor and depressor responses to Ang II and NTP in the two rabbit groups, respectively. AIxs at AA and Br were significantly greater in the KHC rabbit group than in the control rabbit group at the same high blood pressure level during Ang II infusion. We can conclude that changes in AIx of the central pressure waves induced by vasoactive agents are followed by those of the peripheral pressure waves in the two rabbit groups, and that AIx at the peripheral artery well reflects the increased AIx at the central artery due to atherosclerosis in KHC rabbits. [J Physiol Sci. 2008;58 Suppl:S183]

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We reported that the splanchnic blood flow increases within a minute after the beginning of a meal. To investigate the role of chewing and taste, we characterized responses in peripheral blood flow during sham feeding. After five minutes of baseline measurement in the over night fasting state, fifteen healthy subjects repeated chewing and expectorating 60 g solid meal for 4 minutes (sham feeding). We measured mean arterial pressure (MAP), blood velocity (BV) in celiac artery (CA), and blood flow (BF) in forearm. To assess the vascular resistance (VR), the MAP was divided by the BV in CA and the BF in forearm. The MAP did not significantly change throughout the trial. The BV in CA and the BF in forearm significantly decreased at the 1st minute of the sham feeding from the baseline (from 0.41 ± 0.02 to 0.37 ± 0.02 m/s, from 4.6 ± 0.8 to 2.6 ± 0.2 ml/min/100g tissue, mean ± SEM, p < 0.05). The VRs in CA and forearm significantly increased at the 1st minute of the sham feeding from the baseline (from 217 ± 14 to 246 ± 10 mmHg/m/s, from 26 ± 4 to 38 ± 4 mmHg/ml/min/100g tissue). The BV in CA significantly increased at the 3rd minute of the sham feeding from the baseline (from 0.41 ± 0.02 to 0.44 ± 0.03 m/s). These results suggest that the sham feeding, i.e., chewing and taste, increases BF in splanchnic organs without the arrival of chyme at corresponding organs. [J Physiol Sci. 2008;58 Suppl:S183]

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We have demonstrated that the vestibular system has a significant role in the arterial pressure (AP) response during gravitational change. The vestibular system is known to be highly plastic. It has been well reported the plasticity of the vestibulo-ocular and vestibulo-spinal reflex, however, it is still unclear the plasticity of the vestibulo-cardiovascular reflex. The aim of the present study was to examine whether the hypergravity environment alters the AP response via the vestibular system in conscious rats. As the gravitational input, the linear acceleration was employed. The AP and renal sympathetic nerve activity (RSNA) during ± 1 G linear acceleration was measured in conscious rats reared under usual 1 G environment (n = 12) or 2 weeks 3 G environment (n = 8). Six directions of the linear acceleration were employed; i.e., tail-to-nose, nose-to-tail, left-to-right, right-to-left, ventral-to-dorsal and dorsal-to-ventral. The AP of the 1 G rat was increased by 22 ± 1 mmHg (tail-to-nose), 17 ± 1 mmHg (nose-to tail), 19 ± 1 mmHg (left-to-right), 20 ± 1 mmHg (right-to-left), 14 ± 1 mmHg (ventral-to-dorsal) and 16 ± 1 mmHg (dorsal-to-ventral). This pressor response was significantly attenuated in the 3 G rat. However, there was no significant difference in the pressor response during air jet stimulation between 1 G and 3 G rats. These results indicate that the AP response via the vestibular system was specifically attenuated by maintaining under hypergravity environment. [J Physiol Sci. 2008;58 Suppl:S183]

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Serotonin constricts directly a vascular smooth muscle, and indirectly dilates it through endothelium-dependent mechanism. Many study support that vasoresponses to serotonin are mainly related to some subtypes of 5-HT receptors; 5-HT_2A, 5-HT_1B and 5-HT_1D. Functional roles of these serotonin receptors in cerebral artery, including their agonist and antagonist, have not been fully clarified. In this study, we intended to examine the vascular reaction in rat and rabbit cerebral arteries to sarpogrelate hydrochloride, a 5-HT_2A receptor antagonist, in the absence of serotonin. Cerebral artery segments obtained from posterior cerebral arteries (100-300 μm in diameter) were cleaned out of blood, cannulated on glass pipettes and pressurized at 60mmHg. Arteries showed stable myogenic tone in a myograph chamber filled with oxygenated Krebs solution at 37°C and pH7.4. We measured artery diameter under administration of sarpogrelate hydrochloride at varying concentration from 10⁻⁹ to 10⁻³M. In rats, sarpogrelate hydrochloride at concentration of 10⁻⁸-10⁻⁵M did not show any effect. On the other hand, in rabbits, sarpogrelate hydrochloride caused approximately 10% vasoconstriction at 10⁻⁹-10⁻⁴M and approximately 20% vasodilatation at 10⁻⁵-10⁻³M. These data suggest that sarpogrelate hydrochloride may have some direct effects on vascular smooth muscle in rabbits per se but not in rat. [J Physiol Sci. 2008;58 Suppl:S183]

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In this study on anesthetized rabbits, we recorded from Purkinje cells in and around the folium-p on the left side, and determined the effects of defense area stimulation during the 1 sec poststimulation period of the peristimulus histogram. With stimulation of hypothalamus, about 40% of the cells tested were excited and about 45% inhibited. With PAG stimulation, about 30% of the cells tested were excited and about 70% inhibited. The excitation was blocked by iontophoretically applied orexin receptor-1 antagonists and was markedly depressed after orexinergic neurons were lesioned using saporin conjugated with orexin-B. We confirmed the presence of orexin-immunopositive neurons in the hypothalamus and their axons in the PAG and flocculus, in rabbits. These results indicate that axons of orexinergic hypothalamic neurons extending through PAG reach the flocculus and mediate excitation to folium-p Purkinje cells. DiI labeling showed that folium-p Purkinje cells project to the lateral parabrachial nucleus known as a sensitive pressor site. We propose the folium-p as a specific microzone involved in the brainstem cardiovascular control system. [J Physiol Sci. 2008;58 Suppl:S184]

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The deletion mutation of a single lysine residue (ΔK210) in cardiac troponin T is known to cause a form of familial dilated cardiomyopathy CMD1D (OMIM 601494), which is associated with the development of ventricular tachycardia and torsades de pointes that lead to suddern cardiac death. Using a knock-in (KI) mouse model of CMD1D, in which the ΔK210 mutation of cardiac troponin T was incorporated by gene targeting, electrophysiological properties of their ventricular cells were studied using the whole-cell clamp technique under physiological conditions. In the homozygous KI mice, the cells exhibited the action potentials with a plateau phase that had more depolarized peak level and a longer duration than those observed in the cells from wild-type (WT) mice. Also in the KI cells, application of isoproterenol induced early after depolarization and abnormal automaticity, neither of which occured in the WT cells. In the membrane current of the KI cells, peak amplitude of the transient outward K current was smaller, and the inward Na/Ca exchange current associated with the Ca transient was larger than those in the WT cells. On the other hand, no obvious change was observed in the peak amplitude of L-type Ca current. The observed changes in the membrane currents were consistent with the altered action potentialwaveform and the development of the arrhythmogenic afterpotentials in the KI cells. [J Physiol Sci. 2008;58 Suppl:S184]

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It has been generally believed that cardiomyocytes (CMs) are terminally differentiated cells and have little ability to proliferate. Consequently, acutely injured hearts do not regenerate, and develop fibrosis and scarring. It has been previously reported that the mammalian heart induces CMs- proliferation after injury but the rate of proliferation is too low to repair the heart. In addition, recent studies have shown that co-treatment of CMs with FGF1 and p38 MAPK inhibitor (p38i) induces proliferation of cardiomyocytes. However, the detailed mechanisms for the proliferation ability of CMs have not been fully understood. In this study, we have tried to characterize changes in the proliferation ability by co-treatment with FGF1 and p38i. In addition, we also performed immunocytochemical and Western blot analyses to identify the expression and distribution of connexin 43, a primary gap junction protein in CMs. Finally, we examined changes in the spontaneous beating of CMs by co-treatment with FGF1 and p38i. The present findings are expected to develop novel approaches for the regeneration of the heart after injury. [J Physiol Sci. 2008;58 Suppl:S184]

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The aim of the present study was to prove the different energetics in isoproterenol-induced hypertrophied hearts compared to normal hearts. Myocardial O₂ consumption per minute (mVO₂) in myocardial slices was measured without and with 1-Hz field stimulation (stim.). mVO₂ without stim. corresponds to basal metabolic mVO₂. Delta mVO₂ (= mVO₂ with stim.-mVO₂without stim.) corresponds to O₂ consumption in excitation-contraction (E-C) coupling. Basal metabolic mVO₂ was significantly smaller but delta mVO₂ was significantly larger in the hypertrophy. Na⁺-Ca²⁺ exchange (NCX1) current was markedly increased associated with depressed sarcoplasmic reticulum Ca²⁺ ATPase (SERCA2) activity due to decreased phospho-Ser¹⁶ phospholamban expression, resulting in the increase of delta mVO₂. Since the NCX1 protein expression level did not increase, the marked increase in NCX1 current is attributable, at least in part, to attenuation of the intrinsic inactivation mechanisms of NCX1. It is plausible that decreased basal metabolic mVO₂ is due to depressed Na⁺/K⁺ ATPase (NKA) expression and/or activity because of phospholemman overexpression in this hypertrophy. However, measured NKA current was not decreased. We concluded that the different origin of the O₂ consumption in E-C coupling in the hypertrophy was derived from decreased SERCA2 activity (1ATP: 2Ca²⁺) and increased NCX activity coupled to NKA activity (1ATP: Ca²⁺). [J Physiol Sci. 2008;58 Suppl:S184]

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To study electrogenecity and voltage-dependence of mitochondrial Na⁺-Ca²⁺ exchange (NCX_mit), we measured mitochondrial membrane potential (ΔΨ_mit) and mitochondrial Ca²⁺ (Ca²⁺_mit) using TMRE and Rhod-2, respectively, in permeabilized rat ventricular myocytes. The induction of forward mode of NCX_mit depolarized ΔΨ_mit in the mitochondria preloaded with 300 nM Ca²⁺, when the respiratory chain was suppressed. On the other hand, ΔΨ_mit hyperpolarized when the reverse mode of NCX_mit was induced by applying 600 nM Ca²⁺ under the conditions that mitochondrial Ca²⁺ uniporter was suppressed by ruthenium red and that ΔΨ_mit was depolarized by FCCP. These results indicated that NCX_mit is electrogenic. In agreement with the above findings, applying 600 nM Ca²⁺ augmented Ca²⁺_mit by about 500% when ΔΨ_mit was depolarized by FCCP + oligomycin or antimycin A + oligomycin, while it did not induce significant change in Ca²⁺_mit when ΔΨ_mit was intact. However, the ΔΨ_mit depolarization did not significantly affect Ca²⁺ efflux rate via the forward mode of NCX_mit in mitochondria preloaded with 300 nM Ca²⁺. Our computer simulation supported the electrogenic and voltage-dependent property of NCX_mit and suggested that the net Ca²⁺ efflux via the forward mode largely saturated at negative ΔΨ_mit when Ca²⁺_mit is relatively low. It was concluded that NCX_mit is electrogenic and voltage-dependent. [J Physiol Sci. 2008;58 Suppl:S185]

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The hcn4 gene encodes the hyperpolarization activated nucleotide-gated cation channel, which is well known as cardiac pacemaker channel and specifically expressed in the sinoatrial node. However, its gene regulatory mechanism is still unclear. To examine the cis-regulatory sequences responsible for spatiotemporal hcn4 expression, we focused the evolutionally conserved non-coding sequences (CNS), which are often involved in the regulation of gene expression. The VISTA Enhancer Browser identified 16 conserved regions (CNS1-16) within the hcn4 gene locus, their enhancer effect on the activity of hcn4 minimal promoter were investigated using neonatal rat cardiac myocytes. The 160 bp fragment termed CNS13 mediated a prominent enhancer activity, more than 30-fold increase compared to the hcn4 promoter activity. We screened transcription factor binding motifs in the sequence of CNS13 by using the TRANSFAC database, and found putative AP1- and MEF2-biding sequences. A mutation in either the AP1- or MEF2-binding sequences significantly reduced the transcriptional activity of CNS13 reporter construct, and a double mutation completely abolished the enhancer activity in cardiac myocytes. We also confirmed the protein bindings to AP1- and MEF2-binding sequences within the CNS13 by EMSA. Our results suggest that a novel enhancer containing AP1- and MEF2-site may play a pivotal role for the hcn4 expression, and present a perspective for the mechanisms of cardiac electrophysiological differentiation. [J Physiol Sci. 2008;58 Suppl:S185]

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The aim of this study was to examine how cardiac gene transfer of sarcoplasmic reticulum calcium-ATPase (SERCA2a) can influence left ventricular (LV) mechanoenergetics in normal rats. Wistar rats were randomized to receive an adenovirus carrying either SERCA2a or β-galactosidase (βgal), or saline by a catheter-based technique. LV mechanical and energetics was analyzed in cross-circulated heart preparations 2-3 days after the infection. "SERCA2a" group showed the upward-shifted end-systolic pressure-volume relation, higher end-systolic pressure at 0.1 ml of intraballoon water and higher equivalent maximal elastance, i.e., the enhanced LV contractility, compared with "Normal", "βgal" and "Saline" groups. Moreover, faster LV relaxation rate was found in "SERCA2a" group. There was no significant difference in relation between myocardial oxygen consumption per beat and systolic pressure-volume area among all groups. Finally, oxygen cost of LV contractility in "SERCA2a" group was decreased to subnormal levels, but in "βgal" and "Saline" groups it remained unchanged. This lowered oxygen cost of LV contractility in "SERCA2a" hearts indicates energy saving in calcium handling during excitation-contraction coupling. Thus, the overexpression of SERCA2a was capable of transforming the normal energy utilization into a more efficient state in calcium handling, and super-inducing the supranormal contraction/relaxation due to the enhanced calcium handling. [J Physiol Sci. 2008;58 Suppl:S185]

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Sarcalumenin (SAR), a Ca²⁺-binding protein located in the longitudinal sarcoplasmic reticulum (SR), interacts with cardiac SR Ca²⁺-ATPase (SERCA2a) to modulate its activity and expression. We have demonstrated that SAR deficiency resulted in mild cardiac dysfunction in young mice (JBC 2005). Since it is well known that SERCA2a activity is decreased with aging, we examined the effects of aging on cardiac function in SAR knockout mice (SAR-KO). Cardiac function assessed by in vivo hemodynamic study and the expression levels of SERCA2a protein were progressively decreased in senescent SARKO (n=13) when compared with senescent wild-type (WT) (n=12) or young SARKO (4month old, n=12). LV dp/dtmax (mmHg/s) was 3897 ± 134, 7091 ± 657, and 6836 ± 298 in senescent SARKO, senescent WT, and young SARKO, respectively. The expression levels of SERCA2a protein (% of young WT) were 28 ± 8, 84 ± 17, and 44 ± 17 in senescent SARKO, senescent WT, and young SARKO, respectively. Interestingly, downregulation of SAR preceded downregulation of SERCA in aging cardiac muscles of wild-type mice . These findings indicated that SAR plays a critical role in age-dependent reduction in cardiac function and SR Ca²⁺ reuptake. [J Physiol Sci. 2008;58 Suppl:S185]

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Hypovolemic shock arising during ultrafiltration in hemodialysis patients is one of the most important cardiovascular complications. To maintain mean arterial pressure (MAP), iso- or hyperosmotic solutions are intravenously adminstered to supplement or expand plasma volume. To examine a difference among the hemodynamic responses evoked by rapidly infusing such iso-osmotic solutions, we measured the changes in central venous pressure (CVP), MAP, and heart rate (HR) during acute volume expansion by a Ringer's solution (Ringer) or 5% D-glucose solution (glu) with a volume of 2% body weight in anesthetized rats. The infusion of the Ringer increased MAP gradually, depending upon a rise in CVP during volume expansion. In contrast, during infusion of a 5% D-glu, there were no significant changes in CVP and MAP. Furthermore, to determine whether no significant homodynamic responses by 5% D-glu was due to glucose metabolism, we examined the hemodynamic responses during infusion of 5% L-glu which lacked physiological glycolysis metabolism. There were no significant differences in the CVP and MAP responses between 5% D- and L-glu. Taken together, the Ringer was iso-osmotic and had the similar electrolyte concentrations as the interstitial fluid. On the other hand, the glu had a chemical gradient of glucose against the interstitial fluid, which might rapidly spread into the interstitial space. The above characteristics of the iso-osmotic solutions may explain the different hemodynamic responses. [J Physiol Sci. 2008;58 Suppl:S186]

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The high concentration of Mg (HMg) during hypoxia or ischemic post-conditioning (IPT) shows the protective effects on the cardiac hypoxia-reoxygenation injury. We examined if the combination of HMg with IPT (HMg+IPT) potentiates the protective effects on the cardiac hypoxia-reoxygenation injury. Male SD rat hearts were excised and perfused with Langendorff manner. After stabilization, heart was made hypoxic for 45 min and reoxygenated for 30 min. In control, the Mg concentration was 1.2 mM and in HMg group it was 6 mM during hypoxia. IPT was 3 cycles of 10 sec ischemia and 10 sec reperfusion before reoxygenation. The left ventricular developed pressure and heart rate were monitored throughout the experiments. At various timing of the experiment, perfusion was stopped and heart tissue was fixed to examine mitochondrial ultrastructure by electron microscopy. In HMg and IPT groups, the recovery levels of pressure rate product (%PRP) by reoxygenation were higher than that of control group. In HMg+IPT group,%PRP was significantly higher than that of HMg, IPT and control group. Mitochondria were swollen by hypoxia and incompletely recovered by reoxygenation. However, in HMg, IPT and HMg+IPT groups, the structure recovered to almost normal. These results suggest that HMg during hypoxia with IPT potentiate protective effects on myocardium and facilitates the functional recovery of the hearts. [J Physiol Sci. 2008;58 Suppl:S186]

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Magnesium (Mg) is involved in development of metabolic syndrome (diabetes mellitus, ischemic heart disease, lipid metabolism etc.). We reported that 1) hypoxic condition decreases intracellular Mg concentration, and reoxygenation further decreases it, 2) intracellular Mg is important to maintain the cardiac function. Insulin facilitates the incorporation of Mg into cardiac myocyte glucose-dependently. We hypothesized that application of insulin during hypoxia could increase intracellular Mg concentration and improve the hypoxia-reoxygenation injury. We examined whether hypoxia-reoxygenation injury could be inhibited by insulin using Langendorff perfused rat heart model. Under hypoxic condition (30 min), application of insulin (1 mU/ml) did not improve the recovery of cardiac function and cardiac damage by reoxygenation (30 min). When insulin was applied during reoxygenation, the recovery of pressure-rate product (PRP) at 30 min was better (73.9±5.4%) than that of time-matched control (60.2±3.4%, p<0.05), but elevation of left ventricular end-diastolic pressure (LVEDP) and coronary perfusion pressure (CPP) were not inhibited. Although hypoxic perfusion in the presence of glucose (45 min) induced elevation of LVEDP and CPP, application of insulin in this condition inhibited their elevation during hypoxic perfusion, and improved the recovery of PRP and cardiac damages by reoxygenation. We conclude that insulin can protect the cardiac function from hypoxia-reoxygenation injury, which mechanisms are 1) cardioprotective effects by Mg, and 2) acceleration of glucose uptake by insulin. [J Physiol Sci. 2008;58 Suppl:S186]

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Bacgroud: Acute hypoxia is one of life threatening event. To test the effect of hypoxia on AMI in beating rat hearts with X-ray-diffraction (XRD) analysis using SPring-8. Methods: Eight isolated isovolumically contracting rat hearts were paced at 120 bpm after complete heart block, mounted so that the X-ray beam (15.0 keV) passed the deeper layer of left ventricular (LV) free wall, and perfused with Tyrode solution bubbled with 100% oxygen (Normo) and 100% Nitrogen (Hypo). We recorded XRD images and LV pressure (LVP) at End-diastolic LVP (EDP) of 0 and 20 mmHg. We compared the amount of AMI from the reduction of intensity ratio of inner and outer equatrial reflections and developed LVP during contraction. Results: During normoxia, increasing EDP significantly increased developed LVP (EDP0:104±26 vs EDP20:141±25, p<0.01) accompanied with significantly increased AMI (1.05±0.12 vs 1.38±0.21, p<0.01). During hypoxia, developed LVP and AMI did not show significant difference compared with those at EDP of 0 mmhg during normoxia. However, increasing EDP during hypoxia significantly decreased developed LVP (96±16 vs 72±13, p<0.01) without significant change in AMI (0.93±0.23 vs 0.97±0.32, NS). Conclusion: Hypoxia itself does not attenuate the crossbridge formation at EDP of 0 mmHg, but significantly attenuates it at EDP of 20 mmHg. [J Physiol Sci. 2008;58 Suppl:S186]

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Some reports demonstrated that heat shock proteins (HSPs) contribute to cardio-protective effects against the ischemia-reperfusion injury. However, it has been studied that cardiac function decreases after acute endurance exercise (EEx) in human heart. These inconsistent results may be caused due to HSPs cannot produced in acute EEx. Therefore, we studied by using Langendorff-perfused heart model if HSPs are inducted by acute EEx and if they contribute to cardio-protective effects against hypoxia-reoxygenation (H-R) injury. Male Wistar rats (280-320g) were randomly assigned to either a control (CON) group or an acute EEx (3D) group (n=8/group). 3D animals performed 60 minutes treadmill running (–20 m/min) for 3 days consecutively. Although cardiac HSP72 increased significantly in 3D group, pressure-rate product of hearts at 30 minutes reoxygenation did not differ from CON group. In addition, the incidence rate of ventricular fibrillation or tachycardia in 3D group significantly increased compared with CON group (50% vs 13%, p<0.05). These results suggest that the acute EEx may cause cardiac dysfunction regardless of EEx-induced HSP72 in rat. [J Physiol Sci. 2008;58 Suppl:S187]

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Recently, we found the vestibular system is playing an important role for controlling arterial pressure (AP) during posture transition from supine to head-up tilt (HUT) in human subjects. To examine an effect of subthreshold electric vestibular stimulation for controlling AP during posture transition, we applied galvanic vestibular stimulation (GVS) of microcurrent during HUT for human subjects in the present study. The subjects were positioned on a tilt table in the supine position. AP was measured in the right middle finger with a continuous blood pressure monitor. After stabilization of AP, the volunteers were subjected to 2 min of 60°HUT. The six volunteers who showed decrease in mean AP more than 5 mmHg within 15 seconds after initiation of HUT were used for the study. GVS of biphasic 200 msec duration was applied during the measurement. The amplitude was changed each session from 0.1 mA to 0.6 mA randomly. All volunteers did not feel any stimulation at these currents. Without GVS, AP dropped by 11 mmHg with posture transition from supine to HUT. However, with one specific current of GVS between 0.3 to 0.5 mA for each subject, AP was maintained at the value of supine position. These results suggest that microcurrent vestibular stimulation might enhance afferent signal due to vestibular input during posture transition, and might be useful tool for preventing orthostatic hypotension. [J Physiol Sci. 2008;58 Suppl:S187]

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The alkaline phosphatase (ALP) is widely distributed in animal tissues. Butits biological meaning remains still unclear. To elucidate the cause of the increase in ALP the effects of hypertension induced by left renal artery partial constriction were studied on capillary networks in the left ventricular wall by the use of double staining enzymatic methods. In addition, the hypotensive effects of an angiotensin converting enzyme inhibitor, delapril, were studied. Goldblatt clips having a space of 0.22 mm were made with silver ribbon. Anesthetized 6-week old male rats were leparatomized to expose left renal artery, which was then vasoconstricted with a clip. In the sham-operated group a loose clip was placed on the artery. The clipping caused a hypertension higher than 160 mmHg in 4 weeks after the surgery. They were randomly divided into two groups: RCR-water group drank water and RCR-delapril, delapril-containing water groups. Hearts were removed under anesthesia and treated as previously reported. Left ventricular weight and myocyte cross area were strongly increased in RCR-water group (1707 mg, 1108 um2) compared with sham-operated (1191 mg, 453 um2) and RCR-delapril (1090 mg, 438 um2) ones. The hypertrophy resulted in the decrease in the total capillary density: RCR-water group showed 1550/mm2 versus 1867/mm2 in Sham-op and 2175/mm2.RCR-delapril. The density of ALP-expressing capillaries was increased in RCR-water group (328/mm2) compared with sham-operated group (219/mm2).In conclusion,the hypertrophy results in the increase in ALP expression. [J Physiol Sci. 2008;58 Suppl:S187]

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Background: Hypertension is a common disease and uncontrolled, long-term hypertension is associated with serious complication of vital organs such as brain, heart and kidneys. Although elevation of blood pressure (BP) is based on rise in peripheral vascular resistance, the role of vasoconstriction on the rheologic blood properties is unknown due in part to limited methodologies. Methods: Since spontaneous hypertensive rat (SHR) is a popular and excellent model of human hypertension, we investigated the role of erythrocyte deformability on the maintenance of high BP using 13-week-old SHR. BP was measured by tail sphygmomanometry. Erythrocyte filterability was rheologically considered as whole cell deformability, and was evaluated by gravity-based nickel mesh filtration technique. Results: We found that erythrocyte filterability was significantly (p<0.001) impaired in SHR (51.5 ± 11.5%) relative to that of 13-week-old Wistar rat (73.1 ± 8.3%). Hypertension was established in SHR whereas BP in Wistar rat remained constant in this stage (168/133 mmHg vs 108/84 mmHg in average). Conclusion: Erythrocyte filterability of SHR is still impaired in the stage of established hypertension. This is contradictory to the results of a previous study (Chabanel A, et al: Hypertension 10: 603, 1987) and this difference may stem from methodological quantitativity and reproducibility. [J Physiol Sci. 2008;58 Suppl:S187]

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We estimated the time course of the junctional sarcoplasmic reticulum (JSR) Ca²⁺ stores repletion from a family of the mechanical restitution curves after twitches of various magnitudes in cardiac muscle of hypertensive rat (SHR) using a method described previously , to evaluate abnormality in Ca²⁺ handling by cardiac JSR in hypertension. There were no differences in contractility nor the time course of mechanical restitution between SHR and control at 3 wks of age. 7 and 20 wk-old SHR showed a greater rested state contraction (RST) and a similar or smaller rapid cooling contracture compared to control, suggesting that their JSR contains a similar amount of Ca²⁺ at saturation and releases a greater amount of Ca²⁺ upon stimulation, compared to control. The adult SHR showed a similar time course of mechanical restitution to control, except a longer pretwitch latency in SHR than control. A function G(t) representing the time course of JSR Ca²⁺ stores repletion was greater in the adult SHR than control at t < 0.5 s, while a function H(t) representing JSR [Ca²⁺] change corresponding to the mechanical restitution after RST was smaller in the adult SHR than control at t < 0.5 s, resulting in smaller H(t)/G(t), in the adult SHR than control at t < 0.5 s. Deviation of G(t), H(t) and H(t)/G(t) from control were greater at 20 than 7 wks in SHR. The results suggest an acceleration of the JSR Ca²⁺ stores repletion and an alternation of the Ca²⁺-induced release of Ca²⁺ from the JSR in young adult SHR. [J Physiol Sci. 2008;58 Suppl:S188]

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Aging, obesity and underexercise are one of the risk factors for atherosclerosis. We evaluated the effect of dietary restriction and physical exercise to risks for atherosclerosis in spontaneously hypertensive rats (SHR). We randomly assigned 42 rats to two experimental diet groups, 100% group taking food ad libitum, and 70% group taking food 70% of the average food consumption. Each group was further assigned to two exercise conditions, sedentary group (Sd100, Sd70) and exercise group (Ex100, Ex70), swimming for 1 hour/day, 5 days/week. Chronic swimming exercise and experimental diet were started at the same time and continued for 8 weeks. After physiological examination every 2 weeks, we observed the distribution of superoxide and NO production in endothelial cells around aorto-renal bifurcation by using confocal laser-scanning microscopy. We evaluated the endothelial function with the oxidative stress index: the ratio of superoxide production to NO production. Ex- and -70% groups independently decreased the physiological risks for atherosclerosis: growth rate of body weight, blood pressure and serum HDL. It showed tendency that the oxidative stress index in cranial and caudal portion of aorto-renal bifurcation and Ex70 was high. Superoxide dismutase activity of heart, kidney, and serum in Ex70 was the highest. These data indicate that dietary restriction and exercise conditions improve the risk for atherosclerosis in SHR, through the mechanism which is not connected with oxidative stress. [J Physiol Sci. 2008;58 Suppl:S188]

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Background : The QT interval reflects the repolarization process of the ventricular myocardium. Berger et al presented QT variability index (QTVI) shown the lability of repolarization, and evaluated proarrhythmia in adults with the heart diseases and the prognosis. The aim was to find the standard value with the healthy children to evaluate the proarrhythmia in the healthy children with the heart diseases by using QTVI. Materials and Methods : The subjects are 120 normal children without heart disease. ECG was recorded by using MP-150. RR and QT intervals of 120 consecutive beats were measured, and calculated QTVI. Averaged QTVI of infant, first grader of elementary school and healthy students were compared. In addition, we calculated heart rate variability of 120 consecutive beats. The relation between the standardized characteristic (LF/HF, RSA/TF) and the QTVI value was examined. P < 0.05 was considered statistically significant. Results : Significant difference (p = 0.0018) was observed between the average QTVI (-1.50 ± 0.21) of first graders and that (-1.15 ± 0.39) of infants. RSA/TF that reflected the vagal nerve activity and QTVI showed a significantly negative correlation (y = -1.077–0.733 x, r = -0.412, p = 0.0015). Conclusion : The QT values of the newborn baby decreased with growth and became equal with an adult value for a first graders. The change of QTVI was suggested by the vagal nerve activity. This standard curve will be beneficial tool to evaluate proarrhythmia of children. [J Physiol Sci. 2008;58 Suppl:S188]

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Objectives: Decreased heart rate variability (HRV) has been demonstrated in children with atrial septal defect (ASD). It has been reported that myocardial damage decreased HRV, increased lability in repolarization, and induced proarrhythmia. In this study, we examined whether increased left-to-right shunt would affect repolarization in ASD. Subjects and Methods: Thirty-four patients without heart failure were employed. QT variability (QTVI) was calculated using a linear regression based on the QT time at 120 beats and precedent RR. Left-to-right shunt ratio was determined by Doppler ultrasound to categorize patients into the high- (2.0 or more) and low-shunt (less than 2.0) groups. In addition, power of low, high, total, and respiratory frequency domains were determined by HRV, a QT/RR linear regression was drawn and the correlations between QTVI and power value examined in both groups. Results: Linear regression of the high-shunt group was distributed more broadly than that of the low-shunt group (p=0.0004). By contrast, QTVI was -1.29±0.32 in the low and -0.51±0.37 in the high (p<0.0001). Log₁₀ RSA and QTVI showed a significant negative correlation (p<0.0001). Conclusion: Lability in repolarization was significantly increased in the high-shunt group, even in children without organic myocardial failure. This finding may derive from decreased vagal nerve activity. QTVI is assumed to reflect the input from the autonomic nerve to the heart, as well as HRV. [J Physiol Sci. 2008;58 Suppl:S188]

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Background: Cardiomyocytes lose their capacity to proliferate soon after birth. Therefore, we can not obtain large amount of cardiomyocytes in vitro. Here, we report the amplification of the cardiomyocyte population using retrovirus-mediated transfer of simian virus 40 large T (SV40T) antigen. SV40T was subsequently removed by Cre-loxP-based site-specific recombination.Methods and Results: Cultured neonatal rat cardiomyocytes were transduced with a retroviral vector expressing SV40T which is flanked by a pair of loxP recombination targets. Transduced cardiomyocytes yielded clones with greatly extended life spans up to population doubling level 142. Laser scanning cytometry analysis revealed that the transduction caused an induction of cell cycle progression. Complete elimination of the transferred SV40T gene was achieved after infection with a recombinant adenovirus expressing the Cre recombinase. Loss of SV40T caused G1-phase cell cycle arrest and discontinuance of cellular proliferation. DNA microarray analysis of cells that had lost SV40T showed increases in expression levels of cardiomyocyte-specific genes (cardiac actin alpha, Troponin T, myosin light chain and actinin alpha2)Conclusion: This study provides a means to obtain large numbers of well-differentiated and safe cardiomyocytes. [J Physiol Sci. 2008;58 Suppl:S189]

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The ductus arteriosus (DA), a fetal arterial connection between the pulmonary artery and the descending aorta, is essential for fetal circulation. After birth, the DA closes immediately through the contraction of its smooth muscle. In addition, intimal cushion formation (ICF) plays an important role in DA closure. Since a number of studies have indicated an important role of growth hormone (GH) and insulin-like growth factor (IGF) on cardiovascular development and tissue growth response, we hypothesized that growth hormone may play a role in ICF of DA. We found that the expression of GH receptor (GHR) mRNA in DA was eight times higher than that in aorta, and the GHR was up-regulated in DA during a perinatal period. Immunohistochemical analysis revealed that GHR was predominantly expressed in the endothelium and smooth muscle layer of DA. Using modified Boyden chamber method, the migration of DA smooth muscle cells (SMC) was significantly promoted by 50% in the presence of 20ng/mg GH in the condition media. We found that GH has no effect on SMC proliferation and hyaluronic acid production. These results suggested that GH play a role in intimal cushion formation though increasing migration of DA SMCs. [J Physiol Sci. 2008;58 Suppl:S189]

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Background: Idiopathic pulmonary arterial hypertension (IPAH) is a progressive disease characterized by inappropriate increase of pulmonary artery smooth muscle cells (PASMCs) leading to occlusion of pulmonary arterioles. In this study, we assessed the inhibitory effects of simvastatin, an HMG-CoA reductase inhibitor, on proliferation and migration of PASMCs obtained from patients with IPAH. Methods and Results: PASMCs were obtained from 6 patients with IPAH who underwent lung transplantation. Platelet-derived growth factor (PDGF) (10 ng/mL) stimulation caused a significantly higher growth rate of PASMCs from patients with IPAH than that of control cells assessed by 3H-thymidine incorporation (P<0.05). Simvastatin at 0.1 μmol/L significantly inhibited PDGF-induced cell proliferation of PASMCs from IPAH patients but did not inhibit proliferation of control cells at the same concentration. Simvastatin at 1 μmol/L also inhibited PDGF-induced migration of PASMCs from IPAH patients assessed by a transwell migration assay (P<0.05) and a time-lapse microscopy assay with a dish that has micro-lithographed squared pattern (Kuraray, Japan) (P<0.0001). Conclusions: Simvastatin may be useful for treatment of patients with IPAH. [J Physiol Sci. 2008;58 Suppl:S189]

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Objective Intimal cushion formation (ICF) is a characteristic vascular remodeling process in the ductus arteriosus (DA). Progressive smooth muscle cell (SMC) migration results in ICF immediately after birth in rodents. We hypothesized that rising oxygen tension plays a role in SMC migration after birth. Methods and Results 1) Isolated SMCs from rat termed-fetal DA were cultured in a hypoxic condition (1% oxygen; the hypoxic group). To investigate the effect of rising oxygen tension on SMC migration, they were transferred in a normoxic condition (21% oxygen; the normoxic group). Using a modified Boyden chamber method, we found that SMC migration was increased by 2.1-fold in the normoxic group when compared with that in the hypoxic group (p<0.05). 2) Since our previous DNA microarray analysis has identified several gene candidates that respond to changes from fetal to neonatal circulation and play a role in migration and proliferation, we examined the direct effect of oxygen on the expression of these genes. Rising oxygen tension from 1% to 21% significantly up-regulated the expression of early growth response gene-1 (3.0-fold), endothelin-1 (2.7-fold), cyclooxygenase-2 (1.9-fold), and fibronectin (1.9-fold) mRNAs in cultured rat DA SMCs. Conclusion Rising oxygen tension promotes migration and regulates gene transcription in rat DA SMCs. These findings may contribute to profound ICF after birth. [J Physiol Sci. 2008;58 Suppl:S189]

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Sentinel lymph nodes (SNs) are defined as the first nodes which receive lymph fluid from the primary tumor site. We aimed to detect SNs in vivo by using ultrasonography. In this study, contrast medium for ultrasonography, phospholipids-coated nanobubbles, was tried to be observed in the lymph node. Male Japan White rabbits were anesthetized with pentobarbital sodium (20 mg/kg iv.). Centripetal cannulation was performed in one of the popliteal afferent lymph vessels. Ultrasound contrast medium (2 mg/ml in physiological saline solution) was infused through the lymphatic cannula. A probe was fixed on the popliteal region of the rabbit. To evaluate a relationship between the amount of the contrast medium and degree of the enhancement, the infusion rate was increase in step from 0.74 ml/h to 14.7 ml/h. The contrast medium could be detected by Doppler ultrasonography at the region of the popliteal lymph node. Degree of the enhancement was increased in the infusion rate-dependent manner. When size of the contrast medium had been adjusted by passing through the polycarbonate membrane with 0.1 μm pores, efficiency of the enhancement was increased. These results suggest that development of efficient contrast medium enables to ultrasonographically detect sentinel lymph nodes in vivo. [J Physiol Sci. 2008;58 Suppl:S190]

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The lymphatic system plays a quite important part of microcirculation. The main function of the system is drainage of body fluid that leaks out of blood capillaries into the tissues, especially plasma protein, in the physiological condition. In addition, it is known that the lymphatic system works under low oxygen condition comparing with the blood system. In the present study, we have investigated critical roles of ROS in the regulation of a heart-like lymphatic pump in vitro. Male Wistar rats (7-8 weeks old) were anesthetized with pentobarbital-Na and the afferent lymph vessels of iliac lymph nodes were isolated. The lymph vessels were cannulated with glass micropipettes and pressurized at 6 cmH₂O. Changes in the diameter of the lymph vessels and frequency of the pump activity were measured by a video-microscope system. DPI (diphenyleneiodium; an inhibitor of NADPH oxidase), but not allopurinol (an inhibitor of xanthine oxidase), significantly reduced the frequency of the pump activity. The frequency of the pump activity was also significantly decreased after treatment with catalase. Exogenous application of hydrogen peroxide significantly constricted the lymph vessels. These results suggest that NADPH-derived ROS such as hydrogen peroxide may be involved in the regulation of lymphatic pump activity. [J Physiol Sci. 2008;58 Suppl:S190]

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Structural and functional changes of the pulmonary circulation during the pathogenesis of pulmonary arterial hypertension (PAH) remain to be fully elucidated. Conventional angiography has considerable limitations for visualizing pulmonary microvessels, particularly in a closed-chest animal. We assessed the effectiveness of monochromatic synchrotron radiation (SR) for microangiography of the pulmonary circulation in the intact-chest rat. Male SD rats were exposed to normoxia (N-Rat) or chronic hypoxia (10% O₂; CH-rat) for 28 days. Rats were anesthetized and microangiography was performed on the left pulmonary arteries to assess the branching distribution of pulmonary arteriole blood flow and internal diameter responses to acute hypoxia (8% O₂) before and after β-adrenoceptor blockade. We were able to visualize pulmonary microvessels <100 μm diameter (the 4th generation of branching from the left axial artery). The number of opaque 3rd and 4th generation vessels (100-300 μm) for CH-rats was significantly fewer than that of N-rats. The magnitude of hypoxic pulmonary vasoconstriction (HPV) was not different between CH-rats and N-rats. β-Blockade accentuated the HPV in 200-300 μm vessels for CH-rats, but even more so in N-rats. However, in CH-rats alone β-blockade also accentuated HPV in 100-200 μm vessels. These results highlight the benefits of SR for assessing PAH in a closed-chest rat model. [J Physiol Sci. 2008;58 Suppl:S190]

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Purpose:Metabolic syndrome (MS) is a well known modern ailment. In order to prevent the conditions, it is important to visualize microvessels (MV, 20-200 μm) and to evaluate them quantitatively in patients with MS. In this study we examined whether rCX could be used for microangiography to obtain vessel images in isolated dog heart (IDH) and rabbit ear (RE).Methods:A catheter was inserted into the left coronary artery of IDH and iodine microspheres (IM) was injected. The vessel was then ligated after the catheter was removed. A similar procedure was used to inject IM into the central artery of resected RE. Each tissue was then soaked in 10% formalin solution. We used an S band acceleration pipe rCX (S-rCX) system equipped with one of the three detectors characterized by a high spatial resolution.Results:With the imaging plate, we succeeded in visualizing intracardiac MV with an estimated diameter of 108 μm in IDH. Similarly, vessels of 80 μm diameter were visualized in RE.Discussion:In this study we showed that an S-rCX device could visualize MV whose diameter was at the limit of resolution of the detector. We intend to examine whether a higher-resolution scan would successfully obtain images of MV by increasing the output of reverse Compton scattering. [J Physiol Sci. 2008;58 Suppl:S190]

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