PACAP is a pleiotropic neuropeptide that belongs to the secreting/glucagon/VIP family. PACAP functions as a hypothalamic hormone, neurotransmitter, neuromodulator, vasodilator, and neurotrophic factor. Its structure has been remarkably conserved during evolution. The PACAP receptor is G protein-coupled with seven transmembrane domains and also belongs to the VIP receptor family. PACAP, but not VIP, binds to PAC1-R, whereas PACAP and VIP bind to VPAC1-R and VPAC2-R with a similar affinity. Despite the sizable homology of the structures of PACAP and VIP and their receptors, the distribution of these peptides and receptors is quite different. At least eight subtypes of PACAP specific, or PAC1-R, result from alternate splicing. Each subtype is coupled with specific signaling pathways, and its expression is tissue or cell specific. Although PACAP fulfills most requirements for a physiological hypothalamic hypophysiotropic hormone, it does not consistently stimulate secretion of the adenohypophysial hormones, except for stimulation of IL-6 release from the FS cells of the pituitary. The major regulatory role of PACAP in pituitary cells appears to be the regulation of gene expression of pituitary hormones and/or regulatory proteins that control growth and differentiation of the pituitary glandular cells. These effects appear to be exhibited directly and indirectly through a paracrine or autocrine action. Although PACAP stimulates the release of AVP, the physiological role of neurohypophysial PACAP remains unknown. One important action of PACAP in the endocrine system is its role as a potent secretagogue for adrenaline from the adrenal medulla through activation of TH. PACAP also stimulates the release of insulin and increases [Ca2+]i from pancreatic β-cells at an extremely small concentration. The stage-specific expression of PACAP in testicular germ cells during spermatogenesis suggests its regulatory role in the maturation of germ cells. In the ovary, PACAP is transiently expressed in the granulosa cells of the preovulatory follicles and appears to be involved in the LH-induced cellular events in the ovary, including prevention of follicular apoptosis. In the central nervous system, PACAP acts as a neurotransmitter or neuromodulator, which has been supported by IHC and electrophysiological methods. More important, PACAP is a neurotrophic factor that may play an important role during the development of the brain. In the adult brain, PACAP appears to function as a neuroprotective factor that attenuates the neuronal damage resulting from various insults.
Intestinal ischemia/reperfusion (I/R) causes serious systemic injury, mainly from a variety of bioactive substances released from the injured intestine. To assess the possible roles of serotonin (5-hydroxytryptamine, 5-HT), a bioactive amine mainly stored in the intestine, in I/R injury, we assayed the levels of tryptophan, 5-HT, and 5-hydroxyindole acetic acid (5-HIAA) in the blood and intestine in a rat I/R model. Plasma 5-HT increased significantly over time after reperfusion; the plateau level was obtained 4h after reperfusion and was associated with an increase in 5-HIAA. Plasma tryptophan levels declined gradually after reperfusion. The ratio of 5-HIAA/5-HT was significantly higher in I/R rats than in control rats, suggesting that elevated 5-HT was quickly metabolized in the systemic circulation. In the intestine, 5-HT decreased dramatically, whereas tryptophan increased. This phenomenon was prominent in the severely damaged intestine. These findings suggest that the injured intestine released large amounts of 5-HT, whereas its synthesis in the injured intestine was suppressed. An increase in 5-HT in the circulation may be related to various circulatory disturbances observed in humans after intestinal ischemia.
This study tested the hypothesis that the afferent input from the respiratory muscles may be involved in the neural mechanisms inducing cough responses. Coughing was evoked in conscious healthy humans by the inhalation of citric acid aerosol of several concentrations either during or not during chest wall vibration (100 Hz) at the right second intercostal space or during vibration of the right thigh. The mean threshold citric acid concentration to induce coughing was significantly higher during chest wall vibration (geometric mean, 131.8 mg/ml) than without vibration (75.9 mg/ml). Vibration after topical anesthesia of the chest wall skin did not significantly change the threshold concentration of citric acid. The threshold citric acid concentration during vibration of the right thigh did not significantly differ from that without vibration. We concluded that inputs from the chest wall afferent, presumably from the intercostal muscle or costovertebral joint, may have an inhibitory effect on the initiation of coughing at the higher neural structure in conscious humans.
The aim of the present study was to clarify the effects of O2 diffusion limitation resulting from hypoxic interventions on O2 uptake (VO2) in unloaded (that is, near-zero initial force) and loaded skeletal muscle in a high-frequency stimulation. We measured VO2, muscle venous PO2 (PVO2) and initial force in gastrocnemiusplantaris muscle in situ of anesthetized dogs: (1) during hypoxic hypoxia at 1 Hz tetanic stimulation, and (2) during hypoxia induced by the perfusion with high O2-affinity erythrocytes (having a low value of PO2 at 50% saturation of hemoglobin (P50)) at 4 Hz twitch stimulation. Averaged unloaded VO2 during normoxia was 10. 2 ml·min-1·100 g-1 at averaged blood flow of 74 ml·min -1·100 g-1 (n=6). Hypoxic hypoxia of a decreased O2 delivery (arterial O2 concentration × flow) significantly decreased both unloaded and loaded VO2 with a decrease in PVO2 (p<0.05). The unloaded VO2 was reduced to 8.5 ml·min-1·100 g-1. Low P50-hypoxia decreased VO2 at high and low initial force conditions with a decrease in PVO2 (p<0.05) at the same O2 delivery. If these decreases in VO2 correspond with a decrease in VO2 correspond with a decrease in VO2 at zero initial force (unloaded VO2), the unloaded VO2 value is calculated to be 7.57 ml·min-1·100 g-1 from VO2-initial force data. Despite the different conditions of O2 delivery, the unloaded VO2 decreased by both hypoxia showed similar values. Thus the decreased unloaded VO2 does not seem to be derived from only the limited O2 delivery. Some other factors such as the limitation of O2 diffusion may contribute to the decreased VO2.
The effects of hyperthyroidism and hypothyroidism on brown adipose tissue (BAT) thermogenesis and phospholipid fatty acid composition were investigated in rats. Chronic triiodothyronine (T3) treatment (hyperthyroidism) increased the interscapular BAT pad weight, its triacylglycerol content, and its DNA content. It did not affect basal and noradrenaline-stimulated in vitro oxygen consumption of BAT expressed per μg DNA, although it significantly increased the oxygen consumption of the whole BAT pad. T3 treatment had little effect on phospholipid content and phospholipid fatty acid composition. In contrast, chronic methimazole treatment (hypothyroidism) decreased the BAT pad weight and the triacylglycerol content, but did not significantly change the DNA content in comparison with the control. It significantly decreased the noradrenaline-stimulated BAT oxygen consumption expressed per μg DNA and per BAT pad, but did not change the basal oxygen consumption. Methimazole treatment significantly affected phospholipid content and phospholipid fatty acid composition. Among the major fatty acids of BAT, it decreased docosahexaenoic acid (DHA), arachidonic acid, palmitic acid, palmitoleic acid, and oleic acid, and it increased linoleic acid, stearic acid, and eicosapentaenoic acid. A regression analysis revealed a positive relationship between in vitro respiration and DHA levels in phospholipids (r=0.404, p<0.05. These results suggest that thyroid hormones have trophic action on BAT and are necessary for BAT thermogenic activity. This study also suggests that DHA is involved in the regulation of BAT thermogenic activity, as we previously indicated.
The purpose of this study was to clarify whether peripheral vascular response to alteration of transmural pressure is changed by endurance exercise training. The healthy male subjects (training group; n=6) performed endurance exercise training that consisted of cycle ergometer exercise 5 d·week-1 and 30 min·d-1 for a period of 8 weeks. Changes in the peripheral vascular response to alteration of transmural pressure in the human finger were measured by a differential digital photoplethysmogram (ΔDPG) and blood pressure during passive movement of the arm to different vertical hand positions relative to heart level. Following 8 weeks of endurance training, percent changes in ΔDPG from heart level in the training group increased significantly (mean±SD, −48.1±7.3 to −58.7±9.3% at the lowered position, 46.1±13.4 to 84.6±8.8% at the elevated position, p<0.05). Similarly, the arterial compliance index, which was calculated from ΔDPG-P wave amplitude and arterial pulse pressure, also significantly changed in the training group over the 8 weeks (5.6±1.3 to 2.7±1.6 mV·V-1·s-1·mmHg-1 at the lowered position, 30.0±12.4 to 54.5±18.9 mV·V-1·s-1·mmHg-1 at the elevated position). Maximal oxygen uptake (VO2max) was significantly increased in the training group. On the other hand, the control group (n=6) showed no significant changes in all parameters for 8 weeks. Therefore these results suggest that endurance exercise training induces an increase in peripheral vascular response to alteration of transmural pressure in the human finger.
How different the effects of caffeine on cardiac mechanoenergetics in failing hearts are from those of normal hearts remains to be fully elucidated. First we successfully instituted a new experimental model of acute mild heart failure in the rat by 0.005 mM Ca2+ Tyrode perfusion. These failing hearts neither decreased left ventricular end-systolic pressure nor increased left ventricular end-diastolic pressure, indicating unchanged left ventricular mechanics. However, their myocardial mitochondrial respiratory function examined by respiratory control index (RCI) and oxygen consumption rate in state III (State III O2) was significantly depressed compared with normal hearts. From these results, we judged that this Ca2+ protocol could make mild Ca2+ overload acute failing hearts and that this model would be appropriate for comparing the effects of caffeine on cardiac mechanoenergetics between normal hearts and these failing hearts. We investigated the effects of caffeine on cardiac mechanoenergetics above a concentration of 0.05 mM that corresponds to the maximum blood concentration after a healthy human subject drinks a cup of coffee or tea. We obtained results indicating that caffeine depressed left ventricular systolic and diastolic functions and decreased a measure of total mechanical energy per beat in terms of systolic pressure-volume area (PVA) more severely in these failing hearts at concentrations (20-fold higher than the concentration in a cup of coffee) lower than those in normal hearts. This result implies that these acute failing hearts are Ca2+ overloaded.
The role of myosin subfragment-2 (myosin S-2) in muscle contraction was studied by using an in vitro motility assay system in which the ATP-dependent sliding between myosin-coated polystyrene beads and actin filament arrays (actin cables) of giant algal cells were recorded under constant external loads provided with a centrifuge microscope. With antibody to myosin S-2 below 0.3 mg/ml, the maximum “isometric” force generated by myosin molecules on the bead decreased markedly, but the unloaded bead-sliding velocity along actin cables did not change appreciably, indicating a decrease in the number of myosin molecules interacting with actin scables. The antibody at 0.3-1.5 mg/ml decreased not only the maximum isometric force, but also the unloaded bead-sliding velocity in a dose-dependent manner. With the antibody at 1.5-3 mg/ml, the beads eventually stopped moving to remain attached to actin cables. These beads could be readily detached from actin cables with very small centrifugal forces, indicating very weak actin-myosin linkages. The antibody had no effect on rigor actin myosin linkages fromed before the antibody application. These results are consistent with the view that myosin S-2 plays an essential role in muscle contraction.
The effects of genistein, a protein tyrosine kinase inhibitor, on the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel were studied in guinea pig ventricular myocytes and in NIH3T3 mouse fibroblasts stably transfected with CFTR cDNA by the whole-cell patch-clamp technique. Genistein did not activate whole-cell Cl- currents when applied to the intracellular (pipette) solution. In contrast, when applied to the extracellular solution, genistein alone promptly activated the Cl- current in a fully reversible manner. Also, extracellular genistein reversibly potentiated the forskolin-activated Cl- current. However, both basal and forskolin-activated Cl- currents were not affected by other protein tyrosine kinase inhibitors, including herbimycin A, lavendustin A, tyrphostin 21, tyrphostin 47, and tyrphostin 51. A nonspecific inhibitor of protein phosphatases, orthovanadate, had no effect on the genistein-induced activation of CFTR. Pretreatment with a protein kinase inhibitor, either H-89 or H-7, or with an adenylate cyclase inhibitor, SQ 22536, also had no effect on the genistein-induced response. Thus, it is concluded that genistein alone activates CFTR by a protein tyrosine kinase-independent and protein phosphatase-independent mechanism from the extracellular side, but not from the intracellular side.