To characterize the cardiac function of buffaloes in terms of their electrocardiogram (ECG), the correlations between RR intervals and partial conduction times in ECG were compared between buffaloes and Holstein cattle. The body sizes and body weights of buffaloes were smaller than those of Holstein cattle.
Two buffaloes and two Holstein cattle were exposed to a heat stress to change their heart rates. The RR, PQ and QT intervals were measured from the ECG in each species. A common positive correlation in the two species was recognized in the RR-PQ and RR-QT.
No differences in wave characteristics were found in the ECGs. Although the heart rate per minute in the resting state of buffalo is lower than that of Holstein cattle, the characteristics of the partial conduction times of the heart do not differ between the two species.

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Fluctuations of the plasma atrial natriuretic peptide (ANP) concentration were observed in normal cattle and dog. Statistical analysis using Bartlet test and two-way analysis of variance (two-way ANOVA) did not support any circadian rhythm in the pasma ANP concentration in both species. The present study indicates that the length of the sampling time is not necessary to be considered at the time of determination of the plasma ANP concentration to estimate the intra-cardiac pressure.

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We studied the effects of the intravenous infusion of dopmine on hepatic circulation at doses of 3, 7 and 15μg/kg/min. Six mongrel dogs weighing 19.1±6.1kg were studied under sodium pentobarbital anesthesia. Cardiac output was measured by thermodilution methods. Portal venous blood flow (PVBF) and hepatic arterial blood flow (HABF) were measured by an electromagnetic flowmeter. Hepatic oxygen supply and consumption were calculated from the blood flow and the oxygen contents.
Dopamine at all doses caused a significant increase in PVBF and a significant decrease in HABF. However, dopamine at doses of 3 and 7μg/kg/min demonstrated no significant changes in the total hepatic blood flow (THBF). Dopamine at a dose of 3μg/kg/min showed no effects on the hepatic and systemic oxygen supply-demand relationship. Dopamine at a dose of 7μg/ kg/min resulted in increased in the systemic oxygen supply and consumption under a fixed oxygen extraction ratio. Dopamine at a dose of 15μg/kg/min caused a significant increase in THBF accompanied by an increased systemic oxygen consumption and an increased systemic oxygen extraction ratio.
From these results, it is suggested that dopamine at doses of 3 and 7μg/kg/min has minimum effects on the hepatic circulation and oxygen supply-demand relationship, but that dopamine at a dose of 7μg/kg/min is the most effective for improvement of the systemic circulation and oxygen supply-demand relationship.

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Effect of intravenous infusion of dobutamine on hepatic circulation at doses of 5, 10, and 15μg/kg/min were studied in 6 mongrel dogs under pentobarbital sodium anesthesia. Hepatic arterial and portal venous blood flows were measured. Dobutamine increased the heart rate and the cardiac index, but decreased the systemic vascular resistance with a dose-dependence. Each dose of dobutamine did not change the mean arterial pressure. The 5μg/kg/min-adminstered group demonstrated an increased total hepatic blood flow accompanied by increased hepatic arterial and portal venous blood flows. The 10μg/kg/min-administered group showed an increased total hepatic blood flow accompanied by an increased portal venous blood flow with no change in hepatic arterial blood flow. The 15μg/kg/min-infused group showed an increased total hepatic blood flow accompanied by an increased portal venous blood flow and a decreased hepatic arterial blood flow. Portal and hepatic venous pressures were not changed with no relation to dose-dependence. Hepatic oxygen supply was increased with a dose-dependence, but the hepatic oxygen consumpution was maintained at the control level. Hepatic oxygen extraction ratio was decreased with a dose-dependence. To summarize the data, dobutamine significantly improves the hepatic circulation, accompanied by a hepatic oxygen supply increment.

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In order to obtain direct evidence of the genesis of “positive” T wave on the standard limb lead II electrocardiogram (ECG) in the rat, ventricular activation and its recovery patterns were investigated by recording direct cardiac electrograms. Multiple unipolar electrograms were recorded from 7 sites in the left ventricle including the septum, subendocardium and subepicardium under the constant sinus rhythms in 12rats. The unipolar electrograms and their differentiated waves were analyzed for local QT intervals and local activation times, respectively. In addition, the direct bipolar electrograms between the subendocardium and the subepicardium of the left ventricle were also recorded in 6 rats. The proceeding times from the septum (initial) to the subepicardium (terminal) were very short as less than 10 msec. Nevertheless, the activation sequence in the left ventricle was clearly shownin accordance to the following order ; the septum, subendocardium and subepicardium. The local QT intervals in the subepicardial sites were significantly shorter than those in the corresponding subendocardial sites (p<0.05). These activation sequences and local QT intervals in the rat ventricle suggest a presence of transmural gradient of depolarization and repolarization, with an earlier depolarization at the endocardium and with an earlier repolarization at the epicardium. Such a transmural gradient might produce an electrical dipole which would contribute to the configuration of positive T wave on the rat ECG. In fact, the positive waves recorded by the direct bipolar electrograms between the subendocardia and the subepicardia can account for the formation of an electrical dipole having a positive charge at the subepicardia against the subendocardia.

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The blood pressure (BT) and the heart rate (HR) during lactation in rats were measured by an indirect tail-caff method. The plasma osmotic pressure and hemotocrit (Ht) values were also measured as factors affecting the viscosity resistance of blood. Two groups were assigned in this study, i. e., (1) lactating group in which the litter size was adjusted to twelve pups at parturition and (2) control group in which the litter was removed from dams following parturition. The experiments were carried out on days 3, 5, 7, 10, 13 and 18 of lactation. The day of parturition was designated as day 0 of lactation. As a result, no noticeable changes in BP and HR were recognized between lactating and control groups. Ht (except for day 5) and plasma osmotic pressure (day 5 and after day 10) of the lactating group was significantly lower than those of control group through the lactation days.

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