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Biomedical subjects

S Imai

Publications and source records attributed to S Imai.

At least 775 records · Page 43Linked to original sources
PubMed1978

Antiarrhythmic effect of oxprenolol on halothane-epinephrine and coronary ligation induced ventricular arrhythmias in beagle dogs.

Antiarrhythmic effects of oxprenolol, a beta-blocker, were studied quantitatively on arhythmias produced by epinephrine during halothane anesthesia and by two-stage coronary ligation, and were compared to those of other beta-blockers, propranolol and Kö 1400, which have been already reported. Though oxprenolol has potent beta-blocking activity, the antiarrhythmic effect on halothane-epinephrine arrhythmia was significantly weaker than those of propranolol and Kö 1400. The effective dose of oxprenolol was 60 +/- 18 microgram/kg (mean +/- S.E., N = 6), which is in the range of the so-called beta-adrenergic blocking dose. The weaker antiarrhythmic effect of oxprenolol as compared to propranolol and Kö 1400 is probably due to the intrinsic positive chronotropic effect, which is most clearly observed in oxprenolol as compared to the other two drugs. As for two-stage coronary ligation arrhythmia, oxprenolol suppressed only that observed 48 hours after coronary ligation using higher doses (5 to 10 mg/kg). Other beta-blockers also showed similar effects. Because of the high doses necessary for the antiarrhythmic effects on the coronary ligation arrhythmia, the mechanism for suppressing the arrhythmia is probably due to the local anesthetic action of the beta-blockers.

Adrenergic beta-Antagonists↗
PubMed1978

Hypotensive and vascular effects of labetalol in the normotensive rat and dog.

A new antihypertensive agent, labetalol, has potent hypotensive effects in the anesthetized rat and dog when given intravenously and also in the unanesthetized beagle when given orally. Labetalol slightly increased renal blood flow of the anesthetized dog while decreasing blood pressure. Labetalol slightly increased blood flow of canine femoral artery under constant pressure perfusion. However as compared with hydralazine, labetalol seems to have no marked vasodilatatory effect which accounts for its hypotensive effect. Pharmacologically, labetalol possessed both alpha- and beta-blocking activities, though weaker than phentolamine and propranolol respectively. Another specific action of labetalol was that it has stronger beta-blocking action on beta1 receptor (heart rate response) than on beta2 receptor (blood pressure response). Like several other beta-blockers, labetalol seems to block neuronal uptake of noradrenaline.

Adrenergic alpha-Antagonists↗
PubMed1978

In vitro analysis of Ca-antagonistic effects of prenylamine as mechanisms for its cardiac actions.

Ca-antagonistic properties of prenylamine were studied using isolated guinea-pig and canine cardiac preparations. Prenylamine is a weak Ca-antagonist compared to nifedipine, verapamil and diltiazem. Lower doses of prenylamine slightly increased the tension, but higher doses decreased the tension of both the guinea-pig and canine cardiac preparations. It decreased the tension while maintaining the action potential of the normal guinea-pig atrial preparation and decreased both the tension and Ca-action potential of the depolarized guinea-pig atrial preparation. Similar to antiarrhythmic agents, prenylamine also decreased the max dV/dt of the normal guinea-pig atrial action potential.

Action Potentials↗
PubMed1977

Antiarrhythmic and electrophysiological effects of CH-200.

A new antiarrhythmic drug CH-200, 5-phenacyl-thieno[3,2-c]yridinium, was compared with procainamide and lidocaine in a two-stage coronary ligation arrhythmia model for its efficacy and electrophysiological properties. CH-200 suppressed arrhythmia in beagle dogs more effectively than did procainamide and lidocaine. The antiarrhythmic effects of CH-200 and procainamide developed slowly and lasted longer than those of lidocaine. Electrophysiological studies with CH-200 showed that it decreased max dV/dt of the action potential. This effect was dependent on the heart rate: the higher the rate, the stronger the effect. CH-200, procainamide and lidocaine prolonged the effective refractory period and this effect seemed to be responsible for suppressing the arrhythmia after coronary ligation. CH-200 and procainamide increased the frequency of ventricular pacemaker activity, while lidocaine decreased it. These effects appear to be unimportant for the antiarrhythmic effects.

Acetophenones↗
PubMed1977

[Drug effects on blood pressure and heart rate in unanesthetized animals. (1). Effects of beta-blocking agents (author's transl)].

beta-Blocking actions of orally administered Kö 1400 and tiprenolol, new beta-blocking agents, were studied in unanesthetized rats and dogs, using a fall of blood pressure and an increase in heart rate produced by isoproterenol as a measure of beta-receptor activation. Blood pressure was recorded from the aorta of the dog and the caudal artery of rat via indwelling catheter, and heart rate of the dog was recorded by a cardiotachometer triggered by R waves of the lead II electrocardiogram. Mean resting blood pressure was 116 mmHg in rats and 93 mmHg in dogs, and heart rate was 99 beats/min in dogs. Isoproterenol (0.5 microgram/kg) was injected via indwelling venous catheter. Kö 1400, tiprenolol and propranolol inhibited the hypotension and tachycardia induced by isoproterenol at an oral dose level of 2 mg/kg or more. beta-blocking action in these preparations was found to be tiprenolol greater than Kö 1400 greater than propranolol. Pharmacological half life of tiprenolol was longer than that of propranolol, whereas that of Kö 1400 was shorter. No selectivity of beta-blocking actions was observed with all three beta-blockers. These findings are in agreement with the results obtained in isolated atrial and tracheal preparations of the guinea pig.

Adrenergic beta-Antagonists↗
PubMed1977

Effects of coronary vasodilators on large and small coronary arteries of dogs.

Using the isolated perfused heart preparation supported by a donor the effects of vasodilators on the large conductance artery were studied and were compared with those on the small resistive artery and arterioles. Nitroglycerin produced a preferential dilation of the large conductance artery, while dipyridamole produced a dilation only of the small resistive artery and arterioles. Among the "calcium antagonistic" vasodilators tested, only diltiazem produced a dilatation of the large conductance artery, verapamil and nifedipine producing a dilatation only of the small resistive artery and arterioles. These findings indicate that the mechanism of contraction of the large conductance artery is different from that of the small resistive artery and arterioles.

Adenosine↗