Oscillations of cardiac rate induced by acetylcholine in the isolated guinea pig heart.
1. The effects of acetylcholine (ACh) on cardiac rate (electrocardiogram), contractile force and coronary flow recorded simultaneously were investigated in isolated guinea pig hearts perfused with Locke solution by the method of Langendorff. 2. Bolus injections of 0.5-550 nmol ACh induced oscillations of cardiac rate. These changes were not directly related to the doses of ACh injected (chi 2 test, P greater than 0.05). 3. The presence of 10 microM physostigmine in the Locke solution increased the number of heart rate oscillations elicited by ACh. 4. The electrocardiogram showed that the heart rate oscillations were due to wandering pacemakers, such as slow or fast junctional rhythm, and slow or fast idioventricular rhythm, which were intermingled with sinus rhythm, A-V block or sinus bradycardia. 5. In most experiments, the increase in ventricular rate was associated with an increase in ventricular contractile force ("Bowditch Effect") and a simultaneous reduction of coronary flow. 6. The heart rate oscillations were not prevented by reserpine or blockade of nicotinic receptors (hexamethonium plus gallamine) but were prevented by blockade of muscarinic receptors with atropine. 7. We conclude that the heart rate oscillations induced by ACh are due to several electrophysiological mechanisms (automatism and/or conduction disturbances) related to activation of muscarinic receptors.
Alpoim
N C
NC
Departamento de Fisiologia e Biofisica, Universidade Federal de Minas Gerais, Belo Horizonte, Brasil.
Almeida
A P
AP
Santos
P E
PE
Freire-Maia
L
L
D000109:Acetylcholine / Q000008:administration & dosage*; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000139:chemically induced; D003326:Coronary Circulation / Q000187:drug effects*; D004562:Electrocardiography; D006168:Guinea Pigs; D006339:Heart Rate / Q000187:drug effects*; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D010477:Perfusion; D012110:Reserpine / Q000008:administration & dosage
D012110:Reserpine; D000109:Acetylcholine