Abstract
Rats were adapted to the continuous action of moderate immobilization stress for 1, 5, and 15 days. Thereafter the threshold of ventricular fibrillation and the heart rate were compared with biochemical indexes of adrenergic and cholinergic regulation of the heart, namely, catecholamine, cAMP, and cGMP content, acetylcholinesterase and choline acetyltransferase activity, the number and affinity of cardiac muscarinic receptors, and the catecholamine content in the adrenals. The threshold of ventricular fibrillation fell on the 1st day due to a predominance of the adrenergic regulatory effect over the cholinergic. Adaptation for 5 days is attended by a rise of the threshold of ventricular fibrillation to the norm and by marked bradycardia, both these shifts being abolished by atropine. Elevation of the heart's resistance to arrhythmias stems from the prevalence of cholinergic regulation. Equilibrium between the cholinergic and adrenergic effects on the heart was found as a results of 15-day adaptation. The normal threshold of ventricular fibrillation and the increased cardiac resistance to arrhythmia were preserved and dictated largely by adaptive changes at the cardiomycyte level.
Published Version
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