[Role of the opioid system in prevention of ischemic disorders of cardiac rhythm during adaptation to cold and physical exertion in rats].

It was found that adaptation of rats to cold and physical exercise prevented ventricular fibrillation caused by occlusion of the left anterior coronary artery. Adaptation to cold or only to physical exercise did not prevent ventricular arrhythmias. A significant increase of the beta-endorphin content in the hypophysis and hypothalamus was demonstrated in all adapted rats. An increased content of meth-enkephalin (ME) in the myocardium was found only in rats adapted to cold and physical exercise. It is suggested that increase of the myocardial ME content is of essential significance in the antiarrhythmic action of adaptation.