[Effect of adaptation to stress exposures on the cholino- and adrenoreactivity of the atria and their content of acetylcholine in rats with myocardial infarct].

The effect of left-ventricular myocardial infarction (MI) on cholino- and adrenoreactivity of an isolated right atrium and acetylcholine (AC) content of both atria was evaluated experimentally in Wistar rats, adapted or unadapted (control) to stress. In the control sample, 24-hour-long MI increased the chronotropic response to AC, while atrial endogenic AC dropped fourfold. Those changes were accompanied by no marked changes in pacemaker adrenoreactivity. Adaptation to stress reduced pacemaker choline reactivity without any significant effect on pacemaker adrenoreactivity or atrial AC. At the same time, adaptation largely prevented MI-induced increase in pacemaker choline reactivity and atrial AC drop. Increased pacemaker choline reactivity, seen in MI, enhances pacemaker sensitivity to cognition of ectopic excitation foci and, hence, cholinergic effects, that may promote the emergence of arrhythmia. Therefore, pacemaker resistance to cholinergic action, increasing in the course of adaptation, may be an important element of the protective antiarrhythmic effect of adaptation to stress in MI.