In August rats more resistant to acute stress-induced gastric damage than Wistar rats, preadaptation to nondamaging stress exposure did not prevent damage and even potentiated these damages. By contrast, in Wistar rats such adaptation decreased gastric damage caused by acute stress. Higher initial resistance of August rats to stress damage was associated with higher serotonin level and lower norepinephrine/serotonin ratio in the gastric mucosa than in Wistar rats. The negative effect of adaptation in August rats was associated with decreased serotonin level and increased norepinephrine/serotonin ratio in the stomach during stress. In Wistar rats exposed to stress the protective effect of adaptation was associated with an increase of serotonin content and a decrease of the norepinephrine/serotonin ratio in the stomach. Hence, the degree of resistance to stress-induced gastric damage can be due to genetically determined serotonin level and norepinephrine/serotonin ratio in the stomach.

Adaptation to transauricular electrostimulation decreases the content of epinephrine in the adrenal glands and norepinephrine in the heart, hnmobilization stress has no appreciable effect on the content of catecholamines in the heart and adrenal glands. In animals with myocardial inl~arction, the content of norepinephrine in the hem"~ decreases 2-fold, while the content of epinephrine in the adrenals decreases inconsiderably. Adaptation to transauricular electrostimulation is associated with a rise in met-enkephalin concentration. Preadaptation induces a more pronounced rise of met-enkephalin and promotes normalization of epinephrine hi the adrenals, without changing the content of norepinephrine in the hem~.

Three months after myocardial infarction the severity of heart failure and size of postinfarction scars in August rats with inherently reduced adrenoreactivity of the myocardium were similar to those in Wistar rats. The mortality rate in August rats was 2.5-fold lower than in Wistar rats. During the postinfarction period, myocardial adrenoreactivity in August rats remained lower, while the efficiency of cardiac function was 62% higher than in Wistar rats. The incidence of epinephrine-induced arrhythmias in August rats was much lower than in Wistar rats.