The effect of the acute and chronic administration of dalargin to mongrel rats on cardiac chronotropism at rest and under physical loading]

In chronic experiments on untrained awakening males of white rats it has been shown that the prolonged intraperitoneal injection of the opiate receptor agonist delargin (during 4, 5 days; 10 mkg/kg; twice a day) leads the chronotropic heart response to the maximum level of exercises and simultaneous decrease of heart rate variability. All this is accompanied by animals' undue fatiguability. It has been concluded that the chronic injection of opioid agonist receptors causes the decrease of sensitivity of these receptors to the action of endogenic opioids and as a consequence--the increase of sympathetic regulatory action on the heart rate at physical exercises and growth of fatiguability.