[Participation of the endogenous opioid system in the formation of the body's response to stress].

Autonomic responses to acute stressors in unanesthetized, chair-restrained baboons and macacas include elevations in heart rate, blood pressure and respiratory rate. Naloxone, in a dose of 1.0 mg/kg intravenously, as well as morphine (1.0 mg/kg) suppresses autonomic alterations produced by the introduction of conditioned and unconditioned stimuli. When given in a dose of 0.1 mg/kg, naloxone, on the contrary, facilitates autonomic responses. The autonomic changes induced by electrical stimulation of the medial hypothalamus and nucleus tractus solitarius are influenced by naloxone--in both doses--and by morphine in the opposite manner. These data, as well as those derived from experiments on the effects of micro-injections of naloxone and morphine into the medial hypothalamus and nucleus tractus solitarius suggest that the endogenous opioid system is necessary to display complete autonomic response pattern in monkeys. A hypothesis is proposed to the effect that endogenous opioid system is important for establishing a precise correspondence between the body's potentialities and behavior, and environmental demands.