Effect of naloxone on physostigmine-induced pressor response in adrenalectomized rats

Physostigmine-induced pressor response was studied in adrenalectomized rats. The increase in mean arterial blood pressure elicited by intravenous administration of physostigmine was not altered by adrenalectomy or sham-operation. The pressor response to intracerebroventricular administration of physostigmine was found to be partially inhibited in both acutely adrenalectomized and sham-operated rats, but not in those adrenalectomized 24 h earlier. This inhibition was completely prevented by naloxone pretreatment. The results suggest that endogenous opioid peptide release induced by surgical stress may be responsible for inhibition of the pressor effect of centrally administered physostigmine in rats.