Surgical stress inhibits physostigmine-induced pressor effect.

Physostigmine-induced pressor response was studied in adrenalectomized rats. The pressor response to intracerebroventricular administration of physostigmine was found to be inhibited in both acutely adrenalectomized and sham-operated rats, but not in animals adrenalectomized 24 h earlier. Laparatomy performed just before the experiment also inhibited the pressor effect of physostigmine. This inhibition was completely prevented by naloxone pretreatment. Endogenous opioid peptides released as a response to the stress induced by surgical manipulation, could be accounted for inhibition of the pressor effect of centrally administered physostigmine in rats.