Antagonism of the hypertensive effect of physostigmine in anesthetized rat by morphine.

The effect of morphine was studied on physostigmine-induced hypertensive response in anesthetized rats. Physostigmine caused dose-dependent increase in blood pressure. When given at a dose (2 mg/kg i.v.) that did not alter blood pressure, morphine significantly inhibited the hypertensive effect of physostigmine administered either i.v. or i.c.v. Oxotremorine evoked a hypertensive response which was also inhibited by morphine. This inhibitory effect of morphine was prevented or reversed by naloxone. These results support the view that cholinergic and opiatergic systems interact on regulating arterial blood pressure.