Naloxone suppresses the vasodepressor action of captopril in the anaesthetized dog.

The effects of intracisternal injection of captopril (0.3 mg/kg) on the systolic pressor response elicited by afferent stimulation of the vagus were investigated in the anaesthetized dog. The captopril-induced decrease in the systolic pressor response to vagal stimulation was reversed by a subsequent injection of naloxone (0.1 mg/kg i.v.). These results suggest the involvement of central opioid mechanisms in the hypotensive properties of captopril.