Naloxone reverses the effects of enalapril and enalaprilic acid on the pressor responses to afferent vagal stimulation

The effects of intracisternal injection of enalapril (MK 421) or its bioactive form enalaprilic acid (MK 422) (0.075 mg/kg) on the pressor responses elicited by afferent stimulation of the vagus were investigated in the urethane-anaesthetized dog. The angiotensin converting enzyme inhibitors (ACEl)-induced decrease in the systolo-diastolic pressor responses to vagal stimulation was reversed by naloxone (0.1 mg/kg iv). The same doses of ACEl injected by intravenous route remain inactive. These data support evidence for an additional central site of action of ACEl and suggest the involvement of central opioid mechanisms in the hypotensive properties of ACEl.