Central effect of captopril on baroreflex.

To clarify effect of converting enzyme inhibitors (CEI) on heart rate regulation, captopril (2 mg/kg) was injected intravenously (i.v.) with or without pretreatment of atropine and also responses to intracisternal (i.c.) injections were examined. Captopril induced bradycardia with lowering blood pressure, and this bradycardia was abolished by pretreatment of atropine. Reduction of heart rate by i.c. injection of captopril was significantly larger than those of i.v. injection. Furthermore, to determine whether CEI can modify baroreflexes centrally, the aortic depressor nerve (ADN) was stimulated electrically in captopril treated rats. Vasodepressor and sympatho-inhibitory responses induced by ADN stimulation were significantly attenuated by captopril, while the bradycardiac response was not changed. These findings suggest that captopril attenuated centrally vasodepressor and sympatho-inhibitory responses of the baroreflex and activated centrally cardiac vagal efferent activity.