Effects of an orally active converting-enzyme inhibitor, SQ 14225, on pressor responses to angiotensin administered into the brain ventricles of spontaneously hypertensive rats.

1. Two hours after oral feeding of normotensive Wistar Kyoto rats with the converting-enzyme inhibitor SQ 14225 (1 and 10 mg/kg), an increase of angiotensin I plasma concentrations from 892 +/- 113 to 1660 +/- 167 and 2951 +/- 405 pg/ml was observed. 2. Administration of SQ 14225 with the drinking fluid overnight suppressed the pressor responses to intravenous angiotensin I, although the blood pressure increase after intravenous angiotensin II was not altered in normotensive and spontaneously hypertensive rats. No change of pressor effects after injections of angiotensin I and II into the brain ventricles was observed after oral SQ 14225. 3. Intracerebroventricular infusions of SQ 14225 in spontaneously hypertensive rats abolished the central pressor responses to angiotensin I. 4. The results show that SQ 14225 effectively blocked the conversion of endogenous and exogenous angiotensin I into angiotensin II in plasma, and the conversion of exogenous angiotensin I in brain. Under the conditions studied, SQ 14225 does not cross the blood-cerebrospinal fluid barrier in spontaneously hypertensive rats.