Effect of low doses of angiotensin II perfusion on the hypotensive action of captopril in anaesthetized normotensive and spontaneously hypertensive rats

The effect of intravenous (i.v.) captopril on mean arterial blood pressure (MABP) of anaesthetized normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats perfused i.v. with two doses of angiotensin II (ANG II; 2.9 and 5.8 pmol/kg per min) was studied to determine the role of the suppression of plasma ANG II in the hypotensive action of captopril. The reduction of MABP by captopril was attenuated in WKY and abolished in SHR by the highest dose of ANG II; it was unchanged in WKY and attenuated in SHR by the lowest dose of ANG II. The suppression of plasma ANG II thus explains a minor part of the acute reduction of MABP by captopril in WKY and a major part of this action in SHR. Plasma ANG II contributes to the maintenance of high blood pressure in SHR.