Hypotensive action of captopril and saralasin in intact and anephric spontaneously hypertensive rats.

Intravenous injection of the converting enzyme inhibitor SQ14,225 (captopril, 2 mg/kg) reduced the blood pressure of anesthetized, spontaneously hypertensive rats (SHR) progressively over a 3-hour period. An indistinguishable fall in blood pressure occurred in SHR that were bilaterally nephrectomized 1 hour prior to injection of the converting enzyme inhibitor. In the nephrectomized animals, plasma renin activity (PRA) had fallen to less than 30% of its initial values at the time of injection. Injection of the vehicle alone had no effect on blood pressure in either anephric or intact SHR. The converting enzyme inhibitor produced no significant change in the blood pressure of either intact or anephric normotensive Wistar-Kyoto (NT-WK) rats. Infusions of Sar1-Ala8-angiotensin II (saralasin, 10 micrograms/kg-1/min-1) similarly reduced blood pressure of both intact and anephric SHR. These results indicate that captopril and saralasin lower blood pressure in the SHR by some mechanism(s) independent of the kidneys, circulating renin, or bradykinin potentiation. It is suggested that angiotensin II, locally produced at some critical tissue site(s), is involved in the maintenance of raised blood pressure in SHR.