Hypotension induced by inhibition of angiotensin-converting enzyme in pentobarbital-anesthetized dogs.

The mechanism of the hypotensive response produced by inhibition of the angiotensin converting enzyme was studied in pentobarbital anesthetized dogs. A recently developed potent inhibitor of the converting enzyme, SQ 14,225 (D-3-mercapto-2-methyl propanoyl-L-proline), administered i.v. to intact dogs resulted in a rapid marked decrease in blood pressure. In nephrectomized dogs, SQ 14,225 retained significant hypotensive activity, although the absolute magnitude of the decreases in blood pressure were less than had been observed in dogs with intact kidneys. SQ 14,225 also lowered blood pressure when administered to intact dogs in which angiotensin II receptors had been blocked with the receptor antagonist Sar1,Ala8-angiotensin II. This apparent ability of SQ 14,225 to decrease blood pressure in the absence of a functional renin angiotensin system was shared by a structurally dissimilar, nonapeptide, angiotensin converting enzyme inhibitor, SQ 20,881 (Glu-Trp-Pro-Arg-Pro-Gln-Ile-Pro-Pro). SQ 20,881 also produced significant decreases in blood pressure in nephrectomized dogs. These findings indicate that the angiotensin converting enzyme inhibitors, SQ 14,225 and SQ 20,881 may lower blood pressure in anesthetized normotensive dogs via a mechanism unrelated to either the renin angiotensin system or the renal kinin system.