Regional vasodilating effects of spirapril diacid and enalapril diacid in anesthetized dogs.

The acute regional hemodynamic effects of spirapril diacid, a novel nonsulfhydryl angiotensin-converting enzyme inhibitor, and enalapril diacid at an equidepressor dose were examined in anesthetized dogs by simultaneously measuring renal, coronary, vertebral arterial and aortic blood flow. Spirapril diacid (30 micrograms/kg, i.v.) lowered aortic pressure and increased aortic and renal blood flow associated with no marked change in heart rate, myocardial contractility, vertebral and coronary blood flow in a similar manner to enalapril diacid (30 micrograms/kg, i.v.). Both inhibitors thus produced an increase in stroke volume and a decrease of the rate-pressure product. The decrease of renal vascular resistance after administration of both agents was greater than that in vertebral and coronary vascular beds. A relatively more prolonged renal vasodilatation and a shortened coronary vasodilatation were seen with spirapril diacid as compared with enalapril diacid, despite practically identical reductions in total peripheral resistance. Each of the drugs markedly inhibited the pressor and renal vasoconstrictor responses to angiotensin I. These results indicate that the two inhibitors exhibit a similar profile of regional differences in vasodilatory effects, although they might display different durations of regional vasodilatation.