Different effects of captopril and other angiotensin converting enzyme inhibitors on cardiovascular preparations

The effects of captopril and of other angiotensin-converting enzyme inhibitors (zofenopril, fosenopril and enalaprilic acid) were tested on the isolated rabbit heart and aorta. Captopril elicited an erratic negative inotropic effect and a reduction in basal coronary perfusion pressure (10(-5)-10(-4) M). The increase of coronary perfusion pressure induced by vasopressin, methoxamine, angiotensin II and Bay K 8644 was partially antagonized by captopril (10(-7)-10(-4) M) in a non-specific manner. These actions were not modified by saralasin or indomethacin and by ex vivo pretreatment with captopril itself. On the aortic strips, the contraction plateau induced by KCl and angiotensin II was partially inhibited (10(-6)-10(-4) M), while no effect was observed on those induced by noradrenaline, serotonin and PGF2 alpha. The Ca2+ concentration-response curve appeared shifted to the right in a non-competitive manner. The other angiotensin-converting enzyme inhibitors showed no effect up to 10(-4) M on isolated heart or aorta. Results obtained with captopril were consistent with vasorelaxant activity independent of the tissue renin-angiotensin system. Modulatory activity on the intracellular calcium movement may be involved.