We have investigated the effects of angiotensin-converting enzyme (ACE) inhibitors on intracellular Ca2+ levels in human cultured endothelial cells and on endothelial autacoid formation in endothelium-intact bovine coronary arteries and in isolated perfused rabbit and rat hearts. Incubation of cultured endothelial cells with ramiprilat (0.3 microM) caused a maintained increase in resting intracellular Ca2+. This effect was long-lasting, accompanied by an increased formation of both nitric oxide (NO) and prostacyclin (PGI2), and was abolished by the specific B2-kinin receptor antagonist Hoe 140. Ramiprilat also significantly enhanced the increase in intracellular Ca2+ elicited by bradykinin (3 nM). In endothelium-intact bovine coronary arteries, moexiprilat (0.3 microM), like bradykinin (30 nM), caused a nearly twofold increase in the vascular cGMP content which was abolished by both NG-nitro-L-arginine (30 microM) and removal of the endothelium. The functional consequences of this ACE inhibitor-induced increase in vascular cGMP content were reflected by a distinct relaxation of the coronary segments preconstricted with prostaglandin F2 alpha. In the isolated perfused rabbit heart, ramiprilat (0.3 microM) affected neither resting vascular tone nor endothelial autacoid release; however, the vasodilation and release of PGI2 in response to exogenously applied bradykinin (10 nM) were significantly enhanced by ramiprilat. This effect was also seen using moexiprilat (0.1 microM) in the isolated perfused rat heart. Although these findings suggest that endothelium-derived bradykinin is not involved in the control of resting vascular tone in the coronary microcirculation of the rabbit and the rat, there appears to be significant ACE activity to modulate bradykinin-induced endothelial autacoid formation.(ABSTRACT TRUNCATED AT 250 WORDS)