Ramiprilat enhances endothelial autacoid formation by inhibiting breakdown of endothelium-derived bradykinin

We studied whether inhibition of angiotensin converting enzyme stimulates the formation of nitric oxide and prostacyclin in cultured human and bovine endothelial cells by an enhanced accumulation of endothelium-derived bradykinin. Nitric oxide formation was assessed in terms of intracellular cyclic GMP accumulation, prostacyclin release by a specific radioimmunoassay. Inhibition of angiotensin converting enzyme by ramiprilat dose- and time-dependently increased the formation of nitric oxide and prostacyclin. These increases, peaking within 10 minutes, were maintained for at least 60 minutes. The ramiprilat-induced cyclic GMP increase was completely abolished by the stereospecific inhibitor of nitric oxide synthase, NG-nitro-L-arginine. The B2-kinin receptor antagonist, Hoe 140 (0.1 microM), markedly attenuated the cyclic GMP accumulation and abolished the increase in prostacyclin release. The supernatant of endothelial cells, incubated with ramiprilat (0.3 microM) for 15 minutes, elicited a significant nitric oxide release (as assessed by a guanylyl cyclase assay) in untreated endothelial cells used as detector tissue. Preincubation of the detector cells with Hoe 140 completely abolished this nitric oxide release. These data indicate that cultured endothelial cells from different species are capable of producing and releasing bradykinin into the extracellular space in amounts that lead to a sustained stimulation of nitric oxide and prostacyclin formation, provided that bradykinin degradation is prevented by angiotensin converting enzyme inhibition. Thus, the protective effect of angiotensin converting enzyme inhibitors observed on endothelial vasomotor function in hypertension may be explained by the local accumulation of endothelium-derived bradykinin that acts in an autocrine and paracrine manner as potent stimulus for endothelial autacoid formation.