Kinins are metabolized by metallopeptidases present in different tissues. The aim of this study was to evaluate, employing functional studies in isolated human umbilical vein, the possible participation of angiotensin-converting enzyme, neutral endopeptidase and aminopeptidase P as an inactivation pathway of bradykinin, as well as assess if the endothelial layer is involved in this process. Concentration-response curves to bradykinin were constructed after 120 min incubation period on human umbilical vein rings with and without endothelium and enzymatic inhibitors were applied 30 min before construction of concentration-response curves. The presence of endothelium was confirmed by histological studies. Bradykinin-induced contractile responses were potentiated in human umbilical vein without endothelium when compared to intact tissues. Application of captopril 1 μM (angiotensin-converting enzyme inhibitor) or phosphoramidon 10 μM (neutral endopeptidase inhibitor) induced a leftward shift of bradykinin-elicited responses in human umbilical vein with endothelium while no effect was observed in tissues denuded of endothelium under the same treatment. Exposure to apstatin 10 μM (aminopeptidase P inhibitor) did not potentiate bradykinin-induced effects in intact human umbilical vein. When angiotensin-converting enzyme and neutral endopeptidase were concomitantly inhibited, there was a higher potentiation of bradykinin-elicited responses compared to the effects observed under individual inhibition of either enzyme. Moreover, concentration-response curves to FR190997, a non-peptidic bradykinin B(2) receptor agonist, were not modified under dual enzymatic inhibition. In conclusion, our results demonstrate for the first time the functional relevance of angiotensin-converting enzyme and neutral endopeptidase, localized on the endothelial layer, acting concurrently as a bradykinin inactivating pathway in isolated human umbilical vein.
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