In this study, we investigated the short-term effect of 17β-oestradiol on functional enzyme activity (FEA) of endothelin-converting enzymes in vitro using human internal mammary arteries (n = 7–8) and human saphenous veins (n = 16–17) obtained from patients undergoing coronary artery bypass graft surgery. Vascular rings were preincubated with either solvent control (0.2% ethanol) or 17β-oestradiol (1µM) for 30min and concentration–response curves to big ET-1 (0.1–100nM) or ET-1 (0.1–100nM) were performed. FEA for each concentration was calculated as the percentage activity [(contraction to big ET-1/contraction to ET-1)×100] normalized to KCl (100mM). In control experiments, at low concentrations FEA was lower in internal mammary arteries than in saphenous veins (P<0.05). While FEA was suppressed in saphenous veins by 10nM (4±1 versus 22±5%, P<0.01) and 30nM (26±4 versus 48±7%, P<0.05) 17β-oestradiol, FEA was markedly enhanced in internal mammary arteries by 10nM (33±12 versus 1±1%, P<0.001) and 30nM (44±12 versus 8±3%, P<0.01) 17β-oestradiol . FEA was not affected by 100nM 17β-oestradiol. These results demonstrate for the first time that short-term exposure to 17β-oestradiol affects FEA in vitro. Human internal mammary arteries have lower FEA than the saphenous veins, but FEA is differentially affected by acute exposure to 17β-oestradiol in human arteries and veins. Whether changes in FEA play a role in the vascular effects of 17β-oestradiol in vivo remains to be determined.

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