Effects of 17 beta-oestradiol on rat isolated coronary and mesenteric artery tone: Involvement of nitric oxide

Pre- and post-menopausal women receiving oestrogen replacement therapy have a significantly reduced risk of cardiovascular disorders. It has been sugg ested that this protection might be partly a result of a direct relaxant ef fect of oestrogens on coronary arteries. This study examines and directly c ompares the effects of 17 beta-oestradiol on rat isolated coronary and mese nteric vessels. The influence of nitric oxide on these responses was also i nvestigated. 17 beta-Oestradiol caused similar concentration-dependent relaxation of iso lated coronary and mesenteric resistance arteries pre-contracted with eithe r KCl (60 mM) or 9,11-dideoxy-11 alpha,9 alpha-epoxymethanoprostaglandin (U 46619; 1 mu M). The relaxation responses to 17 beta-oestradiol were signifi cantly reduced, but not totally inhibited, in the presence of N-omega-nitro -L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase; t hey were not altered by indomethacin, an inhibitor of prostaglandin synthes is. The responses to 17 beta-oestradiol in the presence of L-NAME were not dependent on the vessel studied or the precontracting agent used. These results suggest that nitric oxide might contribute to the vasodilator y effects of 17 beta-oestradiol in rat isolated coronary and mesenteric res istance arteries.