17-BETA-ESTRADIOL ENHANCES NITRIC-OXIDE SYNTHASE ACTIVITY IN ENDOTHELIUM-DENUDED RAT AORTA

1. It has been suggested that oestrogen-produced vasodilatation is due to induction of endothelial nitric oxide synthase (NOS), but there ar e many reports of direct effects on vascular smooth muscle. in thr pre sent study, these processes were investigated ia rat aorta isolated fr ont ovariectomized rags, 2. Short-term treatment (10 min) with 17 beta -oestradiol (10 mu mol/L) produced a smalt attenuation of the phenylep hrine (PE)-induced constriction, which was unaffected by the nitric ox ide synthase inhibitor L-N5(-1-iminoethyl)ornithine (NIO; 100 mu mol/L ), Long-term treatment (6h) with 17 beta-oestradiol (10 mu mol/L) did not affect acetylcholine-mediated vasorelaxation in endothelium-intact aortic rings, but did attenuate PE-induced constriction. This attenua tion was also observed in endothelium-denuded preparations after 17 be ta-oestradiol (10 mu mol/L for 6h) and was far greater than the acute effect of 17 beta-oestradiol (10 mu mol/L), 3. The attenuation produce d by 17 beta-oestradiol (10 mu mol/L for Gh) was significantly inhibit ed bg concomitant treatment with cycloheximide (1 mu mol/L), suggestin g that protein synthesis vias involved, NIO (100 mu mol/L,) also atten uated the effect, which suggests that the anti-constrictor effect of 1 7 beta-oestradiol occurs through the increased production of nitric ox ide (NO). 17 beta-Oestradiol increased NO production, as assessed by d ire conversion of [H-3]-arginine to [H-3]-citrulline in rat aorta, The se effects were prevented by; cycloheximide and NIO, The anti-constric tor effect of oestrogen was blocked hy the oestrogen receptor antagoni st ICI 182 780 (100 nmol/L), 4. Western blotting using an antibody spe cific for inducible nitric oxide synthase (NOS) revealed that 17 beta- oestradiol (10 mu mol/L for 24 h) treatment induced the formation of i nducible NOS protein in the aorta, an effect blocked by cycloheximide. Tile results indicate that 17 beta-oestradiol can attenuate the vasoc onstrictor effect of PE by a specific receptor-mediated process that i nvolves induction of inducible NOS.