Effect of 17β-oestradiol on cytokine-induced nitric oxide production in rat isolated aorta

1 Studies were performed on isolated aortic rings without endothelium to investigate the effect of 17 beta-oestradiol on cytokine-induced nitric oxide production by the inducible nitric oxide synthase (iNOS). 2 Treatment of the isolated aortic rings with interleukin-1 beta (IL-1 beta, 20 mu ml(-1)) led to the expression of iNOS mRNA and protein, as well as significant nitrite accumulation in the incubation media and suppression of phenylephrine (1 nM-10 mu M)-evoked contraction. 3 Cycloheximide (1 mu M), a protein synthesis inhibitor, prevented iNOS protein expression, nitrite accumulation and the suppression of contractility by IL-1 beta on the isolated aortic rings. 17 beta-oestradiol (1 nM-10 mu M) and the partial oestrogen receptor agonist 4-OH-tamoxifen (1 nM-10 mu M) produced concentration-dependent inhibition of IL-1 beta-induced nitrite accumulation and restored vasoconstrictor responsiveness to phenylephrine, similar to the iNOS inhibitor aminoguanidine (100 mu M). 4 Semiquantitative PCR demonstrated decreased iNOS mRNA in the IL-1 beta-induced and 17 beta-oestradiol-treated rings. Western blot analysis of rat aorta homogenates revealed that 17 beta-oestradiol treatment resulted in a reduction in IL-1 beta-induced iNOS protein level. 5 Incubation with tumour necrosis factor alpha (TNF alpha, 1 ng ml(-1)) resulted in significant nitrite accumulation in the incubation media and suppression of the smooth muscle contractile response to phenyrephrine, similar to IL-1 beta. The effects of TNF alpha were also inhibited by co-incubation of the rings with 17 beta-oestradiol and 4-OH-tamoxifen (1 mu M). 6 The anti-transforming growth factor-beta 1 (TGF-beta 1) antibody, which inhibited TGF-beta 1-induced suppression of nitrite production from IL-1 beta-treated vascular rings, did not affect the inhibitory action of 17 beta-oestradiol, suggesting that the effect of oestrogen on iNOS inhibition was not mediated by TGF-beta 1. 7 These results show that the ovarian sex steroid, 17 beta-oestradiol is a modulator of cytokine-induced iNOS activity in rat vascular smooth muscle and its mechanism of action involves decrease of iNOS mRNA and protein.