EFFECT OF 17-BETA-ESTRADIOL 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 ni tric 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 Cycl oheximide (1 mu M), a protein synthesis inhibitor, prevented iNOS prot ein expression, nitrite accumulation and the suppression of contractil ity by IL-1 beta on the isolated aortic rings. 17 beta-oestradiol (1 n M-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 responsiven ess to phenylephrine, similar to the iNOS inhibitor aminoguanidine (10 0 mu M). 4 Semiquantitative PCR demonstrated decreased iNOS mRNA in th e IL-1 beta-induced and 17 beta-oestradiol-treated rings. Western blot analysis of rat aorta homogenates revealed that 17 beta-oestradiol tr eatment resulted in a reduction in IL-1 beta-induced iNOS protein leve l. 5 Incubation with tumour necrosis factor alpha (TNF alpha, 1 ng ml( -1)) resulted in significant nitrite accumulation in the incubation me dia and suppression of the smooth muscle contractile response to pheny rephrine, similar to IL-1 beta. The effects of TNF alpha were also inh ibited 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 ni trite production from IL-1 beta-treated vascular rings, did not affect the inhibitory action of 17 beta-oestradiol, suggesting that the effe ct of oestrogen on iNOS inhibition was not mediated by TGF-beta 1. 7 T hese results show that the ovarian sex steroid, 17 beta-oestradiol is a modulator of cytokine-induced iNOS activity in rat vascular smooth m uscle and its mechanism of action involves decrease of iNOS mRNA and p rotein.