Effects of estrogen on nitric oxide synthase expression in rat aorta allograft and smooth muscle cells

Background: We find that chronic estradiol treatment inhibits the developme nt of transplant arteriosclerosis (TA). The mechanism of this inhibition re mains unclear. The objective of this study is to investigate in a non-cyclo sporin-requiring TA model whether estradiol-17 beta treatment modulates the expression of both endothelial nitric oxide synthase (ecNOS) and inducible nitric oxide synthase (iNOS) in the early phase following transplantation Methods: Orthotopic abdominal aorta allograft transplantation was performed in male rats using Brown-Norway rats as donors and Lewis rats as recipient s. The recipients (n = 50) were treated with estradiol 20 mu g/kg/day or pl acebo by osmotic minipump from 2 days prior to surgery until sacrifice on p ost-operative days 1, 3, 7, 14, and 21. The allografts were harvested and c ross-sections of the vascular tissues were used for immunohistochemical sta ining of ecNOS and iNOS. The effects of estradiol on cytokine-induced (tumo r necrosis factor-alpha and interleukin-l beta) iNOS protein and messenger RNA (mRNA) expression were also evaluated on rat aorta smooth muscle cells by Western blotting and RT-PCR in vitro, respectively. Results: The expression of ecNOS and iNOS was graded semiquantitatively fro m 0 to +3. Estrogen elevates ecNOS expression in the intima in the early ph ase following transplantation, 0.85 +/- 0.14 (day 7) and 1.08 +/- 0.11 (day 14) vs 1.53 +/- 0.25 (day 7) and 1.60 +/- 0.17 (day 14) for placebo and es tradiol treated groups respectively, p < 0.01. Estrogen suppresses iNOS exp ression in neointima (0.67 +/- 0.17 vs 0.24 +/- 0.04, p < 0.01, day 14), me dia (1.03 +/- 0.15 vs 0.4 +/- 0.09, p < 0.01, day 7), and adventitia (1.55 +/- 0.12 vs 1.02 +/- 0.10, p < 0.05, day 14) in the same phase. Estradiol t reatment inhibits cytokine-induced iNOS mRNA expression in cultured smooth muscle cells. Conclusions: Chronic estrogen treatment modulates both ecNOS and iNOS expre ssion in the early phase following transplantation. This is associated with the estrogen-protective effects on TA.