17β-Estradiol Decreases Nitric Oxide Synthase II Synthesis in Vascular Smooth Muscle Cells*

Several studies have provided evidence for a direct effect of 17beta-estradiol on vessel wall via interaction with the constitutively expressed nitric oxide synthase (NOS) by endothelium. The aim of the present study was to investigate the effect of 17beta-estradiol on inducible NOS (NOS II) in primary culture of smooth muscle cells (SMC) from rat aorta. We here prove that 17beta-estradiol decreases the content and activity of NOS II in SMC. This effect appears to be the consequence of ER activation, because: 1) ER alpha and ER beta are expressed in rat aorta SMC grown in culture; 2) low concentrations of hormone modulate NOS II activity; 3) the specific ER alpha antagonist ICI182,780 completely blocks 17beta-estradiol effect. On the other hand, progesterone is deprived of any effect on NOS II content or activity, proving the specificity of 17beta-estradiol effect. In addition, we show that 17beta-estradiol can counteract the increase in NOS II activity following cytokine treatment. The observation could indicate a novel mechanism for the protective effects exerted by these hormones in cardiovascular diseases and atherosclerosis in particular.