Diabetes Undermines Estrogen Control of Inducible Nitric Oxide Synthase Function in Rat Aortic Smooth Muscle Cells Through Overexpression of Estrogen Receptor-

Background—Previous reports from our group have shown that 17 -estradiol reduces the synthesis and activity of inducible nitric oxide synthase (iNOS) in rat aortic smooth muscle cells (SMC) in response to inflammatory mediators. In this study, we investigated the effect of 17 -estradiol on iNOS function in aortic SMC from streptozotocin-diabetic rats. Methods and Results—Comparative analysis of NO release and of iNOS mRNA and protein content after 24-hour stimulation with a cytokine mixture revealed milder iNOS activation in diabetic than in control SMC. Furthermore, 17 -estradiol dose-dependently blocked iNOS synthesis and activity in control but not in diabetic SMC. The defective estrogen response in diabetic SMC at 24 hours could not be attributed to reduced expression of estrogen receptors (ER). In fact, mRNA and protein levels of ER and, to a greater extent, of ER , were increased in diabetic compared with nondiabetic SMC. Cytokines decreased ER and ER expression in both groups. However, 17 -estradiol dosedependently restored the expression of ER but further downregulated that of ER , indicating a differential regulation of ER isoforms. Conclusions—Estrogenic control of iNOS was impaired in diabetic SMC. This was associated with a larger increase of ER than of ER protein, whereas 17 -estradiol regulated the two isoforms in an opposite fashion. Thus, modifications in the estrogen modulation of iNOS and in the expression pattern of ER may be involved in diabetic vascular dysfunction. (Circulation. 2003;108:211-217.)