Estrogen-mediated up-regulation of the Ca-dependent constitutive nitric oxide synthase in the rat aorta and heart

The role of endogenous estrogens has been studied in the regulation of the Ca-dependent constitutive nitric oxide synthase (cNOS) enzyme activity in aortic and cardiac tissues of the rat. The activity of cNOS enzyme was measured by the citrulline assay in the abdominal aorta and in the left ventricle of the heart obtained from male, sham-operated female and ovariectomized female Wistar rats. Estrogen replacement therapy (17-beta-estradiol, 20-100 microg/kg/day, s.c.) has been performed in ovariectomized rats over two weeks. We found that cNOS activity was higher in the aorta and heart of female rats compared to males. Ovariectomy decreased cNOS activity in both tissues to that level what could be observed in males. Estrogen supplementation caused a dose-dependent elevation of cNOS enzyme activity in cardiac and aortic tissues, where the higher dose (100 microg) completely restored cNOS enzyme activity to the levels found in females. We concluded that endogenous estrogens up-regulate the activity of the cNOS isoenzymes in the rat aorta and heart.