Increased expression of endothelial constitutive nitric oxide synthase in rat aorta during pregnancy.

The mechanisms underlying enhanced vascular reactivity in pregnancy are not yet defined. In this study we have investigated the potential role of endothelium-derived vasodilator nitric oxide (EDNO). EDNO-mediated dilatory responses in vitro were markedly increased in aorta of pregnant as compared with nonpregnant rats. This increase in EDNO-releasability was accompanied by a two-fold increase in mRNA of endothelial constitutive nitric oxide synthase (NOS-III). Chronically substituted estrogen, but neither progesterone nor testosterone induced an upregulation of NOS-III mRNA in aorta of gonadectomized rats which amounted to about half that induced in aorta of pregnant rats. Thus, increased EDNO-releasability and increased NOS-III mRNA contribute to enhanced vascular reactivity in pregnancy.