Experiments were designed to determine whether or not normal fluctuations in sex steroid hormones affect gene transcription for endothelial nitric oxide synthase (ecNOS) and preproendothelin-1. Messenger RNA (mRNA) was extracted from aortic endothelial cells of adult, gonadally intact or ovariectomized (for four weeks) Yorkshire female pigs. Northern blot analysis of constitutive nitric oxide synthase (ecNOS) and preproendothelin-1 was quantified by densitometry relative to expression of mRNA for GAPDH and cyclophilin. There were no differences in circulating levels of endothelin-1 among gonadally intact or ovariectomized pigs. On the contrary, plasma levels of nitric oxide were significantly decreased in ovarectomized compared to gonadally intact females. Expression of mRNA for both ecNOS and preproendothelin-1 were increased significantly in aortic endothelial cells from ovarectomized pigs. These results suggest that the ovarian hormones regulate production of nitric oxide and endothelin-1 at the level of gene transcription.