UP-REGULATION OF ENDOTHELIAL AND NEURONAL CONSTITUTIVE NITRIC-OXIDE SYNTHASE IN PREGNANT RATS

Pregnancy is characterized by hemodynamic and body fluid alterations. Increased nitric oxide (NO) production has been suggested to play a ro le in the hemodynamic alterations of pregnancy and has also been repor ted to increase arginine vasopressin (AVP) release. We therefore hypot hesized that gestation could increase both NO synthase (NOS) constitut ive isoforms, neuronal NOS and endothelial NOS, and thereby contribute to the hyposmolality and peripheral arterial vasodilation of pregnanc y, respectively. The present study was therefore undertaken to examine the constitutive NOS isoforms in aortas, mesenteric arteries, and hyp othalami of pregnant rats on day 20 of gestation compared with age-mat ched nonpregnant rats. Plasma AVP was determined by radioimmunoassay a nd hypothalamic mRNA AVP by solution hybridization assay. Hypothalamic neuronal NOS was assessed by Northern blot and Western blot; endothel ial NOS was assessed by Western blot in arteries and hypothalamus. The results demonstrated that 1) plasma AVP and hypothalamic AVP mRNA are increased in pregnant rats (n = 8), 2) neuronal NOS protein and mRNA are increased in hypothalamus of pregnant rats (n = 4), and 3) endothe lial NOS expression, as assessed by Western blot analysis, is increase d in both conductance (aorta) as well as resistance (mesenteric) arter ies of pregnant rats (n = 4). We conclude that both of the constitutiv e NOS isoforms are increased in pregnant rats, suggesting that the per ipheral arterial vasodilation and hyposmolality of pregnancy could be mediated by these isoforms.