Increased Nitric Oxide Synthase Activity and Expression in the Human Uterine Artery During Pregnancy

Evidence exists that NO plays a role in the vasodilation that occurs during pregnancy. The purpose of the present study was to determine whether the role of NO is associated with an increase in the activity and protein expression of NO synthase (NOS) in the human uterine artery. Uterine arteries were obtained from pregnant patients (P arteries) and nonpregnant patients (NP arteries). NOS activity was estimated with the L-(3)H-arginine-to-L-(3)H-citrulline conversion method and on the basis of changes in tissue levels of cGMP. Western immunoblotting and immunohistochemistry were used to assess NOS protein expression. Ca(2+)-dependent NOS activity was 8 times greater (P:NP arteries (follicular)>NP arteries (luteal). The neuronal NOS was located in the adventitia of P and NP arteries. Basal NO-dependent and bradykinin-stimulated levels of cGMP were higher (P:<0.05) in P than in NP arteries. These results indicate that an upregulation of eNOS protein expression could account for the increased NO synthesis/release in the human uterine artery during pregnancy.