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 r ole of NO is associated with an increase in the activity and protein expres sion of NO synthase (NOS) in the human uterine artery. Uterine arteries wer e obtained from pregnant patients (P arteries) and nonpregnant patients (NP arteries). NOS activity was estimated with the L-[H-3]-arginine-to-L-[H-3] -citrulline conversion method and on the basis of changes in tissue levels of cGMP. Western immunoblotting and immunohistochemistry were used to asses s NOS protein expression. Ca2+-dependent NOS activity was 8 times greater ( P<0.01) in P than in NP arteries. Although most of this pregnancy-induced i ncrease in NOS activity was Ca2+ dependent (64%), a considerable portion wa s Ca2+ independent. Expressions of endothelial NOS (eNOS) and neuronal NOS, but not inducible NOS, were demonstrated in P and NP arteries. The eNOS wa s located in the endothelium and stained with a qualitative order of P arte ries>NP arteries (follicular)>NP arteries (luteal), The neuronal NOS was lo cated in the adventitia of P and NP arteries. Basal NO-dependent and bradyk inin-stimulated levels of cGMP were higher (P<0.05) in P than in NP arterie s. These results indicate that an upregulation of eNOS protein expression c ould account for the increased NO synthesis/release in the human uterine ar tery during pregnancy.