NITRIC-OXIDE SYNTHASE ISOFORMS IN THE RAT UTERUS - DIFFERENTIAL REGULATION DURING PREGNANCY AND LABOR

Production of nitric oxide in the uterus is increased during pregnancy and decreased during delivery. In this study the isoform of nitric ox ide synthase which may be responsible for the changes in nitric oxide production was investigated in relation to pregnancy and delivery. Mon oclonal antibodies were used to measure changes in neuronal nitric oxi de synthase (NOS I), macrophage nitric oxide synthase (NOS II) and end othelial cell nitric oxide synthase (NOS III) protein in the rat uteru s by densitometric scanning of specific bands. Results show that: (I) NOS II protein concentrations in the uterus were substantially increas ed during pregnancy and were decreased during delivery, both at term a nd preterm (induced by RU486); (2) NOS III protein was present at all stages examined but the concentrations were unchanged; (3) NOS I was p resent in the rat uterus during the nonpregnant stage but not during p regnancy and delivery. The changes in uterine NOS II protein concentra tions during pregnancy and delivery were further confirmed by the chan ges in the Ca2+-independent, but not Ca2+-dependent, nitric oxide synt hase activity. Therefore, an increase in NOS II, thus in nitric oxide production during pregnancy, may play a role in maintaining uterine qu iescence.