The localization and expression of NADPH-diaphorase and isoforms of nitric oxide synthase in the porcine gravid uterus.

The aim of the present study was to investigate the localization and expression of NADPH-diaphorase (NADPH-d) as well as endothelial (eNOS) and inducible (iNOS) nitric oxide synthase isoforms in the porcine uterus on Days 20, 30, 40, 60, 75 and 90 of gestation. The significant increase (p<0.001) in NADPH-d reaction was found in the trophoblast. The positive NADPH-d staining was also observed in the luminal and glandular epithelium and vascular endothelium. eNOS immunoreactivity was found in the endothelium of placental and maternal blood vessels, in the luminal epithelium and endometrial glands. The trophoblast displayed a slight increase in eNOS immunoreactivity starting from Day 20 of gestation. In comparison to eNOS, a stronger iNOS staining was found in the placental and endometrial blood vessels and in the trophoblast cells. Western blot analysis revealed a gradual increase in eNOS protein expression from Day 30 (p<0.001) and iNOS from Day 60 of gestation (p<0.001) in the placental zone. The significant increase in the NADPHd/iNOS expression after day 60 of gestation suggests a contribution of iNOS in uterine NO generation during the second half of pregnancy. A gradual increase in eNOS expression starting on Day 30 of pregnancy may indicate a synergistic, supportive effect on uterine vascular and myometrial contractility in pigs affecting the maintenance of the uterine quiescence.