Expression and cellular distribution of NADPH-diaphorase and nitric oxide synthases in the porcine uterus during early pregnancy

Nitric oxide plays a key role in the regulation of various female reproductive processes such as ovulation, implantation and myometrial relaxation. The aim of the present study was to determine the histochemical activity and cellular localization of NADPH-d in the porcine uterus during early pregnancy, including the implantation period. Tissue samples collected from the pig uteri on days 5, 10, 12, 15 and 17 of pregnancy were stained histochemically for NADPH-d activity and immunohistochemically for NOS isoforms localization. In the luminal epithelium a significant increase of NADPH-d activity was observed on days 5-12 of pregnancy. On day 17 of pregnancy, two different staining patterns were observed: 1) a significant (p0.001) decrease in NADPH-d activity at the site of implantation and 2) the high NADPH-d activity at inter-implantation regions. The endometrial glands showed a significant (p0.001) increase in NADPH-d staining with high activity in individual glands. The arterial endothelium expressed stronger NADPH-d staining compared with venous vessels. Immunoreactivity of eNOS was similar to NADPH-d staining but no optical differences in the intensity of staining were observed. Clear iNOS immunoreactivity was detected in the luminal epithelium, endometrial stroma and individual endometrial glands. The vascular endothelium displayed weak iNOS staining.