Distribution of NADPH-diaphorase and nitric oxide synthase (NOS) in different regions of porcine oviduct during the estrous cycle

Nitric oxide synthase (NOS) is responsible for the biological production of nitric oxide (NO) in several organs, including those of the reproductive t ract. We investigated potential changes in NADPH-diaphorase (NADPH-d) activ ity (marker for NOS activity) and the presence and distribution of NOS in t he porcine oviduct. Tissues were obtained from gilts (n=16) on different da ys of the estrous cycle. One fallopian tube was used for histo-and immunohi stochemistry and the other for Western blotting analysis. NADPH-d activity was much higher in the epithelium of the mucosa than in the myosalpinx. The highest activity of NADPH-d was always found in the epithelium of the isth mus. The intensity of the reaction (arbitrary units +/- SEM) in isthmus epi thelium increased from the postovulatory period until early proestrus (96.2 +/- 11.2) and then gradually decreased. The lowest intensity of NADPH-d re action in the epithelium of the isthmus was seen at estrus (58.4 +/- 7.7). The most intense NADPH-d activity in myosalpinx of all parts of the oviduct was observed at the postovulatory stage of the estrous cycle (isthmus 38.3 +/- 2.5; ampulla 35.6 +/- 4.2; infundibulum 24.7 +/- 0.8) and then decreas ed during the remaining stages of the estrous cycle (p< 0.001). The presenc e of endothelial NOS (eNOS) was detected in epithelial cells of mucosa and in endothelium of vascular tissues and myosalpinx during all studied days o f the estrous cycle. The positive reaction for inducible NOS (iNOS) was res tricted only to the endothelium of lymph vessels and some blood vessels. Be cause our Western blotting analysis revealed that porcine oviduct contains eNOS but not iNOS, we suggest that eNOS is the main isoform of NOS expresse d in the porcine oviduct. We concluded that the different activity of NADPH -d in the various regions of the oviduct, accompanied by changes in its act ivity during the course of the estrous cycle, could indicate an important r ole of NO in regulation Of tubal function.