Endothelin-1 and endothelial nitric oxide synthase immunoreactivity in lymphatic vessels of the uterine broad ligament during the estrous cycle in the pig

Immunohistochemical localization and distribution of endothelin (ET-1) and nitric oxide synthase (eNOS) were investigated in precollector and collector lymphangions of lymphatic vessels leaving the ovary and were found in the vascular subovarian plexus (mesovarium) as well as in those emanating from the oviductal isthmus and uterine horn (mesosalpinx and mesometrium, respectively) forming the paraovarian lymphatic plexus in the broad ligament of the uterus during different phases of the estrous cycle in pigs. The polyclonal antibody for ET-1 and the monoclonal antibody for eNOS isoform were used for studies on the light-microscopic level. Immunoreactivities to both ET-1 and eNOS were observed in the endothelial cell cytoplasm of precollector and collector lymphangions and were not demonstrated in smooth muscle cells of the lymphatics examined. In the endothelium, the intensity of immunostaining for ET-1 and eNOS was found to be estrous phase-dependent and differed between precollector and collector lymphangions. In general, immunoreactivity to ET-1 was more intense in the endothelium of shrunken lymphangions, whereas that for eNOS was more intense in lymphangions with the large lumen. These results suggest that ET-1 and eNOS can play a role in mechanisms regulating the vascular contractile activity promoting lymph flow during the estrous cycle in the porcine broad ligament.