Distribution of neuronal and non-neuronal NADPH diaphorases and nitric oxide synthases in rat uterine horns under different hormonal conditions.

Since pharmacological evidence indicates that nitric oxide (NO) operates in the control of uterine motility, we have studied the distribution of NADPH diaphorase and NO synthases in the rat uterus using histochemical and immunohistochemical methods. Numerous nerve fibers displayed NADPH diaphorase activity and immunoreactivity to antisera raised against neuronal NO synthase. Nerve fibers appeared in all stages of the estrous cycle and also after ovariectomy. NADPH diaphorase activity was also present in endothelia and cells dispersed in the different uterine layers. Most NADPH diaphorase-positive (ND) cells had eosinophilic granules with occasional cells expressing the ED1 macrophage-monocyte marker. Immunoreactivity for an inducible NO synthase was found in a small number of macrophage-like cells without NADPH diaphorase activity. Thus, ND cells may express another NO synthase isoform not detected by the available antisera. In normal cycling rats, ND cells were most abundant during proestrus, and their number further increased after estrogen treatment. ND cells were not observed after ovariectomy but were present after estrogen replacement therapy. ND cells could be involved in the estrogenic control of in vivo and in vitro uterine.