LOCALIZATION OF NITRIC-OXIDE SYNTHASE IN THE REPRODUCTIVE-ORGANS OF THE MALE-RAT

Nitric oxide synthase (NOS), which catalyzes the production of nitric oxide (NO), was characterized within the reproductive tract of adult m ale Sprague-Dawley rats by means of biochemical and immunohistochemica l techniques. Tissues examined included the testis, epididymis (caput, corpus, and cauda regions), vas deferens, ejaculatory duct, seminal v esicle, and coagulating gland. NOS activity was measured by use of an assay based on the stoichiometric conversion of [H-3]-L-arginine to [H -3]-L-citrulline and NO, catalyzed by NOS. Low levels of NOS activity were detected in the testis and seminal vesicle (< 0.5 fmol [H-3]-L-ci trulline formed/min/mg protein in each tissue). The highest levels of NOS activity were present in the cauda segment of the epididymis and i n the vas deferens, each having a sevenfold greater amount of NOS acti vity than the testis (P < 0.05). Intermediate levels of NOS activity w ere detected in the coagulating gland (0.863 +/- 0.248 fmol [H-3]-L-ci trulline formed/min/mg protein), caput epididymidis,(0.457 +/- 0.180 f mol [H-3]-L-citrulline formed/min/mg protein), and corpus epididymidis (0.631 +/- 0.215 fmol [H-3]-L-citrulline formed/min/mg protein). NADP H diaphorase histochemistry and NOS immunohistochemistry localized NOS to neuronal fibers coursing throughout the smooth musculature and sub epithelial regions of the epididymis, vas deferens, and ejaculatory du ct. Endothelial cells and nerve plexuses within the adventitia of bloo d vessels supplying reproductive tissues were also positive for NOS. A dditional localizations of NOS were within epithelial cells of the epi didymis and coagulating gland. Taken together, these results support a n extensive role for NO in contractile, hemodynamic, and secretory pro cesses in the male reproductive tract and imply that this novel mediat or participates in regulatory mechanisms required for male reproductiv e function.