Immunocytochemical distribution of nitric oxide synthase in the human corpus cavernosum: an electron microscopical study using the tyramide signal amplification technique

Nitric oxide has proven to be an important mediator in the relaxation of hu man cavernosal smooth muscle. Nevertheless, there are many inconsistencies in the literature regarding the cellular and subcellular distribution of en dothelial nitric oxide synthase in the human penis. The purpose of this stu dy was to reexamine the localization of eNOS and nNOS in the cellular anato my of the human cavernous body by means of electron microscopical immunocyt ochemistry in combination with the tyramide signal amplification technique (TSA). Using specific antibodies against eNOS and nNOS, the NAPDH-diaphoras e reaction and advanced protocols for fixation and staining procederes, the occurrence of NOS isoenzymes eNOS and nNOS were examined in cavernosal spe cimens of ten male patients who were subjected to surgery for penile deviat ion. eNOS immunoreactivity and NADPH-d staining was seen to be significantl y present in the endothelial cells covering the cavernous spaces and in the endothelium of helicine arteries. In endothelial cells, the NADPH-d reacti on product BSPT-formazan was abundantly detectable attached to membranes of the endoplasmatic reticulum and the mitochondria whereas posititve eNOS im munostaining was seen in the endothelial cells throughout their cytoplasm w ithout any particular relation to organelles. No considerable eNOS immunore activity was detectable in the trabecular smooth muscle cells. nNOS stainin g was found in nerve fibers innervating the cavernous body and cavernosal a rteries. Our results counteract the hypothesis of the cavernous smooth musc le as a local source of NO and underline the importance of an intact endoth elial function for penile erection and the contribution of eNOS to this pro cess.