Evidence for the involvement of endothelial nitric oxide synthase from smooth muscle cells in the erectile function of the human corpus cavernosum

Nitric oxide (NO) is an important mediator in the relaxation of cavernosal smooth muscle. The present study examines the existence and location of the constitutive isoform eNOS (endothelial NO synthase) accompanying the already substantiated neurogenic NOS (nNOS) in the human corpus cavernosum of men with and without erectile dysfunction. Activities of NOS enzymes were examined in specimens of 11 potent and nine long-term impotent patients by means of light and electron microscopy using NADPH-diaphorase staining and immunohistochemical eNOS-specific, smooth muscle actin-specific and nNOS-specific markers. Cavernosal smooth muscle shows a distinct expression of eNOS. In contrast to the weaker expression of eNOS and nitrinergic innervation found in larger veins, the small intracavernosal helicine arteries express large quantities of eNOS and possess a dense nitrinergic innervation. Long-term impotent patients display a broad heterogeneity in eNOS expression and nitrinergic innervation while no overall correlation between NOS expression and erectile function was observed. The expression of eNOS indicates eNOS as a main source of NO alongside nNOS. The differentiated localization of eNOS supports at least a role of this isoform in vascular regulation.