Role of Nitric Oxide and Nitric Oxide Synthase in Penile Erection

Jung, Hee Chang; Suh, Jun Kyu; Park, Tong Choon

Abstract

Nitric oxide(NO) is known to act as an important neural mediator of penile erection. Nitric oxide synthase(NOS), which produces NO, has been recently identified in autonomic neurons supplying genitourinary organs including penis. The present study was undertaken to investigate the role played by NO in erectile physiology by correlating its action with the existence and activity of NOS. Initial experiments were performed to elucidate NOS expression in the human and rat penis. Western blotting analysis identified a protein of 155KDa molecular weight identical to neural form of NOS. The NOS blot density in the human and rat penis was similar each other, which was lower than that in the cerebellum. Additional studies of NOS using assay of NADPH diaphorase activity and nitrite measurement were performed in various organs of the rat. NOS activity regionally predominated in the cerebellum, urethra, penis, and urinary bladder in the order Subsequent investigations focused on the physiologic role of NO, which was determined using an in vivo electroerection model in the rat. ntracavernous injections of NOS inhibitor (L-NOARG or L-NAME from 0.000001M to 0.001M) were found to suppress the nerve-induced erection in concentration dependent manner. Subsequent intracavernous injection of L-arginine(0.01M) partially restored penile erection suppressed by L-NOARG or L-NAME(0.001M). These results indicate that the neural form of constitutive NOS in the corpora cavernosa of the penis synthesizes NO by its catalytic action, which mediates penile erection. Furthermore, determination of cavernosal NOS expression and/or activity may allow to characterize certain pathological conditions which cause neurogenic impotence.