Role of Nitric Oxide in the Physiology of Erection1

Penile erection is understood to be a neurally regulated physiologic event, although the underlying mechanisms have eluded characterization for more than a century. The classical autonomic parasympathetic and sympathetic nervous systems are involved, but the process of erection does not appear to require cholinergic or adrenergic mechanisms. As the search for the principal mediator of penile erection has continued over time, nitric oxide (NO), a gaseous messenger molecule, has been rapidly advanced to fulfill this elusive role. In the recent past, various biochemical and functional data have accumulated to support this understanding. These have shown that NO is an important mediator of corpus cavernosal smooth muscle relaxation and have revealed its potential sources and mechanisms of action in the penis. Additional work involving animal erection models has established that NO mediates physiologic penile erection. This minireview presents these data and includes results from recent clinical trials that have preliminarily evaluated the efficacy of NO-generating or -releasing compounds for the treatment of erectile dysfunction.