Pharmacology of penile erection in humans.

The pharmacologic aspects of erection, including neuropharmacology and erectile responses to exogenous agents, are reviewed. The pharmacology of erection is complex and still incompletely understood. Older evidence suggesting acetylcholine as the primary neurotransmitter has been shown to be insufficient. Our recent experiments utilizing strips of human corpus cavernosum indicate the need to consider the roles of other erectogenic substances, such as vasoactive intestinal polypeptide, endothelium-derived relaxation factor (EDRF), and prostaglandins. From the results of these studies, three stages in the development of an erection are postulated: (1) withdrawal of alpha-adrenergic neuromuscular activity, (2) inhibition of alpha-adrenergic neuromuscular activity by endogenous substances such as prostaglandin E1 and vasoactive intestinal polypeptide, and (3) activation of NANC neurotransmission and direct relaxation of smooth muscle by endogenous substances such as EDRF.