The role of nitric oxide in penile erection

Expert Opin Pharmacother. 2001 Jan;2(1):95-107. doi: 10.1517/14656566.2.1.95.


The functional state of the penis, flaccid or erect is governed by smooth muscle tone. Sympathetic contractile factors maintain flaccidity whilst parasympathetic factors induce smooth muscle relaxation and erection. It is generally accepted that nitric oxide (NO) is the principal agent responsible for relaxation of penile smooth muscle. NO is derived from two principal sources: directly from non-adrenergic non-cholinergic parasympathetic nerves and indirectly from the endothelium lining cavernosal sinusoids and blood vessels in response to cholinergic stimulation. The generation of NO from L-arginine is catalysed by nitric oxide synthase (NOS). There has been controversy over the relative prevalence of endothelial or neuronal NOS within the penis of different animal species. This review examines the role of NO in the penis in detail. Established and new treatments for erectile dysfunction whose effects are mediated via manipulation of the NO pathway are also described.

Publication types

  • Review

MeSH terms

  • Animals
  • Arginine / therapeutic use
  • Erectile Dysfunction / drug therapy
  • Erectile Dysfunction / physiopathology
  • Genetic Therapy
  • Humans
  • Male
  • Muscle Relaxation / drug effects
  • Muscle Relaxation / physiology
  • Muscle, Smooth, Vascular / drug effects
  • Muscle, Smooth, Vascular / physiology*
  • Nitric Oxide / biosynthesis*
  • Nitric Oxide / physiology*
  • Papaverine / adverse effects
  • Papaverine / therapeutic use
  • Penile Erection / drug effects
  • Penile Erection / physiology*
  • Penis / metabolism
  • Penis / physiopathology
  • Phosphodiesterase Inhibitors / adverse effects
  • Phosphodiesterase Inhibitors / therapeutic use
  • Piperazines / adverse effects
  • Piperazines / therapeutic use
  • Purines
  • Sildenafil Citrate
  • Sulfones


  • Phosphodiesterase Inhibitors
  • Piperazines
  • Purines
  • Sulfones
  • Nitric Oxide
  • Arginine
  • Sildenafil Citrate
  • Papaverine