Erectile dysfunction (ED) is when a man consistently struggles to achieve and maintain an erection sufficient for satisfying sexual intercourse, lasting at least 3 months. It has significant impacts on both the physical and psychological health of men worldwide and can affect the quality of life for both sufferers and their partners.

The process of achieving a penile erection involves a complex balance of the nervous system, blood vessels, and body tissues. This includes arterial dilation, relaxation of trabecular smooth muscle, and activation of the corporal veno-occlusive mechanism that prevents blood from flowing back.

Common risk factors for ED include cardiovascular disease, hypertension, diabetes mellitus, hyperlipidemia, hypogonadism, lower urinary tract symptoms, metabolic syndrome, depression, and smoking.

ED affects over 150 million men globally, across various age groups, including younger men.

While ED symptoms may appear temporary to some men, they can persist and cause considerable frustration if left untreated. Many men facing ED do not acknowledge the issue and may hesitate to consult a sexologist.

How does an erectile dysfunction occur?

The physiological state of the penis, whether flaccid or erect, is determined by the contraction or relaxation of smooth muscle cells in the corpus cavernosum. This balance between contraction and relaxation is controlled by central and peripheral factors involving numerous neurotransmitters and signaling systems.

Factors that mediate contraction in the penis include noradrenaline, endothelin-1, neuropeptide Y, prostanoids, angiotensin II, and other unidentified factors. Factors that mediate relaxation include acetylcholine, nitric oxide (NO), vasoactive intestinal polypeptide, pituitary adenylate cyclase-activating peptide, calcitonin gene-related peptide, adrenomedullin, adenosine triphosphate, and adenosine prostanoids.

Penile erection is a spinal reflex initiated by autonomic and somatic afferents from the penis, as well as supraspinal influences from visual, olfactory, and imaginative stimuli. Several central neurotransmitters are involved in the control of erection, some facilitating and others inhibiting its occurrence.

Central neurotransmitters that facilitate penile erection include:

  • Dopamine
  • Acetylcholine
  • Nitric oxide (NO)
  • Peptides like oxytocin and adrenocorticotropic hormone/α-melanocyte-stimulating hormone.

Neurotransmitters that inhibit penile erection include serotonin, which can have both facilitating and inhibiting effects, and enkephalin, which primarily inhibits.

Nitric oxide is released during sexual stimulation. It activates an enzyme called guanylate cyclase, leading to increased levels of cyclic guanosine monophosphate (cGMP) in the corpus cavernosum. This, in turn, causes relaxation of smooth muscle cells, allowing increased blood flow into the penis. The level of cGMP is regulated by the rate of synthesis via guanylate cyclase and the rate of degradation via phosphodiesterases that hydrolyze cyclic guanosine monophosphate (PDEs).

In summary, penile erection is a complex process involving various physical and chemical factors in the body. It begins with sexual stimulation triggering the release of nitric oxide (NO). Nitric oxide then stimulates guanylate cyclase to increase cyclic guanosine monophosphate (cGMP) levels in the corpus cavernosum, ultimately causing smooth muscle relaxation and increased blood flow to the penis.

Central neurotransmitters like dopamine, acetylcholine, and specific peptides such as oxytocin play crucial roles in facilitating this process. Conversely, neurotransmitters like serotonin and enkephalin can either inhibit or facilitate erection depending on the context. A deep understanding of these mechanisms is essential for developing more effective therapies for treating erectile dysfunction.