The Molecular Mechanism for Penile Erection

For the first time the metabolic mechanism has been elucidated for the continuous production of nitric oxide that maintains penile erection over time. The findings were published in the March 19, 2002, issue of the Proceedings of the National Academy of Sciences.

A key element in the attainment of erection is the continuous activation of the source of nitric oxide in blood vessel walls, according to Dr. Arthur Burnett, associate professor of urology at John Hopkins University (Baltimore MD, USA) and senior author of the study. Two principal discoveries helped to fill in the picture of the complex physiology of erection: the source of nitric oxide--a special form of the enzyme endothelial nitric oxide synthase (eNOS)--and the fact that the pressure of flowing blood against a vessel wall could induce it to produce nitric oxide.

Researchers discovered ten years ago that release of nitric oxide from nerve endings in the penis caused erection, but since nitric oxide is a neurotransmitter that survives just a few seconds before breaking down, they couldn't explain how erections are naturally sustained over time. "Once blood starts flowing into the penis,” says Dr. Burnett, "the source of nitric oxide in the blood vessels is continuously activated so that more nitric oxide is released, more tissue relaxes, more blood comes in and a sustained erection is achieved.”

Dr. Burnett explained that the process begins when erotic thoughts or physical sensations produce nitric oxide release in nerve endings in the penis. Nitric oxide is a relaxant that allows blood vessels to open up or dilate, bringing increased blood flow and swelling of tissues. The flow of blood also creates a minor stress on the blood vessel wall that activates the release of more nitric oxide. This time it is from cells in the wall of the blood vessel rather than from nerves. Endothelial nitric oxide causes more tissues to relax, and the process repeats until the penis is fully erect. The new findings will have direct application towards new and improved therapies for erectile dysfunction.




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