Viagra

The sildenafil citrate (compound UK-92.480), sold under the Viagra, Revatio and other brand, is a drug used to treat erectile dysfunction and pulmonary (HPP) hypertension. It was originally developed by British scientists and then brought to market by the pharmaceutical company Pfizer.1 acts by inhibiting specific phosphodiesterase type 5 cyclic GMP (PDE5), an enzyme that promotes the degradation of cGMP, which regulates blood flow in the penis. Since its availability in 1998, sildenafil has been the main treatment for erectile dysfunction, its main competitors in the market are vardenafil (Levitra) and tadalafil (Cialis).

Part of the physiological process of erection includes the parasympathetic nervous system causing the release of nitric (NO) oxide in the corpus cavernosum of the penis. NO binds to receptors on the enzyme guanylate cyclase, resulting in increased levels of cyclic guanosine monophosphate (cGMP), leading to smooth muscle relaxation of corpus cavernosum, by vasodilating the arteries helicine inside the penis. Vasodilation increases blood flow into the penis, causing the erección.17 Robert F. Furchgott won the Nobel Prize in Physiology and Medicine in 1998 for the discovery and analysis of the factor of endothelium-derived relaxing (EDRF in acronyms English: endothelium-derived relaxing factor), which was later identified nitric comoóxido or other related compound very close.

Sildenafil is a potent and selective phosphodiesterase inhibitor specific type 5 (PDE5) which is responsible for degradation of cGMP in the corpus cavernosum. The molecular structure of sildenafil is similar to the cGMP competing for binding it to PDE5. The result is that the cGMP remains longer inside the penis, leading to stronger and maintained erections. The active substances as tadalafil (Cialis®) and vardenafil (Levitra®) act by the same mechanism. Without sexual stimulation, and therefore, in the absence of activation of the NO / cGMP system, these drugs do not cause an erection.

Sildenafil is metabolized by liver enzymes and excreted by both the liver and the kidneys. Taken with a high fat diet, its absorption time increases by more than an hour and its maximum concentration in blood plasma is reduced by two thirds, thus considerably reducing its effects.

Source: wikipedia