Viagra® (sildenafil) was originally developed as a treatment for high blood pressure. This drug aimed to reduce blood pressure by causing blood vessels to dilate and loosen up. However, during the clinical trials many men refused to return the left-over medicine due to its potent ability to cause a penile erection.
L-arginine comes primarily from dietary intake, and is the only starting point for the Nitric Oxide Synthase pathway. When the electrical signal of sexual arousal activates the NOS pathway, L-arginine becomes converted into nitric oxide. Nitric oxide acts as a vasodilator and promotes yet another more powerful element, cyclic-GMP, a very potent vasodilator.
What results is a build-up of this potent vasodilator thus creating a penile erection. Though the producer of this drug (Pfizer Pharmaceuticals) has tried to prove this drug effective for women, there have been little positive results. The reason that sildenafil cannot be proven to be beneficial for women is probably due to the fact that the NOS pathway is very sensitive to, and in need of adequate testosterone and estrogen. Remember, women are complex!
While the Nobel Prize in Medicine was not awarded for the knowledge that to have an orgasm it is essential to become maximally sexually aroused with a clitoral erection, the discovery of the science underlying genital erection did. The physiology that enables a woman to establish a clitoral erection (and a man a penile erection) is the Nitric Oxide Synthase Pathway. The discovery of this pathway was the basis of the 1998 Nobel Prize in Medicine. Now we know that the NOS pathway explains how a signal originating in the brain and traveling via the nerves (esp. the clitoral nerve) causes the release of nitric oxide, the key event that results in clitoral engorgement and clitoral erection.
This NOS pathway relies on the presence of L-arginine, a semi-essential amino acid that is usually contained in most cells of the body (esp. blood vessels). It is this amino acid that causes the dilation of blood vessels, an important step resulting in vaso-congestion and thus an erection. While it is not L-arginine itself that acts directly on the tissue, L-arginine and only L-arginine makes this possible by its conversion into other compounds.
This induced production of two important vasodilators is like throwing gasoline onto a smoldering fire, causing a large and rapid reaction. This NOS mechanism creates maximum sexual arousal and clitoral erection by inducing the activity of nitric oxide with L-arginine.
