Mechanism of action
Acetylcholine is released by nerves in the walls of penile blood vessels which causes nitric oxide (NO) to be released by endothelial cells in the vessel lining. NO binds to the enzyme guanylyl cyclase in the smooth muscle cells of the blood vessel which catalyses the production of cyclic GMP (cGMP) from GTP. The smooth muscle cells respond to this by relaxing which allows the blood vessel to dilate.
cGMP is quickly degraded by cGMP phosphodiesterase. This enzyme hydrolyses cGMP to GMP. Viagra works to competitively inhibit cGMP phosphodiesterase so that intracellular levels of cGMP remain high, meaning penile blood vessels are dilated for a longer period of time.
- ↑ Francis, Sharron H., Corbin, Jackie D. (2005). Sildenafil: efficacy, safety, tolerability and mechanism of action in treating erectile dysfunction. Expert opinion on drug metabolism and toxicology. 1 (2), p283-293.
- ↑ Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K., Walter, P (2008). Molecular Biology of the Cell. 5th ed. New York: Garland Science. p888-889.