[Phosphodiesterase 5--the enzyme inhibited by XXXX (Viagra)].

@entity323 @entity377 @entity7855 @entity8613 @entity8262 @entity1919 @entity842
Phosphodiesterases are enzymes that catalyze the degradation of the @entity8613 , @entity1919 and @entity8262 , to the corresponding 5' @entity377 monophosphates. Ten different phosphodiesterase families have been described to date. These enzymes exist as homodimers and there is structural similarity between the different families. However, they differ in several respects like selectivity for @entity8613 , sensitivity for inhibitors and activators, physiological roles and tissue distribution. Interest in these enzymes has increased tremendously, both within the medical community and in the general public as a consequence of @entity7855 (Viagra), the medication recently introduced for the treatment of @entity323 . @entity7855 mediates its effects by inhibiting phosphodiesterase 5. Some biochemical and molecular biological aspects of this enzyme are presented here. To achieve satisfactory erection, normal penile innervation is required. @entity842 , the transmitter substance in these nerves, activates guanylyl cyclase, thereby increasing @entity8262 production. The increased levels of @entity8262 cause relaxation of smooth muscles in penile vessels and this leads to an erection. Erection is dependent on elevated levels of @entity8262 and @entity7855 mediates its effects by inhibiting the degradation of @entity8262 . Other functions that are mediated by the phosphodiesterases explain visual disturbances, flushing and decreased blood pressure that are some of the side effects seen with @entity7855 treatment. Furthermore, the potentially fatal consequence of combining @entity7855 and nitrovasodilators is discussed.
