Viagra

Viagra is a drug for the treatment of erectile dysfunction, which acts on the natural mechanisms of erection. It is used in men suffering from erectile dysfunction of various origins. Sildenafil is a selective inhibitor of cGMP-specific phosphodiesterase type 5 (PDE5).

The physiological mechanism of penile erection involves the release of nitric oxide (NO) in the cavernous body with sexual stimulation. Nitric oxide activates the enzyme guanylate cyclase, which leads to an increase in the level of cyclic guanosine monophosphate (cGMP), relaxation of smooth muscles of the cavernous body, and increased blood flow in the penis. Sildenafil does not have a direct relaxing effect on an isolated cavernous human body, but actively enhances the relaxing effect of NO on this tissue by inhibiting PDE5, which is responsible for the disintegration of cGMP in the cavernous body. With sexual excitement, local release of NO under the influence of sildenafil leads to oppression of PDE5 and an increase in the level of cGMP in the cavernous body, resulting in a relaxation of smooth muscles and increased blood flow in the cavernous body. A mandatory condition for the effectiveness of sildenafil is sexual stimulation.