Viagra, or sildenafil, primarily targets cGMP, a molecule crucial for penile erection. Specifically, it inhibits phosphodiesterase-5 (PDE5), an enzyme that breaks down cGMP. By blocking PDE5, Viagra increases cGMP levels within the smooth muscle cells of the corpus cavernosum.
Elevated cGMP levels trigger relaxation of these smooth muscles, leading to vasodilation. This vasodilation increases blood flow into the penis.
Simultaneously, increased blood flow and reduced smooth muscle tone facilitate engorgement of the erectile tissue. This engorgement, coupled with compression of the veins, sustains the erection.
The effect is directly related to sexual stimulation; Viagra does not initiate erections independently. Neural stimulation is required to trigger the release of nitric oxide, a crucial step in initiating the cGMP pathway.
The duration of Viagra’s effects varies, but generally lasts several hours. The body gradually metabolizes sildenafil, allowing cGMP levels and blood flow to return to their baseline.
