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essays service Viagra – a product of Pfizer – is used for the treatment of male impotency known as Erectile Dysfunction. The active ingredient in Viagra is a specific inhibitor of phosphodiesterase 5. Phosphodiesterase 5 (PDE5) cleaves the ring form of cyclic GMP (cGMP) a cellular second messenger similar to cAMP. The inhibition of the phosphodiesterase allows for the persistence of cGMP that promotes the effects of cGMP production. In this case, it allows for increased blood flow into the penis, which may result in an erection.
Normally, sexual stimulation in the male is followed by release of nitric oxide (NO) in the corpus cavernosum of the penis. Nitric oxide (NO) activates the enzyme guanylate cyclase in the smooth muscle cells that allows for the relaxation of the penile arteries and an increase flow of blood into the penile cavity. The effect of Viagra is to allow the accumulation of cGMP by inhibiting the phosphodiesterase action, which tends to magnify the effect of NO release.
Clearly, the mechanism of penile erection is a case of when NO means yes.
One of the curious side effects of Viagra is an effect on the visual discrimination of certain colors. This appears to be due to the reduced affinity of the drug for the phosphodiesterase enzyme found in the retina (PDE6). Viagra has an even more reduced affinity for PDE3, which is critical since PDE3 is active in heart muscle cells. |
