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by wickedwillie on April 16th, 2005

wickedwillie

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How does Viagra work?

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  • by Erin Albrecht on April 17th, 2005

    Erin Albrecht

    During sexual stimulation, nitric oxide (NO) is released in the corpora cavernosa (two cylinders of spongy erectile tissue in the penis). The nitric oxide activates an enzyme called guanylate cyclase, increasing levels of a smooth-muscle relaxant known as cyclic guanosine monophosphate (cGMP). Smooth muscle acts involuntarily -- the conscious mind has no control over its actions. This kind of muscle is located in blood vessels, intestines, the stomach, and other areas. When Viagra (sildenafil) is tossed into the equation, it inhibits the effect of phosphodiesterase type 5 (PDE5) and enhances the effect of NO. Normally, PDE5 degrades cGMP. With sildenafil present, the increased levels of cGMP cause smooth muscle relaxation. Consequently, blood can flow into the corpora cavernosa more easily. In a normal erection, these two cylinders hold 90% of the blood that flows into the penis, with the balance going to the corpus spongiosum, a smaller cylinder containing the urethra.

    Interestingly, this plays a role in one of Viagra's more unsual side effects. Some men who take this drug develop a bluish cast to their vision or have difficulty telling blue from green. Sildenafil is selective for PDE5, which means it has a greater effect on that particular phosphodiesterase than it does on others. In fact, it is 4,000 times more selective for PDE5 than for PDE3, which is responsible for heart muscle contraction! Unfortunately, it is only 10 times more selective for PDE6, an enzyme found in the retina and involved in phototransduction.


    * Prescribing information for Viagra: http://www.pfizer.com/download/uspi_viagra.pdf
    * Pretty much what is stated above, but with a nice, colorful diagram: http://health.howstuffworks.com/viagra5.htm
    * Phototransduction: http://wolfstone.halloweenhost.com/TechBase/litadv_AdvancedLightingConcept.html#HowDoRodsAndConesWork

    EDIT:
    As per Relsqui's request, a "paraphrase for laymen":

    Viagra causes smooth muscle relaxation, allowing blood to easily flow into the penis. Sometimes, Viagra will make your vision blue.

    Comments

    • Extremely detailed, perhaps too much so--a paraphrase for laymen would be much appreciated.

      Relsqui

      by Relsqui on January 19th, 2006

    • detail is good!

      davoomac

      by davoomac on April 17th, 2006

    • detail is great!If someone needs to understand further they can look at the sites highlighted above!Great answer~+1(newbie) :)

      mtndewman44

      by mtndewman44 on January 1st, 2009

    • great answer.....thanks

      MegaKamster

      by MegaKamster on November 9th, 2009

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