Puncturing one's penis with a needle is not for the squeamish. Piercing the penis with a needle and then injecting a chemical to enhance one's sexual potency sounds more like a bizarre, sadomasochistic nightmare from the annals of Krafft-Ebing Psychopathia Sexualis than a doctorrecommended treatment of impotence. Nevertheless, many men, with guidance from their physicians, practice self-injection of the penis to achieve an erection. Three types of medications -- phentolamine (an alphablocker), papaverine (a smooth-muscle relaxant), and alprostadil (a prostaglandin) -- may be loaded into syringes and injected directly into the penile erectile chambers to provoke an erection.
Phentolamine, papaverine, and alprostadil are all effective in stimulating erections because they overcome neurologic signals that normally keep the penis in a limp or flaccid state and help encourage the release of intrapenile chemicals like nitric oxide and cyclic GMP to increase blood flow into the corpora cavernosae. Neurologic control of erections is vested in the sympathetic nervous system.
To understand how the sympathetic nervous system works, it is useful to create a simple scary example. Imagine that you are alone at night walking down a dark street. There is no sound. Then, as you are absorbed with your thoughts, someone comes up behind you and says, "Boo!"
Your sympathetic nervous system immediately swings into action to cause, among other reactions, an increase in pulse rate and blood pressure. The change in pulse and blood pressure is caused by internally produced adrenalinelike compounds with unique properties designated "alpha" or "beta." Beta forces cause you to have palpitations and an increase in pulse rate, while alpha influences raise your blood pressure.
What does this have to do with erections? The penis is richly endowed with extensions of the sympathetic nervous system, specifically nerves of the alpha type. Alpha signals either facilitate or inhibit normal erections.
When the alpha forces dominate, the penis remains at rest. An injection of a medication that blocks the erection-inhibiting alpha nerves makes it possible for a full and unrestrained flow of blood to be directed into the