Viagra (sildenafil) raised levels of the hormone oxytocin in rats, the team at the University of Wisconsin-Madison reported in theJournal of Physiology. This hormone is involved in nursing and childbirth, and also in orgasm and feelings of sexual pleasure.

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It appears that Viagra and related drugs act on the part of the brain that controls release of oxytocin, said Wisconsin physiology professor Meyer Jackson.

"This is one piece in a puzzle in which many pieces are still not available," Jackson said in a statement. "But it raises the possibility that erectile dysfunction drugs could be doing more than just affecting erectile dysfunction."

Breast milk production
Viagra, made by Pfizer Inc., is an inhibitor of an enzyme called phosphodiesterase type five. Related drugs such as Eli Lilly and Co.'s Cialis, known generically as tadalafil, and Levitra or vardenafil, sold by GlaxoSmithKline, Bayer AG and Schering-Plough, are also PDE-5 inhibitors.

They block this enzyme, which in turn breaks down other compounds. This increases blood flow in the muscles and it also affects a brain structure known as the posterior pituitary.

This, in turn, boosts oxytocin, at least in the rats. It probably does the same thing in people, Jackson said. "It does the same thing it does in smooth muscle. Instead of (levels) coming down in a minute or two, they stay up a little longer," Jackson said.

Oxytocin was known for years to be involved in labour and it is the hormone that stimulates the production of milk for breastfeeding. Only in recent decades has it been found to have a function in men - in sexual arousal and function.

This could suggest other uses for Viagra and related drugs, Jackson said, perhaps promoting social bonding.

Jackson said, "I hope that this doesn't cause some wild orgy of inappropriate recreational use". Some groups have complained that people use the impotence drugs for fun instead of using them as prescribed for sexual dysfunction.

The drugs can cause fatal side effects if used in combination with some other drugs, and some studies also suggest they may affect the vision in some patients.

Again, the doctors stress that these drugs are not for casual use. – (Maggie Fox, ReutersHealth)

Read more:
Will Viagra improve your sex life?
Viagra now used recreationally
 

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