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Viagra users' sperm short on firepower

Men who use the anti-impotence drug Viagra could be impairing their fertility, say scientists, after laboratory experiments indicated the drug can damage sperm.

They are now warning younger men to use caution before taking the drug recreationally.

Researchers from Queen's University in Belfast found that sperm exposed to Viagra became more active. But at the same time a mechanism used by sperm to penetrate the egg wall during fertilisation was greatly speeded up.

Known as the "acrosome reaction", it involves firing an armour-piercing warhead of digestive enzymes at the egg.

If the sperm release their "ammunition" too early, before reaching the egg, they do not get another shot and are rendered infertile. The study showed that this was likely to happen to sperm exposed to Viagra.

The university's Sheena Lewis said: "The fact that this sperm function is impaired by the presence of Viagra is worrying."

The scientists, who presented their findings to a recent British Fertility Society conference, studied 45 samples of semen. Half were treated in the lab with a dose of Viagra equivalent to the amount in the blood of a man who has taken a 100-milligram pill.

These sperm were found to be more motile than untreated sperm: they had more energy and moved around more.

This would normally be considered a positive effect, since sperm motility is linked to fertility. But the extra energy given to the sperm also seemed to speed up the acrosome reaction. Most of the untreated sperm spontaneously released their acrosome enzymes after about three hours.

But sperm exposed to Viagra released the enzymes after only one hour. Although no attempt was made to fertilise eggs, this was too fast to have allowed successful fertilisation in a real-life situation.

Dr Lewis said while Viagra had become popular for sexual enhancement, men should exercise caution if hoping to start a family.

Posted by thinkum at April 26, 2004 02:01 PM