April 26, 2004 08:30am
Viagra May Impair Sperm's "Warhead" Aim
by: Science & Tech News
(BELFAST, IRELAND) -- Men who use the anti-impotence drug Viagra could be impairing their fertility, according to scientists.
Laboratory experiments indicate the drug can damage sperm. Scientists 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 fertilization was greatly speeded up.
"Caution should be taken when using recreational drugs if you are hoping to start a family"
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.
Dr Sheena Lewis, director of the Reproductive Medicine Research Group at Queen's said: "The fact that this sperm function is impaired by the presence of Viagra is worrying."
The scientists, who presented their findings at the British Fertility Society's recent annual conference in Cheltenham, studied 45 samples of human semen.
Half were treated in the laboratory with a dose of Viagra equivalent to the amount in the blood of a man who has taken a 100mg 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.
However sperm exposed to Viagra released theirs' 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.
"We measured them after one hour and 79 percent more of the sperm exposed to Viagra had acrosome reacted," said Lewis.
The findings were supported by the results of tests on mice which showed that Viagra impaired their ability to father offspring. Significantly fewer eggs were fertilised when females mated with males given the drug.
In other cases, embryo development stopped early, indicating that more processes may be involved than simply the ability of a sperm to penetrate an egg.
Lewis said the acrosome reaction involved the channelling of charged calcium atoms, or ions. This was known to influence numerous cellular mechanisms and could effect early embryonic development.
Lewis said: "When Viagra came out in 1998 it was aimed at men with impotence problems, primarily older men not interested in having children. Now it has become a very popular drug for sexual enhancement.
"I think the message we want to get across is that caution should be taken when using recreational drugs if you are hoping to start a family."
Her group had also conducted research which indicated that smoking cannabis could impair fertility. - Sapa-DPA