Gynecology  Infertility

01 April 2004

"Viagra was introduced in 1998 and since then it has been prescribed to over 16 million men," says David Glenn, one of the team that conducted the test tube experiments at Queen's University in Belfast, Northern Ireland.

"Most use it for impotence and aren't contemplating having a family, so this has no implications for them," he says. However, younger men are using it recreationally, and they may be trying to start a family. Furthermore, an audit of fertility clinics by the team revealed that 42 per cent use Viagra to help men produce sperm samples on demand.

Glenn stresses the work is preliminary but adds that, if confirmed, would-be fathers and fertility clinics would need to re-examine their use of Viagra.

Plasma level

The team took 45 semen samples from men attending a fertility clinic and treated half with Viagra and used half as a control. They used a concentration equivalent to the levels of Viagra seen in blood plasma after a man takes a single 100 milligram dose.

Within 15 minutes, the sperm treated with Viagra started to speed up, and this lasted for 135 minutes. Observations after two hours showed up to 79 per cent more sperm were fully "reacted" in the Viagra samples than in the control experiments.

This acrosome reaction is the process by which the head of the sperm releases digestive enzymes to break down the outer shell of an egg, which then allows the sperm to enter and fertilise the egg.

The new findings are supported by previous work by the group in mice. Male mice given Viagra and then mated with females produced 40 per cent fewer embryos than those given a control pill. And in culture, these embryos were also less likely to survive to the five-day blastocyst stage.

Messenger molecules

Glenn told New Scientist that Viagra triggers the acrosome reaction early by increasing the movement of calcium into the cell, which changes its pH.

Viagra is also inhibits an enzyme called phosphodiesterase that normally break down messenger molecules involved in the energy process. "By inhibiting the breakdown of energy, Viagra raises levels of energy in the cells," he explains. "This causes the increase in motility."

However, John Dean, secretary general of the European Society for Sexual Medicine, cautions that lab results often do not reflect what actually happens in the body.

He says sperm is highly sensitive when removed from its natural environment. "Childless couples - and the general population - should be aware that in the five years that Viagra has been around no overall detrimental effect on fertility has been observed," he told the BBC.

However, Glenn is confident his study subjects sperm to the same levels of Viagra they would encounter in the body. The team is now studying the effects of Viagra on the sperm of men actually taking the drug. The initial findings in 17 men show Viagra does speed up sperm.

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