By The Mirror

The Holy Grail of male contraception is a pill that would be 100% effective in preventing pregnancy but leave a man free to enjoy a full sex life.

So far, attempts to accomplish this have been disappointing, having largely focused on getting men to produce non-functioning sperm.

But some drugs used for this purpose produce intolerable side effects and have been abandoned one by one.

Drugs can induce infertility, but they may also affect sexual appetite or cause permanent alterations to sperm production.

But a completely new approach seems to promise success. Scientists in Australia have found a reversible way to stop sperm getting into the ejaculate, without affecting sexual function. A sort of biological snip.

Tests on animals showed the sperm could be “kept in storage” during sex and the findings were published in the journal Proceedings Of The National Academy Of Sciences.

The team of scientists at Monash University in Australia used a novel approach. Normally, sperm are moved out of the storage area in the testes (vas deferens) just before ejaculation.

The scientists bred genetically modified mice that were unable to squeeze the sperm out of the vas deferens, so they stayed in the storage site. When the mice ejaculated there was no sperm present. In other words, they were infertile.

The great advantage of this is that the process is reversible and the sperm are unaffected. The remaining task for the researchers is to show that this can be done with drugs – probably two drugs.

So far, the research group has made the mice infertile by changing their DNA to stop them making two proteins needed to move the sperm.

The researchers’ goal is to find a pair of drugs that can do the same thing. They believe one has already been developed and has been used for decades in patients with benign prostate enlargement. However, they would have to work from scratch to find the second one – a job that could take a bit of time.

The proteins targeted also have a role in controlling blood vessels, so there could be side effects on blood pressure and heart rate. That’s yet to be followed up.

There could also be an impact on the volume of ejaculate. But, in the mice at least, the researchers found only a “very slight” drop.

Dr Allan Pacey, senior lecturer in andrology at the University of Sheffield is impressed.

He says: “It’s a very good study, almost like a biological vasectomy in that it stops the sperm coming out.”