The production of a male contraceptive pill has moved a step closer after scientists developed a way to dramatically reduce sperm ejaculation in mice.

The scientific journal Nature reports that an international team of researchers genetically engineered mice to reduce stimulation of the vas deferens, the duct that propels sperm from the testes into the semen prior to ejaculation.

This was done by removing a cell protein called P2X1.

The researchers, from Leicester University and Glaxo-Wellcome Biomedical Research Institute in Geneva, successfully reduced fertility in the mice by 90%.

There was no effect on copulation or on the health of the sperm.

P2X1 is a receptor on the surface of the vas deferens cell that causes the cell to respond to a signal from the nervous system.

By blocking P2X1, the contraction of the vas deferens was greatly reduced - rather as if a spring-loaded gun had not been wound up - and the sperm were not sent to the semen, the fluid that is ejaculated during orgasm.

Non-hormonal pill

Despite the difference in physiology between mice and men, the way could be open for a non-hormonal pill that would block P2X1 in men, the researchers said.

Alternatively, a pill that stimulated P2X1 "may be helpful in the treatment of male infertility" as it could help the vas deferens to deliver the sperm, they said.

Scientists have tried for years to develop a hormone-based birth control pill for men, but there have always been drawbacks, such as toxicity or causing impotence or long-term infertility.

Dr Sally Hope, an Oxford GP and chairwoman of the primary care gynaecology group, said: "It is an exciting and interesting idea, but I don't know if I would trust a man to take a contraceptive pill.

Professor Ian Craft, director of the London Fertility Centre, said infertility had not been linked to defects in the vas deferens, but he said it was quite possible that could be the case.

He said: "Anything that is reversible and safe is worth looking at in clinical trials."