London: For the first time, scientists have discovered the signal of "fertile attraction" between egg and sperm that leads to fertilisation, a breakthrough which they say has raised the possibility of developing a non-hormonal contraceptive pill.
Laboratory experiments by a team at the University of California, San Francisco (UCSF), showed that a hormone released by an egg ready to be fertilised acts as a "come hither" message to sperm -- which then reacts in less than a second.
The discovery means, the researchers said, it may be possible to develop non-hormonal contraceptives to turn the signal off, thus replacing the Pill, the Daily Mail reported.
For their study, published in the science journal Nature, the UCSF researchers led by Dr Polina Lishko carried out experiments on mouse and human sperm to investigate how they detect an egg ready for fertilisation.
They measured the electrical currents that drive the wiggling movements of a sperm's tail on its journey towards an egg newly released from the ovary.
It was found that when the sperm gets a boost of progesterone -- a hormone released by cells surrounding the egg -- the electric current increases in strength and their tails move faster.
This violent flicking of the sperm's tail also gives it the ability to penetrate the egg, leading to fertilisation. For decades, biologists have known that egg cells provide sperm with a little chemical encouragement as part of the mating game, but the exact nature of the relationship has not been identified.
"This is one of the first times people have figured out at a molecular level how an egg signals to a sperm," said Dejian Ren, a physiologist at the University of Pennsylvania
in Philadelphia.
This discovery offers the chance to create non-hormonal birth control that prevents the egg wooing the sperm, he said. The traditional oral contraceptive pill works in women by
using hormones to suppress ovulation or the release of an egg.
As there is no egg to be fertilised, pregnancy cannot occur. Though the oral contraceptives are largely safe, they can raise the risk of certain cancers and cardiovascular disease.
Dr Lishko said: "We've finally solved the question of what progesterone does to human sperm. "It represents a promising target for the development of a new class of non-hormonal contraceptives."
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