A new study proves that human male sperm will swim toward chemical attractants to find the female egg, a discovery researchers say could lead to new ways to treat infertility or to new contraceptives that do not use hormones.

In a study appearing Friday in the journal Science, researchers report they have found that human sperm has a receptor, or chemical sensor, that causes the sperm to swim vigorously toward concentrations of a chemical attractant.

The new study used a laboratory compound called bourgeonal to prove that sperm are attracted by chemical signals, said Richard K. Zimmer, a professor of biology at the University of California, Los Angeles, who co-authored the study.

A precise compound in the human female reproductive tract that works like bourgeonal has not been found, but it is widely believed among experts that such a chemical exists.

Zimmer said the researchers also identified another compound, called undecanal, that shuts down the sperm chemical sensor and keeps it from responding to an attractant.

Although much more research must be done, Zimmer said the twin discoveries could lead to new drugs that could, depending on their use, overcome some fertility problems or inhibit conception.

Some human reproduction researchers said the study by Zimmer and his co-authors is a significant advance in understanding how the sperm and egg find each other.

“This is a landmark piece of work,” said Dr. Donner F. Babcock, a researcher at the University of Washington in Seattle. “The holy grail in reproductive biology has been to find the sperm attractant and to understand how it works.

“This is the strongest evidence we have so far that the egg signals its location to the sperm and the sperm responds by swimming toward the egg,” said Babcock.

New reproductive research
In the study, Zimmer and his co-authors at UCLA and the Ruhr University Bochum in Germany demonstrate that the surface of human sperm has a receptor, called hOR17-4, that causes the sperm to navigate in a specific direction when it detects a concentration of bourgeonal.

It long has been known that there are chemical signals between the female egg and the male sperm that help the two to find each other. But the new study is the first to demonstrate that the sperm will respond in a predicable and controllable way to a chemical signal.

Now, Zimmer said, the goal is to find the precise compound provided by the egg that activates the sperm’s directional swimming. Once such an attractant is found, he said, researchers should be able to develop techniques that would inhibit conception without the use of hormones.

Zimmer said it may be possible to develop a compound, inserted into the female reproductive tract, that would confuse the directional signals the sperm needs to find and fertilize the egg.

“You may not stop fertilization completely, but what this would do is discourage it or inhibit as much as possible,” he said.

Babcock said understanding how sperm and egg find each other might lead to solutions for infertility in some couples.

“A large number of human infertility problems are not understood,” he said. “If we know for certain that this sperm receptor plays a role, then it would be possible to develop tests to determine if the egg is making the attractant or if the sperm has the receptor.”

Couples who are infertile because of poor signaling between sperm and egg could then be identified and treated, he said.

Marc Spehr of Ruhr University, a co-author of the study, said in a statement that bourgeonal may have a role in fertility clinics by helping to identify healthy, high-quality sperm cells that would be most successful in fertilizing the egg.