The search for a male contraceptive (search) has taken an unexpected twist. Researchers may have found a way to prevent sperm from swimming forward, which could lead to a new form of birth control that doesn’t tamper with men’s hormone levels.

Once ejaculated, sperm swim forward toward the egg cells to fertilize them. Disabling motility (search) of the sperm may provide a new form of male contraception that is nonhormonal.

“We were very surprised at this finding,” says Deborah O’Brien, PhD, of the University of North Carolina at Chapel Hill’s medical school, in a news release.

O’Brien and colleagues discovered that a certain chemical, only found in sperm cells, is needed to generate the energy sperm need to swim forward. The researchers studied mice, but male humans have a similar enzyme.

The mouse chemical has a long name — glyceraldehydes 3-phosphate dehydrogenase-S — and a much shorter abbreviation, GAPDS. In humans, it’s called GAPD2.

In lab experiments, the researchers manipulated the gene that makes GAPDS in order to prevent mice from making the chemical. The mice were then unable to impregnate female mice, although their sperm counts and mating was normal.

The researchers found that without GAPDS, the sperm of the mice could only bob sluggishly from side to side, but couldn’t propel forwards to fertilize the egg of the female mice.

At present it is unclear whether the chemical deficiency would also lead to sperm having the inability to penetrate and fertilize eggs if placed in contact with them.

If a drug could be developed that has the same effect on humans, it could create a male contraceptive that doesn’t affect hormone levels.

A drug based on the same idea could also be deposited in the female reproductive tract to stop sperm movement, says Louis De Paolo, PhD, of the National Institute of Child Health and Human Development, in a news release.

The finding could also influence studies and treatments of male infertility.

A recent study of more than 1,000 sperm samples from infertile men showed that “81percent had defects in motility,” which is the forward motion sperm need for egg fertilization, write the researchers.

Their study appears online in the Nov. 16 early edition of the journal Proceedings of the National Academy of Sciences.

Meanwhile, other researchers are working on hormone-based male contraceptives. In addition, scientists recently reported that a new immunization strategy might hold promise. But for now, short of abstinence, male birth control options are limited to condoms and vasectomies.

By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: Miki, K. Proceedings of the National Academy of Sciences, online early edition, Nov. 16, 2004. News release, University of North Carolina at Chapel Hill. News release, National Institute of Child Health and Human Development/National Institutes of Health.