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Biology

Biology

Time for the Male Pill

By Melissa Hendricks

Alarmed by burgeoning global population growth, Kirsten Thompson had an Aha! moment several years ago. Reducing population growth must involve men as well as women, she realized, and that means giving men new choices beyond condoms and vasectomies.

She launched the international Male Contraception Coalition in 2005 and hosts the website MaleContraceptives.org.

"From the perspective of public health, there are still millions of couples out there who need contraception and a broader range of family planning choices," says Thompson, a Sommer Scholar working on her MPH.

Barry Zirkin couldn't agree more. He's been working on male contraception for more than two decades—specifically on a hormone-based approach, akin to "the pill" used today by millions of women around the world. Zirkin's research rests upon the work of colleague Larry Ewing, who was the director of the Division of Reproductive Biology until his death in 1990. Ewing designed a promising contraceptive implant that suppressed a hormone required for testosterone synthesis in the testes. As testosterone levels drop, so does sperm production.

The experimental contraceptive has proven extremely effective in rats, says Zirkin, the current head of the Reproductive Biology division and a professor of Biochemistry and Molecular Biology. However, "it doesn't work in all men," Zirkin says. In tests in China, the contraceptive was almost 100 percent effective at reducing sperm count to zero. But when researchers tested the hormonal contraceptive in Caucasian volunteers, they found that sperm count did not fall to zero in about 25 to 40 percent of the volunteers, making it unreliable in a sizable group of men.

Zirkin and Jonathan Jarow, a professor of Urology, are now examining why the two groups responded so differently. First, they are measuring the level of testosterone in the testes of Caucasian and Asian men to see if they can detect differences that might explain the results. Genetic factors or diet or something else such as sensitivities to testosterone could account for the findings. "We don't really know which," says Zirkin, PhD.

If a male pill (or implant) ever does come to fruition, it could offer a health benefit along with its contraceptive benefits. Here's why: When Zirkin and colleagues use the implant in young rats, and then remove the contraceptive when the rats are old, the animals' testosterone-producing cells have not aged. Testosterone remains at its youthful levels. If the contraceptive were to work the same way in men, it could potentially prevent the consequences of aging related to testosterone decline—weakening bones, reduced muscle mass and loss of libido. "But right now, that's pie in the sky," says Zirkin.

Clinical trials of the hormone contraceptive are under way in the U.S. and abroad.

Elsewhere, several research groups are investigating the use of nylon or silicone plugs and gels to prevent sperm from exiting the testes. These techniques target the vas deferens, the coiled tube that serves as the sperm's exit ramp from the testis. Researchers are trying to demonstrate that the barriers are both reliable contraceptives and reversible.

Those are tough challenges, indeed. But Zirkin believes that offering one more contraceptive option—one that engages the male partner—would be a great choice for many couples. "Should women bear the full brunt of responsibility for preventing pregnancy? I think most reasonable people would say no," says Zirkin. "If the responsibility can be shared, it should be shared."

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