Contraceptive concerns about HIV.

A study showing that the hormone progesterone thins the vaginal wall of monkeys has raised concerns that the use of certain contraceptives may increase a woman's risk of infection by HIV, the AIDS virus.

The worrisome data result from experiments in which researchers implanted progesterone-secreting devices under the skin of macaque monkeys. The implants simulate popular contraceptive implants such as Depo-Provera and Norplant, which release progestin, a synthetic version of progesterone, into a woman's bloodstream. In the United States alone, several million women depend on such devices.

Scientists squirted SIV, the monkey version of HIV, into the vaginas of 18 monkeys that had progesterone implants. Of that group, 14 became infected, report Preston A. Marx of the Aaron Diamond AIDS Research Center at Rockefel- ler University in New York and his colleagues in the October Nature Medicine. In contrast, only 1 of 10 monkeys not receiving progesterone became infected when inoculated that way.

To explain the difference, Marx's group examined another group of monkeys given progesterone implants. In those monkeys, the layer of cells forming the vaginal wall was much thinner than in normal animals. "There appears to be a thinner barrier and therefore less protection [from SIV infection]," says Marx.

Marx and other researchers caution that these results are difficult to inter- pret in terms of humans. Because the synthetic hormone may generate different effects than progesterone does, Marx intends to repeat his simian studies with progestin.

In June, the National Institutes of Health in Bethesda, Md., convened a work- shop to consider the then-unpublished data from Marx's group. Past epidemiological studies offered conflicting results about whether Depo-Provera, Norplant, and similar devices change a woman's risk of getting infected with HIV. Investigators agree that, since the previous work is not convincing one way or the other, new studies must be conducted, says Marx.

Several research groups also intend to study the thickness of the vaginal wall in women using progestin-based contraceptives.

Despite Marx's data, scientists say there is not enough information to warrant a warning about such devices. "The scientists at the meeting concluded that there should be no change in prescribing practices for contraceptives. At the same time, there are questions still open and several lines of inquiry being pursued," says Robert Spirtas, chief of the contraceptive and reproductive evaluation branch at NIH's National Institute of Child Health and Human Development.