Of Monkeys and Women, Continued
by Cynthia Pearson
Last summer Network News readers learned that preliminary experiments conducted in monkeys showed that increased levels of progesterone dramatically increased the monkeys' likelihood of infection with SIV, a close relative of HIV. The experiment was designed to simulate exposure through vaginal intercourse. The researchers also found that the vaginal epithelium of the progesterone-treated animals was much thinner than untreated monkeys and speculated that some sort of natural defense mechanism may have been weakened by thinning the vaginal tissues. The experiment immediately raised questions about the possible vulnerability of women using progestin-only contraceptives to infection with HIV. At a small meeting convened by the National Institutes of Health (NIH) last summer, recommendations were made for follow-up experiments of various types ranging from basic research on exactly how infection occurs after vaginal exposure, further studies with monkeys and prospective studies of women using various methods of birth control.
In February, the NIH held a related meeting on the reproductive tract and HIV infection. Not much progress has been made in determining the actual route of infection in women. Researchers assume that much of the infection takes place in the cervix which is open and welcoming to outside organisms for a few days each month, but experiments in monkeys and a few reports from women have shown that infection can take place even in the absence of a cervix. One researcher at the conference speculated that some infections take place inside the uterus and fallopian tubes, which if true would make the development of an effective microbicide even more challenging as it would have to kill viruses very quickly.
What little news was reported at the February meeting concerned vaginal thinning as a result of Depo Provera and Norplant. Sheri Petito reported on experiments conducted on monkeys given Depo Provera and Norplant in doses equivalent to those used by women. Both Depo Provera and Norplant caused the vaginal epithelium to thin dramatically. The animals were treated for 3 months; after the treatment had worn off, the vaginal tissues returned to their original thickness. Christine Mauck reported on a similar study conducted in women using Depo Provera, but no results were available. While the findings from the monkey study do nothing to assuage the worry raised by the original monkey/progesterone experiment, at this point it is not known if thin vaginal tissues are a risk factor for HIV infection or not.
The real question which needs to be answered is what is the effect of Depo Provera, Norplant, and progestin-only birth control pills as well as other contraceptive methods on women's vulnerability to HIV infection. At the meeting last June, many epidemiologists emphasized the need for a prospective study of uninfected women who receive good counseling about HIV and STD prevention at the time they choose a new method of birth control. Any study such as this will be expensive and time consuming, but until it is conducted, women will not be able to truly weigh the pros and cons of birth control in the era of AIDS.
Contact the Network for a copy of the agenda of the NIH meeting on the reproductive tract and HFV infection, or a free copy of our 6/96 statement on monkeys, progesterone and HIV infection.