Monkeys with estrogen implants completely resisted SIV infection while those with progesterone had a higher rate of infection compared to the control group that didn't receive either implant. Estrogen, which causes the vaginal wall to thicken, appears to play a significant role in increasing natural resistance to vaginal infection.
Progesterone blocks the effect of estrogen.
Both hormones occur naturally within the female body, but the study suggests that the suppression of estrogen, either through menopause or the use of injected or implanted progesterone-only based contraceptives, may make women more susceptible to infection. Our next step is to see how we can maximize and prolong the benefits of estrogen. The researchers' goal is to see if topically administered estrogen creams, much like those used by women after menopause, has the same protective effect as the implants. Both phases of the study are a collaborative effort of Tulane Health Sciences Center, St. Michael's Hospital in Newark, New Jersey, and the Aaron Diamond AIDS Research Center in New York City. Established in 1964, the Tulane Regional Primate Research Center is the largest of the eight federally funded primate research centers.