The idea that pollutants may interfere with sex hormones has gotten a lot of press lately—stories of alligators and otters with shrunken penises have received wide publicity. In spite of these deformed male organs, most research has focused on estrogen, the female sex hormone: males make it, too, and besides its role in the female reproductive cycle, it carries crucial signals in developing embryos of both sexes. Just as vulnerable, though, are testosterone and other male sex hormones—androgens, as they’re called. This past year a Vanderbilt University School of Medicine study showed that androgens may actually be even more sensitive to interference than estrogen is.
Pesticide by-products, plastic components, red dye no. 3—a wide range of chemical compounds have been shown to bind to estrogen receptors inside cells and thereby block the hormone’s signal. The problem has been that until a few years ago everyone was considering these pollutants as strictly estrogenic, says Benjamin Danzo, a reproductive endocrinologist at Vanderbilt, and had never given thought to the fact that they might also be androgenic.
For his study, Danzo gathered ten pollutants and put each one in a test tube containing either estrogen or androgen. Each tube also contained one of four types of protein that bind estrogen or androgen (the two kinds of cell receptors and two other proteins that help move the hormones around the body). Danzo then compared how well the hormone and the pollutant bound to each protein. To his surprise, of the ten pollutants, five bound easily to the androgen receptors, while only two bound to the estrogen receptor. One pollutant—a by-product of the insecticide lindane—bound particularly well to a protein that helps move androgens along after they are secreted by the testes.
Danzo is now running experiments to see what effects these pollutants have on living guinea pigs. It’s important to keep in mind that while pollutants may bind to hormone receptors and other proteins, natural hormones do so far more effectively. But there are so many pollutants around, Danzo warns. We’re not exposed to one of them at any given time—we’re exposed to large numbers of them.