Uranium, the newest ‘hormone’

From New Orleans, at the e.hormone 2004 conference

The incidence of several cancers is especially high on the Four Corners Navajo Reservation, which straddles the Arizona–New Mexico border. Because the region hosts more than 2,000 abandoned uranium mines, many of which release dust into the air and water, area researchers wondered whether mine pollution might partially explain the high rate of reproductive-organ cancers in teenage Navajo girls—a rate 17 times that of U.S. girls generally.

New animal studies led by Cheryl A. Dyer and Stefanie R. Whish of Northern Arizona University in Flagstaff support that suspicion.

The researchers exposed young female mice to a soluble form of uranium similar to what enters groundwater from mines. To limit the animals’ production of natural estrogens, the researchers removed the ovaries—the hormones’ main source—from all the mice in the study. Estrogens are known to be a leading cause of many reproductive cancers.

For 1 month, most mice received drinking water laced with uranium or diethylstilbestrol (DES), an estrogen-mimicking drug. Concentrations of the uranium were half the amount that the Environmental Protection Agency permits in drinking water and roughly one-tenth the concentration found in some water wells on the reservation.

Mice getting DES- or uranium-treated water showed classic markers of heavy estrogen exposure, but mice receiving plain water didn’t, Whish notes. In animals drinking the spiked water, for instance, the external opening of the vagina developed early, cells lining the vagina were bigger than normal and exhibited protein changes akin to those that produce nails and corns, and the uterus weighed significantly more than normal. In related test-tube experiments, uranium exposure increased the proliferation of breast-cancer cells, just as estrogen does.

None of these changes accompanied uranium exposure if the animals also received injections of a chemical that blocks estrogen’s access to cells. This evidence strongly suggests that “uranium is acting as an estrogen,” says Whish.

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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