Endocrine Disrupters: Dioxin Causes Reproductive System Defects

"If dioxin does that, what else might it be doing? Is it affecting the reproductive health of human beings?" said Dr. Mary Dienhart, a reproductive biologist from the University of Maryland School of Medicine.

She presented research findings on August 5 to the Society for the Study of Reproduction annual meeting in Portland, Oregon.

Dienhart is a member of a research team headed by Dr. Anne N. Hirshfield, professor of anatomy and neurobiology at the UM medical school. Working with Dr. Richard Peterson at the University of Wisconsin, they examined the offspring of pregnant laboratory rodents exposed to single doses of dioxin, a highly toxic chlorinated byproduct from the bleaching of pulp to make paper. It also is produced by many incineration processes. The dose was 1,000 times that of the typical environmental exposure of people in industrialized countries.

Within less than a week after exposure, three out of four of the unborn female rats had developed the vaginal defect.

The toxic chemical, known to be a disrupter of the endocrine system, persists in the environment. It enters the food chain and is accumulated in livestock and fish, where it is stored in fat, which is the major route of human exposure.

Although the mechanism is not known, dioxin is known to cause changes in hormones and growth factors that could have profound effects on the growth and development of the reproductive system. "Hormones are signaling molecules; they tell genes when to turn on and turn off," Dienhart explained. "Development is a complex genetic program. If you interfere with it anywhere along the line, you could cause an entire cascade of events that could adversely affect reproductive health."

Next, the Maryland researchers want to look at the molecular mechanism underlying the development of the vaginal defect, to determine if it is interfering with cell formation or programmed cell death.

Their study of the developmental effects of dioxin was funded in part by the Bressler Foundation and the National Institutes of Health.

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