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Lead upsets menstrual cycle in monkeys.

Lead upsets menstrual cycle in monkeys

Although people have known for centuries that lead can disrupt health and reproduction, the toxic metal permeates modern life in vehicle exhaust, pipe solder and certain industrial settings. It now appears lead's reproductive tampering may be even more insidious than previously believed. A study of rhesus monkeys shows how lead in the bloodstream -- even at levels too low to trigger other symptoms -- can subtly upset the menstrual cycle, interfering with the animals' fertility.

After drinking lead-tainted water for 33 months, seemingly healthy female monkeys produced less of the hormone progesterone than their unexposed counterparts, report toxicologists at the University of Wisconsin-Madison in the December BIOLOGY OF REPRODUCTION.

Normally, mammalian ovaries produce a burst of progesterone a few days after ovulation. Without enough progesterone, the reproductive system cannot properly nurture a fertilized egg. The lead-exposed monkeys showed a smaller progesterone peak in the first days after ovulation in addition to lower total production, says coauthor Nellie K. Laughlin. Similar changes have been noted in lead-exposed rats, she says, but the monkey reproductive system more closely resembles that of humans.

In 1987, Laughlin and co-workers reported that long-term lead exposure made monkeys' menstrual cycles longer and more irregular. Menstrual timing is regulated during the first phase of the cycle, before ovulation. The 1987 finding and the new study suggest low concentrations of lead can disrupt both phases, and so might reduce fertility by making ovulation irregular and implantation less likely, Laughlin says.

Studies have documented that women who work with lead in factories suffer higher rates of sterility, miscarriage, premature birth and birth defects. In cases of low-level exposure without other symptoms, Laughlin says, a woman who does not keep precise records of her menstrual periods might never recognize a lead-related hormonal change.

The monkeys' blood lead concentration was roughly 10 times higher than that of most women in the general population, notes Paul B. Hammond of the University of Cincinnati Medical Center. However, because the monkeys appeared otherwise healthy, the findings are "sufficiently provocative" to warrant attention from researchers studying human reproduction, he says.
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Author:McKenzie, A.
Publication:Science News
Date:Dec 9, 1989
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