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Enzymatic, my dear Watson.

Among spotted hyenas, the females take charge. They are the bigger, more aggressive sex and exhibit male-like sex organs, presumably because their fetal ovaries made too much testosterone.

Endocrinologists have now shown that a mother hyenas ovaries and placenta may conspire to give developing daughters the upper hand, demonstrating how some traits get passed on by nongenetic means.

While at the University of California, San Francisco,-School of Medicine, Tamer M. Yalcinkaya and his colleagues first discovered that ovarian tissue from hyenas does not produce much testosterone; instead, it releases lots of an inactive chemical, called androstenedione, that enzymes can convert to either testosterone or estrogen.

Then the scientists compared the activity of these enzymes in placental tissue from four humans and six spotted hyenas. The enzyme aromatase, which makes estrogen from androstenedione, is 20 times more active in humans. "The ability of hyenas to make estrogen is low," says Pentti K. Siiteri, who now works at a branch of the National Cancer Institute in Rockville, Md. In contrast, the activity of the enzyme that makes testosterone from this chemical is about the same in the two species, the researchers report in the June 25 SCIENCE.

Experiments in rodents show testosterone can reduce the number of ovarian follicles that develop in fetuses, which may explain why adult female hyenas have so much extra androstenedione in the first place, Siiteri says. Normally, cells in follicles use up androstenedione to make estrogen, so having fewer follicles means that more of this chemical is available for conversion to testosterone by placental enzymes, he explains.

"There are parallels in human pregnancy," he adds. Sometimes, abnormal fetal adrenal glands make too much of another chemical that can become excess testosterone in the placenta and lead to male features. In addition, hyenas' ovaries resemble the abnormal ovaries in women with polycystic ovarian syndrome, a disease that may begin in the fetus, Siiteri says.
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Title Annotation:ability to make estrogen is lower in hyenas than in humans due to lower activity of enzyme aromatase
Publication:Science News
Article Type:Brief Article
Date:Jun 26, 1993
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