Laboratory studies have shown that male mice who are exposed in the womb to bisphenol A, or BPA, a chemical compound found in some hard plastics and can linings, appear to be less masculine and less attractive to females once they mature. This raises controversies that human boys could be similarly affected. The findings were published Monday on the website of the journal Proceedings of the National Academy of Sciences.
In the study male deer mice whose mothers were fed BPA while pregnant had more difficulty navigating a maze and displayed less interest in exploring than unexposed males. This was a sign of “demasculinization,” researchers say, since navigational skill and a propensity for exploration are considered classic male traits in this particular species of mice. What's more, this reduction in masculinity appears to make BPA-exposed mice less attractive to those potential mates.
In the second part of the experiment female mice who were released into cages containing two male mice, only one of which was exposed to BPA, spent roughly half as much time in “nose-to-nose contact”-- an expression of sexual interest - with the BPA-exposed mice, perhaps because the females sensed differences in their behavior, pheromones, or both.
Cheryl Rosenfeld, Ph.D., the lead author of the study and an associate professor of biomedical sciences at the University of Missouri, Columbia said, “The [BPA-exposed] mice outwardly look normal. We have measured their motor skills and done sensory skill assessments, and they look normal; you can't tell which were exposed. But when you go deeper, that's when you find this difference emerging. The fact that we found this sexually selected behavior is different.”
Rosenfeld and her colleagues say their study may lead to new ways of exploring the effects of BPA exposure in humans. For instance, the levels of testosterone and another hormone in adult BPA-exposed mice were no different from those in the unexposed mice, which suggests that BPA exposure affects the behavior of male mice without altering their adult hormone levels.
It also suggests that researchers may need to look beyond adult hormone levels when designing BPA studies in humans, says John Meeker, Sc.D., an assistant professor of environmental health sciences at the University of Michigan School of Public Health, in Ann Arbor. He explained, “In a human study, we often depend on an outcome like hormone levels.” He was not a part of this study. He went on to say, “It's possible that BPA could be impacting reproduction in a way that wouldn't be picked up in our typical way of studying things. [This study] may inform how we go about studying those things in the future.”
In 2010, the Food and Drug Administration issued a statement expressing concern about the potential effects of BPA on fetuses and small children, but the agency has stopped short of declaring the chemical toxic (as Canada has done) or banning its use in certain products. The European Union and Canada have banned the use of BPA in baby bottles. However, there is no scientific consensus on the dangers BPA poses, the study said.
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