Low Chemical Exposure May Speed Male Puberty

Population Council researchers have found that exposure to low levels of phthalates can alter the levels of testosterone (the male sex hormone), increase the proliferation of cells in the testes, and significantly accelerate the onset of male puberty.

For immediate release from the September 2005 Population Briefs

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Gina Duclayan, +1-212-339-0510
[email protected]

NEW YORK (9 September 2005)— Population Council biomedical researchers have found that exposure to low levels of phthalates can alter the levels of testosterone (the male sex hormone), increase the proliferation of cells in the testes, and significantly accelerate the onset of male puberty. Phthalates are chemicals used to make plastics—such as those used in food packaging and infant toys—more flexible. They are also used as stabilizers in many common cosmetic products.

Population Council reproductive biologist Matthew P. Hardy and his colleagues are studying the most abundant phthalate in the environment, DEHP. To mimic typical human exposures, Hardy and his colleagues use low, chronic chemical doses in their experiments.

For four weeks or longer, Hardy and his team exposed male prepubertal rats to DEHP. They found that prolonged exposure to DEHP induced high levels of luteinizing hormone (LH), the primary regulator of testosterone production. Similarly, the researchers found that blood levels of the sex hormones estradiol and testosterone increased by more than 50 percent in exposed rats.

Paradoxically, however, testosterone output by individual Leydig cells, which produce the hormones, actually decreased. The rise in blood hormone levels came about because the total number of these hormone-producing cells increased by between 40 and 60 percent. While none of the DEHP rats developed cancer, proliferation of Leydig cells has been implicated in some testicular cancers.

Next, Hardy and his colleagues looked at the effect of DEHP on the onset of puberty in young male rats. During each of the 28 days of the study, the researchers gave rats either a low oral dose of DEHP in vegetable oil, a high oral dose of the chemical in vegetable oil, or vegetable oil alone. Although testosterone levels in control rats and in those receiving a low dose of DEHP were the same at day 14, testosterone levels were significantly higher in the low-dose rats at day 28. In contrast, testosterone levels were significantly lower in high-dose rats than in control rats by day 14. By day 28, testosterone levels in high-dose rats had returned to control levels. Moreover, puberty started significantly earlier in rats receiving a low dose of DEHP than in high-dose or control rats.

“We think all of these findings fit with the idea that DEHP is an anti-androgen. We propose that DEHP inhibits the production of testosterone by Leydig cells. The lowered testosterone levels signal the brain to release luteinizing hormone,” explained Hardy. “We think that a chronic over-stimulation with LH may cause the proliferation in Leydig cells that we observed. Though individual Leydig cells produce less testosterone, there are significantly more cells, so the blood testosterone level increases. Thus, our findings indicate that low levels of DEHP may shift the male body’s hormonal equilibrium to a higher level as the endocrine system struggles to overcome the anti-androgenic propensities of the chemical. The overall increase in circulating testosterone is sufficient to significantly speed the onset of puberty in male rats. An early onset of puberty could conceivably disrupt cognitive development or increase the risk of hormone-related cancers, such as prostate cancer, later in life.”

The September 2005 issue of Population Briefs is now available at http://www.popcouncil.org/publications/popbriefs/pb11(3).html

Other articles in the September 2005 issue are:
• Physical Abuse Common During Pregnancy in South Asia, Studies Find
• Expanding a Successful Health Care Initiative in Ghana
• Can Livelihoods Training Alter Girls’ Lives?

Population Briefs highlights the Population Council’s research in biomedicine, public health, and social science as well as its international collaborations. The free newsletter is available in print and electronically. To receive e-mail when a new issue of Population Briefs is available online, register at the Population Council Media Center: www.popcouncil.org/signup.

The Population Council is an international, nonprofit, nongovernmental organization that seeks to improve the well-being and reproductive health of current and future generations around the world and to help achieve a humane, equitable, and sustainable balance between people and resources. The Council conducts biomedical, social science, and public health research and helps build research capacities in developing countries. Established in 1952, the Council is governed by an international board of trustees. Its New York headquarters supports a global network of offices.
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Published: 11 Sep 2005


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http://www.popcouncil.org/publications/popbriefs/pb11(3).html September 2005 issue of Population Briefs