BPA-exposed rats develop polycystic ovarian syndrome.

Jun 15, 2010

Fernandez, M, N Bourguignon, V Lux-Lantos and C Libertun. 2010. Neonatal exposure to Bisphenol A and reproductive and endocrine alterations resembling the polycystic ovarian syndrome in adult rats. Environmental Health Perspectives http://dx.doi.org/10.1289/ehp.0901257.

Synopsis by Emily Barrett

Rats exposed to bisphenol A (BPA) early in life develop symptoms resembling polycystic ovarian syndrome, a leading cause of infertility in women.

New evidence shows that very early exposure to BPA exerts effects on the female reproductive system that can last into adulthood and impact fertility.

This animal study is among the first to show that early exposure to BPA can cause symptoms similar to PCOS in adulthood. It is not yet known whether BPA exposure during early life can also produce the metabolic effects common in PCOS, such as elevated insulin levels, obesity and insulin resistance.

Occurring in 4 to 8 percent of women, polycystic ovarian syndrome (PCOS) is the most common hormonal abnormality in young women as well as one of the leading causes of infertility. Despite how common the disorder is, very little is known about what causes women with PCOS to have irregular menstrual cycles, abnormally developing eggs and a suite of hormonal irregularities including elevated testosterone and insulin levels. Although PCOS strikes women during their reproductive years, the origins of the disorder may occur years before, as the reproductive system develops under hormonal control.

The widely used environmental chemical BPA disrupts hormonal activity and has been shown to interfere with the normal development and function of the reproductive system. Scientists have suggested that early exposure to hormone disrupting chemicals, such as BPA, may therefore play a role in the development of PCOS. A team of Argentine researchers recently tested this hypothesis, examining whether exposure to BPA during a critical period of development might contribute to this common disorder. They found that rats exposed to BPA shortly after birth showed symptoms similar to those that characterize PCOS in women, including altered hormone levels, differences in the ovaries and impaired fertility.

In the experiment, three groups of rats were injected with BPA for the first 10 days after birth, a period when the portions of the brain involved in reproductive hormone release develop. One group of rats received a high dose of BPA (500 micrograms per microliter (μg/μl) per kilogram of body weight) each day, while two other groups received doses at or below those deemed by the Environmental Protection Agency to be acceptable levels of daily intake – 50 μg/μl/kg/day and 5 μg/μl/kg/day. The researchers measured hormone levels in the rats at four months of age, finding elevated testosterone and estrogen levels in the two groups that had received higher doses of BPA. Those rats also showed lower progesterone levels and irregularities in the secretion of GnRH, a hormone in the brain that normally regulates the activity of other reproductive hormones. Both of these changes are characteristic symptoms of PCOS.

The ovaries of the BPA-treated animals were affected as well, with the overall size of the ovary reduced. In the highest BPA dose group, animals showed many ovarian cysts, similar to those seen in many women with PCOS, as well as a large number of degenerating eggs compared to relatively few healthy, developing ones. These animals failed to ovulate or conceive a pregnancy. Those animals given the middle dose of BPA also showed impaired fertility, with fewer pups delivered compared to control animals, while the lowest dose group did not show any noticeable decline in fertility.

 The amount of BPA administered in the current study was several thousand times higher than humans are typically exposed to, however, and in order to better understand the possible connection between BPA and PCOS in humans, more environmentally relevant doses will need to be tested.