In the study, which will be published in an upcoming issue of Neurotoxicology, the researchers exposed newborn rats to physiologically relevant doses of the phytoestrogens genistein and equol, and then looked at reproductive health markers in the rats throughout their adulthood. The neonatal stage of development in rats is comparable to the latter stages of pregnancy for humans, Patisaul says. Genistein is a phytoestrogen that is found in various plants, including soybeans and soy-based foods. Equol is a hormone-like compound that is formed when bacteria found in the digestive system metabolize another phytoestrogen. However, only approximately a third of humans have the necessary bacteria to produce equol.
The study shows that both genistein and equol result in the early disruption of the rats' estrus cycle which would be corollary to early onset of menopause in a human. The study also showed that genistein caused the early onset of puberty. The disruption of the estrus cycle could stem from problems with the brain or the ovaries, so the researchers decided to determine if the compounds had any effect on brain development or function.
Patisaul explains that the brains of both female rats and female humans have a region that regulates ovulation. "That part of the brain," Patisaul says, "is organized by hormones during development which is the neonatal stage for rats and during gestation for humans." Patisaul says the new study shows that the female brain is "critically sensitive" to genistein and equol during this crucial stage of development and that this may indicate that the brain is also especially sensitive during this period to all phytoestrogens and possibly other man-made chemicals, such as bisphenol-A.
|Contact: Matt Shipman|
North Carolina State University