Powers Fraites, MJ, RL Cooper, A Buckalew, S Jayaraman, L Mills and SC Laws. 2009.

Characterization of the hypothalamic-pituitary-adrenal axis response to atrazine and metabolites in the female rat. Toxicological Sciences 112(1):88-99.

Synopsis by Heather Patisaul, Ph.D.

Exposure to the common herbicide atrazine rapidly induces the release of stress hormones in rats, which may explain how the weed killer produces some its harmful reproductive effects.

A new study reveals that female rats fed atrazine at the time of ovulation released a flow of hormones that are associated with stress and that are known to interfere with hormones essential for reproduction. The stress reaction is similar to that seen when the animals are restrained against their will, say the authors in an article published in the journal Toxicological Sciences.

The findings reveal one way atrazine may impact female reproduction. Elevated stress hormones can disrupt the hormone signals that spur ovulation. Such a stress response to atrazine could partially explain why previous studies find that the herbicide inhibits reproduction.

Atrazine is one of the most frequently used herbicides in the US. It is primarily used during the spring to control weeds in agricultural fields. The chemical frequently washes off the fields and into aquatic systems, contaminating surface and ground water. In field and laboratory studies, the herbicide can alter the levels of hormones important to reproduction, delay or advance development and induce other reproductive abnormalities in vertebrates, including amphibians and rodents.

For this study, the researchers fed groups of adult female rats either atrazine or one of its two common metabolites – DIA or DACT – either once at a dose of 75 miligrams/kilogram or every day for four days at doses of 12.5 or 75 miligrams/kilogram. The doses were somewhat higher than would be considered relevant for humans but were in the range of what has previously been tested in similar studies. A variety of hormones were measured in the rats’ blood. Determining how atrazine affects stress and reproduction in animals is important for making predictions about how atrazine exposure might affect people.

The researchers found that exposure to a single, oral dose of atrazine or to one of its common metabolites provoked the release of the stress hormones – including corticosterone and progesterone – within 15 minutes of exposure. Animals exposed in the same way for four days showed similar effects.

Although the stress hormones elevated by atrazine and one of its metabolites are known to suppress the hormone signalling cascade needed for ovulation, future studies will need to establish if a true cause-and-effect relationship exists. The data presented in this study suggest that such a relationship – where atrazine activates stress hormones which then suppress hormones important for reproduction – is plausible.