Hormones, Frogs & You

A few weeks ago, I attended a talk by Dr. Tyrone Hayes that was presented by Environmental Defence. Dr. Hayes is a biologist and professor of Integrative Biology at the University of California, Berkeley. He is best known for his work on the effect of the herbicide Atrazine on frogs.

At the talk, we learnt that Atrazine is a widely used herbicide developed by Syngenta and is an endocrine-distrupting chemical. It has been sprayed on millions of bushels of corn, sorghum and sugarcane for years.

Dr. Hayes and his team have done extensive research on the effects of atrazine on the metamorphosis and sex differentiation of frogs. They discovered that Atrazine causes a percentage of male frogs to be demasculinized or chemically castrated and completely feminized. In other words, atrazine can change male frogs into female frogs when the tadpoles are exposed to small doses of the chemical.

Atrazine causes testosterone levels to decline by converting testosterone into estrogen though the aromatase pathway. Testosterone is the male sex hormone that promotes the development of male sex characteristics. Without testosterone, the tadpoles are unable to grow male genitalia and become feminized. In some cases, they were found to produce eggs. This results in these frogs being genetically male but physically and physiologically female.

For more information, here is a list of some of Dr. Hayes research papers on Atrazine:

Hayes, T.B., A. Collins, M. Lee, M. Mendoza, N. Noriega, A.A. Stuart, and A. Vonk (2002) Hermaphroditic, demasculinized frogs following exposure to the herbicide, atrazine, at ecologically relevant doses. Proc. Nat. Acad. Sciences (USA). 99(8): 5476-5480.

Hayes, T.B, K. Haston, M. Tsui, A. Hoang, C. Haeffele, and A. Vonk (2002) Hermaphrodites beyond the corn field: Atrazine-induced testicular oogenesis in leopard frogs (Rana pipiens). Nature 419: 895-896.

Hayes, T.B, K. Haston, M. Tsui, A. Hoang, C. Haeffele, and A. Vonk (2003) Atrazine-induced hermaphroditism at 0.1 ppb in American leopard frogs: Evidence from the laboratory and the wild. Environ. Health. Perspect. 111(4): 1-8.

Hayes, T.B., P. Case, S. Chui, D. Chung, C. Haeffele, K. Haston, M. Lee, V.P. Mai, Y. Marjuoa, J. Parker, M. Tsui (2006) Pesticide mixtures, endocrine disruption, and amphibian declines: are we underestimating the impact? Environ Health Perspect. 114: 40-50.

Fan, W., T. Yanase, H. Morinaga, S. Gondo, T. Okabe, M. Nomura, T. Komatsu, K. Morohashi, T.B. Hayes, R. Takayanagi, H. Nawata (2007) Atrazine-induced aromatase expression is SF-1 dependent: implications for endocrine disruption in wildlife and reproductive cancers in humans. Environ Health Perspect. 115(5):720-7.

Hayes T.B., V. Khoury, A. Narayan, M. Nazir, A. Park, T. Brown, L. Adame, E. Chan, D. Buchholz, T. Stueve, S. Gallipeau (2010) Atrazine induces complete feminization and chemical castration in male African clawed frogs (Xenopus laevis). Proc Natl Acad Sci (USA) 107(10):4612-7.

Hayes T.B., L.L. Anderson, V.R. Beasley, S.R. de Solla, T. Iguchi, H. Ingraham, P. Kestemont, J. Kniewald, Z. Kniewald, V.S. Langlois, E.H. Luque, K.A. McCoy, M. Muñoz-de-Toro, T. Oka, C.A. Oliveira, F. Orton, S. Ruby, M. Suzawa, L.E. Tavera-Mendoza, V.L. Trudeau, A.B. Victor-Costa, E. Willingham (2011) Demasculinization and feminization of male gonads by atrazine: consistent effects across vertebrate classes. J Steroid Biochem Mol Biol. 127(1-2):64-73.

If your thinking, why should I care about frogs and frog sex hormones? It has nothing to do with me. As it turns out, frog sex hormones and human sex hormones are very similar. They are so similar in fact that from the 1930s to the 1950s doctors used the African clawed frog as pregnancy tests. When the frogs were injected with the urine of pregnant females, the female frogs would produce eggs. The hormones produced by pregnant females were so similar to frog sex hormones that they caused the female frogs to ovulate. So, if Atrazine can cause frog testosterone to change to frog estrogen, what is it doing to human testosterone and other sex hormones?

There might not be definitive research on the effect of Atrazine on humans and Dr. Hayes work has been questioned. However, I am not willing to be a guinea pig and take risks with my health. I would encourage you to learn everything you can about Atrazine and then make an informed decision about what goes into your body.

Let’s stop blindly shovelling food into our mouths and start paying more attention to what we allow into our bodies.