Arctic ground squirrels are clearly the “studs” of the squirrel world. They have testosterone levels that are up to two hundred times greater than other species of squirrel.
The Arctic ground squirrel hibernates for eight months during the long Arctic winter. Unlike other hibernators who use stored bodyfat as fuel during hibernation, these squirrels rely on store muscle mass to provide fuel during this period. This is due to the extreme Arctic cold that prevents the squirrels from burrowing below the permafrost meaning that they spend much of their time at temperatures as low as -23° C.
These squirrels’ bodies have evolved to produce high endogenous levels of anabolic steroids that allow them to produce additional protective muscle mass during the summer and fall. These naturally produced anabolic steroids allow the squirrels to increase their muscle mass by 25%. These extreme levels of anabolic steroids have no negative consequences for the health of the squirrel.
Researchers at the University of Toronto Scarborough have discovered how the squirrels can tolerate large amounts of natural androgen steroids and remain healthy: They are able to selectively suppress androgen receptors in all tissues in their bodies except for muscle tissue.
The negative effects of anabolic steroids experienced by bodybuilders arise from the steroid action on androgen receptors in other tissues outside of the muscle. Androgen receptors exist throughout the human body and account for many of the negative side effects. For example, androgen receptors in the skin contribute to the negative side effects of acne, baldness and hirsutism experienced by some steroid users.
While bodybuilders have learned to manage many of the side effects such as those arising from conversion to estrogen and dihydrotestosterone, they have not been able to selectively target the androgen receptors in muscle tissue.
The discovery of the Arctic ground squirrel’s ability to selectively suppress androgen receptors outside of muscle has exciting implications, not only for bodybuilders but, for human health in general.
The mechanism by which Arctic ground squirrel accomplish the selective androgen receptor suppression is currently unknown.
Source
Boonstra, R, et al. (August 22, 2011). Preparing for hibernation in ground squirrels: adrenal androgen production in summer linked to environmental severity in winter. Retrieved from http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2435.2011.01890.x/abstract
