Arctic Squirrels Use Steroids to Bulk Up But Don’t Suffer the Consequences

Fat alone couldn’t get these squirrels through hibernation in burrows that get almost as chilly as -10 degrees Fahrenheit

arctic ground squirrel
James Hager/Robert Harding World Imagery/Corbis

Steroid abuse can give men breasts and infertility, while it strikes women with excessive hair and a deepening voice. Anybody injecting too much testosterone and other muscle-building anabolic steroids risks heart enlargement, liver cancer, high blood pressure, heart attacks — and the mania and delusions called 'roid rage

Squirrels, however, do fine.

Some squirrels running around with extremely high steroid hormone levels, which help them build muscle before hibernation. But how do they avoid all the negative effects that steroids have on other mammals, like, oh, us? That’s the question that a team of Canada-based scientists have addressed in a new paper, published in Biology Letters

Arctic ground squirrels, male and female, can ramp up the concentration of androgens in their blood to levels that are 10 to 200 times higher than normal. These androgens—testosterone and other hormones typically higher in males—allow the squirrels to pack on 30 percent more muscle mass before they start their eight-month winter hibernation, the team, led by Rudy Boonstra, reports. These squirrels are carrying an amazing amount of muscle mass—four times that of related Columbian ground squirrels.

The Arctic ground squirrels likely evolved this muscle-bulking ability to deal with the harsh conditions of their habitat. Other hibernating mammals dig into the ground below the frost line and enjoy relatively balmy temperatures near zero degrees. That's not the case in the Arctic, according to CBC News

Arctic ground squirrels, which range from Hudson Bay to Alaska, live on the tundra, where it's impossible to dig through the permafrost to a layer of soil that never freezes.

"It's like concrete," Boonstra said.

The squirrels' burrows can get as cold as -23 C while they're hibernating, forcing them to burn huge amounts of energy to keep their body temperature above freezing. Under those conditions, fat alone can't generate enough energy in the form of glucose to keep their brain and heart alive.

"And so what they do is they burn muscle."

But the androgen gain doesn’t affect the squirrels’ immune system the way it normally would. The team found the secret to this quirk by comparing the the muscle tissue of seven arctic squirrels and six Columbian. The arctic grounds squirrels had tons of androgen receptors in their muscles and few in their immune system, reports Canadian Geographic. This uneven distribution means that the excess steroids will pump up muscle without throwing the immune system out of wack and causing all the problems we associate with steriod abuse.

Despite the risks, the lure of performance enhancement still gets professional athletes like A-Rod—who, the Miami Herald reported this week, admitted earlier this year that, yes, he had used steroids—in trouble. The new research just underscores exactly how our bodies are not equipped to handle excess hormones.

"I think the salient point from the perspective of humans is you do not have the [right] genetic machinery… so don't take the bloody stuff," Boonstra told CBC News. "You're not an Arctic ground squirrel."

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