What Hibernating Animals Can Teach Humans

Courtesy of Hannah Carey
Program Director, Physiological and Structural Systems

Punxsutawney Phil is best known for his ability to "forecast" whether there will be six more weeks of winter each year. Few people are aware, however, that groundhogs like Phil provide science with even more important information throughout the year. That's because groundhogs are hibernators.
Many animal species, like Phil, enviably spend the winter hibernating including bears, wood chucks, bats hedgehogs, lemurs and some squirrels. Hibernators curl their bodies into tight balls and slow their breathing and other bodily functions to a near standstill that would kill other mammals. For months they remain in a state of suspended animation, yet their bones and muscles do not atrophy and they awaken in spring completely healthy. Some animals even hibernate while pregnant, giving birth upon waking in the spring. In the case of hibernating squirrels, these creatures can lose up to 60% of their blood volume and survive at least 10 hours.
Scientists at several universities including the University of Wisconsin School of Veterinary Medicine have studied hibernators for clues about how their functions might be mimicked in humans to improve our health or ability to treat disease. For example, if doctors were able to prevent human bone and muscle from atrophying during periods of inactivity they could help patients better recover from immobilizing illness or injury. Other possibilities include:

• Surviving traumatic injury. Compared with summer squirrels or non-hibernating species, during the hibernation season ground squirrels are more resistant to the damaging effects of ischemia-reperfusion injury, when blood loss to an organ is interrupted and fresh blood is subsequently restored to the ischemic area. Hibernators can also survive massive blood loss much longer than non-hibernators, by maintaining their blood pressure even if they lose blood at rates that would send other animals into shock and death. Understanding how they do this may help humans better survive massive blood loss.
• Preservation of organs for transplant. Currently, a human liver harvested and placed in cold storage remains viable for no more than 12 hours. Yet, the organs of hibernators naturally experience long periods when their organs have low blood flow and are cooled to cold storage temperatures. Studies have confirmed that livers harvested from hibernating ground squirrels survive extended periods of cold storage much better than do livers from summer squirrels or non-hibernating species. If researchers can one day understand and replicate this ability it may improve our ability to preserve and transport organs for transplant.
• Weight regulation and appetite suppression. Animals eat enough through the spring, summer and early fall to sustain their normal metabolism and to lay down fat for the winter. But just prior to hibernation they are able to "turn off" their appetites and fast for several months. Understanding how they do this may help scientists understand how to help humans who cannot suppress their appetites even when they are full.

There are other research projects currently investigating how to achieve a mild state of "induced hibernation" in humans. The ability for humans to hibernate would be useful for a number of reasons, such as saving the lives of seriously ill or injured people by temporarily putting them in a state of hibernation until treatment can be given. These are excellent examples of what scientists mean when we talk about "comparative physiology."