Posted by: Elizabeth Barilleaux | November 15, 2010

The Science of Hibernation

Some days, the idea of hibernation has a real appeal for me.  Taking a nice, long, cosy nap and waking up a few pounds lighter – what’s not to like?  Once I started digging around, I found that hibernation can be a lot more complicated and interesting than a simple, winter-long snooze.

Call it torpor, dormancy or – if you’re not into the whole brevity thing – carnivorean lethargy, but the basic idea is significantly slowing the metabolism.  This adaptation is nature’s clever way of coping with shortages of food, water or decent living conditions.  Scientists that study hibernation are also looking for information that will yield human benefits such as preserving organs for transplant, buying time for wounded soldiers, treating cancer and allowing long-distance space travel. 

One of the common requirements for hibernation is the storage of body fat.  Not just any fat – brown fat.  Built of smaller lipid droplets, more iron-rich mitochondria (which give it the brown color) and a higher density of capillaries, brown fat helps generate body heat while acting as a back-up source of fuel.  Larger mammals such as bears store larger amounts of fat, which allows them to sleep more deeply and for longer periods.  Black bears can rest for up to 100 days without needing to eat, pee, poop or move around.  Their core body temperatures drop by 120 F and their heart rates slow from 40-50 beats a minute down to eight.  Small mammals aren’t able to bank big masses of fat and must wake up every few days to nibble on a little something and go to the bathroom before they settle back down.  Interestingly, the body temperatures of smaller mammals can reach much colder ranges.  Ground squirrels routinely lower their abdominal temperature to 00 C, which is pretty impressive considering that blood freezes between -2 and -30 C.

So how does learning about this help us non-hibernators?  For starters, a chemical called hibernation induction trigger (HIT) that’s found in the blood of hibernating animals can help extend the life of transplant organs.  Currently, isolated organs can “survive” for about 6 hours outside of the body – HIT can prolong that for up to 18 or more.  Researchers working on methods to induce human hibernation have discovered an injectable plasma of salt and ice that quickly cools the body from 98.60 F to 500 F for several hours.  For trauma victims and wounded soldiers, this suspended animation could buy precious time to reach a medical facility.  Other researchers have successfully induced short-term hibernation  in mice simply by exposing them to air mixed with hydrogen sulfide gas.  The mixture slowed cell functions to almost total inactivity for six hours, after which the mice were revived with normal functions and no long-term damage.  This process could help people suffering from sudden, severe fevers as well as aiding and improving cancer treatments.  And finally, studies have isolated two genes that may trigger hibernation and regulate the fat-to-energy process that would allow long-term space travel.


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