Science News - February 25, 2012

After six months of bed rest Human

s Blood clots s Heart failure s Oxidative and energetic stress s Blood vessel dysfunction

90% reduction in muscle mass Severe disuse osteoporosis Carbohydrate, protein and fat breakdown Bed sores No bed sores

Physiological feats Hibernators are somehow able to survive six months of stillness, even though a similar lack of movement would threaten human health. Studying the changes that hibernators go through may one day make their skills transferable. SOURCE: O. FRÖBERT

brown bears undergo each winter, includ-
ing how they have such high cholesterol
but no increased risk for heart disease.
“ We see the brown bear as a living library
of information,” Fröbert says. “It’s an
animal that has solved a multitude of
problems that humans face.”
Insights gleaned from bears and
ground squirrels may also help research-
ers prevent or reverse bone and muscle
loss in space travelers, elderly people
and children with muscular dystrophy.
Such lessons could reveal ways to ren-
der people confined to bed rest immune
to blood clots, bed sores and muscle
and bone atrophy. Therapies designed
to mimic ground squirrel hibernation
strategies could save soldiers and acci-
dent victims from bleeding to death. And
these critters just might hold secrets for
reducing damage from strokes or heart
attacks, and even for preserving organs
for transplant after they are cut off from
a blood supply and put on ice.

Skin
Circulatory
system
Muscle
Bone
Metabolism
Hibernator

Extra pounds, no problem

Nearly everything about the way an animal’s body works changes when it hibernates, and preparations start weeks or months in advance. The first order of business is to fatten up.

“Fat is where it’s at for a hibernator,” says Matthew Andrews, a molecular biologist at the University of Minnesota Duluth who studies 13-lined ground squirrels. “You bring your own lunch with you.” Packing lunch is necessary because the animals go on the world’s strictest diet during the winter, surviving entirely off their white fat. “They have their last supper in October; they don’t eat again until March,” Andrews says.

Bigger fat stores mean a greater chance of surviving until spring. “If they go in really chunky, nice and roly-poly, that’s going to be a good hibernator,” he says.

Bears also watch their waistlines
arteries that can’t be collected from live
bears come from bears killed by hunters
during the legal hunting season.

COURTESY OF O. FRÖBERT

Researchers race to gather fat samples from a tranquilized hibernating brown bear after tracking it down in a forest in Sweden. The bear has to be back in its den within 60 minutes, when the sedative wears off.

expand in the months before settling in for the season. The brown bears Fröbert studies pack on the pounds by chowing down on up to 40 kilograms of blueberries a day. Such gluttony among humans could have severe consequences: Obesity is associated with a greater risk of heart disease and diabetes, among other ailments.

To see how fattening up affects Scandinavian brown bears, Fröbert and his colleagues ventured into the wilds of Sweden following signals given off by radio transmitters or GPS devices on tagged bears.

Bears can be dangerous close-up. Even hibernating bears can rouse to action quickly, so scientists tracking down bears in the winter use darts to tranquilize the animals from a distance. Scientists studying the bears in the summer tranquilize them from a helicopter.

Once a bear is under the tranquilizer’s influence (which takes about five minutes), the scientists have 60 minutes max to get the animal from its den, weigh and measure it, draw blood samples and do minor surgeries to collect fat and other tissues. The bear is returned to its den by minute 61.

Precious materials collected during this high-pressure encounter need to be analyzed within 24 hours, so the researchers often test for levels of cholesterol or certain proteins in the blood while working in the snow or at a nearby research station. A pilot sometimes flies samples from field sites to a lab in Denmark in order to meet the deadline, Fröbert says. Samples such as bones and

Sturdy skeletons

The bears’ cholesterol-defying arteries are just one of the evolutionary tricks allowing hibernators to spend six months as furry couch potatoes without negative side effects.