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Learning from Sleeping Bears

Posted By Prucia Buscell, Thursday, March 06, 2014

While bears hibernate through bitter cold winters, they don't eat, drink, or excrete, their kidneys shut down, their heart rate falls to a few beats a minute, their oxygen intake and blood flow plunge, and because they're living off their own mighty stores of fat, their cholesterol skyrockets. And when they wake up they're fine. They're not suffering from diabetes, hardening of the arteries or gall stones, and they haven't lost muscle or bone density.

Scientists think the mysteries of bear hibernation may have much to teach us about human health issues ranging from obesity to kidney disease to organ preservation and long distance space travel.

Kevin Corbit, a senior scientist at the biotechnology company Amgen calls hibernation by black bears and grizzly bears an "astonishing feat of evolution." In a New York Times story he explains that when bears halt their renal functions during hibernation, the result is badly scarred kidneys and levels of blood toxin that would kill a human. Yet full function is restored when the bear wakes, and scientists find no lasting damage. Before hibernation, bears eat and drink prodigiously, and quickly gain the weight and fat they'll need for their long sleep, which can last up to seven months. During hibernation, Corbit writes, bears become insulin resistant, making them in effect diabetic. Unlike diabetic humans, however, they maintain normal blood sugar levels. And again, when they wake up, their insulin responsiveness is restored.

At the top seasonal weight, male black bears can weigh up to 900 pounds and females can weigh up to 500 pounds.They may lose up to 30 percent of their body weight during hibernation. See a Nova report and a National Park Service piece on bear hibernation.

"Bears naturally and reversibly succumb to diabetes," Corbit writes. "Since we know when they make this switch, we hope to pinpoint how they do this."

The bears scientists have studied don't handle fat the same way humans do. It doesn't cause tissue inflammation in bears, and Corbit writes that bears store their excess winter weight harmlessly in fat tissue, rather in the liver and muscles as humans do. Corbit's research on bears, supported by his company, is focused on finding innovations in treating obesity. Hibernation itself is an adaptation to seasonal food shortages, extreme cold and snow. Millions of years of evolution has produced genetic adaptations that make fluctuating weight and obesity benign for bears. Corbit figures maybe scientists can figure out how to do that for humans.

A Science article by Sara Reardon says the mysteries of bear metabolism during hibernation could give doctors the ability to slow down the metabolism of accident victims, thereby extending the time when treatment is most effective. Findings could also help extend the preservation of organs for donation. Understanding how bear brains continue to function with low oxygen, and the mechanisms by which sleeping bears conserve their muscle and bone mass during months of inactivity could be useful in managing long term space travel.

Tags:  buscell  complexity matters  medicine  nature 

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