Sunday, February 04, 2007

Groundhogs, Other Hibernators, Could Aid Human Health

(HealthDay News) -- When Punxsutawney Phil popped up to look for his shadow Friday morning, he was not just forecasting how long winter will last.

Biologists now think that Phil and his fellow groundhogs, along with other animals in hibernation, could foreshadow advances in human health.

In fact, hibernators' amazing ability to manipulate their own metabolisms could lead to breakthroughs in improving organ transplant and in fighting such illnesses as obesity, diabetes, heart disease and even Alzheimer's, research shows.

"Remember, our physiology, and even our genetic makeup, isn't that different, in terms of basic bodily functions, [from] these hibernating mammals," said Hannah Carey, a professor in the School of Veterinary Medicine at the University of Wisconsin-Madison.

"The blueprint, the genes to do these things are there -- we're just not activating the same physiological pathways," said Carey, who is also president-elect of the American Physiological Society.

A wide range of mammals hibernate, from tiny squirrels to the grizzly bear. And hibernation isn't restricted to cold-weather climates: Scientists recently discovered that a Madagascar primate, the fat-tailed lemur, also goes into the hibernating state known as "torpor" during that tropical island's dry season.

"Torpor is a word we use for this state of physiological down-regulation," Carey explained. "Hearts slow down to a few beats per minute, and the animals are breathing only a few breaths per minute. Blood flow is very slowed, and their metabolism is suppressed."

Body temperature during torpor can fall to near-freezing in many hibernating squirrels, Carey added. In fact, the Arctic ground squirrel's hibernating temperature actually drops below freezing.

Close investigation of hibernating states is giving scientists new insight into animal physiology and, as a bonus, human health and disease as well. Some examples:
  • Organ transplant. Harvested human organs kept at cold temperatures can only remain viable for a few days at most. So, how do squirrels' livers and intestines stay perfectly healthy at less than 40 degrees Fahrenheit for weeks on end? In one study, "we found that [hibernating] squirrels maintain, in a much healthier state, the microcirculation of the liver," Carey said. Insights into just how this happens could increase the viability and number of human organs available for transplant, she said.
  • Heart attack. Rousing from weeks of torpor, hibernating mammals flood their near-dormant organs with fresh blood, a process called reperfusion. But doctors know that the speedy reperfusion of hearts after heart attack is, in itself, a major cause of damage to cardiac tissues. "But hibernators, faced with the very same kind of experimental insult, are very well-protected," Carey said. "They seem to have bumped up their defenses." Understanding those natural defenses might lead to better heart attack care, she said.
  • Obesity. Gregory Florant, a biology professor at Colorado State University, has been studying the role in hibernation of a fat cell-secreted hormone called leptin. He explained that leptin, along with other biochemical signals, may help typically ravenous animals shut down their appetites as winter approaches. "Likewise, if we can determine what the hierarchy here is for shutting down the appetite, that may allow us to make gains on how to curb people's appetites so they don't eat as much," he said.
  • Diabetes. Gearing up for hibernation means packing on weight -- a lot of weight. And hibernation means mammals turn into "the ultimate couch potatoes," Florant said. So, why don't these fattened-up bears, groundhogs and squirrels slip into type 2 diabetes, as humans so easily do? "That's a really interesting health perspective," Florant said. "They never go into frank diabetes, even though they become almost morbidly obese." Unraveling that mystery could lead to new ways to fight diabetes, he added.
  • Alzheimer's. Carey pointed to another intriguing phenomenon: As the time mammals spend in torpor increases, vital cell connections begin to weaken within their brains. However, most hibernating mammals actually rouse themselves in their burrows every so often, and this appears to help these neural connections reestablish themselves. "So, people are saying, 'these guys are great models for things like Alzheimer's disease and [brain] lesions such as neurodegeneration,' " Carey said. In essence, hibernating mammals experience real brain damage, "but then they reverse themselves," according to Carey.

Finding out how that happens could further human brain research, she said.
With all of these physiological advantages, Punxsutawney Phil and his mammalian brethren appear to be on to something, the experts said.

"Different animals come up with different ways to cope with environmental stresses," Carey said. "Of course, we use our brains, so we have coats, electric heaters, that kind of thing. But it's really cold here in Wisconsin right now: Sometimes I look out there and think that maybe hibernation is a pretty smart idea."

More information
Find out more about groundhogs and Groundhog Day at Cornell University.

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