FunNature & AnimalBears' hearts change as they hibernate

Bears' hearts change as they hibernate

grizzly-inviernoAn investigation published in the journalPhysiological and Biochemical Zoology reveals the complex series of changes that grizzly bears’ hearts undergo (Ursus) while hibernating.

Typically, aoso grizzlyhibernates between five and six months a year. During that time, eHis heart rate drops below 84 beats per minutewhen activejust 19. “If a human heart reduced its beats in this way, a lot of harmful things would happen,” explains Bryan Rourke, a co-author of the study. To begin with, such a slow heartbeat causes the blood to “pool” in the chambers of the heart (atria and ventricles). In a human, the increased pressure would cause the chambers to expand, and the dilated muscle would be weaker and less efficient, eventually leading to congestive heart failure. “Bears are able to avoid it, but until now we didn’t know how,” adds Rourke.

Using data obtained from bears in captivity at Washington State University with the help of aechocardiogram, as well as analyzing the heart tissue of wild bears, the scientists discovered thatproteins in the heart change to match the rhythm of the heartbeat. Contractions of the heart muscle are controlled by a protein calledmiosinawith two varieties, alpha and beta. The alpha version produces a faster but weaker heartbeat. “During hibernation, the muscle in the left atrium of the heart of bears produces more alpha protein,” explains Rourke. This makes the beat weaker and prevents damage to the heart as the atrium pushes on the left ventricle, a chamber that becomes stiffer to avoid overstretching when blood pools.

Scientists hope that the finding will one day have application in humans for the treatment of certain diseases.

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