Hibernation provides clues to heart disease

PULLMAN – In hibernation, a bear’s heart function mimics certain heart diseases of humans and other animals. When a bear comes out of hibernation, its heart resumes normal functioning, unlike humans and other animals with diseased hearts.

Hibernating bears have heart rates of
about 18 beats per minute. In humans, heart rates this slow would cause congestion and heart failure, usually within a matter of weeks. The bears show no illeffects, even after four or five months of slow heart rates.

Lynne Nelson, a cardiologist in WSU’s College of Veterinary Medicine, and Charles Robbins, director of the university’s Bear Research, Education and Conservation Center, are collaborating on a study to assess the myocardial function in grizzly bears during hibernation. Luna, Mica, Kio and Peeka, four hand-raised grizzly bears, have been participating in a study designed to evaluate a bear’s heart function during hibernation. The bears routinely coorperate in echocardiograms studies to assess heart rate and rhythm, how much blood their heart chambers are pumping, and how well heart muscles contract and relaxes.

In humans, it is well recognized that the symptoms of heart failure occur more frequently due to abnormalities in heart relaxation versus contraction or pumping. Heart failure is also often accompanied by changes in heart muscle stiffness or elasticity.

With bears, though, the heart muscle’s ability to relax appears enhanced. This adaptation may help the bears’ heart chambers cope with the increased stress on the muscle that likely develops during the long pauses between heart contractions during slow heart rates. The enhanced relaxation of the muscle could help avoid congestion and congestive heart failure.
Nelson and her colleagues are evaluating the mechanisms by which bears can adapt to hibernation and that these adaptations may be applicable to treatment for humans and animals with heart disease.
“Often, if we can understand the biology and how things happen — how certain receptors are being stimulated — then therapies can be developed to target muscle protein changes, block the receptors or stimulate the receptors to give that effect,” Nelson said.

For more information, check out this short video overview of research at the WSU Bear Research, Education and Conservation Center: http://tinyurl.com/5zxmmj or visit the Bear Center Web site at http://tinyurl.com/5rowl9.