Young grizzly bears being studied at WSU may help scientists develop new therapies for people with heart disease.
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 have echocardiograms performed to assess the heart rate and rhythm, how much blood the heart chambers are pumping, and how well the heart muscle contracts and relaxes. The bears are studied once a month in the summer and three times during their hibernation period (from mid-October through March).
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. Check out a PBS video of a hibernating bear in Yellowstone »
Lynne Nelson, a cardiologist in Washington State University’s College of Veterinary Medicine, and Charles Robbins, director of the university’s Bear Research, Education and Conservation Program, are collaborating on a research project that studies how the bears’ hearts work during hibernation.
The research shows that the bears’ heart rates decrease from around 80-90 beats per minute in the summer to about 18 beats per minute in the winter (ranging between 8-24 beats per minute). In people, heart rates this slow would cause congestion and heart failure to occur, usually within a matter of weeks. The bears show no signs of congestion even after four or five months of slow heart rates.
Even though heart muscle contraction appears normal, the heart muscle’s ability to relax and accept blood volume 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 hibernation. The enhanced relaxation of the muscle could help avoid congestion and congestive heart failure.
In addition, early protein analysis suggests that the heart muscle becomes stiffer which may help the muscle avoid excess stretching during the slow heart rate period. In people, it is well recognized that the symptoms of heart failure occur more frequently due to abnormalities in heart relaxation, verses contraction or pumping. Heart failure is also often accompanied by changes in heart muscle stiffness or elasticity. Researchers in WSU’s College of Veterinary Medicine are evaluating the mechanisms by which bears can adapt to the hibernation period and believe 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 the Bear Center Web site, the Large Carnivore Conservation Lab (look for the videos of cougar kittens toward the bottom of the page), and the Department of Natural Resource Sciences.