Protein metabolism in the black bear before and during hibernation
Lundberg, D.A.; Nelson, R.A.; Wahner, H.W.; Jones, J.D.
Mayo Clinic Proceedings 51(11): 716-722
1976
ISSN/ISBN: 0025-6196 PMID: 825685 Document Number: 106787
It was known that American black bears (Ursus americanus) during hibernation do not defaecate, urinate, eat or drink; they are not deep hibernators and can always be roused. Four adult males in Minnesota were caged in the open air and fed on dry dog food; during hibernation they had access to a dry cellar with straw bedding but no food or water. One failed to hibernate, lost 30% of bodyweight in under 2 weeks, urinated and died. Blood taken at autopsy had urea 650 mg/100 ml. The others throughout hibernation lost 15 to 25% of bodyweight but not a significant amount of lean body mass. Total body water did not change in 1 bear and results for the other 2 may not be valid. Urine was sampled by catheter and the bears were given intravenous injections of bear serum [125I]albumin, of 3H2O and of [14C]leucine. From results, protein turnover was 3 to 5 times greater during hibernation than during activity, though urea synthesis was less. There was no significant change with hibernation in haematocrit, serum albumin, thyroxine or thyroxine-binding globulin, but triiodothyronine tended to fall. Increasing protein turnover suggests a strong protein-anabolic mechanism tending to compete with catabolic pathways for amino acids. A consequence of increased protein turnover would be thermogenesis; bears hibernate with higher body temperature than some animals. Better understanding of bear physiology may contribute to management of persons with faulty kidneys or none, to control of obesity in man and to comprehension of the aging process.