Meeting Abstract

43.2  Jan. 6  Skeletal Muscle Conservation and Adaptive Fasting by Hibernating Black Bears HARLOW, H.J.*; LOHUIS, T.D.; LASKE, T.G.; GARSHELIS, D.L.; ROURKE, B.C.; IAIZZO, P.A.; Univ. of Wyoming, Laramie; Dept. of Fish & Game, Soldotna, Alaska; Medtronic, Inc., Minneapolis, Minnesota; Minnesota Dept. of Natural Resources, Grand Rapids; California State Univ., Long Beach; Univ. of Minnesota, Minneapolis hharlow@uwyo.edu

The black bear Ursus americanus represents a paradox among �hibernating� mammals. They remain in their winter den for 3 to 5 months in mild, continuous hypothermia (about 33�C); all the while not eating or drinking but capable of remarkable mobility when disturbed. Fat is a major energy resource that correlates with plasma leptin levels. Fatty acid saturation index is relatively maintained throughout the winter. Plasma amino acid profiles and urea/creatinine ratios suggest bears are adaptive long-term fasters with an extended protein conservation phase. Many muscle groups remain stable throughout 120 days of fasting and inactivity, while others show only marginal atrophy. Skeletal muscle protein degradation is matched by synthesis; fiber morphology (number, size and myosin heavy chain isoforms) show limited alteration and use of labile protein reserves may help preserve myofibrilar protein. Bouts of daily muscular contractions in concert with protein conserving processes result in marginal loss of skeletal muscle strength measured in vivo and in vitro. When injured during the winter, bears demonstrate remodeling of dermal layers and remarkable wound healing. We found that small mammals entering either deep or shallow torpor achieve similar overwinter retention of skeletal muscle protein and strength. This may be in part due to the process of urea recycling. We have identified UTB urea transporters in the bladder and large intestine of small mammals which may work in concert with gut microbes to recycle urea important for skeletal muscle retention.