Date of Award
Master of Science
Brynn H. Voy, Edward C. Ramsay
American black bears have an intricate seasonal physiology, eating an entire year’s worth of food in 7-9 months, and then losing that weight during hibernation with almost no activity. The black bear thus represents a novel model in which to study seasonal regulation of food intake and metabolism. What controls the seasonal changes in fat deposition and metabolism in bears is unknown. Adipokines, such as leptin, regulate food intake and metabolism, and we hypothesized that these adipokines vary seasonally in bear adipose tissue, in a manner that correlates with fat storage. The study population consisted of wild bears from the Great Smoky Mountains National Park (GSMNP) and New Jersey and captive bears from facilities in Tennessee and North Carolina. Blood and subcutaneous fat were collected from all bears, and abdominal fat and liver samples were collected from euthanized bears. Body length and weight were measured and converted into a modified body mass index score. Circulating levels of triglycerides, non-esterified fatty acids, beta-hydroxybutyrate, leptin, and adiponectin were measured to assess lipid and glucose metabolism. A radioimmunoassay was validated for use in bears to measure serum leptin concentrations. Quantitative PCR was used to measure mRNA expression of leptin, adiponectin, pyruvate dehydrogenase kinase isoenzyme 4 (PDK4), and protein kinase, AMP-activated, alpha 1 catalytic subunit (PRKAA1) in the fat samples collected across seasons. Adipocyte size was measured as an additional index of adiposity. There were significant variations in body mass due to sampling lean bears in the GSMNP as compared to obese captive bears. PRKAA1 and adiponectin expression in subcutaneous fat were significantly greater in captive fall bears as compared to captive summer and captive winter bears. Circulating levels of beta-hydroxybutyrate were significantly less in captive bears as compared to wild bears. Circulating levels of leptin and leptin expression in subcutaneous fat did not change by season. Circulating levels of adiponectin were significantly higher in the fall as compared to summer and winter. Analysis of fatty acids revealed that cis-vaccenic, palmitic acid and stearic acids were prevalent in the bear. Correlation analyses identified significant relationships among adipokines, expression of metabolic genes and lipid metabolites.
Hill, Elizabeth Marie, "Seasonal Changes in White Adipose Tissue in American Black Bears (Ursus americanus). " Master's Thesis, University of Tennessee, 2013.