C - Michigan Technological University

1.7.6 Hypothesis 2: OCN interacts with energy metabolismA third explanation of the discrepancy between histomorphometric data and boneturnover markers is that some of the factors quantified may be up-regulated in the serumduring hibernation as hormonal signals to other tissues. For instance, circulating OCNcan function as a hormone to regulate energy metabolism (for review see: [150, 151]). Inmice, the undercarboxylated form of OCN (ucOCN) increases adiposity and thesecretion of adiponectin from adipocytes, it promotes the proliferation of pancreaticβ-cells and their secretion of insulin, and it enhances insulin sensitivity [152, 153]. Thus,increased OCN, especially ucOCN, could have an array of complex effects on thephysiology of energy metabolism during hibernation. ucOCN could increase adiponectinsecretion during hibernation [152, 153], thus promoting more efficient glucose uptakeand fatty acid oxidation [154, 155]. In addition, an increase in adiponectin duringhibernation could potentially offset disuse-induced osteoblast loss by increasingosteoblast differentiation and proliferation [156-158]. Thus, it is possible that bearsincrease circulating OCN levels during hibernation as a mechanism to controlenergy metabolism during this period of low energy expenditure.(2) The second Aim of this study was to quantify total and ucOCN, glucose,insulin, and adiponectin in the serum of black bears every 10 days fromOctober through the beginning of May. The hypothesis was that OCN,ucOCN, insulin, and adiponectin would all increase and glucose woulddecrease in the serum of hibernating bears (compared to that of activebears). ucOCN levels were expected to have a positive relationship toinsulin and adiponectin, and a negative relationship to glucose levels.1.7.7 Hypothesis 3: Reduced apoptotic serum factors during hibernationIn addition to asking why bone turnover markers do not match histomorphometricindices, another question was asked: how do hibernating bears maintain bone structureand strength during this extended period of disuse? It has been suggested that bearbones (and muscles) are mechanically loaded during hibernation by shivering, thuspreventing atrophy [19, 159]. During hibernation periods greater than one hour, captive15