C - Michigan Technological University

measured serum values. However, all statistical analyses were blocked by bear tocontrol for inter-bear variability.3.4.3 SummaryBone is a complex organ which responds to many stimuli. It is likely that multiplefactors work together to maintain bone integrity during hibernation in bears. Thesefactors could include direct neural stimulation, as well as endocrine control. The anabolicrole of circulating PTH was previously hypothesized to help maintain hibernating bearbone, due to its positive correlation to osteocalcin, a marker for bone formation [34]. Thecurrent study brings to light more potential endocrine effectors of bone preservationduring hibernation. Maintaining serum leptin concentrations longer into hibernation couldhelp inhibit disuse-induced bone loss. Reduced IGF-1 and increased NPY in the serumof hibernating bears could suppress bone resorption and formation rates whilesustaining balanced turnover, thus conserving energy during this extended anorecticperiod. The endocrine changes observed in this study may help explain the reduced,balanced bone turnover that occurs during the unique physiological setting in whichbears fast, reduce energy expenditure to a minimum, and remain eucalcemic despite nourine excretion for half a year.3.5 Tables and figuresTable 3.1—Summary of assaysThe number of bears and assays that were performed in each hibernation season. Thenumber of bears that gave birth to cubs is in parentheses. Unknown values are indicated as“UK.”Season Bears Age (years) Assays Data Location2002‐2003 3 (UK) UK LeptinFigure 3.1Tables 3.2‐3.42003‐2004 5 (5) 3‐12 Leptin, IGF‐1Figures 3.1, 3.5Tables 3.2‐3.42006‐2007 2 (1) UK Serotonin, NEFigures 3.3, 3.4Tables 3.2‐3.52007‐2008 4 (3) 5‐14 NPY, NE, SerotoninFigures 3.2‐3.4Tables 3.2‐3.52008‐2009 5 (3) 2‐21 NPY Tables 3.2‐3.556