C - Michigan Technological University

post-hibernation sampling in the beginning of May, whereas the previous study ended inJune. When examining the graphs of serum total calcium over time, both studies have apeak in November and a downward slope through April (Figure 2.3) [35]. In our study,the overall decrease was 4.7% between prehibernation and post-hibernation. Such areduction in total calcium could explain the increased mineral content observed in bearbones during hibernation [20]. A 1% reduction in total serum calcium corresponds to a3% increase in lumbar spine BMD in human patients undergoing an exercise regimewhile confined to bed [176]. Total serum calcium can be separated into three fractions:free ionized calcium (approximately 47%), protein-bound calcium (40%), and anionboundcalcium (13%) [177, 178]. Calcium is only bioactive in the ionized form. Therefore,ionized calcium was quantified in this study. “Seasonal means” analysis revealed anincrease in ionized calcium during the post-hibernation season (Table 2.3). It is probablethat ionized calcium increases in the spring despite reduced total serum calciumbecause of the decreased availability of serum proteins like albumin that bind calcium[179]. The current study found that total serum protein and albumin both decreasedsignificantly in the spring (Tables 2.6 and 2.7).This study showed that BSALP and TRACP decreased significantly duringhibernation in black bears (Table 2.3). This matched histomorphometric data, whichsuggested a balanced reduction in osteoclast and osteoblast activities during hibernation[18, 20]. Such a decrease in bone turnover would help hibernating bears preserveenergy during this extended anorectic period. Despite this decrease in BSALP andTRACP, the finding that serum OCN increases during hibernation [34] was confirmed bythe current study (Tables 2.2 and 2.3), suggesting that OCN should not be used as anindicator of bone formation in the hibernating bear. As stated earlier, hibernating bearscan be compared to hemodialysis patients because of their reduced renal functionduring denning [113, 114]. BSALP and TRACP are good indicators of bone turnover inhemodialysis patients because they are not removed from the blood by renal filtration[143-145, 148, 149]. In contrast, OCN accumulates in the blood of hemodialysis patientsbecause it is normally excreted in urine. Therefore, it is not an ideal indicator of boneturnover in patients with reduced renal function [143-146]. In humans, a 30% decreasein glomerular filtration rate results in an approximate 65% increase in serum OCN [148].In hibernating bears, serum OCN increased by 285% compared to prehibernation values29