Changes in the body composition of fasting polar bears (Ursus maritimus): The effect of relative fatness on protein conservation
Changes in the body composition of fasting polar bears (Ursus maritimus): The effect of relative fatness on protein conservation
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DOI：
10.1086/physzool.69.2.30164186
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发表时间：
1996-03-01
期刊：
影响因子：
--
通讯作者：
Ramsay, MA
中科院分区：
文献类型：
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作者：
Atkinson, SN;Nelson, RA;Ramsay, MA
熊属的熊类，尤其是北极熊，被认为在它们长时间的季节性禁食中能够高效地避免身体蛋白质的净损失。然而，大多数支持这一观点的数据都来自于圈养熊在禁食时明显保持恒定瘦体重的研究。使用氧化氘稀释，我们量化了自由放养的北极熊在每年禁食期间身体成分的变化。对于10只成年和亚成年雄性北极熊的样本，研究开始时的身体状况为0.12至0.58千克脂肪/千克LBM。随后，在79 d的时间间隔内，个体之间的脂肪和脂肪损失差异很大。与先前对禁食熊的研究相反，蛋白质的分解代谢似乎满足了一些个体维持能量需求的很大一部分。当转化为能量单位时，观察到的身体能量含量损失的74%至99%可归因于身体脂肪的分解代谢。此外，从脂质储存中获得最高比例能量需求的熊是那些第一次被捕获时相对较胖的熊。我们认为，在北极熊和一般的熊类动物中，之前提到的在长时间禁食期间将蛋白质损失降到最低的能力，在一定程度上取决于某些个体在食物充足的季节可以积累的巨大的脂肪储存。
Bears in the genus Ursus, in particular polar bears, are thought to be highly efficient at avoiding a net loss of body protein during their prolonged seasonal fasts. Most data supporting this idea, however, originate from studies in which captive bears apparently maintained a constant lean body mass (LBM) while fasting. Using deuterium oxide dilution, we quantified changes in the body composition of free-ranging polar bears during an annual period of fasting. For a sample of 10 adult and subadult male polar bears, body condition at the start of the study ranged from 0.12 to 0.58 kg of fat/kg of LBM. Subsequently, over an interval of 79 d, losses of LBM and fat varied considerably among individuals In contrast to previous studies on fasting bears, catabolism of protein appeared to meet a significant proportion of maintenance energy demands in some individuals. When converted into energetic units, between 74% and 99% of the observed losses in body energy content were attributable to the catabolism of body fat. Furthermore, bears that derived the highest proportion of their energy needs from lipid stores were those that were relatively fat when first captured. We suggest that in polar bears, and ursids in general, the previously noted ability to minimize protein loss during extended fasts is in part dependent on the extraordinary magnitude of fat stores that some individuals can accumulate in seasons when food is abundant.