Whole-body urea cycling and protein turnover during hyperphagia and dormancy in growing bears (Ursus americanus and U-arctos)
Whole-body urea cycling and protein turnover during hyperphagia and dormancy in growing bears (Ursus americanus and U-arctos)
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DOI：
10.1139/z97-848
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发表时间：
1997-12-01
影响因子：
1.4
通讯作者：
Robbins, CT
中科院分区：
文献类型：
--
作者：
Barboza, PS;Farley, SD;Robbins, CT
研究人员对亚成年熊秋季进食过多 (n = 3) 和冬季休眠 (n = 6) 期间的熊进行了研究。使用 C-14-和 N-15-尿素测量尿素动力学，使用 N-15-甘氨酸估计蛋白质周转率，并使用 H-3-水评估身体成分。冬季氨基酸降解减少表现为血浆尿素和转氨酶活性下降，尿素产量低于秋季（4.7 vs. 27.5 mmol urea-N.kg(-0.75).d(-1)）。贪吃的熊体内产生的尿素中只有 7.5% 被降解，只有 1.1% 的降解氮被重新利用为氨基氮。休眠的熊重复利用了 99.7% 的尿素，表明微生物尿素分解和尿素氮吸收已彻底。休眠期间体内氮损失率较低，表明非尿素氮以肌酐形式损失。不同季节的蛋白质周转率（15.2-21.5 g.kg(-0.75).d(-1)）相似，反映了休眠期间肝脏、肠道和肌肉功能的明显维持。蛋白质合成占休眠能量消耗的32%，其中主要（91.5%）来自脂肪氧化。休眠熊的器官功能和体温保持一致，可以回收尿素-N，从而最大限度地减少体内蛋白质损失并保持活动能力。与异温冬眠相比，熊类休眠在冬季提供更大的灵活性，并有利于春季快速恢复觅食和生长。
Subadult bears were studied during their autumn hyperphagia (n = 3) and winter dormancy (n = 6). Urea kinetics were measured with C-14- and N-15-urea, protein turnover was estimated with N-15-glycine, and body composition was assessed with H-3-water. Reduced amino acid degradation in winter was indicated by declines in plasma urea and aminotransferase activities, and lower urea production than in autumn (4.7 vs. 27.5 mmol urea-N.kg(-0.75).d(-1)). Only 7.5% of urea produced in hyperphagic bears was degraded and just 1.1% of the degraded N reutilized as amino-N. Dormant bears reutilized 99.7% of urea produced, indicating thorough microbial ureolysis and urea-N resorption. Low rates of body N loss during dormancy suggested losses of non-urea N as creatinine. Protein turnover rates (15.2-21.5 g.kg(-0.75).d(-1)) were similar between seasons and reflected the apparent maintenance of hepatic, intestinal, and muscular functions through dormancy. Protein synthesis accounted for 32% of energy expended in dormancy, which was mainly (91.5%) derived from fat oxidation. Consistent organ function and body temperature in dormant bears enables recycling of urea-N, which minimizes body protein loss and conserves mobility. In comparison with heterothermic hibernation, ursid dormancy would provide greater flexibility during winter and facilitate rapid resumption of foraging and growth in spring.