Smith O K
Am J Physiol. 1976 Jul;231(1):174-8. doi: 10.1152/ajplegacy.1976.231.1.174.
Rats were exposed to 4 or 25 degrees C for 6, 12, and 24 h or for longer periods up to 2 wk, then eviscerated. The hourly changes in plasma alpha-amino nitrogen were followed for 4 h after operation, which because of functional removal of the liver allows amino acids released from the extrahepatic tissues to accumulate in the blood. Although cold exposure of tissues to accumulate in the blood. Although cold exposure of 24-h-fasted rats for 6 h before eviscerated resulted in an increased rate of rise of plasma alpha-amino nitrogen postoperatively, the rise was not significantly greater than warm controls until after 12 h of exposure. Thereafter, similar results were obtained whether cold was 12, 24, or 48 h or 14 days duration. Fasting in the cold produced an immediate sharp rise after evisceration so that the concentration was 2 times the control value in 2 h. By contrast, animals allowed to eat adlibitum showed the rise after evisceration but it was progressively smaller in amount as the exposure extended beyond the 1st day. After 5 days there were no longer significant differences from control values. The reduction in rate of rise in plasma alpha-amino nitrogen coincided with cold-induced increases in food intake. The findings support the view that protein metabolism of muscle, the predominant extrahepatic tissue, may participate in thermogenesis when other sources of energy in the body have been depleted.
将大鼠置于4℃或25℃环境中6、12和24小时或长达2周的更长时间，然后取出内脏。术后4小时追踪血浆α-氨基氮的每小时变化，由于肝脏功能被去除，肝外组织释放的氨基酸会在血液中积累。尽管在取出内脏前将24小时禁食的大鼠冷暴露6小时会导致术后血浆α-氨基氮的上升速率增加，但直到暴露12小时后，其上升幅度才显著大于温暖对照组。此后，无论冷暴露持续12、24或48小时还是14天，都得到了类似的结果。在寒冷环境中禁食的动物在取出内脏后立即出现急剧上升，以至于在2小时内浓度达到对照值的2倍。相比之下，随意进食的动物在取出内脏后也出现上升，但随着暴露时间超过第一天，上升幅度逐渐变小。5天后与对照值不再有显著差异。血浆α-氨基氮上升速率的降低与寒冷诱导的食物摄入量增加相吻合。这些发现支持了这样一种观点，即当身体其他能量来源耗尽时，肌肉（主要的肝外组织）的蛋白质代谢可能参与产热过程。
