AN EXPERIMENTAL TEST FOR A CEILING ON SUSTAINED METABOLIC-RATE IN LACTATING MICE
AN EXPERIMENTAL TEST FOR A CEILING ON SUSTAINED METABOLIC-RATE IN LACTATING MICE
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DOI：
10.1086/physzool.65.5.30158552
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发表时间：
1992-09-01
期刊：
影响因子：
--
通讯作者：
DIAMOND, J
中科院分区：
文献类型：
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作者：
HAMMOND, KA;DIAMOND, J
据观察，人类和野生动物的时间平均持续代谢率（SusMR）不超过基础代谢率（BMR）的七倍左右，这表明持续代谢范围可能存在上限。我们通过减少或增加幼鼠来实验性地测试了这样的上限，以改变哺乳期母鼠的产仔数，在 5 到 26 只幼鼠之间。母亲可以定期给 14 只幼崽断奶，但不能更多（自然产仔数为 8 - 10 只）。尽管泌乳高峰期的食物摄入量增加至原始值的 3.4 倍，并且随着窝产仔数的增加而增加，但消化效率保持不变。小肠和其他肠道区室的质量在哺乳高峰期增加数倍，因此肠道刷状缘对葡萄糖和脯氨酸的摄取能力也增加了几倍。哺乳高峰时的时间平均持续代谢率达到基础代谢率的7.2倍；这个比例显然已经接近持续代谢范围的上限。对肠道营养吸收能力的估计仅超出了营养摄入量的储备能力的适度安全边际。哺乳期间的肠道肥大往往会保留这些安全裕度，从而维持消化效率。相反，哺乳后肠道萎缩和适度的安全范围往往可以避免生物合成能量的浪费。
Time-averaged sustained metabolic rates (SusMRs) of humans and wild animals have been observed not to exceed about seven times basal metabolic rate (BMR), which suggests a possible ceiling on sustained metabolic scope. We tested experimentally for such a ceiling by subtracting or adding pups to vary the litter size of lactating mother mice between five and 26 pups. Mothers could regularly wean 14 pups but not more (natural litter size is 8 - 10). Although food intake at peak lactation increased to as much as 3.4 times virgin values and increased with litter size, digestive efficiency remained constant. The mass of the small intestine and of other gut compartments increased up to several fold at peak lactation, and as a consequence so did the intestine's brush-border uptake capacities for glucose and for proline. Time-averaged sustained metabolic rate at peak lactation reached 7.2 times BMR; this ratio is evidently close to a ceiling on sustained metabolic scope. Estimates of intestinal nutrient uptake capacities exceeded nutrient intakes by only a modest safety margin of reserve capacity. Intestinal hypertrophy during lactation tended to preserve those safety margins and thus to maintain digestive efficiency. Conversely, postlactational intestinal atrophy and the modest size of the safety margins tended to avoid waste of biosynthetic energy.