Toloza E M, Lam M, Diamond J
Department of Physiology, University of California Medical School, Los Angeles 90024-1751.
Am J Physiol. 1991 Oct;261(4 Pt 1):G608-20. doi: 10.1152/ajpgi.1991.261.4.G608.
We examined the size of the "safety margin," if any, by which the small intestine's daily capacities to absorb nutrients exceed prevailing daily intakes of those nutrients. This safety margin, also known as reserve capacity, is widely assumed to be enormously large. As a test, we suddenly transferred mice from an ambient temperature of 22 to 6 degrees C and measured food intake, apparent digestive efficiency, intestinal morphometrics, and intestinal brush-border uptake capacities for D-glucose and L-proline over the next 28 days. Food intake jumped 68% within the first 12 h and rose in 2 days to a new plateau level 2.5 times the previous intake. Nevertheless, apparent digestive efficiency remained unchanged, even within the first 12 h, and intestinal transit times also remained unchanged, implying the existence of at least some safety margin. Masses of the small and large intestine, liver, kidneys, and spleen nevertheless increased within 4 days by 16-20%. Glucose and proline uptakes per milligram intestine increased by approximately 5%, so that the intestine's summed uptake capacities for these solutes increased by 24-26%. The animal's intestinal adaptation expressed in these increased uptake capacities implies that safety margins at the new plateau value of food intake would otherwise have been dangerously narrow. Comparison of calculated summed uptake capacities with measured dietary intakes suggests that safety margins are approximately 220-300% in mice at 22 degrees C, only 27-50% in mice at 6 degrees C before intestinal adaptation, but 60-88% in mice at 6 degrees C after intestinal adaptation.
我们研究了“安全边际”（如果存在的话）的大小，即小肠每日吸收营养物质的能力超过这些营养物质当前每日摄入量的部分。这个安全边际，也被称为储备能力，人们普遍认为它非常大。作为一项测试，我们突然将小鼠从22摄氏度的环境温度转移到6摄氏度，并在接下来的28天内测量了食物摄入量、表观消化效率、肠道形态学指标以及小肠刷状缘对D-葡萄糖和L-脯氨酸的摄取能力。食物摄入量在最初的12小时内跃升了68%，并在2天内上升到一个新的平台水平，是之前摄入量的2.5倍。然而，表观消化效率即使在最初的12小时内也保持不变，肠道转运时间也保持不变，这意味着至少存在一定的安全边际。尽管如此，小肠、大肠、肝脏、肾脏和脾脏的质量在4天内增加了16% - 20%。每毫克肠道对葡萄糖和脯氨酸的摄取量增加了约5%，因此肠道对这些溶质的总摄取能力增加了24% - 26%。动物肠道在这些增加的摄取能力中所表现出的适应性表明，否则在食物摄入量的新平台值时安全边际会危险地变窄。将计算出的总摄取能力与测量到的饮食摄入量进行比较表明，22摄氏度时小鼠的安全边际约为220% - 300%，6摄氏度时未发生肠道适应的小鼠的安全边际仅为27% - 50%，但6摄氏度时发生肠道适应的小鼠的安全边际为60% - 88%。
