Buddington R K
Department of Physiology, UCLA Medical Center 90024.
J Comp Physiol B. 1987;157(5):677-88. doi: 10.1007/BF00700989.
Two fish species (rainbow trout and common carp) that differ in natural diet also exhibit differences in the adaptive flexibility of their intestinal nutrient transport mechanisms in response to changes in dietary nutrient composition. When carp ingested a feed that was 24% glucose by weight, there was an increase in both the intestinal length and rates of nutrient absorption, particularly for glucose, when compared to carp fed an isonitrogenous diet devoid of digestible carbohydrate. As a result, the intestine's uptake capacity (nmol of glucose and proline absorbed per min per g body weight) was higher in carp fed the 24% glucose feed. Due to the greater increase in glucose uptake, the ratio of glucose uptake relative to proline (G/P ratio) was higher in carp fed the 24% glucose. Thus, carp are able to adapt to the quantity, and apparently also to the type, of digestible carbohydrate in the diet. In contrast, glucose uptake by trout was unresponsive to the quantity of dietary carbohydrate. Instead, the elevated glucose paradoxically resulted in a greater uptake capacity for proline and a lower G/P ratio. Hence, the adaptive capabilities of the intestinal nutrient transport processes are matched to the potential variation in the carbohydrate content of the natural diet.
两种天然食物不同的鱼类（虹鳟鱼和鲤鱼）在肠道营养物质转运机制对饮食营养成分变化的适应性灵活性方面也存在差异。当鲤鱼摄入重量为24%葡萄糖的饲料时，与喂食不含可消化碳水化合物的等氮饲料的鲤鱼相比，肠道长度和营养物质吸收速率均有所增加，尤其是葡萄糖的吸收速率。因此，喂食24%葡萄糖饲料的鲤鱼肠道摄取能力（每克体重每分钟吸收的葡萄糖和脯氨酸的纳摩尔数）更高。由于葡萄糖摄取量增加幅度更大，喂食24%葡萄糖饲料的鲤鱼葡萄糖摄取量与脯氨酸摄取量的比值（G/P比值）更高。因此，鲤鱼能够适应饮食中可消化碳水化合物的数量，显然也能适应其类型。相比之下，鳟鱼的葡萄糖摄取对饮食中碳水化合物的数量没有反应。相反，葡萄糖含量升高反而导致脯氨酸摄取能力增强，G/P比值降低。因此，肠道营养物质转运过程的适应能力与天然食物中碳水化合物含量的潜在变化相匹配。
