Davis T A, Fiorotto M L, Nguyen H V, Reeds P J
Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, Texas 77030.
Am J Physiol. 1993 Aug;265(2 Pt 2):R334-40. doi: 10.1152/ajpregu.1993.265.2.R334.
To compare the sensitivity of muscle protein synthesis to food intake in neonatal and weaned rats, 5- and 16-day-old suckled rats and 28-day-old weaned rats were either fed, fasted for 8-10 h, or refed for 1-4 h after an 8-h fast. Protein synthesis was measured in vivo in soleus and plantaris muscles with a large dose of L-[4-3H]phenylalanine. In fed rats, fractional rates of protein synthesis (KS) decreased with age. Fasting decreased KS, and refeeding increased KS most in 5-day-old animals, less in 16-day-old rats, and least in 28-day-old rats. In 5-day-old rats, there were no differences in KS between soleus and plantaris muscles in the fed state and after fasting and refeeding; at 28 days, KS was higher in soleus than in plantaris in fed rats, and the soleus did not respond to fasting and refeeding. In rats at all three ages, the concentration of most plasma amino acids decreased during fasting; when 5-day-old rats were refed, plasma amino acid concentrations increased, but not to the levels in the fed state. Plasma insulin concentrations increased with age. Plasma insulin concentrations decreased more rapidly with fasting and increased more extensively with refeeding in 5-day-old rats than in older rats. These results suggest that muscle protein synthesis is more responsive to food intake in young suckled rats than in older suckled or weaned rats; this increased responsiveness is accompanied by greater changes in circulating insulin concentrations.
为比较新生大鼠和断奶大鼠肌肉蛋白质合成对食物摄入的敏感性，分别对5日龄和16日龄的哺乳大鼠以及28日龄的断奶大鼠进行以下处理：正常喂食、禁食8 - 10小时，或禁食8小时后再喂食1 - 4小时。使用大剂量的L - [4 - ³H]苯丙氨酸在体内测量比目鱼肌和跖肌中的蛋白质合成。在喂食的大鼠中，蛋白质合成的分数率（KS）随年龄增长而降低。禁食会降低KS，再喂食使KS增加，5日龄动物增加最多，16日龄大鼠增加较少，28日龄大鼠增加最少。在5日龄大鼠中，喂食状态下以及禁食和再喂食后，比目鱼肌和跖肌的KS没有差异；在28日龄时，喂食大鼠中比目鱼肌的KS高于跖肌，且比目鱼肌对禁食和再喂食无反应。在所有三个年龄段的大鼠中，禁食期间大多数血浆氨基酸浓度降低；5日龄大鼠再喂食时，血浆氨基酸浓度升高，但未达到喂食状态下的水平。血浆胰岛素浓度随年龄增加。与大龄大鼠相比，5日龄大鼠禁食时血浆胰岛素浓度下降更快，再喂食时升高更显著。这些结果表明，与大龄哺乳或断奶大鼠相比，幼龄哺乳大鼠的肌肉蛋白质合成对食物摄入更敏感；这种更高的敏感性伴随着循环胰岛素浓度的更大变化。
