White P K, Miller S A
Pediatr Res. 1976 Mar;10(3):158-64. doi: 10.1203/00006450-197603000-00003.
The 3-day-old rat has a high basal level of phosphoenolpyruvate carboxykinase (PEPCK), the activity of which is not increased upon starvation. The lower basal activity of the enzyme in 19-day-old rat liver can, however, be stimulated by starvation. Serum glucose levels increased from 3 days to 19 days of age, with a decrease to adult levels. Liver glycogen concentration increased from 3 days to 19 days of age, with no additional increase observed at 3 months. There was a decrease with age in the specific activity of liver glycogen (from [14C]alanine and [14C]leucine). In fed rats given [14C]alanine, 14CO2 expiration tended to decrease with age. The 14CO2 production from [14C]leucine was less than that from alanine, and also decreased with age. Three-day-old rats showed no change in serum glucose when starved for 4 hr. On the other hand, 19-day-old rats responded with a decrease in serum glucose; although the adult animal's basal level of serum glucose was less than that of the 19-day-old rats, starvation for 15 hr also caused a significant decrease. There was no statistically significant difference in liver glycogen concentration between the fed and starved 3-day-old animals. Liver glycogen concentration in the 19-day-old adult rats was affected, however, by starvation. The 3-day-or glycogen during starvation. Starvation resulted in a tremendous increase in the specific activity of hepatic glycogen in the 19-day-old and adult rats. Starvation decreased the percentage of labeled amino acid expired as 14CO2. The proportion expired also decreased with age. Urinary nitrogen concentration increased significantly between 3 and 19 days of age. Starvation produced differential effects in the animals, with no change being observed in either the 3-day or adult rats; a decrease was observed in the 19-day-old animals. Urinary nitrogen concentration was measured in adult carbohydrate-deprived rats and was significantly higher than control values. These rats had a high gluconeogenic rate, reflected in the increased urinary nitrogen concentration. The young rat is at the mercy of a continuous supply of substrate in that it has a limited capacity for directing substrat
3日龄大鼠的磷酸烯醇丙酮酸羧激酶（PEPCK）基础水平较高，饥饿时其活性不会增加。然而，19日龄大鼠肝脏中该酶较低的基础活性可被饥饿刺激。血清葡萄糖水平从3日龄到19日龄升高，随后降至成年水平。肝糖原浓度从3日龄到19日龄增加，3个月时未观察到进一步增加。肝糖原的比活性（由[14C]丙氨酸和[14C]亮氨酸生成）随年龄增长而降低。在给予[14C]丙氨酸的喂食大鼠中，14CO2呼出量倾向于随年龄增长而减少。[14C]亮氨酸产生的14CO2少于丙氨酸，且也随年龄增长而减少。3日龄大鼠饥饿4小时后血清葡萄糖无变化。另一方面，19日龄大鼠血清葡萄糖会降低；尽管成年动物血清葡萄糖的基础水平低于19日龄大鼠，但饥饿15小时也会导致显著降低。喂食和饥饿的3日龄动物肝脏糖原浓度无统计学显著差异。然而，19日龄成年大鼠的肝脏糖原浓度受饥饿影响。3日龄大鼠在饥饿期间糖原……饥饿导致19日龄和成年大鼠肝脏糖原的比活性大幅增加。饥饿降低了作为14CO2呼出的标记氨基酸的百分比。呼出比例也随年龄增长而降低。3日龄到19日龄期间尿氮浓度显著增加。饥饿对动物产生不同影响，3日龄或成年大鼠均无变化；19日龄动物出现降低。在成年碳水化合物缺乏大鼠中测量尿氮浓度，其显著高于对照值。这些大鼠糖异生率高，反映在尿氮浓度增加上。幼鼠依赖持续的底物供应，因为其引导底物的能力有限。
