GLUCONEOGENESIS IN THE VERY LOW BIRTH WEIGHT INFANT

极低出生体重婴儿难以维持血糖正常，因为这些婴儿由于底物储备不足而处于低血糖的高风险中，但极低出生体重婴儿也是葡萄糖不耐受的。 因此，当他们以高输注速率接受葡萄糖时，他们经常发生高血糖症，以防止低血糖症并提供适当的能量摄入。 本方案的第一个目的是确定VLBW婴儿在接受全胃肠外营养（TPN）（即包括脂质和氨基酸）的葡萄糖时，如何利用促血管生成途径维持正常血糖，葡萄糖转换率约为正常血糖转换率的一半。 由于GNG是一个复杂的过程，很难在体内研究，第二个目的是比较三个最近发表的方法来测量GNG使用[U-13 C]葡萄糖，[2- 13 C]甘油和氧化氘。 待检验的假设是：1。 以低于正常葡萄糖转换率的速率接受葡萄糖作为TPN的一部分（以防止高血糖）的VLBW婴儿主要通过GNG维持正常血糖。 2. TPN的脂质含量在支持胚胎发生方面比氨基酸更重要。 3. 测量GNG的三种方法提供了类似的结果。 主题：三组可比较的VLBW婴儿（n=20;胎龄2710.2周;出生体重996128 g;出生后年龄5.0 ± 10.2天（平均1 SE））接受TPN（葡萄糖17.1 ± 0.2 mmol/kg min;脂质1.6 ± 10.1和蛋白质2.2 ± 10.1 mg/kg min）8-12 h。通过[U-13 C]葡萄糖（n=8）、[2- 13 C]甘油（n=6）或氧化氘（n=6）估计GNG。 结果如下：所有婴儿血糖均正常，血糖平均值为3.0 ± 10.1 mM。葡萄糖出现率（Ra）为28.8 ± 11.1 mmol/kg min，葡萄糖产生率（GPR）为10.7 ± 11.0 mmol/kg min。 [U-13 C]葡萄糖和[2- 13 C]甘油方法提供了几乎相同的异生估计值，分别占葡萄糖Ra的2812%和2612%（即异生速率分别为7.610.6和7.610.8 mmol/kg min），以及GPR的7215%和7319%。 氧化氘估计值（不包括甘油的贡献）与通过[2- 13 C]甘油方法测量的非甘油贡献相当。 甘油是主要的产酶底物，占产酶的65 - 15%. 由于[2- 13 C]甘油方法具有将甘油和非甘油来源的贡献分开的优势，因此我们选择使用该方法来确定从TPN中提取氨基酸对葡萄糖Ra和胰岛素生成的影响。 主题：一组6名婴儿（27.510.4孕周; 1022157克;出生后4.512天），即婴儿与上述受试者相当，接受上述葡萄糖和脂质，但不接受氨基酸。 婴儿研究超过8小时。

Euglycemia is difficult to maintain in VLBW infants, since these infants are at a high risk of hypoglycemia due to inadequate substrate stores, but VLBW infants are also glucose intolerant. Therefore, they frequently develop hyperglycemia when they receive glucose at high infusion rates delivered both to prevent hypoglycemia and to provide an appropriate energy intake. The first purpose of this protocol is to determine how VLBW infants utilize the gluconeogenic pathway to maintain normoglycemia while receiving glucose at a rate about half the normal glucose turnover rate as part of total parenteral nutrition (TPN) (i.e including lipids and amino acids). Since gluconeogenesis (GNG) is a complex process, which is difficult to study in vivo, a second purpose is to compare three recently published methods to measure GNG using [U-13C]glucose, [2-13C]glycerol and deuterium oxide. The hypotheses to be tested are: 1. VLBW infants receiving glucose at a rate less than normal glucose turnover rate (to prevent hyperglycemia) as part of TPN maintain normoglycemia mainly via GNG. 2. The lipid content of TPN is more important in supporting gluconeogenesis than are the amino acids. 3. The three methods to measure GNG provide similar results. Subjects: Three comparable groups of VLBW infants (n=20; gestational age 2710.2 weeks; birth weight 996128 grams; postnatal age 5.010.2 days (mean1SE)) received TPN (glucose 17.110.2 mmol/kg min; lipid 1.610.1 and protein 2.210.1 mg/kg min) for 8-12 h. GNG was estimated by [U-13C]glucose (n=8); [2-13C]glycerol (n=6) or deuterium oxide (n=6). Results: All infants remained normoglycemic, blood glucose averaged 3.010.1 mM. Glucose appearance rate (Ra) was 28.811.1 mmol/kg min and glucose production rate (GPR), 10.711.0 mmol/kg min. None of these parameters varied between the three groups. The [U-13C]glucose and [2-13C]glycerol methods provided almost identical estimates of gluconeogenesis accounting for 2812 and 2612 % of glucose Ra (i.e. gluconeogenic rates of 7.610.6 and 7.610.8 mmol/kg min), respectively, and 7215 and 7319 % of GPR, respectively. The deuterium oxide estimate, which does not include the contribution from glycerol, was comparable to the non-glycerol contribution measured by the [2-13C]glycerol method. Glycerol was the major gluconeogenic substrate contributing 6515 % of gluconeogenesis. Since the [2-13C]glycerol method has the advantage of partitioning the contribution from glycerol and non-glycerol sources, we chose to use this method to determine the impact of withdrawal amino acids from TPN on glucose Ra and gluconeogenesis. Subjects: A group of six infants (27.510.4 gestational weeks; 1022157 grams; postnatal age 4.512 days) i.e. the infants were comparable to the subjects described above, received glucose and lipids as described above, but no amino acids. The infants were studied over 8 h.