Carter B S, Moores R R, Teng C, Meschia G, Battaglia F C
Department of Pediatrics, University of Colorado School of Medicine, Denver 80262, USA.
Biol Neonate. 1995;67(4):295-300. doi: 10.1159/000244177.
The turnover rates of plasma lactate, normalized for O2 consumption rate, are higher in the fetus than in the adult. This occurs despite very low rates of fetal gluconeogenesis which preclude the recycling of lactate carbon into glucose. In an effort to establish the main routes of disposal of fetal plasma lactate, 12 midgestation ovine fetuses (age 74 +/- 1 days) were infused intravenously at constant rate with L-[U-14C]lactate for a 4-hour period. At the end of the infusion, the amounts of 14C retained by the fetus and by the placenta, and the distribution of the retained 14C in free and protein-bound amino acids and in lipids were measured. Of the total 14C infused, 17.0 +/- 1.4% was recovered in the placenta, 4.0 +/- 0.3% in the fetal liver, and 15.0 +/- 0.8% in the extrahepatic fetal tissues. Of the retained radioactive carbon, 45-57% was recovered in the free and protein-bound amino acid fractions and 11-17% in the lipid fractions. Approximately 90% of the 14C in the free amino acid fractions was present as glutamate/glutamine, serine, glycine, and alanine carbon. In conjunction with data on fetal CO2 production from lactate carbon, these results demonstrate that the main routes of fetal lactate disposal are oxidation and synthesis of nonessential amino acids and lipids.
与氧气消耗率归一化后的血浆乳酸周转率，胎儿比成人更高。尽管胎儿糖异生率非常低，这排除了乳酸碳再循环为葡萄糖的可能性，但这种情况仍然发生。为了确定胎儿血浆乳酸的主要处置途径，对12只妊娠中期绵羊胎儿（年龄74±1天）静脉恒速输注L-[U-¹⁴C]乳酸4小时。输注结束时，测量胎儿和胎盘保留的¹⁴C量，以及保留的¹⁴C在游离和蛋白质结合氨基酸及脂质中的分布。在输注的总¹⁴C中，17.0±1.4%在胎盘中回收，4.0±0.3%在胎儿肝脏中回收，15.0±0.8%在胎儿肝外组织中回收。在保留的放射性碳中，45 - 57%在游离和蛋白质结合氨基酸部分中回收，11 - 17%在脂质部分中回收。游离氨基酸部分中约90%的¹⁴C以谷氨酸/谷氨酰胺、丝氨酸、甘氨酸和丙氨酸碳的形式存在。结合来自乳酸碳的胎儿二氧化碳产生数据，这些结果表明胎儿乳酸处置的主要途径是氧化以及合成非必需氨基酸和脂质。
