Hatfield G M, Joyce J, Jeacock M K, Shepherd D A
Br J Nutr. 1984 Nov;52(3):529-43. doi: 10.1079/bjn19840121.
Estimates have been made of the irreversible loss of alanine and of glycine in chronically catheterized fetal lambs and in sucking lambs using [U-14C]-labelled radioisotopes. The experiments in the fetal lambs were carried out at least 5 d after implantation of catheters. The mean concentration of glycine in fetal femoral arterial blood between 102 and 129 d conceptual age was 755 mumol/l and this was not significantly different from that in maternal venous blood. The mean concentration of alanine in fetal femoral arterial blood during the same period of gestation was 229 mumol/l and this was significantly greater than that in maternal venous blood. Assuming a catenary model, the mean irreversible loss of glycine, determined using the single-injection technique, in three fetal lambs of 107, 111 and 127 d conceptual age was 17 mumol/min per kg, whereas in two fetal lambs aged 106 and 109 d into which the isotope was infused continuously the mean irreversible loss, calculated from the specific activity of glycine 5 h after the start of infusion of the tracer ('pseudo plateau'), was 12 mumol/min per kg. In a sucking lamb, 9 d after birth, the irreversible loss of glycine was 11 mumol/min per kg. The mean irreversible loss of alanine, determined by the single-injection technique assuming a catenary model in five fetuses between 112 and 121 d conceptual age was 14 mumol/min per kg, and in two sucking lambs, 9 and 11 d after birth, it was 5.1 mumol/min per kg. When a two-pool model was assumed in which entry of metabolite was not directly into the sampling pool but was by way of the second pool, then the mean irreversible loss of glycine in the three fetuses was 23 mumol/min per kg and of alanine in the five fetuses was 32 mumol/min per kg. Calculations based on the alternative two-pool model did not alter appreciably the rates of irreversible loss of either alanine or glycine in the sucking lambs. From a comparison of the specific activities of the amino acids and of carbon dioxide in blood during the course of the experiments, it was found that in the fetuses 0.96% of the CO2 present in blood was derived from alanine and only 0.12% was derived from glycine. It was calculated that not more than 1.6 mumol alanine/min per kg and 0.29 mumol glycine/min per kg could have been converted to CO2 in the fetal lambs.(ABSTRACT TRUNCATED AT 400 WORDS)
已利用[U - 14C]标记的放射性同位素对长期插管的胎羊和吮乳期羔羊体内丙氨酸和甘氨酸的不可逆损失进行了估算。胎羊实验在导管植入至少5天后进行。在妊娠102至129天的胎羊股动脉血中，甘氨酸的平均浓度为755 μmol/l，与母羊静脉血中的浓度无显著差异。在同一妊娠期，胎羊股动脉血中丙氨酸的平均浓度为229 μmol/l，显著高于母羊静脉血中的浓度。假设为悬链线模型，采用单次注射技术测定，107、111和127天胎龄的三只胎羊中甘氨酸的平均不可逆损失为17 μmol/(min·kg)，而在连续注入同位素的106和109天胎龄的两只胎羊中，根据示踪剂注入开始5小时后甘氨酸的比活性（“假平台期”）计算，平均不可逆损失为12 μmol/(min·kg)。在出生9天的吮乳期羔羊中，甘氨酸的不可逆损失为11 μmol/(min·kg)。采用单次注射技术并假设为悬链线模型，在112至121天胎龄的五只胎羊中，丙氨酸的平均不可逆损失为14 μmol/(min·kg)，在出生9天和11天的两只吮乳期羔羊中，丙氨酸的平均不可逆损失为5.1 μmol/(min·kg)。当假设为双池模型，即代谢物不是直接进入采样池，而是通过第二个池进入时，三只胎羊中甘氨酸的平均不可逆损失为23 μmol/(min·kg)，五只胎羊中丙氨酸的平均不可逆损失为32 μmol/(min·kg)。基于替代双池模型的计算并未明显改变吮乳期羔羊中丙氨酸或甘氨酸的不可逆损失率。通过比较实验过程中血液中氨基酸和二氧化碳的比活性发现，在胎羊中，血液中0.96%的二氧化碳来自丙氨酸，仅0.12%来自甘氨酸。据计算，胎羊中每分钟每千克转化为二氧化碳的丙氨酸不超过1.6 μmol，甘氨酸不超过0.29 μmol。（摘要截于400字）
