Denne S C, Patel D, Kalhan S C
Division of Pediatric Metabolism, Cleveland Metropolitan General Hospital, Case Western Reserve University School of Medicine, Cleveland, OH.
Metabolism. 1991 Dec;40(12):1249-56. doi: 10.1016/0026-0495(91)90024-q.
To examine proteolysis, protein and leucine oxidation, and fuel utilization during a brief fast (approximately 17 hours) in human pregnancy, we determined leucine kinetics, urea nitrogen excretion, and respiratory quotient (RQ) in 11 pregnant subjects during the second half of gestation, and in 11 normal nonpregnant controls. The total rate of appearance (Ra) of leucine was similar in the pregnant and control groups (pregnant 4.99 +/- 0.60 v control 5.25 +/- 1.60 mmol/h [mean +/- SD]). However, leucine Ra per kilogram was significantly lower in pregnant subjects (pregnant 68 +/- 7 v control 82 +/- 13 mumol/kg/h, P less than .01). In addition, urinary urea nitrogen excretion was also significantly less in pregnant subjects (pregnant 3.74 +/- 1.09 v control 5.58 +/- 1.6 mg/kg/h, P less than .01). The RQ measured in the pregnant group was significantly higher than controls (0.82 +/- 0.05 v 0.76 +/- 0.04, P = .01), resulting in higher calculated carbohydrate oxidation rates during fasting in pregnancy. These data suggest that total rates of proteolysis (reflected by leucine flux) are similar in pregnant and nonpregnant subjects after an overnight fast. When normalized to body weight, proteolysis is lower in pregnant subjects. Urea excretion rates are also lower in pregnancy. These findings support the hypothesis that there is a pregnancy-induced adaptation to conserve maternal protein stores during a brief fast. The higher rate of carbohydrate oxidation during fasting in pregnancy may be a reflection of the fetal-placental unit's use of glucose as its predominant oxidative substrate.
为了研究人类孕期短暂禁食（约17小时）期间的蛋白水解、蛋白质和亮氨酸氧化以及能量利用情况，我们测定了11名孕晚期孕妇及11名正常非孕对照者的亮氨酸动力学、尿素氮排泄和呼吸商（RQ）。亮氨酸的总出现率（Ra）在孕妇组和对照组中相似（孕妇组4.99±0.60，对照组5.25±1.60 mmol/h[均值±标准差]）。然而，孕妇每千克体重的亮氨酸Ra显著更低（孕妇组68±7，对照组82±13 μmol/kg/h，P<0.01）。此外，孕妇的尿尿素氮排泄也显著减少（孕妇组3.74±1.09，对照组5.58±1.6 mg/kg/h，P<0.01）。孕妇组测得的RQ显著高于对照组（0.82±0.05对0.76±0.04，P = 0.01），导致孕期禁食期间计算出的碳水化合物氧化率更高。这些数据表明，过夜禁食后，孕妇和非孕妇的蛋白水解总速率（由亮氨酸通量反映）相似。按体重标准化后，孕妇的蛋白水解更低。孕期尿素排泄率也更低。这些发现支持了这样的假设，即孕期存在一种适应性变化，在短暂禁食期间保护母体蛋白质储备。孕期禁食期间较高的碳水化合物氧化率可能反映了胎儿 - 胎盘单位将葡萄糖作为其主要氧化底物的利用情况。
