Shalwitz R A, Reo N V, Becker N N, Hill A C, Ewy C S, Ackerman J J
Department of Pediatrics, Washington University, St. Louis, Missouri 63110.
J Biol Chem. 1989 Mar 5;264(7):3930-4.
An in situ and in vivo surface coil 13C NMR study was performed to study hepatic glycogen synthesis from [3-13C]alanine and [1-13C]glucose administered by intraduodenal infusion in 18-h fasted male Sprague-Dawley rats. Combined, equimolar amounts of alanine and glucose were given. Hepatic appearance and disappearance of substrate and concurrent glycogen synthesis was followed over 150 min, with 5-min time resolution. Active glycogen synthesis from glucose via the direct (glucose----glycogen) and indirect (glucose----lactate----glycogen) pathways and from alanine via gluconeogenesis was observed. The indirect pathway of glycogen synthesis from [1-13C]glucose accounted for 30% (+/- 6 S.E.) of total glycogen formed from labeled glucose. This estimate does not take into account dilution of label in the hepatic oxaloacetate pool and is, therefore, somewhat uncertain. Hepatic levels of [3-13C]alanine achieved were significantly lower than levels of [1-13C]glucose in the liver, and the period of active glycogen synthesis from [3-13C]alanine was longer than from glucose. However, the overall pseudo-first-order rate constant during the period of active glycogen synthesis from [3-13C]alanine (0.075 min-1 +/- 0.026 S.E.) was almost 3 times that from [1-13C]glucose via the direct pathway (0.025 min-1 +/- 0.005 S.E.). The most likely reason for the small rate constant governing direct glycogen formation from duodenally administered glucose compared to that from duodenally administered alanine is a low level of glucose phosphorylating capacity in the liver.
进行了一项原位和体内表面线圈13C核磁共振研究，以研究在禁食18小时的雄性Sprague-Dawley大鼠中，通过十二指肠内输注给予的[3-13C]丙氨酸和[1-13C]葡萄糖的肝糖原合成情况。给予等摩尔量的丙氨酸和葡萄糖。在150分钟内，以5分钟的时间分辨率跟踪底物在肝脏中的出现和消失以及同时进行的糖原合成。观察到通过直接途径（葡萄糖→糖原）和间接途径（葡萄糖→乳酸→糖原）由葡萄糖进行的活跃糖原合成，以及通过糖异生由丙氨酸进行的糖原合成。由[1-13C]葡萄糖合成糖原的间接途径占由标记葡萄糖形成的总糖原的30%（±6标准误）。该估计未考虑肝草酰乙酸池中标记物的稀释，因此有些不确定。肝脏中达到的[3-13C]丙氨酸水平显著低于[1-13C]葡萄糖水平，并且由[3-13C]丙氨酸进行活跃糖原合成的时间比由葡萄糖进行的时间长。然而，在由[3-13C]丙氨酸进行活跃糖原合成期间的总体准一级速率常数（0.075 min-1±0.026标准误）几乎是通过直接途径由[1-13C]葡萄糖进行的速率常数（0.025 min-1±0.005标准误）的3倍。与十二指肠给予的丙氨酸相比，十二指肠给予的葡萄糖直接形成糖原的速率常数较小，最可能的原因是肝脏中葡萄糖磷酸化能力较低。
