Van Zijl P C, Davis D, Eleff S M, Moonen C T, Parker R J, Strong J M
Johns Hopkins University Medical School, Department of Radiology, Baltimore 21205, USA.
Am J Physiol. 1997 Dec;273(6):E1216-27. doi: 10.1152/ajpendo.1997.273.6.E1216.
A new in vivo nuclear magnetic resonance (NMR) spectroscopy method is introduced that dynamically measures cerebral utilization of magnetically labeled [1-13C]glucose from the change in total brain glucose signals on infusion. Kinetic equations are derived using a four-compartment model incorporating glucose transport and phosphorylation. Brain extract data show that the glucose 6-phosphate concentration is negligible relative to glucose, simplifying the kinetics to three compartments and allowing direct determination of the glucose-utilization half-life time [t1/2 = ln2/(k2 + k3)] from the time dependence of the NMR signal. Results on isofluorane (n = 5)- and halothane (n = 7)-anesthetized cats give a hyperglycemic t1/2 = 5.10 +/- 0.11 min-1 (SE). Using Michaelis-Menten kinetics and an assumed half-saturation constant Kt = 5 +/- 1 mM, we determined a maximal transport rate Tmax = 0.83 +/- 0.19 mumol.g-1.min-1, a cerebral metabolic rate of glucose CMRGlc = 0.22 +/- 0.03 mumol.g-1.min-1, and a normoglycemic cerebral influx rate CIRGlc = 0.37 +/- 0.05 mumol.g-1.min-1. Possible extension of this approach to positron emission tomography and proton NMR is discussed.
介绍了一种新的体内核磁共振（NMR）光谱法，该方法通过输注时全脑葡萄糖信号的变化动态测量磁性标记的[1-13C]葡萄糖的脑利用率。使用包含葡萄糖转运和磷酸化的四室模型推导动力学方程。脑提取物数据表明，相对于葡萄糖，6-磷酸葡萄糖浓度可忽略不计，从而将动力学简化为三室模型，并允许根据NMR信号的时间依赖性直接测定葡萄糖利用半衰期[t1/2 = ln2/(k2 + k3)]。对异氟烷（n = 5）和氟烷（n = 7）麻醉猫的研究结果显示，高血糖状态下的t1/2 = 5.10 +/- 0.11 min-1（标准误）。利用米氏动力学和假定的半饱和常数Kt = 5 +/- 1 mM，我们确定了最大转运速率Tmax = 0.83 +/- 0.19 μmol·g-1·min-1、脑葡萄糖代谢率CMRGlc = 0.22 +/- 0.03 μmol·g-1·min-1以及正常血糖状态下的脑内流率CIRGlc = 0.37 +/- 0.05 μmol·g-1·min-1。讨论了将该方法扩展到正电子发射断层扫描和质子NMR的可能性。
