Gruetter R, Novotny E J, Boulware S D, Rothman D L, Mason G F, Shulman G I, Shulman R G, Tamborlane W V
Department of Molecular Biophysics, Yale University School of Medicine, New Haven, CT 06510.
Proc Natl Acad Sci U S A. 1992 Feb 1;89(3):1109-12. doi: 10.1073/pnas.89.3.1109.
Glucose is the main fuel for energy metabolism in the normal human brain. It is generally assumed that glucose transport into the brain is not rate-limiting for metabolism. Since brain glucose concentrations cannot be determined directly by radiotracer techniques, we used 13C NMR spectroscopy after infusing enriched D-[1-13C]glucose to measure brain glucose concentrations at euglycemia and at hyperglycemia (range, 4.5-12.1 mM) in six healthy children (13-16 years old). Brain glucose concentrations averaged 1.0 +/- 0.1 mumol/ml at euglycemia (4.7 +/- 0.3 mM plasma) and 1.8-2.7 mumol/ml at hyperglycemia (7.3-12.1 mM plasma). Michaelis-Menten parameters of transport were calculated to be Kt = 6.2 +/- 1.7 mM and Tmax = 1.2 +/- 0.1 mumol/g.min from the relationship between plasma and brain glucose concentrations. The brain glucose concentrations and transport constants are consistent with transport not being rate-limiting for resting brain metabolism at plasma levels greater than 3 mM.
葡萄糖是正常人类大脑能量代谢的主要燃料。一般认为，葡萄糖向大脑的转运对代谢而言并非限速步骤。由于无法通过放射性示踪技术直接测定脑葡萄糖浓度，我们在给6名健康儿童（13 - 16岁）输注富集的D-[1-¹³C]葡萄糖后，使用¹³C核磁共振波谱法来测量正常血糖和高血糖（范围为4.5 - 12.1 mM）时的脑葡萄糖浓度。正常血糖（血浆浓度4.7±0.3 mM）时脑葡萄糖浓度平均为1.0±0.1 μmol/ml，高血糖（血浆浓度7.3 - 12.1 mM）时为1.8 - 2.7 μmol/ml。根据血浆和脑葡萄糖浓度之间的关系，计算得出转运的米氏参数为Kt = 6.2±1.7 mM，Tmax = 1.2±0.1 μmol/g·min。脑葡萄糖浓度和转运常数表明，在血浆水平大于3 mM时，转运对静息脑代谢而言并非限速步骤。
