Nakanishi H, Cruz N F, Adachi K, Sokoloff L, Dienel G A
Laboratory of Cerebral Metabolism, National Institute of Mental Health, Bethesda, Maryland, USA.
J Cereb Blood Flow Metab. 1996 May;16(3):439-49. doi: 10.1097/00004647-199605000-00010.
The equilibrium brain/plasma distribution ratio for 3-0-methyl-D-glucose (methylglucose) varies with plasma and tissue glucose contents and can be used to determine local glucose levels in brain. This ratio was previously found to rise as brain glucose concentration fell in response to lowered plasma glucose content. The ratios, however, differed with the same tissue glucose levels in conscious and pentobarbital-sedated rats, suggesting that changes in metabolic demand might alter the quantitative relationship between the methylglucose distribution ratio and brain glucose concentration. To examine this possibility, metabolic rate was varied by focal drug application, and hexose concentrations measured in treated and surrounding tissue. When tissue glucose levels were reduced by raised metabolic demand, methylglucose distribution ratios also fell. When brain glucose levels rose due to reduced consumption, the methylglucose distribution ratio also rose. Thus, in contrast to the inverse relationship between brain/plasma methylglucose ratio and brain glucose concentration when brain glucose content is altered secondarily to changes in plasma glucose level, changes in brain glucose content induced by altered glucose utilization cause the brain glucose level and methylglucose distribution ratio to rise and fall in a direct relationship. Determination of brain glucose content from methylglucose distribution ratios must take into account rates of glucose delivery and consumption.
3 - O - 甲基 - D - 葡萄糖（甲基葡萄糖）的脑/血浆平衡分布比会随血浆和组织葡萄糖含量而变化，可用于测定脑内局部葡萄糖水平。先前发现，随着血浆葡萄糖含量降低，脑葡萄糖浓度下降，该比值会升高。然而，清醒大鼠和戊巴比妥镇静大鼠在相同组织葡萄糖水平下该比值却有所不同，这表明代谢需求的变化可能会改变甲基葡萄糖分布比与脑葡萄糖浓度之间的定量关系。为了探究这种可能性，通过局部应用药物改变代谢率，并测量处理过的组织和周围组织中的己糖浓度。当代谢需求增加导致组织葡萄糖水平降低时，甲基葡萄糖分布比也会下降。当由于消耗减少导致脑葡萄糖水平升高时，甲基葡萄糖分布比也会升高。因此，与血浆葡萄糖水平变化继发引起脑葡萄糖含量改变时脑/血浆甲基葡萄糖比与脑葡萄糖浓度呈反比关系不同，葡萄糖利用改变引起的脑葡萄糖含量变化会导致脑葡萄糖水平和甲基葡萄糖分布比呈直接的升降关系。根据甲基葡萄糖分布比测定脑葡萄糖含量时必须考虑葡萄糖的输送和消耗速率。
