GLUCOSE TRANSPORTERS AND LOCAL RATES OF CEREBRAL GLUCOSE UTILIZATION

葡萄糖转运到脑是由促进转运蛋白介导的。在大脑中发现了三种GLUT亚型：GLUT1是血脑屏障转运蛋白，GLUT3是主要的神经元转运蛋白，GLUT5存在于小胶质细胞中。为了研究葡萄糖利用率变化与葡萄糖转运体表达之间的时间关系，我们研究了缺水对Sprague Dawley大鼠下丘脑-神经垂体系统的影响。神经垂体包含位于下丘脑视上核和室旁核的神经元的加压素和催产素分泌终端。它也含有胶质样垂体细胞，但缺乏血脑屏障。仅在神经叶中发现非血管形式的GLUT1和GLUT3，在垂体细胞中检测到GLUT1 mRNA。我们的研究结果表明，缺水3天后，脑垂体室旁核、视上核和神经叶的区域葡萄糖利用率（lCMRglc）分别增加了15%、25%和163%。补液三天后，三个区域的lCMRglc恢复正常。在神经叶中，GLUT1和GLUT3的45 kDa亚型分别增加了28%和43%。补液3天后发现GLUT1浓度正常，但GLUT3仍升高。补液7天后的测量显示GLUT3处于控制水平。我们的研究结果表明，在神经激活和恢复的条件下，lCMRglc的变化与神经垂体中GLUT1和GLUT3的水平存在时间相关性，并提出了GLUT1和GLUT3转运蛋白表达可能受到功能活性慢性变化的调节的可能性。

Glucose transport into brain is mediated by facilitative transporter proteins (GLUT). Three GLUT isoforms are found in brain: GLUT1 is the blood brain barrier transporter, GLUT3 is the predominant neuronal transporter, and GLUT5 is found in microglia. To examine the temporal relationship between alterations in rates of glucose utilization and expression of glucose transporters we studied the effects of water-deprivation in the hypothalamo-neurohypophysial system of Sprague Dawley rats. The neurohypophysis contains vasopressin and oxytocin-secreting terminals of neurons located in the supraoptic and paraventricular nuclei of the hypothalamus. It also contains glial-like pituocytes,but lacks a BBB. Only the nonvascular form of GLUT1 and GLUT3 are found in the neural lobe and GLUT1 mRNA has been detected in pituocytes. Results of our studies show that after 3 days of water deprivation regional rates of glucose utilization (lCMRglc) are increased by 15, 25, and 163% in the paraventricular nuclei, supraoptic nuclei, and neural lobe of the pituitary, respectively. Rehydration for three days restored lCMRglc to normal in all three regions. In the neural lobe increases of 28 and 43% were also observed in the 45 kDa isoform of GLUT1 and GLUT3 respectively. After three days of rehydration normal concentrations of GLUT1 were found, but GLUT3 remained elevated. Measurements made after seven days of rehydration showed GLUT3 at control levels. Our results indicate that, under conditions of neural activation and recovery, changes in lCMRglc and the levels of GLUT1 and GLUT3 in the neurohypophysis are temporally correlated and raise the possibility that GLUT1 and GLUT3 transporter expression may be regulated by chronic changes in functional activity.