Fei Du1,2, Yi Zhang1, Xiao-Hong Zhu1, Wei Chen1
1Radiology, Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States; 2Psychiatry, McLean Hospital, Harvard University, Belmont, MA, United States
The basal brain activity and function depends upon a constant supply of glucose through the specific glucose transport mechanism mediated by transporter molecules, referred to as the blood-brain barierr (BBB). Therein the noninvasive method to reliably measure glucose cerebral metabolic rate and transport constants are of importance for understanding underlying glucose transport mechanism and energy consumption in the various physiological or pathological conditions. For instance, in our previous studies, we observed that compared to the light anesthesia (2% v-v isofulorane), brain glucose concentration significantly decreased although cerebral metabolic rate of glucose (CMRglc) decreased 37% at the iso-electric condition. This observation of glucose reduction seemingly contradicted with other studies showing a decreased brain glucose concentration accompanied by the increased CMRglc due to the elevated stimulations. This apparent discrepancy can be explained by the changes of blood plasma glucose concentrations, which were found to be substantially decreased under the iso-electric conditions. Another possible reason is alterations of glucose transport constants (KT and Tmax). It was reported that pentobarbital reduced blood-brain glucose transfer in the rat brain and the glucose transport constants decreased compared to the awaken condition. Therefore, the aim of the current study is to build-up a noninvasive method to reliably and simultaneously measure CMRglc and transport constants for fully understanding brain glucose concentration changes with alterations of anesthesia depth. The method was introduced and implemented by simultaneously measuring plasma and brain tissue glucose concentration time courses after stopping glucose infusion.