Abstract
With the use of localized ^13^C MRS in conjunction with [1β^13^C]βDβglucose infusion, it is possible to study brain glycogen metabolism in vivo. The purpose of this study was to validate in vivo ^13^C MRS measurements by comparing them with results from a standard biochemical assay. To increase the [1β^13^C] glycogen concentration, 11 rats were subjected to an episode of acute hypoglycemia followed by a mild hyperglycemic recovery period during which [1β^13^C]βDβglucose was infused. The total brain [1β^13^C] glycogen of the same animal was determined from the enzymatically determined total brain glycogen content, which was fixed by focused microwave irradiation (4 kW in 1.4 s) immediately after the end of the in vivo NMR measurements. The corresponding isotopic enrichment (IE) of glycogen was measured by in vitro ^1^H MRS of protons bound to glucose C1βΞ±. The in vivo [1β^13^C] glycogen concentration was strongly correlated to the in vitro [1β^13^C] glycogen content determined by biochemical measurement in a linear manner (R = 0.79). The results are consistent with the notion that localized ^13^C MRS measurements closely reflect ^13^C glycogen content in the brain. Magn Reson Med 57:243β248, 2007. Β© 2007 WileyβLiss, Inc.