The relationship between glycogen turnover and glucose uptake in the heart

The purpose of this study is to determine how glucose uptake and glycogen turnover are related in vivo in the heart. Ketamineanesthettzed fasted rats were hepatic-occluded for 20 min. During the occlusion, the rats were infused intravenously with saline (group 1), insuiin at a rate of 10 mU min^-1 (group 2), or insulin at the same rate plus glucose at a rate of 20.4 μmol-min^-1. The infusion regimes were known to result in up to 30-fold differences in whole-body glucose utilization Glucose uptake was determined by the phosphorylation of [¹⁴C]-2-deoxyglucose, and glycogen synthesis by the incorporation of [3-³H)-glueose into glycogen in the heart. Both glucose uptake and glycugen synthesis in the heart were found to peak in group 2, in spite of a further increase of 5-fold in whole-body glucose utilization in group 3. While the mass of glycogen was found to increased only 0-33%. the incorporation of [3-³H]-glucose into cardiac glycogen in the two insulin-treated rats was found to increase 28 to 59-fold. The isotopic enrichment in cardiac glycogen indicates increases in glycogen turnover Thus, our data suggest that glycogen turnover and glucose uptake are closely associated in vivo in the heart.