Calculation of lipolysis and esterification from glycerol metabolism in rat adipose tissue

Pieces of epididymal fat pad from fed and 48-hr-fasted rats were incubated for various periods of time in Krebs-Ringer bicarbonate containing [1-(14)C]glycerol. The radioactive substrate taken up by the tissue increased linearly with time in both groups and was mainly converted to glyceride-glycerol and CO(2). The slopes of the regressions of (14)C-labeled glyceride-glycerol with time were not different between the groups, while those of (14)CO(2) were smaller in the fasted than in the fed animals. Because the radioactive glycerol in the medium is being continuously diluted with the glycerol coming out of the tissue, it is necessary to take account of this factor in calculating the actual amount of glycerol utilized by the tissue. The glycerol produced by the tissues is higher in the fasted than in the fed animals, and in both groups it increases hyperbolically with time. As negligible amounts of the (14)C-labeled glycerol taken up by the tissue recirculates to the medium, the rates of glycerol release (lipolysis), esterification, and oxidation to CO(2) were calculated.