Metabolic defects in the liver of fasted rats as shown by utilization of C14-labeled glucose and fructose.

It is well established that carbohydrate utilization is impaired in the fasted animal (1, 2). It has also been recently demonstrated that surviving liver slices prepared from fasted rats are incapable of converting C14-labeled glucose to CO2 and fatty acids to the same extent as are slices from livers of non-fasted rats (3). In an attempt to localize the level at which glucose utilization is suppressed, we have studied here the conversion of radioactive glucose and fructose to COZ, fatty acids, and glycogen by livers of normal and fasted rats. The use of fructose as a substrate for liver slices made it possible to by-pass the first reaction in which glucose is involved. The evidence obtained indicates that the defect in glucose utilization occurs most likely at the initial phosphorylative step.