Glucose-6-phosphate utilization in hepatoma, regenerating and newborn rat liver, and in the liver of fed and fasted normal rats.

Abstract

The glucose-6-phosphate (G-6-P) utilization of the Novikoff hepatoma was investigated by studying the four enzymes which are concerned with the immediate utilization of G-6-P as substrate. For control tissues the following ones were used: normal resting liver, liver of embryonic and newborn animals, and regenerating liver. The effect of fasting was also examined to exclude the possible effects of anorexia or cachexia. Enzymatic activities were expressed per wet weight, per mg. nitrogen, and per average cell. 1. The nitrogen content was markedly decreased in the homogenate and supernatant fluid in the Novikoff hepatoma and in the embryonic liver. The cellularity was markedly increased in the Novikoff hepatoma (176 per cent) and in the liver of fasted normal rats (134 per cent), but it did not change significantly in the regenerating liver. 2. Glucose-6-phosphatase (G-6-Pase) activity was absent in the Novikoff hepatoma. There was also no or only minimal G-6-Pase activity in the fetal rat liver. On the other hand, in newborn rat liver the activity was 30–40 per cent higher than in normal adult liver. In the regenerating liver the G-6-Pase activity per unit was not decreased. 3. The phosphohexoseisomerase activity was markedly increased in the hepatoma on a nitrogen basis, but it was in the normal range when it was calculated per average cell. Phosphohexoseisomerase activity (on nitrogen basis) was markedly increased in embryonic and newborn rat liver. In the regenerating liver this enzymatic activity did not change. 4. The phosphoglucomutase activity of the Novikoff hepatoma was decreased to 10 per cent of normal values. This decrease may be one of the specific biochemical changes in this tumor, because no such decrease was found in any of the control tissues. The activity of this enzyme increased in embryonic and newborn liver, but it did not change in regenerating liver. 5. Glucose-6-phosphate dehydrogenase activity was markedly increased (500 per cent) in the Novikoff hepatoma. This may be another of the specific changes occurring in the Novikoff hepatoma. This enzyme was decreased in embryonic liver, but it was in normal range in newborn and regenerating liver. 6. The significance and implications of the results of glucose-6-phosphate utilization studies were discussed.