Behavior and regulation of enzyme systems in normal liver and in hepatomas of different growth rates

Abstract

The activities and behavior of carbohydrate enzyme systems were examined in normal liver and in hepatomas of different growth rates. 1. 1.|The enzymes studied can be divided into three groups according to whether their behavior can be correlated with the growth rate of the hepatomas, whether they are uniformly decreased or increased in all tumors or whether they show no relation at all to growth rates. 2. 2.|The concept of enzyme lesion was discussed in terms of limitation of biological function and physiological range. 3. 3.|The behavior of carbohydrate enzymes in metabolic pathways in normal liver and hepatomas of different growth rates was studied by using cortisone or refeeding of fasted rats as inducers. Results indicate that there is a progressive loss of the biochemical response to cortisone administration as manifested in failure of enzyme induction and nitrogen and glycogen deposition in hepatomas. 4. 4.|The host livers also showed decreased or absent sensitivity to cortisone induction. 5. 5.|Hepatoma 7794-A exhibited behavior different from normal liver in regard to an absence of alterations in glucose-6-phosphate dehydrogenase activity when the tumor-bearing rat was subjected to fasting and refeeding. The altered behavior of enzyme systems in hepatomas was discussed in terms of decreased responsiveness or damage in their respective Enzyme Forming Systems.