Glycogen metabolism in regenerating liver and liver neoplasms.

Summary Maximum DNA synthesis occurred later after partial hepatectomy in mouse liver than in rat liver, and there was a similar delay in maximum glycogen depletion. The decline in activities of glycogen synthetase and phosphorylase did not parallel changes in glycogen concentration in the regenerating rat liver, being less pronounced and occurring later after partial hepatectomy. The glycogen concentration of two slowly growing hepatomas (9618A and 7787) was greater than in the rapidly growing hepatomas examined (5123tc and 7777). In vitro assays of tumor glycogen synthetase activity showed a decrease to less than 25% of the activity in normal or host liver. On addition of glucose 6-phosphate this change was less marked, and in the slowest growing hepatoma (9618A) there was no significant difference in activity. Glycogen phosphorylase activity was decreased in the hepatomas, and, most noticeably in the rapidly growing hepatomas, there was an increase in the stimulation of activity by AMP. The effect of cystcinc on glycogen phosphorylase activity in the rapidly growing hepatoma 7777 differed from that in rat liver or gastrocnemius muscle. Acid α-glucosidase activity was increased in the rapidly growing hepatomas but not in regenerating rat liver. It was concluded that glycogen metabolism in slowly growing hepatomas more closely resembles that in normal rat liver than does glycogen metabolism in rapidly growing hepatomas.