Effects of insulin on the structure and metabolism of glucogen in chemically-induced diabetic rats
Kwan, T.K.; Thambyrajah, V.
Medical Journal of Malaysia 33(2): 178-183
1978
ISSN/ISBN: 0300-5283 PMID: 755172 Document Number: 133405
Male rats initially 2 to 3 months old were starved for 48 h then fed on high-carbohydrate pelleted diet with 5% glucose solution to drink. Some were made diabetic with streptozotocin or alloxan given for 5 days; half of those got insulin daily. Rats were killed before the insulin injection or 2 h after it got on the 2nd, 4th, 6th and 8th days of treatment with insulin. Liver glycogen content per cent of wet tissue fell with the onset of diabetes and rose again rapidly with insulin. There was no significant difference in structure of glycogen between controls given the diet alone and rats made diabetic then given insulin, but for untreated diabetics rats the average chain length of glycogen seemed slightly less than in the other 2 groups. Hexokinase/glucokinase activity of liver decreased in diabetic rats and increased in diabetic rats given insulin. Phosphoglucomutase activity increased in both those groups but more in the group given insulin. Glucose-6-phosphatase activity fell for about 2 days then rose in diabetic rats and continued to fall in diabetic rats given insulin. Succinate dehydrogenase increased in both groups for about 4 days, more in the group given insulin, returning to near initial value by 8 days. Phosphorylase activity fell, more in the group given insulin than in diabetics. Results are discussed and possible mechanisms of the effect of insulin on glycogen synthesis are considered. Variations in glycogen chain length were probably caused by the relative activities of glycogen synthetase, phosphorylase and branching enzyme. Results indicated that insulin activated the glucose-synthesising systems; those included the branching enzyme, otherwise a linear molecule of glycogen would have resulted.