The effects of insulin on transport and metabolism of glucose in skeletal muscle from hyperthyroid and hypothyroid rats.

The effects of insulin on the rates of glucose disposal were studied in soleus muscles isolated from hyper- or hypothyroid rats. Treatment with triiodothyronine for 5 or 10 days decreased the sensitivity of glycogen synthesis but increased the sensitivity of lactate formation to insulin. The sensitivity of 3-O methylglucose to insulin was increased only after 10 days of treatment and was accompanied by an increase in the sensitivity of 2-deoxyglucose phosphorylation; however, 2-deoxyglucose and glucose 6-phosphate in response to insulin remained unaltered. In hypothyroidism, insulin-stimulated rates of 3-O-methylglucose transport and 2-deoxyglucose phosphorylation were decreased; however, a…

Metabolic changes in skeletal muscle of frog during exercise and recovery.

Effects of glucocorticoid excess on the sensitivity of glucose transport and metabolism to insulin in rat skeletal muscle.

This study examines the mechanisms of glucocorticoid-induced insulin resistance in rat soleus muscle. Glucocorticoid excess was induced by administration of dexamethasone to rats for 5 days. Dexamethasone decreased the sensitivity of 3-O-methylglucose transport, 2-deoxyglucose phosphorylation, glycogen synthesis and glucose oxidation to insulin. The total content of GLUT4 glucose transporters was not decreased by dexamethasone; however, the increase in these transporters in the plasma membrane in response to insulin (100 m-units/litre) was lessened. In contrast, the sensitivity of lactate formation to insulin was normal. The content of 2-deoxyglucose in the dexamethasone-treated muscle was …

Fructose 2,6-bisphosphate and glycolytic flux in skeletal muscle of swimming frog

AbstractGlycolytic flux in skeletal muscle is controlled by 6-phosphofructokinase but how this is achieved is controversial. Brief exercise (swimming) in frogs caused a dramatic increase in the phosphofructokinase activator, fructose 2,6-bisphosphate, in working muscle. The kinetics of phosphofructokinase suggest that in resting muscle, the enzyme is inhibited by ATP plus citrate and that the increase in fructose 2,6-bisphosphate is part of the mechanism to activate phosphofructokinase when exercise begins. When exercise was sustained, fructose 2,6-bisphosphate in muscle was decreased as was the rate of lactate accumulation. Glycolytic flux and the content of fructose 2,6-bisphosphate appea…

Effects of insulin-like growth factor I on the rates of glucose transport and utilization in rat skeletal muscle in vitro.

1. The effects of insulin-like growth factor I (IGF-I) on the rates of glucose transport and utilization and its interaction with insulin were investigated in rat soleus muscle in vitro. IGF-I increased the rates of glucose transport, lactate formation, glycogen synthesis and the flux of glucose to hexose monophosphate, but it had no effect on the rate of glucose oxidation or glycogenolysis. 2. In the absence of insulin, low levels of IGF-I (0-30 ng/ml) increased the rate of glycolysis and the content of fructose 2,6-bisphosphate, but the content of glucose 6-phosphate remained unaltered; at higher levels of IGF-I (300-3000 ng/ml) the rate of glycolysis and the content of fructose 2,6-bisph…

6-Phosphofructokinase from frog skeletal muscle: purification and properties