Effects of insulin infusion on human skeletal muscle pyruvate dehydrogenase, phosphofructokinase, and glycogen synthase. Evidence for their role in oxidative and nonoxidative glucose metabolism.

Abstract

To determine whether activation by insulin of glycogen synthase (GS), phosphofructokinase (PFK), or pyruvate dehydrogenase (PDH) in skeletal muscle regulates intracellular glucose metabolism, subjects were studied basally and during euglycemic insulin infusions of 12, 30, and 240 MU/im2 nmn. Glucose disposal, oxidative and nonoxidative glucose metabolism were determined. GS, PFK, and PDH were assayed in skeletal muscle under each condition. Glucose disposal rates were 2.37+0.11, 3.15±0.19, 6.71±0.44, and 11.7±1.73 mg/kg. min; glucose oxidation rates were 1.96±0.18, 2.81±0.28, 4.43±0.32, and 5.22+0.52. Nonoxidative glucose metabolism was 0.39±0.13, 0.34±0.26, 2.28±0.40, and 6.52±1.21 mg/kg. min. Both the proportion of active GS and the proportion of active PDH were increased by hyperinsulinemia. PFK activity was unaffected. Activation of GS was correlated with nonoxidative glucose metabolism, while activation of PDH was correlated with glucose oxidation. Sensitivity to insulin of GS was similar to that of nonoxidative glucose metabolism, while the sensitivity to insulin of PDH was similar to that of glucose oxidation. Therefore, the activation of these enzymes in muscle may regulate nonoxidative and oxidative glucose metabolism.

Insulin signalling in skeletal muscle of subjects with or without Type II-diabetes and first degree relatives of patients with the disease

“…Extraction of muscle samples and assays for glycogen synthase were carried out as previously described [37,38]. Briefly, glycogen synthase was assayed in the presence of a near physiological concentration of glucose-6-phosphate (G6P; 0.1 mmol/l) and in the presence of 10 mmol/l G6P to determine maximal enzyme activity.…”

Skeletal Muscle Insulin Resistance in Normoglycemic Subjects With a Strong Family History of Type 2 Diabetes Is Associated With Decreased Insulin-Stimulated Insulin Receptor Substrate-1 Tyrosine Phosphorylation

“…Blood was drawn every 10 min during the last 30 min of the isotopic equilibration period for measurement of plasma glucose, insulin, and FFA concentrations and tritiated glucose radioactivity. After 60 min of bed rest, a percutaneous muscle biopsy was obtained with a Bergstrom cannula from the vastus lateralis muscle under local anesthesia (23). Muscle biopsy specimens were immediately blotted free of blood, frozen in liquid nitrogen, and stored under liquid nitrogen until processing.…”

Neonatal de-afferentation of capsaicin-sensitive sensory nerves increases in vivo insulin sensitivity in conscious adult rats

“…Glycogen synthase was assayed in duplicate by a modification of the method described by Mandarino et al [21]. Muscle (soleus and psoas) samples (25 mg) were homogenized in ice-cold buffer (0.5 ml) containing (in mmol/l) 50 potassium phosphate, 2.0 dithiothreitol, 2.0 ethylenediaminetetraacetic acid, 20 sodium fluoride (to inhibit phosphatase activity), and protease inhibitors (in Table 1.…”