title: Intracellular skeletal muscle glucose metabolism is differentially altered by dexamethasone treatment of normoglycemic relatives of type 2 diabetic patients.
abstract: Young first-degree relatives of type 2 diabetic patients are insulin-resistant, with the insulin resistance mainly located in skeletal muscle due to decreased insulin-induced nonoxidative glucose metabolism and muscle glycogen synthase activation. We investigated whether the mechanism differs for dexamethasone (dex)-induced insulin resistance in first-degree relatives of type 2 diabetics versus healthy control subjects by quantifying intracellular glucose processing in muscle biopsies taken before and after 5 days of dex treatment (4 mg/d) in 20 normal glucose-tolerant relatives of type 2 diabetic patients and 20 matched controls (age, 29.4 +/- 1.7 v 29.4 +/- 1.6 years; body mass index, 25.1 +/- 1.0 v 25.1 +/- 0.9 kg/m2). In addition, an intravenous glucose tolerance test (IVGTT) combined with continuous indirect calorimetry was performed. Following 5 days of dex treatment, glucose tolerance deteriorated in both the relatives and the control subjects. Fasting dry-weight muscle glucose and fasting intracellular muscle glucose concentrations increased in response to dex only in the relatives (2.43 +/- 0.21 v 2.97 +/- 0.26 mmol/kg dry weight, P < .05; 0.28 +/- 0.07 v 0.45 +/- 0.08 mmol/L intracellular water, P < .05); no increases were observed in the control subjects. Fasting dry-weight muscle lactate also increased post-dex only in the relatives (7.37 +/- 0.40 v 10.77 +/- 1.22 mmol/kg dry weight, P < .001). Both basal muscle glucose and lactate concentrations from the IVGTT study correlated with the 2-hour post-dex glucose value obtained during the OGTT study in the relatives (R = .76 and R = .74, respectively, both P < .0001) but not in the control subjects. Basal intramuscular glycogen synthase activity decreased approximately 25% in both the relatives and control subjects post-dex; the decrement was significant (P < .01) only in control subjects. Indirect calorimetry during the post-dex IVGTT demonstrated increased glucose oxidation (P < .03) and reduced lipid oxidation (P < .03) in the relatives only. We postulate that the insulin resistance induced by dex in first-degree relatives of type 2 diabetic patients is associated with a preferential channeling of glucose into the glycolytic pathway (increased glucose oxidation and lactate production), probably associated with a preexisting downregulation of the glycosen synthase pathway.
authors.affiliation: Diabetes Research Centre, Department of Endocrinology, Odense University Hospital, Denmark.
authors.forename: J E
authors.initials: JE
authors.lastname: Henriksen
authors.forename: F
authors.initials: F
authors.lastname: Alford
authors.forename: A
authors.initials: A
authors.lastname: Vaag
authors.forename: A
authors.initials: A
authors.lastname: Handberg
authors.forename: H
authors.initials: H
authors.lastname: Beck-Nielsen
mesh_terms: D000328:Adult; D015992:Body Mass Index; D016022:Case-Control Studies; D003907:Dexamethasone / Q000494:pharmacology*; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics*; D005260:Female; D005947:Glucose / Q000378:metabolism*; D005951:Glucose Tolerance Test; D051275:Glucose Transporter Type 4; D019298:Glucose-6-Phosphate / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism; D006006:Glycogen Synthase / Q000378:metabolism; D006801:Humans; D007333:Insulin Resistance / Q000235:genetics; D019344:Lactic Acid / Q000378:metabolism; D008055:Lipids / Q000097:blood; D008297:Male; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009124:Muscle Proteins; D018482:Muscle, Skeletal / Q000378:metabolism*; D010375:Pedigree
chemical_list: D051275:Glucose Transporter Type 4; D008055:Lipids; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495692:SLC2A4 protein, human; D019344:Lactic Acid; D019298:Glucose-6-Phosphate; D003907:Dexamethasone; D006003:Glycogen; D006006:Glycogen Synthase; D005947:Glucose