Ole Hother-Nielsen

Reduced glycogen synthase activity in skeletal muscle from obese patients with and without Type 2 (non-insulin-dependent) diabetes mellitus

SummaryIn order to evaluate the importance of a defect in insulin mediated non-oxidative glucose metabolism and glycogen synthase activity in skeletal muscles in obese subjects with and without Type 2 (non-insulin-dependent) diabetes mellitus we studied: 10 lean and 10 obese control subjects and 12 obese diabetic patients using the euglycaemic hyperinsulinaemic clamp technique (basal, 20 mU · (m2)−1 · min−1, 80mU·(m2)−1·min−1) in combination with indirect calorimetry. Muscle biopsies were taken from m. vastus lateralis at each insulin level. We found that non-oxidative glucose metabolism could be stimulated by insulin in all three groups (p<0.01). The values obtained at the highest insulin levels (around 140 μU/ml) were lower in both obese groups compared to the lean control subjects (118±21, 185±31, 249±14 mg·(m2)−1·min−1 (p< 0.01)). Insulin stimulation of the glycogen synthase activity at a glucose-6-phosphate concentration of 0.1 mmol/l was absent in both obese groups, while activities increased significantly in the lean control subjects (19.6±4.2% to 45.6±6.8%, p< 0.01). Glycogen synthase activities at the highest insulin concentrations only differed significantly between lean control subjects and obese diabetic patients (45±7% and 31±5%, p< 0.05). We conclude that insulin resistance in peripheral tissues in obese subjects with and without Type 2 diabetes may be partly explained by a reduced insulin mediated non-oxidative glucose metabolism and that this abnormality might be due to an absent insulin stimulation of glycogen synthase in skeletal muscles. This enzyme defect is correlated to obesity itself.

Classification of newly diagnosed diabetic patients as insulin-requiring or non-insulin-requiring based on clinical and biochemical variables.

In a prospective study of 41 consecutively referred newly diagnosed diabetic patients, we evaluated the predictive value of fasting and glucagon-stimulated C-peptide values, ketonuria, age, and body weight in the classification of subjects as insulin-requiring (IR) or non-insulin-requiring (NIR). The patients were followed up for ≥12 mo and classified as NIR if adequate glycemic control could be achieved without insulin (i.e., fasting plasma glucose < 8 mM and no glycosuria). Patients who needed insulin to obtain this status were classified as IR. We found that all subjects with plasma C-peptide values >0.60 nM 6 min after intravenous glucagon were NIR, whereas all IR subjects together with 3 NIR subjects had C-peptide values below this limit. All NIR subjects but 1 had fasting C-peptide values > 0.30 nM, and all IR subjects but 1 had C-peptide values below this limit. Seventy-five percent of the subjects could be correctly classified by use of age and percent desirable body weight. Thus, all subjects > 40 yr old and >100% ideal body weight were NIR, and all subjects below both these limits were IR. Ketonuria was found in 10 of 12 IR subjects and in 10 of 29 NIR subjects. We conclude that 1) 75% of the subjects could be correctly classified by use of age and percent desirable body weight only and 2) C-peptide measurements are useful in the classification of newly diagnosed diabetes, whereas presence of ketonuria is of limited value.

Effect of insulin on renal sodium handling in hyperinsulinaemic Type 2 (non-insulin-dependent) diabetic patients with peripheral insulin resistance

SummaryThe sodium retaining effect of insulin was studied in ten Type 2 (non-insulin-dependent) diabetic patients (mean age 56 (43–73) years, mean body mass index 29.5 (24.2–33.7) kg/m2) and eight age-matched control subjects (mean age 57 (43–68) years, mean body mass index 23.4 (20.8–26.6) kg/m2). The renal clearances of 99mTc-DTPA, lithium, sodium and potassium were measured over a basal period of 90 min. Then insulin was infused at a rate of 40 mU·mirr−1·m−2. After an equilibration period of 90 min, the clearance measurements were repeated during a new 90 min period. Blood glucose was clamped at the basal level (diabetic patients: 9.9±3.5, control subjects: 5.3±0.5 mmol/l) by a variable glucose infusion. Basal plasma insulin concentration was elevated in the diabetic patients (0.12±0.05 vs 0.05±0.02 pmol/ml, p<0.01). Insulin infusion resulted in comparable absolute increments in plasma insulin concentrations in the diabetic group and in the control group (0.44±0.13 vs 0.36±0.07 pmol/ml, NS). The metabolic clearance rate of glucose during the last 30 min of insulin infusion was lower in the diabetic patients (155±62 vs 320±69 ml·min−1·m2, p<0.01), reflecting peripheral insulin resistance. The decline in sodium clearance during insulin infusion was similar in diabetic subjects (1.8±1.1 vs 0.7±0.4 ml·min−1·1.73 m−2, p< 0.01) and in control subjects (1.7±0.3 vs 0.8±0.3 ml · min−1 · 1.73 m−2, p<0.01). The glomerular filtration rate and lithium clearance was unchanged, consequently calculated distal tubular fractional sodium reabsorption increased (diabetic patients: 92.9±4.1 vs 97.1±1.5, p<0.01, control subjects: 93.1±1.1 vs 96.5±0.6%, p< 0.01). Estimated extracellular fluid volume was 10% higher in the diabetic subjects (16.3±2.1 vs 14.8±2.01·1.73 m−2, NS). In conclusion, the sodium retaining effect of insulin is preserved in Type 2 diabetic patients with peripheral insulin resistance. Insulin may contribute to sodium and fluid retention and thus to the increased frequency of hypertension in hyperinsulinaemic Type 2 diabetic patients.

Mechanism of action of sulphonylureas with special reference to the extrapancreatic effect: an overview.

Sulphonylureas have been in clinical use for more than 25 years and although their hypoglycaemic effect is well documented’ it is still a matter of controversy whether their major effect is to stimulate insulin secretion or to enhance insulin action or both. For several years it was generally agreed that sulphonylureas work solely through a stimulation of insulin secretion,2 but recently it has been shown that the drugs also have extrapancreatic effect^.^ In the present overview the literature encompassing the mechanism of action of sulphonylureas will be reviewed. Much attention will be paid to the extrapancreatic effects in order to define the mechanism of action of sulphonylureas, but the aim is also to eliminate some misinterpretations of the pancreatic effect of sulphonylureas. Very few studies have been carried out in order to compare different sulphonylurea compounds. Therefore, we have chosen only to mention the name of a specific compound if the effect investigated seems to be specific for that drug, or if it is the only compound studied.

Hyperglycaemia compensates for the defects in insulin-mediated glucose metabolism and in the activation of glycogen synthase in the skeletal muscle of patients with Type 2 (non-insulin-dependent) diabetes mellitus

SummaryInsulin resistance and a defective insulin activation of the enzyme glycogen synthase in skeletal muscle during euglycaemia may have important pathophysiological implications in Type 2 (non-insulin-dependent) diabetes mellitus. Hyperglycaemia may serve to compensate for these defects in Type 2 diabetes by increasing glucose disposal through a mass action effect. In the present study, rates of whole-body glucose oxidation and glucose storage were measured during fasting hyperglycaemia and isoglycaemic insulin infusion (40 mU·m−2min−1, 3 h) in 12 patients with Type 2 diabetes. Eleven control subjects were studied during euglycaemia. Biopsies were taken from the vastus lateralis muscle. Fasting and insulin-stimulated glucose oxidation, glucose storage and muscle glycogen synthase activation were all fully compensated (normalized) during hyperglycaemia in the diabetic patients. The insulin-stimulated increase in muscle glycogen content was the same in the diabetic patients and in the control subjects. Besides hyperglycaemia, the diabetic patients had elevated muscle free glucose and glucose 6-phosphate concentrations. A positive correlation was demonstrated between intracellular free glucose concentration and muscle glycogen synthase fractional velocity insulin activation (0.1 mmol/l glucose 6-phosphate: r=0.65, p<0.02 and 0.0 mmol/l glucose 6-phosphate: r= 0.91, p<0.0001). In conclusion, this study indicates an important role for hyperglycaemia and elevated muscle free glucose and glucose 6-phosphate concentrations in compensating (normalizing) intracellular glucose metabolism and skeletal muscle glycogen synthase activation in Type 2 diabetes.

Enhanced hepatic insulin sensitivity, but peripheral insulin resistance in patients with type 1 (insulin-dependent) diabetes.

SummarySensitivity to insulin in vivo was studied in 8 normal weight C-peptide negative Type 1 (insulin-dependent) diabetic patients (age 23±1 years, diabetes duration 6±2 years), and in 8 age, weight and sex matched healthy subjects, using the euglycaemic clamp and 3-3H-glucose tracer technique. Prior to the study diabetic patients were maintained normoglycaemic overnight by a glucose controlled insulin infusion. Sequential infusions of insulin in 3 periods of 2 h resulted in mean steady state insulin levels of 12±2 versus 11±1, 18±2 versus 18±2 and 28±3 versus 24±2 μU/ml in diabetic patients and control subjects. Corresponding glucose utilization rates were 2.4±0.2 versus 2.4±0.1, 2.4±0.2 versus 3.0±0.3 and 2.9±0.3 versus 4.6±O.6 mg·kg−1·min−1, p<0.02. Portal insulin values in the three periods were calculated to 12±2 versus 25±3, 18±2 versus 32±3 and 28±3 versus 37±3 μU/ml in the diabetic patients and control subjects using peripheral insulin and C-peptide concentrations and assuming a portal to peripheral insulin concentration gradient of 1 in diabetic patients and of 2.4 in control subjects. Corresponding glucose production rates were 2.5±0.2 versus 2.4±0.1, 1.6±0.1 versus 0.9±0.2 and 0.7±0.1 versus 0.4±0.2 mg·kg−1·min−1. Using this approach the insulin dose-response curve for the peripheral glucose utilization was right-ward shifted, while the dose-response curve for the hepatic glucose production as a function of portal insulin levels was left-ward shifted. We conclude that in vivo insulin action is increased in the liver but decreased in peripheral tissues in insulin treated Type 1 diabetic patients. Presumably these oppositely directed changes in insulin action are acquired defects, secondary to the present mode of peripheral insulin treatment.

Assessment of Glucose Turnover Rates in Euglycaemic Clamp Studies using Primed‐constant [3‐3H]‐glucose Infusion and Labelled or Unlabelled Glucose Infusates

Underestimation of glucose turnover rates has been a problem in clamp studies using primed‐constant [3‐3H]‐glucose infusion technique. Due to slow mixing in interstitial compartments concealed specific activity gradients may arise between plasma and interstitial compartments during intravenous unlabelled glucose infusion. Such specific activity gradients, however, can be prevented if plasma specific activity is maintained constant. Two euglycaemic clamp studies (insulin infusion 40 mU m−2 min−1) were performed in six lean normal subjects. Using conventional unlabelled glucose infusates plasma specific activity declined by 74%, tracer determined glucose appearance was smaller than actual glucose infusion rates (317 ± 11 vs 366 ± 15 mg m−2 min−1, p< 0.001), and erroneous negative values were calculated for glucose production (‐49 ± 7 mg m−2 min−1). Average underestimation during the first 2 h correlated with glucose infusion rates (r = 0.88, p < 0.02). In contrast, when plasma specific activity was maintained constant, using appropriately labelled glucose infusates, tracer determined glucose appearance and glucose infusion rates were similar (385 ± 16 vs 385 ± 17 mg m−2 min−1), and negative errors for glucose production were avoided. In conclusion, using unlabelled glucose infusates, as in previous studies, suppression of glucose production is overestimated and stimulation of glucose utilization is underestimated. As errors were greater with larger glucose infusions, the mistakes may have been greatest in insulin sensitive control subjects, and smaller in insulin resistant subjects. Therefore, re‐evaluation of hepatic insulin sensitivity seems appropriate in diabetes, obesity, and other insulin resistant states.

Insulin Increases Renal Magnesium Excretion: A Possible Cause of Magnesium Depletion in Hyperinsulinaemic States

The effects of insulin upon renal magnesium excretion were examined. Urinary magnesium excretion rates were measured in seven healthy volunteers (three men, four women) before and during a euglycaemic, hyperinsulinaemic clamp. Insulin was infused at 120 pmol m−2 min−1 and at 240 pmol m−2 min−1. Compared to baseline, the renal magnesium excretion increased 30 % during the infusion of insulin at a rate of 120 pmol m−2 min−1. During infusion of insulin, 240 pmol m−2 min−1, renal magnesium excretion increased 50 % compared to baseline. There were no changes in either glomerular filtration rates, plasma magnesium, urinary volume or general changes in the renal handling of divalent ions as judged by an unchanged urinary excretion rate of calcium (0 % during infusion of insulin, 120 pmol m−2 min−1, and 8 % increase during infusion of 240 pmol m−2 min−1 (NS)). During the 120 pmol m−2 min−1 insulin infusion rate, plasma insulin rose from 46.1 pmol l−1 to 158.8 pmol l−1 and during the 240 pmol m−2 min−1 insulin infusion rate, mean plasma insulin concentration was 361.4 pmol l−1. Thus, physiological concentrations of insulin induce a specific increase in the renal excretion of magnesium. This might partly explain the magnesium depletion observed in various hyperinsulinaemic states, diabetes mellitus, atherosclerosis, hypertension, and obesity.

Impact of ubiquinone (coenzyme Q10) treatment on glycaemic control, insulin requirement and well-being in patients with Type 1 diabetes mellitus

Aim To investigate the effect of ubiquinone (coenzyme Q10) on glycaemic control and insulin requirement in patients with Type 1 diabetes mellitus (DM).

Pathogenesis of type 2 (non-insulin-dependent) diabetes mellitus: the role of skeletal muscle glucose uptake and hepatic glucose production in the development of hyperglycaemia. A critical comment.

ConclusionOur understanding of the pathophysiology of Type 2 diabetes has advanced considerably over the last decade, but many problems and issues remain unresolved. The initiation of this debate mirrors many of the problems that we face today. An understanding of the primary and secondary defects leading to diabetes in “genetically prone” individuals are of crucial importance to further our understanding of the metabolic process involved in the development of the diabetic state. In our contribution to this debate we have pointed out the methodological problems that have arisen in the estimation of HGP and the quantitation of glucose kinetics in normo-and hyperglycaemic Type 2 diabetic individuals. These problems are not yet completely resolved. Therefore, the importance of the liver vs the importance of muscle glucose metabolism in the development of hyperglycaemia will probably have to wait for new and improved techniques. However, the current data strongly indicate that the primary defect (genetic defect?) in insulin action is located to skeletal muscles.The near-normal HGP values in Type 2 diabetes patients with fasting blood glucose values less than 12–15 mmol/1 do not indicate that the insulin sensitivity of liver is normal in Type 2 diabetes, but proves to us that the reduction in insulin action in both liver and muscles are fully compensated —perhaps slightly overcompensated.