A. Mengel

Insulin resistance in relatives of NIDDM patients: The role of physical fitness and muscle metabolism

SummaryFirst degree relatives of patients with non-insulin-dependent diabetes mellitus (NIDDM) are often reported to be insulin resistant. To examine the possible role of reduced physical fitness in this condition 21 first degree relatives of NIDDM patients and 22 control subjects without any history of diabetes were examined employing a 150-min hyper-insulinaemic (0.6 mU insulin kg−1 min−1) euglycaemic clamp combined with the isotope dilution technique (3-3H-glucose, Hot GINF), the forearm technique and indirect calorimetry. During hyperinsulinaemia glucose disposal (Rd) and forearm glucose extraction were significantly diminished in the relatives (p < 0.01 and p < 0.05), but glucose oxidation and the suppressive effect on hepatic glucose production were normal. Arteriovenous differences across the forearm of the gluconeogenic precursors lactate, alanine and glycerol as well as the increments in forearm blood flow during hyperinsulinaemia were similar in the two groups. Maximal oxygen uptake (VO2 max) was lower in the relatives than in the control subjects (36.8 ± 1.9 vs 42.1 ± 2.0 ml kg−1 min−1; p = 0.03). There was a highly significant correlation between Rd and VO2 max in both relatives and control subjects (r = 0.68 and 0.66, respectively; both p < 0.001). Comparison of the linear regression analyses of insulin-stimulated Rd on VO2 max in the two groups showed no significant differences between the slopes (0.10 ± 0.03 vs 0.09 ± 0.02) or the intercepts. In stepwise multiple linear regression analyses with insulinstimulated Rd as the dependent variable VO2 max significantly determined the level of Rd (p < 0.01), whereas forearm blood flow and anthropometric data did not. In conclusion, the insulin resistance in healthy first degree relatives of patients with NIDDM is associated with a diminished physical work capacity. Whether, this finding is ascribable to environmental or genetic factors (e.g. differences in muscle fibre types, capillary density etc) remains to be determined.

Insulin resistance in microvascular angina (syndrome X)

Patients with microvascular angina (syndrome X) may be insulin resistant. We designed a study to establish whether this is the case. 11 patients with microvascular angina were compared with 9 matched subjects with noncardiac chest pain. Patients and controls were evaluated by coronary sinus catheterisation, and by isotopic measurement of glucose turnover, indirect calorimetry, and forearm technique during a 3 h baseline period after overnight fast and during a 2 h hyperinsulinaemic euglycaemic clamp. Pace-induced increase in coronary sinus blood flow was less in patients than in controls, whereas forearm blood flow did not differ between groups. Baseline measures of glucose metabolism were normal. During the clamp, glucose production and lipolysis were equally suppressed in both groups. Mean (SE) total insulin-induced glucose uptake was significantly impaired in patients compared with controls (3.9 [0.7] vs 6.4 [0.7] mg/kg per min; p < 0.01), and insulin-stimulated glucose uptake in the forearm was significantly reduced in patients (0.88 [0.10] vs 1.6 [0.30] mmol/L; p < 0.001). Reduced oxidative and nonoxidative metabolism accounted for the defect in overall glucose uptake in patients. No correlation between changes in coronary sinus blood flow and total body glucose uptake was seen. We found that microvascular angina was associated with substantial insulin resistance. Whether this relation is causal or coincidental is as yet unsettled.

Glucagon-like peptide-1 decreases intracerebral glucose content by activating hexokinase and changing glucose clearance during hyperglycemia

Type 2 diabetes and hyperglycemia with the resulting increase of glucose concentrations in the brain impair the outcome of ischemic stroke, and may increase the risk of developing Alzheimers disease (AD). Reports indicate that glucagon-like peptide-1 (GLP-1) may be neuroprotective in models of AD and stroke: Although the mechanism is unclear, glucose homeostasis appears to be important. We conducted a randomized, double-blinded, placebo-controlled crossover study in nine healthy males. Positron emission tomography was used to determine the effect of GLP-1 on cerebral glucose transport and metabolism during a hyperglycemic clamp with 18fluoro-deoxy-glucose as tracer. Glucagon-like peptide-1 lowered brain glucose (P = 0.023) in all regions. The cerebral metabolic rate for glucose was increased everywhere (P = 0.039) but not to the same extent in all regions (P = 0.022). The unidirectional glucose transfer across the blood-brain barrier remained unchanged (P = 0.099) in all regions, while the unidirectional clearance and the phosphorylation rate increased (P = 0.013 and 0.017), leading to increased net clearance of the glucose tracer (P = 0.006). We show that GLP-1 plays a role in a regulatory mechanism involved in the actions of GLUT1 and glucose metabolism: GLP-1 ensures less fluctuation of brain glucose levels in response to alterations in plasma glucose, which may prove to be neuroprotective during hyperglycemia.

Lack of Effects of Angiotensinconverting Enzyme (ACE)‐inhibitors on Glucose Metabolism in Type 1 Diabetes

To evaluate the impact of ACE‐inhibitors on insulin‐mediated glucose uptake, glucoseinduced glucose uptake, and hepatic glucose production, a sequential glucose clamp was performed in eight normotensive Type 1 diabetic patients after 3 weeks of enalapril therapy 20 mg day−1 and during control conditions. The experiments were carried out in random order. Mean arterial blood pressure was significantly reduced during ACE‐inhibition (95 ± 3 (±SE) vs 84 ± 3 mmHg; p < 0.02), while blood glucose control as assessed by HbA1c was unaltered (7.9 ± 0.5 vs 7.6 ± 0.5%). The night prior to the study normoglycaemia was maintained by a Biostator. A two‐step hyperinsulinaemic euglycaemic clamp (insulin infusion rate 0.3 and 0.8 mU kg−1 min−1) was followed by a hyperinsulinaemic and hyperglycaemic clamp (insulin infusion rate 0.8 mU kg−1 min−1, plasma glucose 11 mmoll−1). Insulin concentrations were comparable with and without enalapril treatment. During the hyperinsulinaemic clamps isotopically determined glucose disposal was unchanged (low dose 2.5 ± 0.3, high dose 4.3 ± 0.7 vs 2.6 ± 0.3 and 4.3 ± 0.7 mg kg−1 min−1 enalapril vs control). Glucose‐induced glucose disposal (9.2 ± 1.2 vs 9.1 ± 1.2 mg kg−1 min1) was also similar, as were non‐protein respiratory exchange ratios (indirect calorimetry). Glucose production was not changed by enalapril. In conclusion, treatment with enalapril has no significant effect on glucose metabolism in Type 1 diabetes.

Basal and insulin stimulated substrate metabolism in tumour induced hypoglycaemia; evidence for increased muscle glucose uptake

SummaryWhile it has very recently been reported that tumour induced hypoglycaemia is characterised by elevated production of insulin-like growth factor 2, the tissues responsible for induction of hypoglycaemia are largely unknown. We have investigated a patient with a large retroperitoneal mass and spontaneous hypoglycaemia. When compared to a reference population the patient displayed: (1) An increased glucose disposal rate and a five-fold elevation of forearm glucose uptake. (2) A decreased endogenous glucose production rate. (3) Decreased circulating levels of lipid intermediates. (4) Increased glucose oxidation and decreased lipid oxidation. (5) Low circulating levels of insulin-like growth factor 2 and insulin-like growth factor-binding protein-3 and normal levels of insulin-like growth factor 1. (6) Normal insulin sensitivity (euglycaemic glucose clamp). Blood concentrations of insulin, C-peptide, proinsulin, glucagon, growth hormone and catecholamines were within normal range, but the growth hormone response to hypoglycaemia was blunted. The data suggest that the mechanisms behind tumour induced hypoglycaemia are of systemic nature and that the tissue most prominently affected is striated muscle.

Decreased hepatic glucagon responses in Type 1 (insulin-dependent) diabetes mellitus

SummaryThe effect of glucagon infusion on hepatic glucose production during euglycaemia was evaluated in seven Type 1 (insulin-dependent) diabetic patients and in ten control subjects. In the diabetic subjects normoglycaemia was maintained during the night preceding the study by a variable intravenous insulin and glucose infusion. During the study endogenous insulin secretion was suppressed by somatostatin (450 μg/h) and replaced by insulin infusion (0.15 mU·kg−1·min−1). 3H-glucose was infused for isotopic determination of glucose turnover. Plasma glucose was clamped at 5 mmol/1 for 2 h 30 min and glucagon (1.5 ng· kg−1·min−1) was then infused for the following 3 h. Hepatic glucose production and glucose utilisation were measured during the first, second and third hour of the glucagon infusion. Basal hepatic glucose production (just prior to glucagon infusion) was similar in diabetic (1.2±0.3 mg·kg−1·min−1) and control (1.6±0.1 mg·kg−1·min−1) subjects. In diabetic patients hepatic glucose production rose slowly to 2.1±0.5 mg·kg−1·min−1 during the first hours of glucagon infusion and stabilized at this level (2.4±0.5 mg·kg−1·min−1) in the third hour. In control subjects hepatic glucose production increased sharply to higher levels than in the diabetic subjects (3.4±0.3 mg·kg−1·min−1) during the first and second hour of glucagon infusion (p<0.05) and then gradually fell (2.9±0.4 mg·kg−1·min−1) during the third hour. In conclusion, when stimulated with glucagon at a physiologic plasma concentration diabetic patients had 1) an overall reduced hepatic glucose production response and 2) an abnormal sluggish response pattern. These abnormalities may imply inappropriate counter-regulation following a hypoglycaemic episode.

Nerve conduction velocity in man: influence of glucose, somatostatin and electrolytes.

SummaryInsufficient metabolic control in diabetes mellitus is associated with a reversible reduction in nerve conduction velocity, but the mechanism behind this phenomenon is unknown. To examine the effect of acute hyperglycaemia on nerve conduction eight non-diabetic men (20–49 years of age) with no signs of peripheral neuropathy were studied before and after 3 h of hyperglycaemic clamping (plasma glucose ≈ 15 mmol/l), while insulin secretion was suppressed by somatostatin [Study 1]. Nerve conduction velocity, as determined in the proximal part of the median nerve, fell by 2.8±3.0 m/s (2p-value: 0.033). However, during euglycaemic clamping (plasma glucose ≈ 5 mmol/l) in five non-diabetic men (19–38 years of age) infused solely with somatostatin [Study 2], a comparable decrement in nerve conduction velocity was found (1.7±1.3 m/s, 2p-value: 0.043). In both studies relative hypoinsulinaemia was present. Serum-sodium decreased significantly (143±1 mmol/l vs 137±1 mmol/l [Study 1] and 143±1 mmol/l vs 142±2 mmol/l [Study 2]), while serum-potassium increased. In conclusion, the slight but significant reduction in nerve conduction velocity observed in both studies appears to be correlated to electrolyte changes. However, an effect of hypersomatostatinaemia or the hormonal changes associated with this cannot be excluded, while short-term hyperglycaemia per se seems to be without effect on nerve conduction velocity.

Influence of GLP-1 on Myocardial Glucose Metabolism in Healthy Men during Normo- or Hypoglycemia

Background and Aims Glucagon-like peptide-1 (GLP-1) may provide beneficial cardiovascular effects, possibly due to enhanced myocardial energetic efficiency by increasing myocardial glucose uptake (MGU). We assessed the effects of GLP-1 on MGU in healthy subjects during normo- and hypoglycemia. Materials and Methods We included eighteen healthy men in two randomized, double-blinded, placebo-controlled cross-over studies. MGU was assessed with GLP-1 or saline infusion during pituitary-pancreatic normo- (plasma glucose (PG): 4.5 mM, n = 10) and hypoglycemic clamps (PG: 3.0 mM, n = 8) by positron emission tomography with 18fluoro-deoxy-glucose (18F-FDG) as tracer. Results In the normoglycemia study mean (± SD) age was 25±3 years, and BMI was 22.6±0.6 kg/m2 and in the hypoglycemia study the mean age was 23±2 years with a mean body mass index of 23±2 kg/m2. GLP-1 did not change MGU during normoglycemia (mean (+/− SD) 0.15+/−0.04 and 0.16+/−0.03 µmol/g/min, P = 0.46) or during hypoglycemia (0.16+/−0.03 and 0.13+/−0.04 µmol/g/min, P = 0.14). However, the effect of GLP-1 on MGU was negatively correlated to baseline MGU both during normo- and hypoglycemia, (P = 0.006, r2 = 0.64 and P = 0.018, r2 = 0.64, respectively) and changes in MGU correlated positively with the level of insulin resistance (HOMA 2IR) during hypoglycemia, P = 0.04, r2 = 0.54. GLP-1 mediated an increase in circulating glucagon levels at PG levels below 3.5 mM and increased glucose infusion rates during the hypoglycemia study. No differences in other circulating hormones or metabolites were found. Conclusions While GLP-1 does not affect overall MGU, GLP-1 induces changes in MGU dependent on baseline MGU such that GLP-1 increases MGU in subjects with low baseline MGU and decreases MGU in subjects with high baseline MGU. GLP-1 preserves MGU during hypoglycemia in insulin resistant subjects. ClinicalTrials.gov registration numbers: NCT00418288: (hypoglycemia) and NCT00256256: (normoglycemia).

Similarity of pharmacodynamic effects of a single injection of insulin glargine, insulin detemir and NPH insulin on glucose metabolism assessed by 24-h euglycaemic clamp studies in healthy humans.

Diabet. Med. 27, 830–837 (2010)

Insulin dose–response studies in severely insulin-resistant type 2 diabetes—evidence for effectiveness of very high insulin doses

Aim: To combat diabetic complications strict glycaemic control is desirable in type 2 diabetes, but some patients are severely insulin resistant and it is not known whether high doses of insulin are effective. This study was designed to determine the acute dose–response effects of insulin in patients with type 2 diabetes and severe insulin resistance.