Comparison of the effects of human recombinant insulin-like growth factor I and insulin on plasma amino acid concentrations and leucine kinetics in humans

Summary We examined the effects of recombinant human insulin-like growth factor I (IGF-I) and insulin on the plasma amino acid (AA) profile and leucine kinetics in eight normal subjects. IGF-I was infused at 52 pmol·kg^–1·min^–1, in combination with prime-continuous [1-¹⁴C] leucine infusion, to obtain steady-state plasma concentrations of total (54±3 nmol/l) and free (7.3±1 nmol/l) IGF-I (study 1). In response to IGF-I, plasma AA levels declined by 37±3% (1975±198 to 1368±120 mol/l) and total branched chain amino acids (BCAA) declined by 34±3% (390±21 to 256±13 mol/l). This hypoaminoacidaemic effect was associated with a decline in endogenous leucine flux of 17±2% (1.88±0.05 to 1.57±0.04 mol·kg^–1·min^–1) and leucine oxidation of 17±1% (0.31±0.02 vs 0.26±0.02 mol·kg^–1·min^–1) (both p<0.01 vs basal). The same subjects underwent a second study (study 2) in which insulin was infused at 6.22 pmol·kg^–1·min^–1 to obtain a steady-state plasma insulin concentration of 530±25 pmol/l while maintaining euglycaemia. The infusion rate was designed to match the declines in plasma BCAA levels and leucine turnover observed during IGF-I infusion. The rates of glucose infusion necessary to maintain euglycaemia during IGF-I and insulin infusion were 4.9±1.0 and 7.8±0.6 mg·kg^–1 ·min^–1, respectively. During insulin infusion total BCAA declined by 39% from 369±23 to 226±20 mol/l, leucine flux declined by 16±2% from 1.90±0.05 to 1.61±0.03 mol·kg^–1·min^–1, and leucine oxidation declined by 19±2% from 0.32±0.02 to 0.26±0.02 mol·kg^–1·min^–1. On a molar basis IGF-I was 7.3% as potent as insulin in inhibiting proteolysis. These results demonstrate that in humans: (i) the hypoaminoacidaemic response to IGF-I can be entirely ascribed to the inhibition of proteolysis; (ii) qualitatively, the effects of IGF-I and insulin on plasma AA profile and protein metabolism are similar; (iii) quantitatively, IGF-I is 14-fold less potent than insulin in suppressing protein degradation.Abbreviations IGF-I Insulin-like growth factor I - AA aminoacid - BCAA branched chain amino acids - KIC alphaketoisocaproate - ELF endogenous leucine flux - NOLD non-oxidative leucine disposal     

Insulin regulation of glucose and lipid metabolism in massive obesity

Summary Eight obese patients and 12 normal individuals underwent a euglycaemic insulin clamp (20 and 40 mU · m^2–1 · min^–1) along with continuous infusion of 3-³H-glucose and 1-¹⁴C-palmitate and indirect calorimetry. Basal plasma glucose concentration (4.7±0.3 vs 4.4±0.2 mmol/l) was similar in the two groups, whereas hepatic glucose production was slightly higher in obese individuals (1.11±0.06 vs 0.84±0.05 mmol/min) in spite of higher plasma insulin levels (17±2 vs 6±1 mU/l; p<0.01). Insulin inhibition of hepatic glucose production was impaired in obese subjects. Glucose disposal by lean body mass was markedly reduced both at baseline (11.7±1.1 vs 15.6±0.6 mol · kg^–1 · min^–1; p<0.05) and during clamp (15.0±1.1 vs 34.4±2.8 and 26.7±3.9 vs 62.2±2.8 mol · kg^–1 · min^–1; p<0.01) Oxidative (12.2±1.1 vs 17.8±1 and 16.1±1.1 vs 51.1±1.7 mol · kg^–1 · min^–1; p<0.05–0.002) and non-oxidative glucose metabolism (3.9±1.1 vs 15.0±2.8 and 12.8±3.3 vs 38.3±2.2 mol · kg^–1 · min^–1; p<0.01–0.001) were impaired. Basal plasma concentrations of non-esterified fatty acids (635±75 vs 510±71 mol/l) and blood glycerol (129±17 vs 56±5 mol/l; p<0.01) were increased in obese patients. Following hyperinsulinaemia, plasma non-esterified fatty acids (244±79 vs 69±16 and 140±2 vs 36±10 mol/l; p<0.01) and blood glycerol levels (79±20 vs 34±6 and 73±22 vs 29±5 mol/l; p<0.01) remained higher in obese subjects. Baseline non-esterified fatty acid production rate per kg of fat body mass was significantly larger in normal weight subjects (37.7±6.7 vs 14.0±1.8 mol/l; p<0.01) and insulin inhibition was reduced in obese patients (–41±9 vs –74±3 and –53±11 vs –82±3%; p<0.05). Basal plasma non-esterified fatty acid utilization by lean body mass was similar in the two groups (9.8±0.9 vs 8.8±2.0 mol · kg^–1 · min^–1), whereas during clamp it remained higher in obese patients (6.0±1.2 vs 2.8±2.5 and 4.9±1.3 vs 1.5±0.6 mol · kg^–1 · min^–1; p<0.1–0.05). Lipid oxidation was higher in obese individuals in spite of hyperinsulinaemia (3.7±0.3 vs 2.4±0.4 and 2.3±0.4 vs 0.9±0.3 mol · kg^–1 · min^–1; p<0.05– 0.02). An inverse correlation was found between lipid oxidation and glucose oxidation (r=0.82 and 0.93; p<0.001) and glucose utilization (r=0.54 and 0.83; p<0.05–0.001) both in obese and control subjects. A correlation between lipid oxidation and non-oxidative glucose metabolism was present only in normal weight individuals (r=0.75; p<0.01). We conclude that in obesity all tissues (muscles, liver, and adipose tissue) are resistant to insulin action. Insulin resistance involves glucose as well as lipid metabolism.     

Contribution of glucose/glucose 6-phosphate cycle activity to insulin resistance in Type 2 (non-insulin-dependent) diabetes mellitus

Summary It has been suggested that increased glucose/glucose 6-phosphate substrate cycling impairs net hepatic glucose uptake in Type 2 (non-insulin-dependent) diabetes mellitus and contributes to hyperglycaemia. To investigate glucose/glucose 6-phosphate cycle activity and insulin action in Type 2 diabetes we studied eight patients and eight healthy control subjects, using the euglycaemic glucose clamp and isotope dilution techniques with purified [2-³H]- and [6-³H] glucose tracers, in the post-absorptive state and eight patients and five healthy control subjects during consecutive insulin infusions at rates of 0.4 and 2.0 mU·kg^–1·min^–1. [2-³H]glucose and [6-³H]glucose radioactivity in plasma samples were determined using selective enzymatic detritiation, allowing calculation of glucose turnover rates for each isotope, the difference being glucose/glucose 6-phosphate cycling. Endogenous glucose production ([6-³H]glucose) was greater in diabetic than control subjects in the post-absorptive state (15.6±1.5 vs 11.3±0.4 mol·kg^–1·min^–1, p<0.05) and during the 0.4 mU insulin infusion (10.1±1.3 vs 5.2±0.3 mol·kg^–1·min^–1, p<0.01) indicating hepatic insulin resistance. Glucose/glucose 6-phosphate cycling was significantly greater in diabetic than in control subjects in the post-absorptive state (2.6±0.4 vs 1.6±0.2 mol·kg^–1·min^–1, p<0.05) but not during the 0.4 mU insulin infusion (2.0±0.4 vs 2.0±0.3 mol·kg^–1·min^–1). During the 2.0 mU insulin infusion endogenous glucose production was suppressed to a similar degree in both groups (2.6±0.5 vs 3.4±0.7 mol · kg^–1·min^–1) but glucose disappearance was lower in the diabetic subjects (30.8±2.0 vs 52.4±4.6 mol·kg^–1·min^–1, p<0.01). During the 2.0 mU insulin infusion glucose/glucose 6-phosphate cycling was greater in the diabetic subjects (3.8±0.7 vs 0.8±0.6 mol·kg^–1·min^–1, p<0.05). In conclusion, both hepatic and peripheral insulin action are impaired in Type 2 diabetes. Increased glucose/glucose 6-phosphate cycling is seen in the post-absorptive state and also during marked hyperinsulinaemia, when insulin resistance is predominantly due to reduced peripheral tissue glucose uptake.     

Insulin resistance and abnormal albumin excretion in non-diabetic first-degree relatives of patients with NIDDM

Summary Microalbuminuria has recently been associated with insulin resistance in both insulin-dependent and non-insulin-dependent (NIDDM) diabetes mellitus. To establish whether microalbuminuria in non-diabetic subjects as well is associated with insulin resistance and associated abnormalities in glucose and lipid metabolism, oral glucose tolerance tests were performed with measurement of urinary albumin excretion rate, lipids and lipoproteins in 582 male non-diabetic first-degree relatives of patients with NIDDM. In addition, insulin sensitivity was assessed in 20 of these subjects with the euglycaemic hyperinsulinaemic clamp technique. Abnormal albumin excretion rate (AER), defined as AER 15–200 g/min, was associated with higher systolic blood pressure (p<0.05), higher fasting glucose values (p<0.05), lower HDL-cholesterol (p<0.05) and lower apolipoprotein A-I (p<0.05) concentrations than observed in subjects with normal AER. The rate of glucose metabolism was lower in subjects with abnormal compared to subjects with normal albumin excretion rate (38.0±2.8 vs 47.3±2.4 mol·kg lean body mass^–1. min^–1; p=0.028). This difference was almost completely accounted for by a reduction in non-oxidative glucose metabolism (17.7±1.9 vs 27.4±2.7 mol·kg lean body mass^–1. min^–1; p = 0.010), which correlated inversely with the AER (r=–0.543; p=0.013). These results suggest that in non-diabetic individuals genetically predisposed to NIDDM, abnormal AER is associated with insulin resistance and abnormalities in glucose and lipid metabolism.Abbreviations LBM lean body mass - IDDM Insulin-dependent diabetes mellitus - HDL high-density lipoprotein - NIDDM non-insulin-dependent diabetes mellitus - VLDL very low density lipoprotein - AER albumin excretion rate - OGTT oral glucose tolerance test     

Oxidation of low-density lipoprotein in NIDDM: its relationship to fatty acid composition

Summary The increased risk of atherosclerotic disease in diabetic subjects may be due to enhanced foam cell formation following an increased susceptibility of low density lipoprotein to oxidative modification. This study has compared fatty acid content and lipoprotein oxidisability in 10 non-insulin-dependent diabetic subjects with that in 10 control subjects. Both groups were normocholesterolaemic and the diabetic subjects had higher triglyceride levels (2.2±0.4 vs 1.2±0.2 mmol/l, p<0.05). The fatty acid composition was compared in low density lipoprotein following Folch extraction, separation by thin layer chromatography (for the lipid classes) and analysis by gas liquid chromatography. Low density lipoprotein oxidisability was assessed by conjugated diene and thiobarbituric acid reacting substance formation in the presence of copper ions. The esterified/free cholesterol ratio was higher in the low density lipoprotein from patients compared to control subjects (2.9±0.1 vs 1.9±0.3, p<0.05). Linoleic acid in the cholesteryl ester fraction of the lipoprotein was higher in the patients than in the control subjects (48.2±2.2% vs 42.4±3.4%, p<0.05) as was the total quantity of linoleic acid in the cholesteryl ester fraction (317.8±68.0 vs 213.2±28.0 g/mg protein, p<0.05) and in the low-density lipoprotein as a whole (443.2±70.0 vs 340.2±28.2 g/mg protein, p<0.05). Lipoprotein oxidisability was also increased in the diabetic group with increased formation of thiobarbituric acid reacting substances (35.6±7.2 vs 22.3±3.5 nmol/mg protein, p<0.05, increased total diene formation (502±60 vs 400±30 nmol/mg protein, p<0.05) and increased rate of diene formation (7.2±0.6 vs 5.1±0.9 nmol diene · mg protein^–1 · min^–1, p<0.05). This study indicates that low-density lipoprotein from diabetic subjects is more susceptible to oxidation. This could, in vivo, accelerate foam-cell formation thereby increasing atherosclerotic risk in diabetic subjects.Abbreviations BHT Butylated hydroxytoluene - EDTA ethylenediaminetetraacetic acid - TBARS thiobarbituric reacting substances - HPLC high performance liquid chromatography - MDA malondialdehyde - HbA_1c glycated haemoglobin     

Enhanced glucose cycling and suppressed de novo synthesis of glucose-6-phosphate result in a net unchanged hepatic glucose output in ob/ob mice

Aims/hypothesis Leptin-deficient ob/ob mice are hyperinsulinaemic and hyperglycaemic; however, the cause of hyperglycaemia remains largely unknown.Methods Glucose metabolism in vivo in 9-h fasted ob/ob mice and lean littermates was studied by infusing [U-¹³C]-glucose, [2-¹³C]-glycerol, [1-²H]-galactose and paracetamol for 6 h, applying mass isotopomer distribution analysis on blood glucose and urinary paracetamol-glucuronide.Results When expressed on the basis of body weight, endogenous glucose production (109±23 vs 152±27 µmol·kg^–1·min^–1, obese versus lean mice, p<0.01) and de novo synthesis of glucose-6-phosphate (122±13 vs 160±6 µmol·kg^–1·min^–1, obese versus lean mice, p<0.001) were lower in ob/ob mice than in lean littermates. In contrast, glucose cycling was greatly increased in obese mice (56±13 vs 26±4 µmol·kg^–1·min^–1, obese versus lean mice, p<0.001). As a result, total hepatic glucose output remained unaffected (165±31 vs 178±28 µmol·kg^–1·min^–1, obese vs lean mice, NS). The metabolic clearance rate of glucose was significantly lower in obese mice (8±2 vs 18±2 ml·kg^–1·min^–1, obese versus lean mice, p<0.001). Hepatic mRNA levels of genes encoding for glucokinase and pyruvate kinase were markedly increased in ob/ob mice.Conclusions/interpretation Unaffected total hepatic glucose output in the presence of hyperinsulinaemia reflects hepatic insulin resistance in ob/ob mice, which is associated with markedly increased rates of glucose cycling. Hyperglycaemia in ob/ob mice primarily results from a decreased metabolic clearance rate of glucose.     

Sulphonylurea stimulates glucose uptake in rats through an ATP-sensitive K+ channel dependent mechanism

Summary We studied the effect of gliclazide, a second-generation sulphonylurea, on rat skeletal muscle glucose uptake using perfused hindquarter muscle preparations. Gliclazide at concentrations of 10 to 1000 g/ml increased (p<0.05) the basal glucose uptake. The effect of gliclazide on glucose uptake was immediate and dose-dependent, reaching a plateau at a concentration of 300 g/ml; the half-maximal effect was obtained between 25 and 50 g/ml. The glucose uptake stimulated by gliclazide (300–1000 g/ ml) did not differ from that achieved by 10^–9 mol/l insulin, and was lower (p<0.05) than that obtained with 10^–7 mol/l insulin. The combination of gliclazide (300 g/ml) and 10^–9 mol/l insulin produced an increase in glucose uptake (7.7±0.6 mol · g^–1 · h^–1, n=8, mean±SEM) which was higher (p<0.05) than that achieved with 10^–9 mol/l insulin (5.6±0.7 mol · g^–1 · h^–1, n=11) and not different from that obtained with 10^–7 mol/l insulin (9.8±1.0 mol · g^–1 · h^–1, n=11). Diazoxide (100 mol/l), an ATP-sensitive K⁺ channel opener, reversed the stimulatory effect of gliclazide (100 g/ml) on muscle glucose uptake from 3.1±0.4 to 0.5±0.2 mol · g^–1 · h^–1, (n=7, p<0.001). The addition of diazoxide prior to gliclazide into the perfusion medium blocked the gliclazide-induced glucose uptake by the hindquarter muscle preparations. In conclusion, gliclazide alone has an immediate stimulatory effect on glucose uptake by skeletal muscle and together with insulin has an additive effect on muscle glucose uptake. The effect of gliclazide on muscle glucose uptake seems to be due to the inhibition of ATP-sensitive K⁺ channels.Abbreviations NIDDM Non-insulin-dependent diabetes mellitus - GLUT glucose transporter     

ACE-inhibition increases hepatic and extrahepatic sensitivity to insulin in patients with Type 2 (non-insulin-dependent) diabetes mellitus and arterial hypertension

Summary To assess the effects of ACE-inhibition on insulin action in Type 2 (non-insulin-dependent) diabetes mellitus associated with essential hypertension, 12 patients with Type 2 diabetes (on diet and oral hypoglycaemic agents) and arterial hypertension were examined on two occasions, in a single blind, cross-over study, after two days of treatment with either captopril or a placebo. The study consisted of a euglycaemic-hyperinsulinaemic clamp (two sequential steps of insulin infusion at the rates of 0.25 mU·kg^–1·min^–1 and 1 mU·kg^–1·min^–1, 2 h each step), combined with an infusion of 3-³H-glucose to measure the rate of hepatic glucose production and that of peripheral glucose utilization. The results show that blood pressure was lower after captopril (sitting, systolic 148±5 mmHg, diastolic 89±2 mm Hg) compared to placebo (155±6 and 94±2 mm Hg) (p<0.05). Captopril treatment resulted in a more suppressed hepatic glucose production (2.7±0.4 vs 4.94±0.55 mol·kg^–1·min^–1), and a lower plasma non-esterified fatty acid concentration (0.143±0.05 vs 0.200±0.05 mmol/l) (captopril vs placebo, p<0.05) at the end of the first step of insulin infusion (estimated portal plasma insulin concentration 305±28 pmol/l); and in a greater glucose utilization (36.5±5.1 vs 28±3.6mol·kg^–1·min^–1, p<0.001) at the end of the second step of insulin infusion (arterial plasma insulin concentration of 604±33 pmol/l). We conclude that captopril improved insulin sensitivity in Type 2 diabetes associated with hypertension at the level of the liver and extrahepatic tissues, primarily muscle and adipose tissue. Thus, in contrast to other antihypertensive drugs such as diuretics and beta-blockers which may have a detrimental effect on insulin action, ACE-inhibitors appear to improve insulin action in Type 2 diabetes and essential hypertension, at least on a short-term basis.     

Changes of lipolytic enzymes cluster with insulin resistance syndrome

Summary The activities of hepatic and lipoprotein lipase and the levels of lipo- and apoproteins were compared in two groups of normoglycaemic men representing the highest (n=18) and lowest (n=15) fasting insulin quintiles of first degree male relatives of non-insulin-dependent diabetic patients. The high insulin group representing insulin-resistant individuals had significantly lower post-heparin plasma lipoprotein lipase activity than the low insulin group (14.2±4.0 vs 20±5.8 mol NEFA·ml^–1·h^–1, p<0.001); hepatic lipase activity did not differ between the two groups (24.2±11 vs 18.0±5.3 mol NEFA·ml^–1·h^–1, NS). The lipoprotein lipase/hepatic lipase ratio in the high insulin group was decreased by 66% as compared to the low insulin group (0.75±0.57 vs 1.25±0.65, p<0.01). In the high insulin group both total and VLDL triglycerides were higher than in the low insulin group (1.61±0.57 vs 0.86±0.26 mmol/l, p< 0.001 and 1.00±0.47 vs 0.36±0.16 mmol/l, p<0.001, respectively) whereas HDL cholesterol and HDL₂ cholesterol were lower (1.20±0.30 vs 1.43±0.22 mmol/l, p<0.05 and 0.49±0.21 vs 0.71±0.17 mmol/l, p<0.05, respectively). Total cholesterol, LDL cholesterol or HDL₃ cholesterol did not differ between the two groups. The mean particle size of LDL was smaller in the high insulin group than in the low insulin group (258±7 vs 265±6 å, p<0.05). We propose that the changes of lipoprotein lipase and lipoprotein lipase/hepatic lipase ratio cluster with insulin resistance and provide a possible mechanism to explain the lowering of HDL cholesterol and elevation of triglyceride concentrations observed in insulin-resistant subjects.Abbreviations LPL Lipoprotein lipase - HL hepatic lipase - VLDL very low density lipoprotein - IDL intermediate density lipoprotein - LDL low density lipoprotein - HDL high density lipoprotein - chol cholesterol - TG triglycerides - NEFA non-esterified fatty acids     

In vivo insulin action and muscle glycogen synthase activity in Type 2 (non-insulin-dependent) diabetes mellitus: effects of diet treatment

Summary Insulin resistant glucose metabolism is a key element in the pathogenesis of Type 2 (non-insulin-dependent) diabetes mellitus. Insulin resistance may be of both primary (genetic) and secondary (metabolic) origin. Before and after diet-induced improvement of glycaemic control seven obese patients with newly-diagnosed Type 2 diabetes were studied with the euglycaemic clamp technique in combination with indirect calorimetry and forearm glucose balance. Muscle biopsies were obtained in the basal state and again after 3 h of hyperinsulinaemia (200 mU/l) for studies of insulin receptor and glycogen synthase activities. Similar studies were performed in seven matched control subjects. Insulin-stimulated glucose utilization improved from 110±11 to 183±23 mg·m^–2·min^–1 (p<0.03); control subjects: 219+23 mg·m^–2·min^–1 (p=NS, vs post-diet Type 2 diabetes). Nonoxidative glucose disposal increased from 74±17 to 138+19 mg·m^–2·min^–1 (p<0.03), control subjects: 159±22 mg· m^–2·m^–1 (p=NS, vs post-diet Type 2 diabetic patients). Forearm blood glucose uptake during hyperinsulinaemia increased from 1.58±0.54 to 3.35±0.23 mol·l^–1·min^–1 (p<0.05), control subjects: 2.99±0.86 mol·l^–1·min^–1 (p=NS, vs post-diet Type 2 diabetes). After diet therapy the increase in insulin sensitivity correlated with reductions in fasting plasma glucose levels (r=0.97, p<0.001), reductions in serum fructosamine (r=0.77, p<0.05), and weight loss (r=0.78, p<0.05). Values of muscle glycogen synthase sensitivity to glucose 6-phosphate (A_0.5 for glucose 6-phosphate) were similar in the basal state. However, insulin stimulation of glycogen synthase was more pronounced after diet treatment (A_0.5: 0.43±0.06 (before) vs 0.30±0.04 mmol/l (after); p<0.03; control subjects: 0.22±0.03 mmol/l). Muscle insulin receptor binding and kinase activity were similar before and after diet treatment and comparable to values in the control group. The data suggest that impaired insulin stimulation of in vivo glucose turn-over and muscle glycogen synthase activity tend to be restored during successful diet treatment of patients with Type 2 diabetes.     

Liver and muscle insulin sensitivity,glycogen concentration and glycogen synthase activity in a rat model of non-insulin-dependent diabetes

Summary Mild diabetes was induced in adult rats with streptozotocin (45 mg/kg body weight), and insulin sensitivity, glycogen deposition and glycogen synthase activity assessed in liver and muscle 5 weeks later. Diabetic rats had significantly elevated fasting blood glucose concentrations (5.6±0.1 versus 3.6±0.1 mmol/l, p<0.001), and blood glucose concentrations 2 h after a 1 g/kg glucose load (12.0±0.6 versus 3.7±0.2 mmol/l, p<0.001). After a 20-h fast hepatic glucose output was significantly elevated (58±3 versus 47±3 mol·min^–1·kg^–1, p<0.05), and failed to suppress at high insulin concentrations during a euglycaemic clamp (hepatic glucose output 21±4 versus 2±4 mol·min^–1·kg^–1, p<0.02). Liver glycogen was lower in the diabetic rats by the end of the clamp (16±3 versus 38±6 mol/g wet wt, p<0.05). At the end of the clamp total glucose turnover was lower in the diabetic rats (107±4 versus 161±17 mol·min^–1· kg^–1, p<0.01), as was skeletal muscle glycogen synthase activity (0.46±0.04 versus 0.67±0.05 U/g wet wt, p<0.01) and glycogen concentration (22±2 versus 33±3 mol/g wet wt, p<0.05). Blood lactate and pyruvate responses suggested that glycolytic pathways were similarly affected. Thus, insulin insensitivity develops in both liver and skeletal muscle after 5 weeks of mild streptozotocin-induced diabetes.     

Insulin resistance in Type 2 (non-insulin-dependent) diabetic patients with hypertriglyceridaemia

Summary Hypertriglyceridaemia, which is frequently seen in Type 2 (non-insulin-dependent) diabetes mellitus, is associated with insulin resistance. The connection between hypertriglyceridaemia and insulin resistance is not clear, but could be due to substrate competition between glucose and lipids. To address this question we measured glucose and lipid metabolism in 39 Type 2 diabetic patients with hypertriglyceridaemia, i. e. mean fasting serum triglyceride level equal to or above 2 mmol/l (age 59±1 years, BMI 27.4±0.5 kg/m², HbA_1c8.0±0.2%, serum triglycerides 3.2±0.2 mmol/l) and 41 Type 2 diabetic patients with normotriglyceridaemia, i. e. mean fasting serum triglyceride level below 2 mmol/l (age 58±1 years, BMI 27.0±0.7 kg/m², HbA_1c7.8±0.2 %, serum triglycerides 1.4±0.1 mmol/l). Insulin sensitivity was assessed using a 340 pmol·(m²)^–1· min^–1 euglycaemic insulin clamp. Substrate oxidation rates were measured with indirect calorimetry and hepatic glucose production was estimated using a primed (25 Ci)-constant (0.25 Ci/min) infusion of [3-³H]-glucose. Suppression of lipid oxidation by insulin was impaired in patients with hypertriglyceridaemia vs patients with normal triglyceride levels (3.5±0.2 vs 3.0±0.2mol·kg^–1· min^–1; p<0.05). Stimulation of glucose disposal by insulin was reduced in hypertriglyceridaemic vs normotriglyceridaemic patients (27.0±1.3 vs 31.9±1.6 mol·kg^–1·min^–1; p<0.05) primarily due to impaired glucose storage (9.8±1.0 vs 14.6±1.4mol·kg^–1·min^–1; p<0.01). In contrast, insulinstimulated glucose oxidation was similar in patients with hypertriglyceridaemia and in patients with normal triglyceride concentrations (16.9±0.8 vs 17.2±0.7mol·kg^–1·min^–1). Hepatic glucose production in the basal state and during the clamp did not differ between the two groups. We conclude therefore that oxidative substrate competition between glucose and lipids does not explain insulin resistance associated with hypertriglyceridaemia in Type 2 diabetes. The question remains whether the reduced nonoxidative glucose disposal observed in the patients with hypertriglyceridaemia is genetically determined or a consequence of increased lipid oxidation.     

Intracerebroventricular administration of melanotan II increases insulin sensitivity of glucose disposal in mice

Aims/hypothesis The present study was conducted to evaluate the effects of central administration of melanotan II (MTII), a melanocortin-3/4 receptor agonist, on hepatic and whole-body insulin sensitivity, independent of food intake and body weight.Methods Over a period of 24 h, 225 ng of MTII was injected in three aliquots into the left lateral ventricle of male C57Bl/6 mice. The animals had no access to food. The control group received three injections of distilled water. Whole-body and hepatic insulin sensitivity were measured by hyperinsulinaemic–euglycaemic clamp in combination with [³H]glucose infusion. Glut4 mRNA expression was measured in skeletal muscle.Results Plasma glucose and insulin concentrations under basal and hyperinsulinaemic conditions were similar in MTII- and placebo-treated mice. Endogenous glucose production (EGP) and glucose disposal in the basal state were significantly higher in MTII-treated mice than in the control group (71±22 vs 43±12 mol·min^–1·kg^–1, p<0.01). During hyperinsulinaemia, glucose disposal was significantly higher in MTII-treated mice (151±20 vs 108±20 mol·min^–1·kg^–1, p<0.01). In contrast, the inhibitory effect of insulin on EGP was not affected by MTII (relative decrease in EGP: 45±27 vs 50±20%). Glut4 mRNA expression in skeletal muscle was significantly increased in MTII-treated mice (307±94 vs 100±56%, p<0.01).Conclusions/interpretation Intracerebroventricular administration of MTII acutely increases insulin-mediated glucose disposal but does not affect the capacity of insulin to suppress EGP in C57Bl/6 mice. These data indicate that central stimulation of melanocortin-3/4 receptors modulates insulin sensitivity in a tissue-specific manner, independent of its well-known impact on feeding and body weight.     

Increased glucose carbon recycling in severely insulin deficient Type 1 (insulin-dependent) diabetic subjects

Summary Six Type 1 (insulin-dependent) diabetic subjects were studied in order to determine the contribution of recycling of glucose carbon to the overproduction of glucose which is characteristic of the fasting hyperglycaemia produced by insulin withdrawal. The subjects were studied on two occasions, once after an overnight insulin infusion and once following 24 h of insulin withdrawal. The difference in turnover rates of 1-¹⁴C-glucose and 3-³H-glucose was used as a measure of glucose recycling. Insulin withdrawal caused a marked metabolic derangement with a rise in non-esterified fatty acids from 0.69±0.23 to 1.11±0.21 mmol/l (mean±SEM, p<0.05), total ketones from 0.27±0.06 to 2.06±0.51 mmol/l (p<0.01), cortisol from 341±43 to 479±31 nmol/l (p<0.05) and growth hormone from 1.1±0.3 to 19+5-mu/l (p<0.05). Glucose turnover rose from 13.8±2.3 mol·kg^–1·min^–1 at a glucose of 6.9±0.7 mmol/l in the insulin infused study to 25.8±4.4 mol·kg^–1·min^–1 (p<0.05) at a glucose of 16.4±0.7 mmol/l in the insulin withdrawn study. Recycling also rose from 3.0±0.4 mol· kg^–1·min^–1 to 9.4±2.2 mol·kg^–1·min^–1 (p<0.05) when insulin withdrawn, accounting for 23±3% and 36±3% of glucose turnover, respectively. We conclude that in the severely insulin deficient Type 1 diabetic subject recycling of glucose carbon is a major contributor to the excess glucose production.     

Effect of dexamethasone on insulin sensitivity,islet amyloid polypeptide and insulin secretion in humans

Summary The response of islet amyloid polypeptide and insulin and their molar ratios were investigated in eight healthy volunteers before and after treatment with dexamethasone by oral and frequently-sampled intravenous glucose tolerance tests. Following dexamethasone treatment the insulin sensitivity index decreased significantly from 6.5±1.3 to 4.1±1.0 (U·ml^–1·min^–1, p<0.05. The area under the curve representing above-basal levels of insulin during oral glucose tolerance test increased significantly following dexamethasone treatment from 48132±9736 to 82230±14846 pmol·l^–1·3 h^–1, p<0.05, the area under the curve of islet amyloid polypeptide increased from 1308±183 to 2448±501 pmol·l^–1·3h^–1, p<0.05. The overall insulin/islet amyloid polypeptide molar ratios calculated from the area under the curve during the 3-h period of the oral glucose tolerance test was not significantly different before and after dexamethasone treatment (42±5 vs 40±4). During the oral glucose tolerance test the insulin/islet amyloid polypeptide ratio increased significantly from baseline to 30 min (p<0.05), then declined towards initial values before and after dexamethasone treatment. In conclusion, dexamethasone induced a significant decrease in insulin sensivity and a significant increase in insulin secretion during the oral glucose tolerance test. However, in contrast to previous animal experiments we did not find a change in the insulin/islet amyloid polypeptide ratio before and after dexamethasone treatment.     

Insulin resistance in Type 1 (insulin-dependent) diabetes following hypoglycaemia — evidence for the importance of β-adrenergic stimulation

Summary The insulin effect, evaluated with the euglycaemic clamp technique, was studied before and after hypoglycaemia in 7 patients with Type 1 (insulin-dependent) diabetes. Following an initial 2 h clamp (clamp I) hypoglycaemia was induced and 2 h later a second clamp (clamp II), identical to the former, was performed. Each subject was studied twice; during infusion with saline (placebo) or propranolol. Glucose production and disposal were studied with the 3(³H)glucose technique. During placebo infusion, hypoglycaemia elicited an insulin resistance leading to approx. 50% reduction in the steady state glucose infusion rate during clamp II as compared to clamp I (clamp I 2.58±0.32, clamp II 1.26±0.08 mg·kg^–1·min^–1, p<0.02). The insulin resistance was prevented by infusing propranolol (clamp I 2.29±0.29, clamp II 2.85±0.56 mg·kg^–1·min^–1). The posthypoglycaemic insulin resistance was due to a less pronounced insulin effect on both glucose production (clamp I 0.29±0.21, clamp II 0.86±0.19 mg·kg^–1·min^–1, p<0.05) and glucose utilisation (clamp I 2.84±0.26, clamp II 2.13±0.23 mg·kg^–1·min^–1, p<0.05). The insulin resistance on both glucose production and utilisation was prevented by propranolol. Thus, the present study demonstrates that hypoglycaemia elicits a prolonged insulin resistance which is due to a less pronounced effect of insulin to both inhibit splanchnic glucose production and to stimulate peripheral glucose utilisation. The insulin resistance is due to -adrenergic stimulation and can be prevented by propranolol.     

Diabetic background retinopathy is associated with impaired coronary vasoreactivity in people with Type 1 diabetes

Aims/hypothesis We examined whether diabetic background retinopathy is associated with reduced coronary vasoreactivity in people with Type 1 diabetes.Methods A total of 21 men with Type 1 diabetes were investigated, including 9 men with background retinopathy and 12 men without retinopathy. In addition, 12 non-diabetic, age-matched subjects were studied. All subjects were non-smokers, otherwise healthy and had no other diabetic complications. Resting myocardial blood flow and hyperaemic dipyridamole-stimulated flow (dipyridamole, 0.56 mg/kg during a 4-min period), a measure of coronary vasoreactivity, were measured during euglycaemic hyperinsulinaemic clamp (1 mU·kg^–1·min^–1) using positron emission tomography and oxygen-15-labelled water.Results Resting myocardial blood flow (0.82±0.13 vs 0.96±0.23 vs 0.88±0.25 ml·g^–1·min^–1, with vs without retinopathy vs non-diabetic subjects) and coronary vascular resistance (111.2±23.4 vs 95.5±15.8 vs 101.9±31.5 mmHg·min·g·ml^–1 respectively) were not significantly different between the groups. Dipyridamole infusion induced an increase in blood flow and a decrease in coronary vascular resistance in all study subjects (p<0.001). However, dipyridamole-stimulated flow and coronary vascular resistance were blunted in diabetic patients with retinopathy (2.9±0.9 ml·g^–1·min^–1 and 34.1±11.3 mmHg·min·g·ml^–1) when compared to diabetic patients without retinopathy (4.0±1.3 ml·g^–1·min^–1, p=0.04 and 24.6±7.5 mmHg·min·g·ml^–1, p=0.03) or non-diabetic subjects (4.5±1.4 ml·g^–1·min^–1, p=0.008 and 22.2±8.7 mmHg·min·g·ml^–1, p=0.01). Myocardial flow reserve was impaired in diabetic patients with retinopathy (3.6±1.0) when compared to non-diabetic subjects (5.3±1.9, p=0.02) but not significantly reduced when compared to diabetic patients without retinopathy (4.2±1.4, p=0.2).Conclusions/interpretation Diabetic background retinopathy appears to be associated with impaired coronary vasoreactivity in young people with Type 1 diabetes.Abbreviations PET positron emission tomography - [¹⁵O]H₂O oxygen-15-labelled waterJ. Sundell and T. Janatuinen contributed equally to this work     

Insulin-like growth factor-I in man enhances lipid mobilization and oxidation induced by a growth hormone pulse

Summary Growth hormone (GH) secretion is suppressed during insulin-like growth factor-I (IGF-I) administration. The aim of the study was to examine whether IGF-I alters the metabolic response to a GH pulse. Seven healthy male subjects (age 27±4 years, BMI 21.8±1.7 kg/m²) were treated with NaCl 0.9% (saline) or IGF-I (8 g · kg^–1 · h^–1) for 5 days by continuous subcutaneous infusion in a randomized, crossover fashion while receiving an isocaloric diet (30 kcal · kg^–1 · day^–1). On the third treatment day an intravenous bolus of 0.5 U GH was administered. Forearm muscle metabolism was examined by measuring arterialized and deep venous blood samples, forearm blood flow by occlusion plethysmography and substrate oxidation by indirect calorimetry. IGF-I treatment significantly reduced insulin concentrations by 80% (p<0.02) and C-peptide levels by 78% (p<0.02), as assessed by area under the curve. Non-esterified fatty acid (NEFA), glycerol and 3-OH-butyrate levels were elevated and alanine concentration decreased. Forearm blood flow rose from 2.10±0.43 (saline) to 2.79±0.37 ml · 100ml^–1 · min^–1 (IGF-I) (p<0.02). GH-pulse: 10 h after i.v. GH injection serum GH peaked at 40.9±7.4 ng/ml. GH did not influence circulating levels of total IGFI, C-peptide, insulin or glucose, but caused a further increase in NEFA, glycerol and 3-OH-butyrate levels, indicating enhanced lipolysis and ketogenesis. This effect of GH was much more pronounced during IGF-I: NEFA rose from 702±267 (saline) and 885±236 (IGF-I) to 963±215 (saline) (p<0.05) and 1815±586 mol/l (IGF-I) (p<0.02), respectively; after 5 h, 3-OH-butyrate rose from 242±234 (saline) and 340±280 (IGF-I) to 678±638 (saline) (p<0.02) and 1115±578 mol/l (IGF-I) (p<0.02) respectively. After injection of GH, forearm uptake of 3-OH-butyrate was markedly elevated only in the subjects treated with IGF-I: from 44±195 to 300±370 after 20 min (p<0.03) and to 287±91 nmol · 100 ml^–1 · min^–1after 120 min (p<0.02). In conclusion, the lipolytic and ketogenic response to GH was grossly enhanced during IGF-I treatment, and utilization of ketone bodies by skeletal muscle was increased.Abbreviations AUC Area under the curve - C-peptide connecting peptide - EE energy expenditure - FFM fat-free mass - GH growth hormone - IGF-I insulin-like growth factor-I - NEFA non-esterified fatty acid - Ra rate of glucose appearance - Rd rate of glucose disposal - FGU forearm glucose uptake - CV coefficient of variation     

Pharmacokinetics,pharmacodynamics and glucose counterregulation following subcutaneous injection of the monomeric insulin analogue [Lys(B28),Pro(B29)] in IDDM

Summary The aim of these studies was to compare the pharmacokinetics, pharmacodynamics, counterregulatory hormone and symptom responses, as well as cognitive function during hypoglycaemia induced by s. c. injection of 0.15 IU/kg of regular human insulin (HI) and the monomeric insulin analogue [Lys(B28),Pro (B29)] (MI) in insulin-dependent-diabetic (IDDM) subjects. In these studies glucose was infused whenever needed to prevent decreases in plasma glucose below 3 mmol/l. After MI, plasma insulin increased earlier to a peak (60 vs 90 min) which was greater than after HI (294±24 vs 255±24 pmol/l), and plasma glucose decreased earlier to a 3 mmol/l plateau (60 vs 120 min) (p<0.05). The amount of glucose infused to prevent plasma glucose falling below 3 mmol/l was three times greater after MI than HI (293±26 vs 90±25 mol · kg^–1 · 60–375 min^–1, p<0.05). After MI, hepatic glucose production was more suppressed (0.7±1 vs 5.9±0.54 mol · kg^–1 · min^–1) and glucose utilization was less suppressed than after HI (11.6±0.65 vs 9.1±0.11mol · kg^–1 · min^–1) (p<0.05). Similarly, plasma NEFA, glycerol, and -OH-butyrate were more suppressed after MI than HI (p<0.05), whereas plasma lactate increased only after MI, but not after HI. Responses of counterregulatory hormones, symptoms and deterioration in cognitive function during plasma glucose plateau of 3 mmol/l were superimposable after MI and HI (p=NS). Post-hypoglycaemia hyperglycaemia was greater after MI than HI (at 480 min 12.1±1 vs 11±1 mmol/l) because of greater hepatic glucose production during insulin waning which occurred at least 135 min earlier with MI as compared to HI (p<0.05). It is concluded that counterregulatory hormones, symptoms and deterioration in cognitive function during hypoglycaemia respond similarly after MI and HI. The biological effect of MI appears greater than that of HI for at least 4 h after the s.c. injection and appears as a good candidate for achieving optimal post-prandial glucose control in IDDM.Abbreviations HI Human insulin - MI monomeric insulin - NEFA non-esterified fatty acid - HGO hepatic glucose production rate - -OH-butyrate -hydroxy-butyrate - IDDM insulin-dependent diabetes mellitus - NIDDM non-insulin-dependent diabetes mellitus     

Factors associated with basal metabolic rate in patients with Type 2 (non-insulin-dependent) diabetes mellitus

Summary To examine determinants of basal metabolic rate we studied 66 Type 2 (non-insulin-dependent) diabetic and 24 healthy age- and weight-matched control subjects with indirect calorimetry and infusion of [³H-3-] glucose. Eight Type 2 diabetic patients were re-studied after a period of insulin therapy. Basal metabolic rate was higher in Type 2 diabetic patients than in control subjects (102.8 ± 1.9 J · kg LBM^–1-min^–1 vs 90.7 ± 2.8 J · kg LBM^–1;min^–1; p<0.01) and decreased significantly with insulin therapy (p <0.01). The basal rate of hepatic glucose production was higher in Type 2 diabetic patients than in control subjects (1044.0 ± 29.9 vs 789.3 ± 41.7 mol/min; p <0.001) and decreased after insulin therapy (p <0.01). Hepatic glucose production correlated positively with basal metabolic rate both in Type 2 diabetic patients (r = 0.49; p <0.001) and in control subjects (r = 0.50; p<0.05). Lipid oxidation was increased in Type 2 diabetic patients compared with control subjects (1.68 ± 0.05 vs 1.37 ± 0.08 mol · kg LBM^–1 · min^–1'; p <0.01) and decreased significantly after insulin therapy (p <0.05). The rate of lipid oxidation correlated positively with basal metabolic rate both in Type 2 diabetic patients (r = 0.36; p <0.01) and in control subjects (r = 0.51; p <0.01). These data demonstrate that basal metabolic rate, rates of hepatic glucose production and lipid oxidation are interrelated in Type 2 diabetic patients. A reduction of the hepatic glucose production, however, is associated with a reduction in lipid oxidation, which in turn, may result in a reduction in basal metabolic rate.