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.     

Serum adiponectin levels predict the effect of short-term dietary interventions on insulin sensitivity in humans

Aims/hypothesis Fat-rich diets can acutely induce insulin resistance. Data from adiponectin knock-out mice suggest that this effect might be increased in the absence of adiponectin. In the present study we tested whether plasma adiponectin concentrations influence changes in insulin sensitivity induced by a short-term dietary intervention in humans.Methods We analysed data from 27 healthy, non-obese men with normal glucose tolerance. These men ate a diet high in fat and a diet high in carbohydrates for three days each.Results The high-fat diet induced a significant drop in insulin sensitivity (determined by euglycaemic–hyperinsulinaemic clamp) compared to baseline (0.100±0.009 vs 0.083±0.007 µmol·kg^–1·min^–1·(pmol·l^–1), p=0.01). The drop in insulin sensitivity was more pronounced in subjects with low serum adiponectin (0.094±0.011 vs 0.077±0.010 µmol·kg^–1·min^–1·(pmol·l^–1), p=0.02) than in subjects with high serum adiponectin (0.103±0.011 vs 0.090±0.040 µmol·kg^–1·min^–1·(pmol·l^–1), p=0.16). In the whole group the high-carbohydrate, low-fat diet did not cause an increase in insulin sensitivity (0.095±0.007 vs 0.102±0.009 µmol·kg^–1·min^–1·(pmol·l^–1), p=0.06). However, insulin sensitivity was significantly increased in the subgroup with low serum adiponectin levels (0.084±0.013 vs 0.099±0.018 µmol·kg^–1·min^–1·(pmol·l^–1), p=0.01). In an additional multivariate analysis post-intervention insulin sensitivity was predicted by pre-intervention insulin sensitivity (p<0.001) and adiponectin concentrations (p=0.001).Conclusions/interpretation These data indicate that the reduction in insulin sensitivity achieved by a short-term high-fat diet is more pronounced in non-obese subjects with low serum adiponectin. Thus it is possible that the restriction of dietary fat and a diet high in carbohydrates might be particularly effective in subjects with low adiponectin such as obese or Type 2 diabetic individuals.     

Multiple defects of both hepatic and peripheral intracellular glucose processing contribute to the hyperglycaemia of NIDDM

Summary Non-insulin-dependent diabetic (NIDDM) patients were studied during a modified euglycaemic state when fasting hyperglycaemia was normalized by a prior (–210 to –150 min) — and later withdrawn (–150–0 min) — intravenous insulin infusion. Glucose metabolism was assessed in NIDDM patients (n=10) and matched control subjects (n=10) using tritiated glucose turnover rates, indirect calorimetry and skeletal muscle glycogen synthase activity determinations. Total and non-oxidative exogenous glycolytic flux rates were measured using appearance rates of tritiated water. A+180 min euglycaemic hyperinsulinaemic (40 mU·m^–2·min^–1) clamp was performed to determine the insulin responsiveness of the various metabolic pathways. Plasma glucose concentration increased spontaneously during baseline measurements in the NIDDM patients (–120 to 0 min: 4.8±0.3 to 7.0±0.3 mmol/l; p<0.01), and was primarily due to an elevated rate of hepatic glucose production (3.16±0.13 vs 2.51±0.16 mg·kg FFM^–1·min^–1; p<0.01). In the NIDDM subjects baseline glucose oxidation was decreased (0.92±0.17 vs 1.33±0.14 mg·kg FFM^–1·min^–1; p<0.01) in the presence of a normal rate of total exogenous glycolytic flux and skeletal muscle glycogen synthase activity. The simultaneous finding of an increased lipid oxidation rate (1.95±0.13 vs 1.61±0.07 mg·kg FFM^–1·min^–1; p=0.05) and increased plasma lactate concentrations (0.86±0.05 vs 0.66±0.03 mmol/l; p=0.01) are consistent with a role for both the glucose-fatty acid cycle and the Cori cycle in the maintenance and development of fasting hyperglycaemia in NIDDM during decompensation. Insulin resistance was demonstrated during the hyperinsulinaemic clamp in the NIDDM patients with a decrease in the major peripheral pathways of intracellular glucose metabolism (oxidation, storage and muscle glycogen synthase activity), but not in the pathway of non-oxidative glycolytic flux which was not completely suppressed during insulin infusion in the NIDDM patients (0.55±0.15 mg·kg FFM^–1·min^–1; p<0.05 vs 0; control subjects: 0.17±0.29; NS vs 0). Thus, these data also indicate that the defect(s) of peripheral (skeletal muscle) glucose processing in NIDDM goes beyond the site of glucose transport across the cell membrane.Abbreviations NIDDM Non-insulin-dependent diabetes mellitus - FFM fat free mass - HGP hepatic glucose production - R_d peripheral glucose disposal (uptake) rate - G6P glucose 6-phosphate - UDPG uridine diphosphate glucose - FV fractional velocity     

The activity of the renin-angiotensin-aldosterone system before and during submaximal bicycle exercise in relation to circulatory catecholamines in patients with Type 1 (insulin-dependent) diabetes mellitus

Summary To evaluate the renin-angiotensin-aldosterone system in relation to circulatory catecholamines, we determined renin activity, angiotensin II, aldosterone, adrenaline, and noradrenaline in plasma before and during a submaximal bicycle exercise test in 23 Type 1 (insulin-dependent) diabetic patients (aged 19–57 years, mean 37; duration of diabetes 2–32 years, mean 16), 17 with signs of cardiac autonomic neuropathy, and in 18 healthy non-diabetic subjects (aged 24–41 years, mean 29). At rest, Type 1 diabetic patients showed significantly lower aldosterone values than control subjects (0.14±0.02 nmol/l and 0.22±0.02 nmol/l; p<0.01) while renin activity (1.0±0.1 nmol·l^–1·h^–1 and 0.9±0.1 nmol·l^–1·h^–1) and angiotensin II (14±1 nmol/l and 18±2 nmol/l) did not differ significantly between patients and control subjects. During exercise, increments (increase from the resting value to the value at 80% of maximal working capacity) in renin (1.5±0.4 nmol·l^–1·h^–1 and 3.7±0.5 nmol·l^–1 ·h^–1; p<0.001), angiotensin II (28±8 nmol/l and 60±8 nmol/l; p<0.01), aldosterone (0.16±0.04 nmol/l and 0.25±0.05 nmol/l; p<0.05), adrenaline (1.96±0.49 nmol/l and 2.92±0.51 nmol/l; ps<0.05), and noradrenaline (12.01±1.25 nmol/l and 18.74±1.45 nmol/l; p<0.01) were significantly lower in the patients than in control subjects. There was no difference in the renin-angiotensin-aldosterone response to exercise between patients with and without cardiac autonomic neuropathy but the impaired catecholamine reaction was confined to patients with cardiac autonomic neuropathy. In conclusion, Type 1 diabetic patients demonstrated low resting plasma aldosterone and reduced increments in renin activity, angiotensin II, aldosterone, and catecholamines during exercise. The low aldosterone values might be related to dysfunction of adrenal zona glomerulosa cells while it is unlikely that the reduced response to exercise of the renin-angiotensin-aldosterone system simply reflects sympathetic nerve failure.     

Contrasting metabolic effects of continuous and pulsatile growth hormone administration in young adults with Type 1 (insulin-dependent) diabetes mellitus

Summary Plasma growth hormone profiles in adolescents with Type 1 (insulin-dependent) diabetes mellitus are characterized by both increases in pulse amplitude and higher baseline concentrations. To determine which of these abnormalities adversely affect metabolic control, we studied six young adults overnight on three occasions. On each night somatostatin (50–100 g·m^2–1·h^–1) and glucagon (1ng· kg^–1·min^–1) were infused continuously and 18mU/kg of growth hormone was given as either: three discrete pulses of 6 mU·kg^–1· h^–1 at 180-min intervals or a 12-h infusion (1.5 mU·kg^–1· h^–1) or buffer solution only on a control night. Euglycaemia was maintained by an insulin-varying clamp. Blood samples were taken every 15 min for glucose and growth hormone and every hour for intermediate metabolites and non-esterified fatty acids. Comparable normoglycaemic conditions were achieved on all three nights. Growth hormone levels achieved (mean±SEM) on study nights were: 32.8±2.2 mU/l (peak level during growth hormone pulses); 9.8± 0.8 mU/l (continuous growth hormone) and 1.1±0.3 mU/l (control level). Pulsatile growth hormone administration led to an increase in insulin requirements (mean±SEM: 0.17±0.03 vs control 0.09±0.01 mU·kg^–1· min^–1, p < 0.05) whereas insulin requirements following continuous growth hormone administration were unchanged. Cross-correlation confirmed an increase in insulin requirements occurring 135 min after a growth hormone pulse (r=0.21, p < 0.001). Growth hormone administration (continuous and pulsatile) led to a significant increase in B-hydroxybutyrate levels compared to the control night: 0.21±0.01 mmol/l (mean±SEM), 0.29±0.01 mmol/l, 0.08±0.01 mmol/l (p< 0.001) during the night with pulsatile growth hormone, continuous growth hormone and control respectively. Mean plasma non-esterified fatty acids were also increased following growth hormone administration: 0.94±0.04 mmol/l (mean±SEM), 1.09±0.07 mmol/l, 0.61±0.05 mmol/l (p<0.003), during the night with pulsatile growth hormone, continuous growth hormone and control respectively. It appears that the pulsatile and baseline growth hormone signals have contrasting metabolic effects in young adults with Type 1 diabetes mellitus.     

Association between left ventricular hypertrophy and erythrocyte sodium-lithium exchange in normotensive subjects with and without NIDDM

Summary The determinants of left ventricular mass in normal control subjects and subjects with non-insulindependent diabetes (NIDDM) are ill-defined. We therefore recorded M-mode and pulsed Doppler echocardiograms and 24-h ambulatory blood pressure in 57 normotensive subjects, 34 with NIDDM and 23 matched non-diabetic control subjects. Measurements of erythrocyte sodium-lithium countertransport, plasma angiotensin II, plasma and platelet catecholamines and fasting plasma insulin were also made. Six control subjects (26%) and 15 diabetic subjects (44%) had some degree of left ventricular hypertrophy. Subjects with left ventricular hypertrophy (n=21) had an elevated mean rate of sodium-lithium countertransport (0.40±0.13 vs 0.31±0.09 mmol·l^–1 ·h^–1; p<0.01), parallel differences being observed in both the diabetic and control groups. Twelve of the subjects with left ventricular hypertrophy (57%) had elevated rates of sodium-lithium counter-transport compared to only seven (19%) of those without (p<0.05). There was no consistent difference between those with and without left ventricular hypertrophy in any other clinical or biochemical variable. Multivariate analysis, with the presence or absence of left ventricular hypertrophy as the dependent variable, demonstrated that the maximal rate of sodium-lithium countertransport was the only variable that independently contributed to left ventricular hypertrophy (partial r=0.35; F _1.55=7.74; p = 0.007). This study demonstrates for the first time an association between left ventricular hypertrophy and erythrocyte membrane cation transport that is independent of hypertension, is present in both diabetic and non-diabetic groups, and may represent a link between elevated rates of membrane sodium transport and cardiovascular risk.Abbreviations Na-Li CT Sodium-lithium countertransport - LVH left ventricular hypertrophy - AER urinary albumin excretion rate     

Peripheral and hepatic insulin sensitivity in subjects with impaired glucose tolerance

Summary Recent evidence suggests that the post-prandial hyperglycaemia in impaired glucose tolerance is primarily due to impaired suppression of basal hepatic glucose output. This in turn appears to be secondary to decreased first phase insulin secretion, although decreased hepatic insulin sensitivity, which is a feature of non-insulin-dependent diabetes mellitus, might also play a role. Eight mildly overweight subjects with impaired glucose tolerance and eight closely matched control subjects with normal glucose tolerance underwent an intravenous glucose tolerance test to assess first phase insulin secretion. Insulin sensitivity was examined by a 150-min hyperinsulinaemic-euglycaemic clamp. Somatostatin was infused from 150 min to suppress endogenous insulin secretion, and glucagon and insulin were replaced by constant infusion. Glucose with added dideuterated glucose (labelled infusion technique) was infused to maintain euglycaemia. First phase insulin secretion ( 0–10 min insulin area ÷ 0–10 min glucose area) was significantly decreased in the subjects with impaired glucose tolerance (median [range]: 1.2 [0.2–19.4] vs 9.1 [2.6–14.5] mU·mmol^–1; p<0.01). During the clamp, circulating insulin (93±8 [mean±SEM] and 81±10 mU·l^–1) and glucagon (54±4 and 44±6 ng·l^–1) levels were comparable. Total glucose disposal was decreased in subjects with impaired glucose tolerance (2.78±0.27 vs 4.47±0.53 mg·kg^–1·min^–1; p<0.02), and was primarily due to decreased non-oxidative glucose disposal. However, hepatic glucose output rates were comparable during the clamp (0.38±0.10 and 0.30±0.18 mg·kg^–1·min^–1). Therefore, the main defects in subjects with impaired glucose tolerance are decreased first phase insulin secretion and peripheral non-oxidative glucose disposal, but hepatic glucose output shows normal responsiveness to insulin.Abbreviations FPIS First phase insulin secretion - PG plasma glucose - NIDDM non-insulin-dependent diabetes mellitus - IGT impaired glucose tolerance - HGO hepatic glucose output - IVGTT intravenous glucose tolerance test - OGTT oral glucose tolerance test     

Basal and 24-h C-peptide and insulin secretion rate in normal man

Summary An understanding of the metabolic abnormalities rising from inappropriate insulin delivery in diabetic patients demands a knowledge of 24-h and basal insulin secretion rates in normal man. We have used biosynthetic human C-peptide to determine its kinetic parameters in 10 normal subjects and applied these to measurements of plasma concentrations in the same subjects to determine pancreatic secretion rate. Metabolic clearance rate measured by stepped primed infusion of biosynthetic human C-peptide at rates of 10, 19 and 26nmol/h was 4.7±0.7 (±SD) ml·kg^–1·min^–1, and was independent of infusion rate. Fractional clearance (T_1/2, 26±3 min) and distribution volume (0.178±0.039 l/kg) were calculated from the decline in concentration after cessation of the highest rate infusion. Basal insulin secretion calculated from the C-peptide metabolic clearance rate and plasma concentrations for the period 02.00 to 07.00 hours was 1.3±0.4U/h. Over 24h total insulin secretion on a standard high carbohydrate diet was 63±15 U, calculated from the area under the C-peptide concentration curve. Basal insulin secretion, therefore, accounted for 50±8% of total insulin secretion. Although only 5.6±1.1% of C-peptide was detected in 24-h urine collections, urinary C-peptide excretion was significantly related to 24-h C-peptide secretion (r=0.74,p<0.02).     

The relationship of urinary albumin excretion rate to ambulatory blood pressure and erythrocyte sodium-lithium countertransport in NIDDM

Summary Increased erythrocyte sodium-lithium countertransport rate is found in non-diabetic subjects with essential hypertension, and in insulin-dependent diabetic subjects with nephropathy. However, relationships between these variables in non-insulin-dependent diabetic subjects are ill-defined. In order to characterise the relationships between blood pressure, urinary albumin excretion, and erythrocyte sodium-lithium countertransport, 66 subjects with non-insulin-dependent diabetes were studied. Urinary albumin excretion rate correlated with mean 24-h ambulatory systolic blood pressure (r=0.57; p<0.001), but not with sodium-lithium countertransport (r=0.06; p=0.31). No significant relationship was observed between 24-h systolic blood pressure and erythrocyte sodium-lithium countertransport (r = 0.16; p=0.17). The principal differences between microalbuminuric and normoalbuminuric subjects (albumin excretion rate >15 g·min^–1 [n=20], and <15 g·min^–1, [n=46]) were: higher 24-h systolic blood pressure (145.9 [16.8] mm Hg vs 131.9 [16.8] mm Hg; p=0.006), nocturnal heart rate (72.4 [8.9] vs 67.4 [8.9] beats·min^–1; p=0.042), and HbA₁ (11.3 [1.5]% vs 10.1 [2.0]%; p=0.028), and a longer median duration of diabetes (10.0 vs 5.0 years; p = 0.02). In contrast, there was no significant difference in sodium-lithium countertransport rate between microalbuminuric (0.41 [0.18] mmol·l^–1·h^–1) and normoalbuminuric subjects (0.39 [0.15] mmol·l^–1· h^–1; p=0.687). In multiple regression analysis controlling for race, age, body mass index and HbA₁, the significant determinants of albumin excretion rate were 24-h systolic blood pressure (B [regression coefficient]=0.029, SE[B] [standard error of B]=0.009, t=2.95, p=0.005), duration of diabetes (B=0.430, SE[B]=0.169, t=2.54, p=0.016) and male gender (B=–1.170, SE[B]=0.457, t=–2.56, p=0.015). In conclusion, albumin excretion rates in non-insulin-dependent diabetic subjects are linked to hypertension and glycaemic exposure, but show no relationship to erythrocyte sodium-lithium countertransport.Abbreviations IDDM Insulin-dependent diabetes mellitus - NIDDM non-insulin dependent diabetes mellitus - SLC sodium lithium countertransport - AER albumin excretion rate - B regression - SE coefficient; standard error of B     

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.     

Sandostatin,a new analogue of somatostatin,reduces the metabolic changes induced by the nocturnal interruption of continuous subcutaneous insulin infusion in Type 1 (insulin-dependent) diabetic patients

Summary With the aim of assessing a new somatostatin analogue to prevent the metabolic changes induced by a 6-h nocturnal arrest of an insulin pump, nine C-peptide negative Type 1 (insulin-dependent) diabetic patients were submitted blindly to two interruptions (from 23.00 to 05.00 hours) of their continuous s.c. insulin infusion, once after a single s.c. injection at 23.00 hours of 50 g SMS 201-995 (Sandostatin, Sandoz) and once after 0.9% NaCl. Plasma SMS 201-995 levels peaked at 24.00 hours and then declined with an elimination half-life averaging 144±15 min. Plasma glucagon and growth hormone levels were significantly reduced after SMS 201-995 whereas the progressive fall in plasma-free insulin levels from 23.00 to 05.00 hours was unaffected. In the control test, blood glucose levels tended to decrease slightly from 23.00 to 02.00 hours and then increased markedly from 02.00 to 05.00 hours (+5.3±1.5mmol/l) while after SMS 201-995 they decreased significantly from 23.00 to 02.00 hours (–2.6±0.5 mmol/l), resulting in values below 3 mmol/l in seven subjects, but showed a secondary increase until 05.00 hours (+3.5±1.5 mmol vs 23.00h; p<0.05 vs 0.9% NaCl). While the rises in plasma non-esterified fatty acid and glycerol levels were not reduced by SMS 201-995, the increase in plasma 3-hydroxybutyrate levels, although similar from 23.00 to 02.00 hours, was significantly reduced from 02.00 to 05.00 hours (+77±20 vs+124±31 mol·l^–1·h^–1 p<0.005). Thus, SMS 201-995 significantly reduced the metabolic alterations due to a 6-h nocturnal interruption of a continuous s.c. insulin infusion but at the cost of a rather high risk of early hypoglycaemia.     

The biochemical basis of increased hepatic glucose production in a mouse model of type 2 (non-insulin-dependent) diabetes mellitus

Summary The mechanism of increased hepatic glucose production in obese non-insulin-dependent diabetic (NIDDM) patients is unknown. The New Zealand Obese (NZO) mouse, a polygenic model of obesity and NIDDM shows increased hepatic glucose production. To determine the mechanism of this phenomenon, we measured gluconeogenesis from U-¹⁴C-glycerol and U-¹⁴C-alanine and relevant gluconeogenic enzymes. Gluconeogenesis from glycerol (0.07±0.01 vs 0.21±0.02 mol · min^–1 · body mass index (BMI)^–1, p<0.005) and alanine (0.57±0.07 vs 0.99±0.07 mol · min^–1 · BMI^–1, p<0.005) was elevated in control mice NZO vs as was glycerol turnover (0.25±0.02 vs 0.63±0.09 mol · min^–1 · BMI^–1, p<0.05). Fructose 1,6-bisphosphatase activity (44.2±1.9 vs 55.7±4.1 nmol · min^–1 · mg protein^–1, p<0.05) and protein levels (6.9±1.1 vs 16.7±2.3 arbitrary units, p<0.01) were increased in NZO mouse livers, as was the activity of pyruvate carboxylase (0.12±0.01 vs 0.17±0.02 nmol · min^–1 · mg protein^–1, p<0.05). To ascertain whether elevated lipid supply is responsible for these biochemical changes in NZO mice, we fed lean control mice a 60% fat diet for 2 weeks. Fat-fed mice were hyperinsulinaemic (76.37±4.06 vs 98.00±7.07 pmol/l, p=0.05) and had elevated plasma non-esterified fatty acid levels (0.44±0.05 vs 0.59±0.03 mmol/l, p=0.05). Fructose 1,6-bisphosphatase activity (43.86±2.54 vs 52.93±3.09 nmol · min^–1 · mg protein^–1, p=0.05) and protein levels (33.03±0.96 vs 40.04±1.26 arbitrary units, p=0.005) and pyruvate carboxylase activity (0.10±0.003 vs 0.14±0.01 nmol · min^–1 · mg protein^–1, p<0.05) were elevated in fat-fed mice. We conclude that in NZO mice increased hepatic glucose production is due to elevated lipolysis resulting from obesity.Abbreviations HGP Hepatic glucose production - NZO New Zealand Obese - FBPase fructose 1,6-bisphosphatase - PC pyruvate carboxylase - PEPCK phosphoenolpyruvate carboxykinase - BMI body mass index - NIDDM non-insulin-dependent diabetes mellitus - NZC lean control mice - NEFA non-esterified fatty acids     

Islet B-cell dysfunction and the time course of recovery following chronic overinsulinisation of normal rats

Summary Appropriate insulin therapy may preserve or improve islet B-cell function whereas the effects of overinsulinisation are unclear. Pancreatic islet B-cell function was therefore studied after overinsulinisation of normal rats for 4 weeks (fed blood glucose 2.2–4.5 mmol/l, controls 4.1–7.0 mmol/l). Insulin secretion was assessed by a 3-h hyperglycaemic clamp (10.0 mmol/l) performed 1, 48, and 120 h after insulin withdrawal (n=6 in each group). When the clamp was performed 1 h after insulin withdrawal, clamp insulin concentration was 1.6±0.1 g/l, compared to 9.3±1.0 g/l in control rats. The integrated area under the plasma insulin concentration curve was also significantly decreased (4.8±0.4 vs 20.3±2.2 g·l^–1·h^–1, p<0.001), but recovered to 9.4±1.0 g·l^–1·h^–1 after 48 h, and to 17.5±1.4 g·l^–1·h^–1 after 120 h. Pancreatic insulin contents were decreased at 1 h (6±1 g/g wet wt) and 48 h (54±12 g/g wet wt) but not at 120 h (221±30 g/g wet wt) after withdrawal (controls, 303±29 /g wet wt) and there was a strong relationship with pancreatic preproinsulin mRNA and the clamp insulin response. Thus, overinsulinisation with prolonged periods of low blood glucose concentrations impairs islet B-cell function, but is reversible over 5 days.     

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.     

Differential effects of insulin therapy on hepatic and peripheral insulin sensitivity in Type 2 (non-insulin-dependent) diabetes

Summary Hepatic glucose production and metabolic clearance rate of glucose were measured using (3-³H) glucose at steady state, basally and during two sequential 2 h insulin (25 and 40mU · kg^–1 · h^–1)/glucose(2 and 3mg · kg^–1 · min^–1) infusion periods. Eight diabetic subjects were studied before and after 1 week of twice daily insulin therapy; six control subjects matched for age, weight and degree of obesity were also studied. In the diabetic patients, pre-treatment hepatic glucose production was 20.0 ± 2.2, 9.9 ± 2.9, and 1.4 ± 0.8 mol · kg^–1 · min^–1 respectively (± SEM) for each of the three periods, and fell significantly with treatment to 12.8 ± 1.7,4.0 ± 1.5 and 1.9 ± 1.0 mol · kg^–1 · min^–1. Hepatic glucose production in normal subjects was 13.2 ± 0.6, 2.2 ± 0.8 and < 1 mol · kg^–1 · min^–1. The pre-treatment metabolic clearance rate in all diabetic studies with insulin levels 30 mU/l was 1.10 ± 0.14 ml · kg^–1 · min^–1 and remained virtually unchanged following insulin therapy; this was significantly lower than in the control subjects (6.83 ± 1.02, p < 0.001). Basal non-esterified fatty acid levels were higher (p < 0.02) in the pre-treated diabetic patients compared to post-treated diabetic patients and control subjects. Non-esterified fatty acids in each group fell to similar levels during the insulin infusions, but the rate of fall was slower in the pre-treated diabetic patients. Insulin receptor binding to erythrocytes was normal in the diabetic subjects and unchanged by treatment. Therefore, following insulin treatment of uncontrolled Type 2 (non-insulin-dependent) diabetes, the initially increased basal hepatic glucose production, and decreased hepatic sensitivity, return towards normal. However, the glucose clearance remains low, despite good diabetic control, and appears to be a major factor in the continuing glucose intolerance. As insulin receptor binding is normal, the defect of glucose clearance in Type 2 diabetes appears compatible with a post-receptor defect of glucose metabolism.     

Characterization of the insulin-antagonistic effect of growth hormone in man

Summary The insulin-antagonistic effect of growth hormone was characterized by infusing the hormone at three different infusion rates (6, 12 or 24 mU·kg^–1·min^–1) for one h in 11 healthy subjects. The insulin effect was measured with the euglycaemic clamp technique combined with D-(3-³H)-glucose infusion to evaluate glucose production and utilization. A control study with NaCl (154 mmol·l^–1) infusion was also performed. The insulin levels during the clamps were similar in all studies (36±0.2 mU·l^–1). Peak growth hormone levels were reached at 60 min (growth hormone 6mU·kg^–1·h^–1: 31±5; growth hormone 12 mU·kg^–1·h^–1: 52±4 and growth hormone 24 mU·kg^–1·h^–1: 102±8mU·l^–1). The insulin-antagonistic effect of growth hormone started after 2 h, was maximal after 4–5 h (39% inhibition of glucose infusion rate between control and growth hormone 24 mU·kg^–1·h^–1) and lasted for 6–7 h after peak levels. The resistance was due to a less pronounced insulin effect both to inhibit glucose production and to stimulate glucose utilization. Growth hormone infusion of 12 mU·kg^–1·h^–1 induced a similar insulin-antagonistic effect as the higher infusion rate whereas 6 mU·kg^–1·h^–1 induced a smaller response with a duration of 1 h between 3–4 h after peak levels of growth hormone. The present study demonstrates that growth hormone levels similar to those frequently seen in Type 1 (insulin-dependent) diabetic patients during poor metabolic control or hypoglycaemia, have pronounced insulin-antagonistic effects. The effects starts after about 2–3 h, is maximal after 4–5 h and lasts for about 6–7 h. Both duration and inhibitory effect of growth hormone are related to the plasma levels, where a maximal effect is seen at about 50 mU·l^–1 or higher.     

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     

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.     

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     

Impaired insulin action in newly diagnosed type 1 (insulin-dependent) diabetes mellitus

Summary Hepatic and peripheral insulin sensitivity were investigated in five newly diagnosed Type 1 (insulin-dependent) diabetic subjects before and after 1 week of twice daily insulin therapy. Eight weight-matched control subjects were also studied. Hepatic glucose production and glucose utilization were measured basally and during two sequential 2-h insulin (25 and 40 mU· kg^–1· h^–1)/glucose infusion periods. In the untreated hyperglycaemic diabetic patients hepatic glucose production was 16.3±2.6, 8.1±1.1 and 3.6±2.8|mol· kg^–1· min^–1 respectively for each of the three periods (mean±SEM), and fell with treatment to 12.5±1.4, 0.5±0.5 and 0.5±0.5 mol· kg^–1· min^–1. Hepatic glucose production for normal subjects was 13.4±0.7, 2.3±0.8 and <0.1 mol-kg^–1· min^–1. Glucose utilization was 12.7±1.4,18.2±0.7 and 22.1±3.4mol· kg^–1· min^–1 before treatment in the diabetic subjects, and 11.8±1.7, 20.9±3.3 and 30.1±3.6 after treatment. These values compare with those in the euglycaemic control subjects (13.4±0.7, 18.7±1.6 and 36.3±2.7 mol · kg^–1· min^–1). The pre-treatment metabolic clearance rate of glucose in all diabetic studies with insulin levels >30mU/l was 2.6 ±0.4 and rose to 3.9 ±0.5 ml· kg^–1· min^–1 following insulin therapy. This was significantly lower than in the control subjects (6.7±0.8 ml· kg^–1 · min^–1; p<0.005). Basal nonesterified fatty acid levels were high in the untreated, but normal in the treated diabetic subjects, and fell in response to insulin infusion. Basal -hydroxybutyrate levels were high in both diabetic groups, but also fell in response to insulin infusion. Erythrocyte insulin receptor binding was normal in the untreated diabetic subjects, and was not changed by treatment. Therefore, treatment of newly diagnosed Type 1 diabetic subjects with insulin reverses the hepatic insensitivity to insulin. In contrast, treatment only partially improves peripheral glucose disposal. Since erythrocyte insulin receptor binding is normal, it is likely that a post-receptor defect in peripheral glucose metabolism exists in Type 1 diabetic patients despite insulin therapy and good diabetic control for a period of 1 week.