Insulin resistant subjects lack islet adaptation to short-term dexamethasone-induced reduction in insulin sensitivity

Aims/hypothesis. To establish whether islet compensation to deterioration of insulin action depends on inherent insulin sensitivity. Methods. We examined insulin and glucagon secretion after iv arginine (5 g) at fasting, 14 and greater than 25 mmol/l glucose concentrations before and after lowering of insulin sensitivity by oral dexamethasone (3 mg twice daily for 2 1/2 days) in 10 women with normal glucose tolerance, aged 58 or 59 years. Five women had high insulin sensitivity as shown by euglycaemic, hyperinsulinaemic clamp (99 ± 12 nmol glucose · kg body weight^–1· min^–1/pmol insulin · l^–1; means ± SD) whereas five women had low insulin sensitivity (34 ± 15 nmol glucose · kg body weight^–1· min^–1/pmol insulin · l^–1). Results. Dexamethasone reduced insulin sensitivity in both groups. Fasting insulin concentration increased by dexamethasone in high insulin sensitivity (72 ± 10 vs 49 ± 9 pmol/l, p = 0.043) but not in low insulin sensitivity (148 ± 63 vs 145 ± 78 pmol/l) whereas the fasting glucose concentration increased in low insulin sensitivity (6.5 ± 0.8 vs 5.8 ± 0.6 mmol/l, p = 0.043) but not in high insulin sensitivity (5.3 ± 0.8 vs 5.3 ± 0.6 mmol/l). Fasting glucagon concentration was not changed. Plasma insulin concentrations after raising glucose to 14 and more than 25 mmol/l and the insulin response to arginine at more than 25 mmol/l glucose were increased by dexamethasone in high insulin sensitivity (p < 0.05) but not changed by dexamethasone in low insulin sensitivity. Furthermore, in high but not in low insulin sensitivity, dexamethasone reduced the glucagon response to arginine (p = 0.043). Conclusion/interpretation. The results show that adaptation in islets function to dexamethasone-induced short-term reduction in insulin sensitivity is lacking in subjects with low inherent insulin sensitivity. [Diabetologia (1999) 42: 936–943] Received: 26 January 1999 and in revised form: 1 March 1999     

Impaired glucose tolerance (IGT) is associated with reduced insulin-induced suppression of glucagon concentrations

Aims/hypothesis: We aimed to examine whether impaired glucose tolerance is associated with reduced suppression of glucagon concentrations. Methods: Eighty-four non-diabetic women of Caucasian origin and 61 years of age, of whom 48 had normal glucose tolerance (NGT) and 36 had IGT, underwent a 75 g OGTT and a hyperinsulinaemic, euglycaemic clamp with measurement of glucagon, insulin and glucose concentrations. Results: At 2 h after 75 g oral glucose, glucagon concentrations were reduced by 7.1 ± 1.1 ng/l in NGT vs 8.0 ± 1.4 ng/l in IGT, (NS). However, the 2 h reductions in glucagon per mmol/l increase in 2 h glucose or per pmol/l increase in 2 h insulin were both impaired in IGT (p = 0.002 and p = 0.043, respectively) because the 2 h increases in glucose and insulin were higher in IGT than in NGT. Furthermore, suppression of glucagon concentrations during a euglycaemic clamp at hyperinsulinaemic concentrations (NGT: 607 ± 19 pmol/l, IGT: 561 ± 21 pmol/l) was lower in IGT (13.6 ± 1.6 ng/l) than in NGT (23.1 ± 1.2 ng/l; p < 0.001). The suppression of glucagon concentrations during the hyperinsulinaemic, euglycaemic clamp correlated with insulin sensitivity (r = 0.24, p = 0.027) and with the 2 h glucose value during the OGTT (r = –0.52, p < 0.001). Conclusion/interpretation: Impaired glucose tolerance is associated with reduced insulin-induced suppression of glucagon secretion, which could be caused by A-cell insulin resistance. Inappropriately high glucagon secretion could therefore contribute to the metabolic perturbations in IGT. [Diabetologia (2001) 44: 1998–2003] Received: 15 May 2001 and in revised form: 13 July 2001     

The size of adrenal incidentalomas correlates with insulin resistance. Is there a cause‐effect relationship?

Context Adrenal incidentalomas (AI) have often been associated with a high prevalence of insulin resistance (IR) and cardiovascular risk factors, although direct measurement of insulin sensitivity (IS) has never been carried out. Objective We aimed to investigate whether the morphological and hormonal features of AI correlate with the presence and severity of IR, using the hyperinsulinaemic euglycaemic clamp (HEC). Design and Measurements Forty patients with AI (22 women) with a mean age of 58·5 ± 11·1 years underwent hormonal and morphological evaluation. Nineteen patients with AI without known history of diabetes mellitus (DM) or impaired glucose tolerance (IGT) and 17 matched controls underwent oral glucose tolerance test (OGTT) and hyperinsulinaemic euglycaemic clamp (HEC). Results Diabetes mellitus was observed in 13 patients (33%), while three (8%) had IGT. Thirty‐one of the AI were nonfunctioning (82·5%), whereas two (5%) secreted cortisol (Cushing’s syndrome) and seven (12·5%) showed subclinical secretion of cortisol. The 19 patients with nonfunctioning AI were more insulin resistant than controls (glucose up‐take: 4·58 ± 1·80 vs 5·85 ± 2·48 mg/kg/min respectively; P = 0·01); IS was inversely related to the mass size (r = ?0·57; P = 0·04), free urinary cortisol (r = ?0·68; P = 0·01), serum cortisol after 1‐mg dexamethasone suppression (?0·65; P = 0·02) and percentage of trunk fat mass (?0·77; P = 0·02) and directly related to serum adreno cortico tropic hormone (ACTH) (r = 0·62; P = 0·03). After performing multivariate regression, the mass size was found to be the most powerful predictor of IR. Conclusion Our study showed a high prevalence of insulin resistance in patients with nonfunctioning AI and suggests its possible involvement in AI growth.     

Lack of acute effect of amylin (islet associated polypeptide) on insulin sensitivity during hyperinsulinaemic euglycaemic clamp in humans

Summary It is suggested that amylin (islet associated polypeptide), co-secreted with insulin from the pancreatic beta cells acts as a circulating hormone which opposes the action of insulin on muscle and increases hepatic glucose production. We have tested the effect of amylin in human subjects on postabsorptive glucose homeostasis and on insulin sensitivity using the euglycaemic hyperinsulinaemic clamp. The amylin used opposed insulin-mediated glucose disposal in rat soleus muscle at concentrations of 10 nmol/l. Seven subjects were studied on two occasions and infused with either amylin or placebo for 6 h, initially when postabsorptive and then during a euglycaemic hyperinsulinaemic clamp. Mean plasma amylin concentrations during the first 3 h were 2006±327 pmol/l during amylin infusion and 20±9 pmol/l during the control infusion. Amylin infusion had no effect on postabsorptive plasma concentrations of insulin (control: 32±16 vs amylin: 25±8 pmol/l) or glucose (5.1±0.1 vs 5.3±0.1 mmol/l). During the clamp, amylin concentrations were 1636 ±422 pmol/l when it was infused and 24±6 during control infusions. Plasma glucose and insulin concentrations were well matched during the control and amylin infusions (glucose: 4.7±0.1 vs 4.8±0.1 mmol/l; insulin: 198±37 vs 195±22 pmol/l). Exogenous glucose infusion rates were a mean of 13 % lower than control values during the amylin infusion but were not statistically different (p =0.17). Therefore, an approximately 100-fold elevation of plasma amylin concentration failed to consistently alter glucose metabolism. Our data suggest that amylin does not act as a circulating hormone to influence glucose metabolism in humans. [Diabetologia (1994) 37: 166–169] Received: 1 June 1993 and in revised form: 16 August 1993     

On the interplay beween insulin secretion and sensitivity as determinants of glucose tolerance

Both insulin secretion and sensitivity have been claimed to be the main characteristics in the determination of future detoriation in glucose tolerance. In this cross-sectional study insulin secretion and insulin sensiturity were determined in 228 subjects with varying degrees of glucose tolerance. Insulin secretion was measured in an intravenous glucose tolerance test (IVGTT) and insulin sensitivity by the hyperinsulinaemic euglycaemic clamp test. Both the early insulin response in the IVGTT (increment) and the glucose disposal rate in the clamp test (M-value) were found to be related hyperbolically to fasting glucose (r=–0.63 and –0.66, respectively; bothP<0.0001) and in a second-order polynomial manner to the glucose disappearence rate (k-value) in the IVGTT (r=0.53 and 0.48, respectively; bothP<0.0001). Multiple regression analysis showed the insulin increment in the IVGTT and theM-value in the clamp test to be equally important determinants of glucose tolerance, together explaining about 50% of the variation in fasting glucose and thek-value in the IVGTT. In conclusion, in this cross-sectional study insulin secretion and sensitivity studied over a broad range of glucose tolerance were found to be of amost equal importance in the determination of glucose tolerance. However, low levels of insulin increment in the IVGTT were more often associated with glucose intolerance than was a low insulin sensitivity.     

Lipolysis in skeletal muscle is rapidly regulated by low physiological doses of insulin

Aims/hypothesis. Both patients with Type II (non-insulin-dependent) diabetes mellitus and normoglycaemic, insulin resistant subjects were shown to have an increased lipid content in skeletal muscle, which correlates negatively with insulin sensitivity. Recently, it was shown that during a hyperinsulinaemic euglycaemic clamp interstitial glycerol was reduced not only in adipose tissue but also in skeletal muscle. To assess whether lipolysis of muscular lipids is also regulated by low physiological concentrations of insulin, we used the microdialysis technique in combination with a 3-step hyperinsulinaemic glucose clamp. Methods. Nineteen lean, healthy subjects (12 m/7 f) underwent a glucose clamp with various doses of insulin (GC I = 0.1, GC II = 0.25 and GC III = 1.0mU · kg^–1· min^–1). Two double lumen microdialysis catheters each were inserted in the paraumbilical subcutaneous adipose tissue and in skeletal muscle (tibialis anterior) to measure interstitial glycerol concentration (index of lipolysis) and ethanol outflow (index of tissue flow). Results. During the different steps of the glucose clamp, glycerol in adipose tissue was reduced to 81 ± 7 % (GC I), 55 ± 8 % (GC II) and 25 ± 5 % (GC III), respectively, of basal. In contrast, glycerol in skeletal muscle declined to 73 ± 5 % (GC I) and to 57 ± 6 % (GC II) but was not further reduced at GC III. Tissue flow was higher in the skeletal muscle and remained unchanged in both compartments throughout the experiment. Conclusion/interpretation. This study confirms the presence of glycerol release in skeletal muscle. Lipolysis in skeletal muscle and adipose tissue are suppressed similarly by minute and physiological increases in insulin but differently by supraphysiological increases. Inadequate suppression of intramuscular lipolysis resulting in increased availability of non-esterified fatty acids, could represent a potential mechanism involved in the pathogenesis of impaired glucose disposal, i. e. insulin resistance, in muscle. [Diabetologia (1999) 42: 1171–1174] Received: 12 March 1999 and in revised form: 21 May 1999     

Insulin sensitivity and insulin clearance in cystic fibrosis patients with normal and diabetic glucose tolerance

OBJECTIVE We studied glucose metabolism and insulin kinetics in cystic fibrosis patients with diabetic and normal glucose tolerance. DESIGN Measurements of blood glucose and serum free insulin concentrations during hyperinsulinaemic normo-glycaemic clamp and post-clamp insulin decay, followed by the calculation of insulin sensitivity (M-value and M/1 ratio), insulin clearance rate, serum half-life and apparent distribution space for insulin. SUBJECTS Cystic fibrosis patients, age range 20–29 years, with diabetes mellitus (n= 10) and normal glucose tolerance (n= 10), and 10 age-matched control subjects. RESULTS During the glucose clamp, diabetic cystic fibrosis patients needed less glucose than cystic fibrosis patients with normal glucose tolerance and control subjects (M-value), and steady-state serum insulin concentrations were lower in cystic fibrosis patients with diabetic and normal glucose tolerance than in control subjects. The quantity of glucose metabolized per unit of serum insulin concentration (M/l ratio) was similar in the three study groups (median ～ 145 (μmol/kg/min)/(nmol/l); range 70–252). insulin clearance rates were higher in cystic fibrosis patients with diabetic (24·4 (19·3–29·9) mi/kg/min) and normal (22·6 (14·9–28·4) mi/kg/min) glucose tolerance than in control subjects (17·5 (15·9–24·2) ml/kg/min). Although Insulin clearance rates were inversely related to body mass index (R(S)=?0·59, P < 0·001), the higher insulin clearance rates in CF patients cannot be accounted for solely by differences in body mass index since the insulin clearance rates were similarly increased in patients with body mass index above and below 20kg/m²(22·7 (14·9–28·4) and 24·4 (19·3–29·9) ml/kg/min, respectively). Serum half-lives for Insulin were shorter in cystic fibrosis patients (～4·3 (3·2–7·2) min) than In control subjects (5·9 (3·8–12·5) min), whereas the apparent distribution spaces for Insulin were similar in the three study groups (～150 (88–391) ml/kg). CONCLUSIONS Insulin sensitivity, calculated as the quantity of glucose metabolized per kg body weight per unit of serum insulin concentration, is normal in cystic fibrosis patients with normal glucose tolerance and with well controlled diabetes mellitus. The insulin clearance rate is increased in cystic fibrosis patients with diabetic and normal glucose tolerance, owing to a shorter serum half-life of insulin, whereas the apparent distribution space for insulin is normal.     

Insulin secretion and sensitivity before and after surgical treatment for aldosterone-producing adenoma

AimPrimary aldosteronism, which is usually caused by an aldosterone-producing tumour, affects glucose metabolism. The effects of this condition on insulin secretion and insulin sensitivity have remained unclear, however. To gain insight into the influence of primary aldosteronism on glucose tolerance, various parameters related to insulin secretion or insulin sensitivity in patients with an aldosterone-producing tumour were comprehensively analyzed.MethodsTo assess 14 patients with an aldosterone-producing tumour, hyperglycaemic and hyperinsulinaemic–euglycaemic clamp tests as well as oral glucose tolerance tests (OGTTs) were performed before and after tumour excision. Time between presurgical analysis and surgery was 27–559 (194 ± 132) days, and 14–142 (51 ± 38) days between surgery and postsurgical analysis. Various parameters related to insulin secretion or sensitivity as determined by OGTT as well as hyperglycaemic and hyperinsulinaemic–euglycaemic clamp analyses were evaluated.ResultsSurgical treatment of tumours ameliorated hypokalaemia and reduced plasma aldosterone levels. First and second phases of insulin secretion during the hyperglycaemic clamp, as well as the insulinogenic index and total insulin secretion measured during OGTT, were also improved after surgery. In addition, the insulin sensitivity index determined during the hyperinsulinaemic–euglycaemic clamp was reduced after surgery.ConclusionPrimary aldosteronism impairs insulin secretion.     

In anorexia nervosa, even a small increase in abdominal fat is responsible for the appearance of insulin resistance

Context The aim of treatment in patients affected by anorexia nervosa (AN) is weight recovery. However, during weight gain, anorectic patients’ body composition is changed, with an increase in abdominal fat, particularly in the visceral compartment. Objective We hypothesized that changes in body composition, particularly in abdominal fat, are responsible for the variability in insulin sensitivity (IS) in different stages of AN. Design and Measurements We compared 20 anorectic patients in the acute stage, 19 in the weight‐recovery stage and 21 controls. All subjects underwent an oral glucose tolerance test, hyperinsulinaemic euglycaemic clamp and dual energy X‐ray absorptiometry to measure body composition. Results The percentage of trunk fat was higher in weight recovery than in the acute phase (47·7 ± 8·4%vs 34·6 ± 7·6%; P ≤ 0·01) and in the control group (33·4 ± 7·6; P < 0·01 vs weight recovery). Although the recovery group gained weight, their body mass index (BMI) was not statistically different from that of the acute group (14·4 ± 1·1 vs 13·6 ± 1·8 kg/m²). Insulin sensitivity was lower in the weight‐recovery group than the acute group (4·7 ± 1·5 vs 7·8 ± 1·6 mg/kg/min; P < 0·01) and controls (7·7 ± 1·4 mg/kg/min; P < 0·01). A linear negative correlation was found between IS and the percentage of abdominal fat in the weight‐recovery and acute groups (r = ?0·51; P = 0·04 and r = ?0·53; P = 0·04 respectively), while IS did not correlate with BMI. Conclusion Although weight‐recovery represents the main aim of treatment in AN, refeeding is associated with an increase in abdominal fat which might be responsible of the onset of insulin resistance. As BMI and weight‐recovery were associated with impaired IS, they cannot be considered the only aim of treatment of AN.     

The short insulin tolerance test lacks validity in adolescents with Type 1 diabetes.

AIMS: The short insulin tolerance test (SITT) has been found to be a simple and valid method for determining insulin sensitivity in healthy adults and patients with Type 2 diabetes. In this study we evaluated the reproducibility and validity of SITT in 16 adolescents with Type 1 diabetes. METHODS: Thirteen patients underwent two SITT and eight patients were examined with both SITT and a euglycaemic hyperinsulinaemic clamp. At the SITT insulin sensitivity was measured from the slope of arterialized blood glucose concentrations determined for 16 min after an intravenous bolus injection of short-acting insulin, 0.1 U/kg body weight, and expressed as glucose disappearance rate (KITT). RESULTS: There was a significant correlation between the insulin sensitivity estimations made at the two SITT (r = 0.73, P = 0.003). The reproducibility was low, however, with a coefficient of variation of 38.7%. KITT showed a strong inverse correlation to the fasting blood glucose concentration (r = -0.74, P < 0.0001). We found no correlation between insulin sensitivity measured by SITT and that measured by the euglycaemic clamp. CONCLUSIONS: We conclude that the short insulin tolerance test cannot be used in adolescent patients with Type 1 diabetes for a simple estimation of insulin sensitivity.     

Hyperinsulinaemic hypoglycaemia associated with a heterozygous missense mutation of R1174W in the insulin receptor (IR) gene

Background  Mutations in the insulin receptor (IR) gene are known to cause severe insulin resistance. Although clinical features due to a mutation can be diverse, hypoglycaemia is found in some cases. A family with a female proband diagnosed with type A insulin resistance syndrome was studied. Clinical characteristics were compared with the Arginine1174Glutamine (R1174N) mutation reported in the literature.
Methods  The proband was a 16-year-old girl who was presented with intermittent hypoglycaemia, hirsutism, darkened skin, acne and oligomenorrhoea. A 5-h oral glucose tolerance test (OGTT), intravenous glucose tolerance test and continuous glucose monitoring system were performed for evaluation of glucose metabolism and insulin secretion. Results from a hyperinsulinaemic euglycaemic clamp on the proband were compared to nine normal glucose tolerance (NGT) controls. The IR gene of the proband, along with her parents and two dizygotic twin brothers were scanned for mutations by direct sequencing.
Results  Elevated serum insulin and insulin : C-peptide ratios were found in the proband, the father and one of the twin brothers, carried a heterozygous missense mutation of Arginine1174Tryptophan (R1174W) in exon20 of the IR gene. The clamp study showed that the nonoxidative glucose disposal rates of the proband were near zero, and that the metabolic clearance rate for insulin was markedly reduced.
Conclusions  R1174 of the IR gene may be a candidate locus for hyperinsulinaemic hypoglycaemia. Clinical heterogeneity is not uncommon within families as well as among mutation carriers with different amino acid replacements. More pedigrees and long-term follow-up data are needed to document the evolution of β-cell function and clarify the role of R1174 on insulin resistance and hyperinsulinaemic hypoglycaemia.     

Effects of T4 replacement therapy on glucose metabolism in subjects with subclinical (SH) and overt hypothyroidism (OH)

Objective To evaluate β‐cell function and insulin sensitivity in subjects with overt (OH) and subclinical hypothyroidism (SH) before and after T4 replacement therapy. Background Disturbances in glucose metabolism have been observed in hypothyroid states. However, the clinical significance and potential reversibility of these alterations by T4 replacement therapy remain to be elucidated especially in patients with SH. Design and patients Parameters of glucose metabolism have been investigated in subjects with OH (n = 12) and SH (n = 11). Insulin sensitivity has been assessed by the euglycaemic–hyperinsulinaemic clamp technique and β‐cell function by mathematical modelling of data derived from an oral glucose tolerance test. Results Fasting and dynamic glycaemia as assessed by the AUC_Glucose remained unaltered following substitution therapy (P > 0·05). Insulin sensitivity significantly improved only in subjects with OH (P < 0·05). Fasting insulin and proinsulin concentrations increased proportionally in both groups (P < 0·05) with the proinsulin : insulin ratio remaining unchanged (P > 0·05). Total insulin secretion was higher in OH before initiation of therapy (P < 0·05). In both groups, dynamic parameters including total insulin secretion, hepatic insulin extraction and the adaptation index were significantly attenuated (P < 0·05) after restoration of thyroid function, whereas the disposition index and the basal insulin secretion rate remained unaltered (P > 0·05). Conclusion In summary, SH and OH are characterized by attenuated basal plasma insulin levels and increased glucose‐induced insulin secretion. T4 replacement therapy partially ameliorates the insulin secretion profile and reduces the demand on pancreatic β‐cells after glucose challenge to an extent that exceeds any effect attributable to the improvement in insulin sensitivity.     

Age-dependent association of serum prolactin with glycaemia and insulin sensitivity in humans

The dopamine agonist bromocriptine has been approved for the treatment of type 2 diabetes in the United States. Bromocriptine inhibits prolactin secretion, and patients with hyperprolactinaemia display impaired insulin sensitivity. We therefore hypothesized that low prolactin levels are associated with lower glycaemia and higher insulin sensitivity in healthy subjects. Prolactin levels were determined from fasting serum in participants without diabetes from the cross-sectional Tübingen family study for type 2 diabetes (m/f = 562/1,121, age = 40 ± 13 years, BMI = 30 ± 9 kg/m²). A 75 g oral glucose tolerance test was performed, and the area under the glucose curve (AUC_0–120Glucose) and insulin sensitivity index were calculated. A subgroup (n = 494) underwent hyperinsulinaemic–euglycaemic clamp tests. Prolactin associated positively with insulin sensitivity (p = 0.001, adjusted for gender, age, and BMI). Age strongly interacted (p < 0.0001) with the effect of prolactin on insulin sensitivity, inverting the positive relationship to a negative one in younger participants. Glycated haemoglobin (HbA1c) and AUC_0–120Glucose correlated negatively with prolactin, and an interaction with age was found as well. Higher prolactin levels are associated with improved insulin sensitivity and lower glucose in individuals without diabetes. This relationship turns to its opposite in younger persons. As prolactin is a proxy for the dopaminergic tone in the central nervous system, these associations may indicate an age-dependent influence of the brain on peripheral insulin sensitivity.     

Strong association between insulin resistance in liver and skeletal muscle in non‐diabetic subjects

Objective To examine the association between insulin resistance in skeletal muscle and liver in non‐diabetic subjects. Research design and methods A total of 182 Mexican American subjects without Type 2 diabetes underwent an oral glucose tolerance test and euglycaemic–hyperinsulinaemic clamp performed with ³[H]glucose. Insulin sensitivity in skeletal muscle was measured as the insulin‐stimulated rate of total glucose disposal during the insulin clamp divided by steady‐state plasma insulin concentration (TGD/SSPI). Hepatic insulin resistance was measured as the product of basal hepatic glucose production and fasting plasma insulin concentration (HGP × FPI). Results Hepatic insulin resistance was strongly correlated (r = 0.68, P < 0.0001) with skeletal muscle insulin resistance. Thirty‐eight per cent of subjects had increased insulin resistance in both liver and skeletal muscle, while 39% were insulin sensitive in both skeletal muscle and liver. Twenty‐three per cent of subjects were discordant for muscle and hepatic insulin resistance (P < 0.0001). Subjects with increased skeletal muscle insulin resistance had a higher 2‐h plasma glucose concentration, greater incremental area under the plasma glucose concentration curve, lower fasting plasma insulin concentration and lower rate of basal hepatic glucose production compared with subjects with increased insulin resistance in liver. Conclusion In non‐diabetic subjects, insulin resistance in skeletal muscle is an important determinant of the fasting and 2‐h plasma glucose concentrations and strongly correlates with hepatic insulin resistance.     

A comparison between enalapril and captopril on insulin sensitivity in normotensive healthy volunteers

Background: Captopril has been shown to improve insulin sensitivity in insulin resistant hypertensive individuals and enalapril has been shown to improve insulin sensitivity in a small group of healthy volunteers, but there has been no direct comparison of the effects of the different angiotensin converting enzyme inhibitors (ACEIs) on insulin sensitivity in either insulin sensitive or insulin insensitive populations. Aim: To compare the impact of two different ACEIs (captopril and enalapril) on insulin mediated glucose uptake in normotensive, non-obese, insulin sensitive subjects. Method: A single blind cross-over study comparing captopril (6.25 mg twice daily) and enalapril (5 mg once daily) for 28 days with a 28 day washout period between drugs. Insulin mediated glucose uptake was measured by means of the euglycaemic hyperinsulinaemic clamp at the start and completion of each period of drug therapy. Results: Both drugs resulted in elevations of fasting insulin levels (mean difference ± SEM for combined data, 2.7 ± 1.8; p < 0.05) and a reduction in insulin mediated glucose uptake (mean difference for combined data, - 0.72 ± 0.37 mg/kg¹ minute^-1; p= 0.056). Results were similar for both agents and suggest a class effect. Conclusions: The increase in fasting insulin levels, and reduction in insulin mediated glucose uptake in this study are in contrast to findings in obese and hypertensive subjects, and indicate that studies of insulin sensitivity of ACEIs in non-obese, normotensive subjects are inappropriate for predicting likely effects in clinical practice. (Aust NZ J Med 1993; 23: 652–655.)     

Independent measures of insulin secretion and insulin sensitivity during the same test: the glucagon-insulin tolerance test

Background. To validate a test for independent assessment of insulin secretion and insulin sensitivity during the same occasion for metabolic studies in clinical practice, i.e. combined glucagon‐stimulated C‐peptide test and insulin tolerance test (GITT). Subjects and methods. We measured C‐peptide response to 0.5 mg of intravenous glucagon followed 30 min later by administration of 0.05 U kg^?1 insulin (insulin tolerance test, ITT). Ten subjects with normal glucose tolerance participated on different days in an ITT, glucagon‐C‐peptide test, ITT followed by glucagon‐C‐peptide test and glucagon‐C‐peptide test followed by ITT to establish whether and how the tests could be combined. The test was then repeated in nine patients with type 2 diabetes to investigate its reproducibility. In 20 subjects with varying degrees of glucose tolerance, the test was compared with the Botnia clamp (an intravenous glucose tolerance test combined with a euglycaemic hyperinsulinemic clamp). Results. When ITT preceded the glucagon test, C‐peptide response was blunted. Therefore, we first administered glucagon and then insulin (GITT). The K_ITT from the GITT was reproducible (CV = 13 %) and correlated strongly with the glucose disposal rate from the Botnia clamp (r = 0.87, r² = 0.75, P < 0.001). The C‐peptide response to glucagon was reproducible (CV = 13 %). The disposition index, providing a measure of beta‐cell function adjusted for insulin sensitivity, calculated from the GITT showed good discrimination between individuals with varying degrees of glucose tolerance. Conclusions. The GITT provides simple, reproducible and independent estimates of insulin sensitivity and secretion on the same occasion for metabolic studies in individuals with normal and abnormal glucose tolerance.     

Co-existence of severe insulin resistance and hyperinsulinaemia in pre-adolescent obese children

Summary To determine the time course of changes in insulin action and secretion that occur early during the development of obesity, we studied children before the onset of puberty. The reason for choosing the prepubertal stage of development is that it is metabolically characterized by both a high sensitivity to insulin and low glucose stimulated insulin responses. Fifteen obese preadolescents (8 male/7 female, age 10 ± 0.4 years, body mass index (BMI) 31 ± 1.2 kg/m² Tanner Stage I) with a duration of obesity of less than 5 years and 10 non-obese preadolescents (6 male/4 female, age 10 ± 0.4 years, BMI 18 ± 0.9 kg/m²) matched for gender were studied. In a cross-sectional analysis, we compared responses in obese preadolescents, with those in obese adolescents and obese adults with a longer duration of obesity. The euglycaemic hyperinsulinaemic clamp with 1-¹³C-glucose (Hot Ginf) and indirect calorimetry were used to quantitate insulin action and the hyperglycaemic clamp used to assess beta-cell function. Insulin-stimulated glucose uptake measured at two physiological levels of hyperinsulinaemia ( ∼ 180 and 480 pmol) was reduced by 20 and 45 % in all three groups of obese compared to non-obese subjects (p < 0.01). Defects in oxidative and non-oxidative glucose metabolism were observed in all three groups of obese subjects at the higher insulin infusion rate. The ability of insulin to inhibit lipid oxidation was impaired in all three obese groups at both levels of hyperinsulinaemia. Increases in basal and glucose-stimulated insulin levels during the hyperglycaemic clamp mirrored the reductions in glucose uptake during the insulin clamp in all obese groups. These results indicate that insulin resistance and hyperinsulinaemia co-exist in preadolescent children with moderate to severe obesity. [Diabetologia (1996) 39: 1489–1497] Received: 23 March 1996 and in revised form: 16 July 1996     

Effect of Aprotinin on Insulin Sensitivity in Non-insulin-dependent Diabetes Mellitus

It has been suggested that kallikrein-kinin system may influence carbohydrate metabolism via a kinin-mediated increment of insulin-mediated glucose uptake. To evaluate the effect of acute inhibition of the kallikrein-kinin system on insulin sensitivity, a randomized, placebo-controlled, double-blind study was performed in 15 male non-insulin-dependent diabetic patients. After basal evaluation of insulin sensitivity with a 2-h euglycaemic hyperinsulinaemic clamp (40 mU m⁻² min⁻¹), patients were infused either with aprotinin (200 000 U.I.C. as intravenous bolus injection) or placebo (10 ml isotonic saline) in a cross-over fashion, at 1 week intervals. After both saline and aprotinin infusions, insulin sensitivity was reassessed by continuing the euglycaemic hyperinsulinaemic clamp for a further 1 h. Resulting data showed that aprotinin significantly improved total glucose uptake (from 16.2 ± 2.9 μmol kg min⁻¹ to 20.6 ± 4.9 μmol kg min⁻¹, p<0.01), and decreased metabolic clearance rate of insulin (from 586 ± 57 ml m⁻² min⁻¹ to 442 ± 155 ml m⁻² min⁻¹, p<0.05). Thus, in spite of the suggested positive effects of kinins on insulin-mediated glucose uptake, acute inhibition of the kallikrein-kinin system resulted in a paradoxical increment of insulin sensitivity, which was probably mediated by the reduced metabolic clearance rate of insulin.     

Eradicating hepatitis C virus ameliorates insulin resistance without change in adipose depots

Chronic hepatitis C (CHC) is associated with lipid‐related changes and insulin resistance; the latter predicts response to antiviral therapy, liver disease progression and the risk of diabetes. We sought to determine whether insulin sensitivity improves following CHC viral eradication after antiviral therapy and whether this is accompanied by changes in fat depots or adipokine levels. We compared 8 normoglycaemic men with CHC (genotype 1 or 3) before and at least 6 months post viral eradication and 15 hepatitis C antibody negative controls using an intravenous glucose tolerance test and two‐step hyperinsulinaemic–euglycaemic clamp with [6,6‐²H₂] glucose to assess peripheral and hepatic insulin sensitivity. Magnetic resonance imaging and spectroscopy quantified abdominal fat compartments, liver and intramyocellular lipid. Peripheral insulin sensitivity improved (glucose infusion rate during high‐dose insulin increased from 10.1 ± 1.6 to 12 ± 2.1 mg/kg/min/, P = 0.025), with no change in hepatic insulin response following successful viral eradication, without any accompanying change in muscle, liver or abdominal fat depots. There was corresponding improvement in incremental glycaemic response to intravenous glucose (pretreatment: 62.1 ± 8.3 vs post‐treatment: 56.1 ± 8.5 mm , P = 0.008). Insulin sensitivity after viral clearance was comparable to matched controls without CHC. Post therapy, liver enzyme levels decreased but, interestingly, levels of glucagon, fatty acid–binding protein and lipocalin‐2 remained elevated. Eradication of the hepatitis C virus improves insulin sensitivity without alteration in fat depots, adipokine or glucagon levels, consistent with a direct link of the virus with insulin resistance.     

Suppression of endogenous insulin secretion by exogenous insulin in patients with insulinoma

OBJECTIVE: Previous studies have demonstrated that endogenous insulin secretion is not suppressed by exogenous insulin in patients with insulinoma. In this study we examined whether insulin secretion in insulinoma patients is suppressed by exogenous insulin during hypoglycaemia. SUBJECTS AND METHODS: Sixteen insulinoma patients (5 men and 11 women) and 10 normal subjects were studied. Hyperinsulinaemic glucose clamp studies were performed at both euglycaemia (4.5 mmol/l glucose) and hypoglycaemia (2.5 mmol/l glucose). RESULTS: In normal subjects, plasma C-peptide levels were suppressed by 66% during the euglycaemic hyperinsulinaemic clamps (P < 0.01). In contrast, in insulinoma patients, plasma C-peptide levels increased by 25% during the clamps (P < 0.05). In the hypoglycaemic hyperinsulinaemic clamps, plasma C-peptide levels were nearly completely (91%) suppressed in normal subjects and partially (39%) suppressed in patients with insulinoma (P < 0.01). The decrease in C-peptide levels during the hypoglycaemic clamps was > 30% in 12 (75%) of 16 insulinoma patients and > 50% in 8 (50%) patients. CONCLUSIONS: This study demonstrated that in patients with insulinoma, insulin secretion was not suppressed by exogenous insulin during euglycaemia but was suppressed during hypoglycaemia, although the degree of suppression was less than that in normal subjects. Our results suggest that the feedback regulation of insulin secretion by exogenous insulin is partially retained in patients with insulinoma.