Enhanced glucose utilization during prolonged glucose clamp studies

How to Achieve Sufficient Endogenous Insulin Suppression in Euglycemic Clamps Assessing the Pharmacokinetics and Pharmacodynamics of Long-Acting Insulin Preparations Employing Healthy Volunteers

The therapeutic effect of basal insulin analogs will be sustained at a rather low insulin level. When employing healthy volunteers to assess the pharmacokinetics (PK) and pharmacodynamics (PD) of long-acting insulin preparations by euglycemic clamp techniques, endogenous insulin cannot be ignored and sufficient endogenous insulin inhibition is crucial for the PD and/or PK assessment. This study aimed to explore a way to sufficiently inhibit endogenous insulin secretion. Healthy Chinese male and female volunteers were enrolled. After a subcutaneous injection of insulin glargine (IGlar) (LY2963016 or Lantus) (0.5 IU/kg), they underwent a manual euglycemic clamp for up to 24 h where the target blood glucose (BG) was set as 0.28 mmol/L below the individual’s baseline. Blood samples were collected for analysis of PK/PD and C-peptide. The subjects fell into two groups according to the reduction extent of postdose C-peptide from baseline. After matching for the dosage proportion of Lantus, there were 52 subjects in group A (C-peptide reduction<50%) and 26 in group B (C-peptide reduction≥50%), respectively. No significant difference was detected in age, body mass index, the proportion of Latus treatment and female participants. A lower basal BG was observed in group B compared to group A (4.35 ± 0.26 vs. 4.59 ± 0.22 mmol/L, p < 0.05). The clamp studies were all conducted with high quality (where BG was consistently maintained around the target and exhibited a low variety). The binary logistic regression analysis indicated low basal BG as an independent factor for the success of sufficient endogenous insulin suppression. In conclusion, setting a lower sub-baseline target BG (e.g., 10% instead of 5% below baseline) might be an approach to help achieve sufficient endogenous insulin suppression in euglycemic clamps with higher basal BG levels (e.g., beyond 4.60 mmol/L).

Influence of liver triglycerides on suppression of glucose production by insulin in men

CONTEXT

The ability of insulin to suppress hepatic glucose production is impaired among subjects with increased intrahepatic triglycerides (IHTG). However, little is known about the roles of insulin on the supporting fluxes of glucose production among patients with fatty liver.

OBJECTIVE

To evaluate the effects of insulin on fluxes through the three potential sources of plasma glucose (glycerol, the citric acid cycle, and glycogen) among patients with fatty liver. Design, Settings, Participants, and Intervention: Nineteen men with a range of IHTG (∼0.5% to 23%) were studied after an overnight fast and during hyperinsulinemia using magnetic resonance spectroscopy and stable isotope tracers.

MAIN OUTCOME MEASURES

IHTG, gluconeogenesis from glycerol, gluconeogenesis from the citric acid cycle, glycogenolysis, and (13)C-labeled glucose produced from the citric acid cycle during hyperinsulinemia were measured.

RESULTS

Men with high IHTG had higher fluxes through all pathways contributing to glucose production during hyperinsulinemia, compared to men with low IHTG, but they had similar fluxes after the fast. Consequently, men with fatty liver had impaired insulin efficiency in suppressing total glucose production as well as fluxes through all three biochemical pathways contributing to glucose. The detection of glucose isotopomers with (13)C arising from [U-(13)C3]propionate ingested during hyperinsulinemia demonstrated continuous gluconeogenesis from the citric acid cycle in all subjects.

CONCLUSIONS

These findings challenge the concept that individual glucose production pathways are selectively dysregulated during hepatic insulin resistance. Overproduction of glucose during hyperinsulinemia in men with fatty liver results from inadequate suppression of all the supporting fluxes of glucose production in response to insulin.

Insulin sensitivity index in type 1 diabetes and following human islet transplantation: comparison of the minimal model to euglycemic clamp measures

Insulin sensitivity is impaired in type 1 diabetes (T1D) and may be enhanced by islet transplantation, an effect best explained by improved metabolic control. While the minimal model index of insulin sensitivity, SI, has been used in studies of T1D, it has not before been evaluated against gold-standard measures derived from the euglycemic clamp. We sought to determine how well minimal model SI derived from an insulin-modified frequently sampled intravenous glucose tolerance (FSIGT) test compared with total body and peripheral insulin sensitivity estimates derived from the hyperinsulinemic-euglycemic clamp in subjects with T1D and following islet transplantation. Twenty-one T1D subjects were evaluated, including a subgroup (n = 12) studied again after intrahepatic islet transplantation, with results compared with normal controls (n = 11 for the FSIGT). The transplant recipients received 9,648 ± 666 islet equivalents/kg with reduction in HbA1c from 7.1 ± 0.2 to 5.5 ± 0.1% (P < 0.01) and 10/12 were insulin independent. FSIGT-derived SI was reduced in T1D pre- compared with posttransplant and with normal [1.76 ± 0.45 vs. 4.21 ± 0.34 vs. 4.45 ± 0.81 × 10(-4)(μU/ml)(-1)·min(-1); P < 0.01 for both]. Similarly, clamp-derived total body, and by the isotopic dilution method with [6,6-(2)H2]glucose, peripheral insulin sensitivity increased in T1D from pre- to posttransplant (P < 0.05 for both). The predictive power (r(2)) between volume-corrected SIC and measures of total and peripheral insulin sensitivity was 0.66 and 0.70, respectively (P < 0.00001 for both). That the minimal model SIC is highly correlated to the clamp-derived measures indicates that the FSIGT is an appropriate methodology for the determination of insulin sensitivity in T1D and following islet transplantation.

Slow-twitch fiber proportion in skeletal muscle correlates with insulin responsiveness

CONTEXT

The metabolic syndrome, characterized by central obesity with dyslipidemia, hypertension, and hyperglycemia, identifies people at high risk for type 2 diabetes.

OBJECTIVE

Our objective was to determine how the insulin resistance of the metabolic syndrome is related to muscle fiber composition.

DESIGN

Thirty-nine sedentary men and women (including 22 with the metabolic syndrome) had insulin responsiveness quantified using euglycemic clamps and underwent biopsies of the vastus lateralis muscle. Expression of insulin receptors, insulin receptor substrate-1, glucose transporter 4, and ATP synthase were quantified with immunoblots and immunohistochemistry.

PARTICIPANTS AND SETTING

Participants were nondiabetic, metabolic syndrome volunteers and sedentary control subjects studied at an outpatient clinic.

MAIN OUTCOME MEASURES

Insulin responsiveness during an insulin clamp and the fiber composition of a muscle biopsy specimen were evaluated.

RESULTS

There were fewer type I fibers and more mixed (type IIa) fibers in metabolic syndrome subjects. Insulin responsiveness and maximal oxygen uptake correlated with the proportion of type I fibers. Insulin receptor, insulin receptor substrate-1, and glucose transporter 4 expression were not different in whole muscle but all were significantly less in the type I fibers of metabolic syndrome subjects when adjusted for fiber proportion and fiber size. Fat oxidation and muscle mitochondrial expression were not different in the metabolic syndrome subjects.

CONCLUSION

Lower proportion of type I fibers in metabolic syndrome muscle correlated with the severity of insulin resistance. Even though whole muscle content was normal, key elements of insulin action were consistently less in type I muscle fibers, suggesting their distribution was important in mediating insulin effects.

Metabolic clearance rate is a more robust and physiological parameter for insulin sensitivity than glucose infusion rate in the isoglycemic glucose clamp technique

BACKGROUND

The metabolic clearance rate (MCR) of glucose has been defined as the value of the glucose infusion rate (GIR) divided by the glucose concentration and could be thus expected to be a robust marker at various glucose concentrations.

METHODS

We evaluated the validity of MCR compared with GIR in 15 healthy subjects and 38 type 2 diabetes patients. The glucose clamp technique was performed at two different glucose levels-isoglycemia (fasting plasma glucose [FPG]) of each subject and euglycemia (100 mg/dL), consecutively. GIR and MCR were obtained at both glucose levels, and ratios of those at isoglycemia to euglycemia were calculated.

RESULTS

Although there was no obvious relationship between FPG levels and GIR ratio, the MCR ratio showed a good linear regression with FPG levels (r=-0.652, P<0.0001). Furthermore, MCR at FPG was excellently (r=0.955) correlated with that at euglycemia in comparison with the modest correlation of GIR between the two plasma glucose levels (r=0.876).

CONCLUSIONS

GIR was rather variable and not proportional to clamped plasma glucose levels. MCR was a less variable parameter than GIR at various plasma glucose levels, and MCR at FPG in the isoglycemic clamp study could be substituted for GIR at the euglycemic clamp study.

Insulin sensitivity and responsiveness in vitro and in vivo

Insulin resistance is evident in several clinical conditions such as obesity, diabetes type II, hypercortisolism. The mechanisms behind this resistance at the level of the target cell can be evaluated with measurements of insulin sensitivity with techniques both in vitro and in vivo. In this review various techniques used to evaluate insulin action are discussed and also some clinical conditions associated with insulin resistance.

Repeatability and reproducibility of the hyperinsulinemic-euglycemic clamp and the tracer dilution technique in a controlled inpatient setting

The objective of the study was to evaluate the reproducibility and repeatability of the combined use of the hyperinsulinemic-euglycemic (H-E) clamp and tracer dilution techniques. Ten nondiabetic men underwent a low-dose (40 mU/[m(2) min]) H-E clamp that was repeated within 3 to 4 days using porcine or human insulin in a double-blinded, randomized, crossover design. Coefficients of variation (CVs) for intraindividual differences and repeatability coefficient were calculated to evaluate reproducibility and repeatability. The Bland and Altman method was used to quantify repeatability. The CVs for intraindividual differences were 5.7% +/- 3.5% for steady-state (SS) insulin; 6.7% +/- 6.2% and 54.2 +/- 38.3% for basal and SS endogenous glucose product (EGP), respectively; and 10.3% +/- 8.5% for total insulin-stimulated glucose disposal (M) values. Basal EGP, SS EGP, and SS glucose and insulin concentrations were similar for the 2 clamps; but glucose infusion rate (P = .02) and M (borderline significant, P = .06) were higher in the first clamp than the second clamp. No significant correlations between mean of differences and average of basal and SS EGP, SS insulin concentration, and M between the 2 clamps were observed. We also found that the different values were less than the repeatability coefficients of these parameters and that the 95% limits of agreement and the interval of repeatability coefficient of these parameters were similar. There were no differences in metabolic responses between clamps when compared by the type of insulin (porcine vs human) infused. Our findings indicate that, although SS EGP has a high CV, the clamp, which measures insulin action (ie, SS insulin, M), and the tracer dilution technique for assessing basal EGP are repeatable and reproducible. Decreased glucose infusion rate and M over a short period in the second clamp may reflect an accumulative effect of continued physical inactivity.

Rate of peripheral glucose change during cognitive testing predicts performance in diabetes mellitus

BACKGROUND

The reason for cognitive deterioration in diabetes mellitus (DM) remains unknown. One suggestion is that despite elevated glucose levels, patients with DM generally have difficulty utilizing glucose during cognitive tasks. This assumption was tested in the present study.

METHODS

Male outpatients with DM (n = 46; age 52-85 years) were administered a series of standard neuropsychological and cognitive tests. In addition to assessing the time to complete the series of tests, peripheral blood glucose levels were measured prior to and following testing.

RESULTS

The rate at which peripheral blood glucose levels changed was examined in relation to cognitive performance. Multiple linear regression analyses revealed significant relationships between the rate of glucose change and performance on tests measuring psychomotor skills, attention, visuoperceptual abilities, sequencing skills, mental flexibility, and planning. Higher rates of decline in peripheral blood glucose levels were associated with better performance on all cognitive measures, except verbal fluency.

CONCLUSIONS

During cognitive testing, higher rates of decline in peripheral blood glucose levels may reflect stronger glucose utilization by the brain, thereby facilitating higher levels of cognitive performance. This non-invasive measure may be useful in primary care settings to provide a link between blood glucose changes and cognitive status.

Insulin detemir under steady-state conditions: no accumulation and constant metabolic effect over time with twice daily administration in subjects with Type 1 diabetes

AIMS

This study investigated the pharmacodynamic and pharmacokinetic characteristics of the novel long-acting insulin analogue insulin detemir (IDet) under single-dose and steady-state conditions in comparison with those of NPH insulin at steady state.

METHODS

Twenty-five subjects with Type 1 diabetes [seven females, 18 males, mean age (+/- sd) 39 +/- 12 years, body mass index 24 +/- 3 kg/m(2)] participated in three 24-h glucose clamps. IDet or NPH were given at 12-h intervals in fixed, individualized doses. The first clamp assessed the metabolic effect of NPH at steady state, the second investigated the effect of two single injections of IDet. Subjects continued IDet treatment for 7-14 days, after which the third clamp was performed to investigate IDet at steady state.

RESULTS

At steady state, the metabolic effect of IDet was constant over 24 h while a clear peak in the metabolic effect [expressed as glucose infusion rates (GIR)] was observed with NPH after each injection. The fluctuation in the metabolic effect (maximum GIR divided by the average of the GIR values at the interval ends) was significantly lower in the second 12 h of the experiments with IDet under steady-state conditions compared with NPH (fluctuation(12-24 h) 1.27 +/- 0.17 vs. 1.56 +/- 0.72, P < 0.05). The overall metabolic effect of IDet at steady state was comparable with that of NPH [GIR-area under curve (AUC)(0-24 h): 5697 +/- 1861 vs. 5929 +/- 1965 mg/kg] whereas a significantly lower effect (5187 +/- 1784 mg/kg, P = 0.01 vs. steady state) was observed following the first two IDet injections. GIR values at the end of clamp day 2 (first doses) and clamp day 3 (steady state) were comparable [GIR(trough 24 h) 3.7 +/- 1.7 vs. 3.8 +/- 1.6 mg/(kg x min) NS], indicating that IDet had reached steady state after the first two injections.

CONCLUSIONS

IDet administered twice daily reached steady state after the second injection and showed a constant metabolic effect over time under steady-state conditions. This should facilitate basal insulin substitution and decrease the risk of hypoglycaemia in insulin-treated subjects.

A mathematical model of the euglycemic hyperinsulinemic clamp

Background

The Euglycemic Hyperinsulinemic Clamp (EHC) is the most widely used experimental procedure for the determination of insulin sensitivity, and in its usual form the patient is followed under insulinization for two hours. In the present study, sixteen subjects with BMI between 18.5 and 63.6 kg/m² were studied by long-duration (five hours) EHC.

Results

From the results of this series and from similar reports in the literature it is clear that, in obese subjects, glucose uptake rates continue to increase if the clamp procedure is prolonged beyond the customary 2 hours. A mathematical model of the EHC, incorporating delays, was fitted to the recorded data, and the insulin resistance behaviour of obese subjects was assessed analytically. Obese subjects had significantly less effective suppression of hepatic glucose output and higher pancreatic insulin secretion than lean subjects. Tissue insulin resistance appeared to be higher in the obese group, but this difference did not reach statistical significance.

Conclusion

The use of a mathematical model allows a greater amount of information to be recovered from clamp data, making it easier to understand the components of insulin resistance in obese vs. normal subjects.

Measurement of insulin absorption and insulin action

For the practical implementation of every type of insulin therapy it is necessary to know both the time course of action of therapeutically used short- and long-acting insulin preparations and the factors influencing such time-action profiles. The only reliable way to obtain the required quantitative information about the pharmacokinetic and glucodynamic properties of insulin preparations has been the use of the euglycemic glucose clamp technique. The first studies with each new insulin formulation or insulin application technique should be performed with healthy subjects in order to have the most comparable study conditions. Thereafter, results from such clinical-experimental studies should be verified in similar studies with patients with diabetes. Earlier investigational approaches, which either had been limited to the determination of the pharmacokinetic properties of insulin preparations or had used the quantitative decrease of the blood glucose level as a measure of the pharmacodynamic properties, do not provide valid quantitative results. The proposed glucose clamp technique makes possible the quantitative study of the pharmacokinetic and pharmacodynamic properties of insulin preparations under comparative and reproducible conditions.

The effect of smoking on peripheral insulin sensitivity and plasma endothelin level

OBJECTIVES

The aim of the present study was to investigate the effect of smoking on peripheral insulin effectiveness.

METHODS

Seven healthy volunteers, nonsmokers, of mean age 39.6 +/- 7.1 Years and mean BMI 22.65 +/- 11.98 kg/m2, without family history of diabetes mellitus, with normal blood pressure participated in the study. All the parameters were studied twice - at baseline as well as after smoking (4 cigarettes per one hour). The study was performed in three days: at the first day we studied peripheral insulin effectiveness (M) in vivo by the artificial endocrine pancreas (Biostator), using the euglycaemic hyperinsulinaemic clamp technique, and insulin-receptor binding on circulating mononuclear blood cells; at the second day - the same parameters after one-hour smoking during the third hour of clamping; at the third day - plasma endothelin level, blood pressure and heart rate at baseline and after one-hour smoking.

RESULTS

There was a significant decrease in glucose utilization during the second clamp test, when the volunteers smoked during the third hour as compared to the test at baseline (p=0.04). This was accompanied by a significant decrease in insulin receptor affinity (p=0.04). Systolic blood pressure and heart rate increased significantly after one-hour smoking (p=0.03 and p=0.001, respectively). Plasma endothelin level increased significantly after smoking (from 0.62 +/- 0.15 pg/ml to 2.05 +/- 1.67 pg/ml, p=0.03).

CONCLUSION

Our results demonstrate that smoking decreases peripheral insulin sensitivity reducing insulin receptor affinity. We have confirmed that smoking increases plasma endothelin level, which probably by causing vasoconstriction and consequent tIssue hypoxaemia could decrease peripheral glucose utilization. We consider that smoking could also have a direct effect on insulin receptor affinity, thus leading to decreased peripheral insulin effectiveness.

Low insulin sensitivity (S(i) = 0) in diabetic and nondiabetic subjects in the insulin resistance atherosclerosis study: is it associated with components of the metabolic syndrome and nontraditional risk factors?

OBJECTIVE

To determine the meaning of S(i) = 0 derived from the frequently sampled intravenous glucose tolerance test.

RESEARCH DESIGN AND METHODS

The issue of assessing insulin resistance in large studies is important because the most definitive method ("gold standard"), the hyperinsulinemic-euglycemic clamp, is expensive and invasive. The frequently sampled intravenous glucose tolerance test (FSIGTT) has been widely used, but in insulin-resistant subjects (especially diabetic subjects), it yields considerable numbers of subjects whose S(i) is zero. The interpretation of an S(i) equaling zero is unknown.

RESULTS

-To address this issue, we examined 1482 subjects from the Insulin Resistance Atherosclerosis Study (IRAS) using an insulin-modified FSIGTT and minimal model calculation of S(i). The proportion of insulin-resistant subjects (S(i) < 1.61 x 10(-4) [min(-1). microU(-1) x ml(-1)] based on the median of the nondiabetic population) was 38.6% in subjects with normal glucose tolerance (NGT), 74% in subjects with impaired glucose tolerance (IGT), and 92% in subjects with type 2 diabetes. The proportion of subjects with S(i) = 0 was 2.2% in subjects with NGT, 13.2% in subjects with IGT, and 35.7% in subjects with type 2 diabetes. In subjects with IGT, those with S(i) = 0 had significantly lower HDL cholesterol levels and higher BMI, waist circumference, fibrinogen, plasminogen-activator inhibitor 1 (PAI-1), C-reactive protein (CRP), and 2-h insulin levels than insulin-resistant subjects with S(i) > 0. In type 2 diabetes, subjects with S(i) = 0 had significantly greater BMI and waist circumference and higher triglyceride, PAI-1, CRP, fibrinogen, and fasting and 2-h insulin levels than insulin-resistant subjects with S(i) > 0. In addition, diabetic subjects with S(i) = 0 had more metabolic disorders related to the insulin resistance syndrome than diabetic insulin-resistant subjects with S(i) > 0.

CONCLUSIONS

We found very few subjects with S(i) = 0 among subjects with NGT and few subjects with S(i) = 0 among subjects with IGT. In contrast, S(i) = 0 was common in subjects with diabetes. Subjects with S(i) = 0 tended to have more features of the insulin resistance syndrome than other insulin-resistant subjects with S(i) > 0, as would be expected of subjects with almost no insulin-mediated glucose disposal, thus suggesting that subjects with S(i) = 0 are correctly classified as being very insulin resistant rather than having failed the minimal model program.

Pharmacokinetic-pharmacodynamic modelling of insulin: comparison of indirect pharmacodynamic response with effect-compartment link models

The pharmacokinetic and pharmacodynamic modelling of insulin has been reported using a combined pharmacokinetic/pharmacodynamic (PK/PD) model, in which a hypothetical effect compartment is linked to a pharmacokinetic compartment. Review of the literature, however, indicated that the recently developed PK/PD models have consisted of an indirect pharmacodynamic response component, but none of them has been applied to the modelling of insulin. To study the relative relevance of the indirect pharmacodynamic response model and the effect-compartment link model in modelling the pharmacokinetics and pharmacodynamics of insulin, regular human insulin was administered intravenously at a dose of 0.1 IU kg(-1) to healthy Yucatan minipigs (after an overnight fasting). The plasma concentrations of insulin were measured by radioimmunoassay at predetermined time intervals, while blood glucose levels were monitored continuously using a glucose monitor. Analysis of the plasma insulin and the blood glucose profiles was performed by fitting with various PK/PD models and the results indicated that all of the 12 sets of plasma insulin data (after normalizing by the basal levels) have been adequately fitted to the two-compartment open pharmacokinetic model (a mean+/-s.e. correlation coefficient of 0.996+/-0.001 was obtained). The mean+/-s.e. correlation coefficient, the weighted residuals sum of squares (WRSS), and the Akaike's information criterion (AIC) were found, respectively, to be 0.935+/-0.008, 624+/-67, and 522+/-9 for the inhibitory indirect pharmacodynamic response model and 0.941+/-0.010, 547+/-63 and 513+/-9 for the stimulatory indirect pharmacodynamic response model, as compared with 0.725+/-0.041, 2309+/-276 and 628+/-10 for the effect-compartment link model. Based on these results, one may conclude that the indirect pharmacodynamic response model is a more appropriate approach for modelling the PK/PD of insulin than the effect-compartment link model.

Assessment of insulin sensitivity by 90 min isoglycaemic hyperinsulinaemic glucose clamp in healthy young men

We aimed to perform a detailed analysis of the isoglycaemic hyperinsulinaemic glucose clamp in relation to the time spent in performing the procedure, and analysed two series performed by independent investigators on different groups (n = 19 and n = 28) of healthy, young men. We calculated glucose disposal rates (GDR) during 20-min periods at different time points during the clamp. There was no difference in 90- and 120-min GDR when comparing the two series. The differences between 90- and 120-min GDR were (mean +/- SD) 0.48 +/- 1.10 mg/kg/min (p = 0.73) and 0.37 +/- 1.05 mg/kg/min (p = 0.71), respectively. The correlations between 90- and 120-min GDR were 0.94 (p < 0.001) and 0.89 (p < 0.001). Correlations between GDR during the second hour of the clamp and fasting plasma insulin ranged from -0.53 (p = 0.020) to -0.55 (p = 0.016) and from -0.44 (p = 0.020) to -0.54 (p = 0.003), respectively, and did not improve after 60 min of clamping. These data suggest that reliable indices of insulin sensitivity in healthy young men may appear even when the isoglycaemic hyperinsulinaemic clamp procedure is shortened from 120 to 90 min. A shorter procedure is time-effective and less expensive, but may be limited to healthy, young Caucasian men.

Influence of non-steady state during isoglycemic hyperinsulinemic clamp in hypertension. A LIFE substudy

We wanted to investigate whether time to steady state was reached within 2 h of insulin infusion during isoglycemic hyperinsulinemic clamp, comparing the glucose uptake index (M/IG) with Bergman's insulin sensitivity index (Sip). We performed a 2-h oral glucose tolerance test and a 3-h isoglycemic hyperinsulinemic clamp in 26 young, healthy subjects and 43 elderly patients with unmedicated essential hypertension and left ventricular hypertrophy. The 3-h Sip correlated strongly with the 2-h M/IG in the patients (r = 0.88, p < 0.001) as well as in the healthy subjects (r = 0.96, p < 0.001) with relatively narrow limits of agreement in the patients. However, during the third hour of insulin infusion, M/IG (10.0 vs 12.21(2) x kg(-1) x min(-1) x mmol(-1), p < 0.001) as well as Sip (7.1 vs 9.41(2) x kg(-1) x min(-1) x mmol(-1), p < 0.001) increased significantly in the patients, but not in the healthy subjects. Because the 2-h M/IG correlated strongly with the 3-h Sip with relatively narrow limits of agreement, it is a good measure of insulin sensitivity. However, a 2-h clamp results in lower insulin sensitivity values in elderly, hypertensive patients due to the fact that steady state is not reached, demonstrating a higher prevalence of insulin resistance in such a population.

Increased dependence of glucose production on peripheral insulin in diabetic depancreatized dogs

We have recently found that in nondiabetic dogs and humans, suppression of glucose production (GP) is mediated by both peripheral and hepatic effects of insulin. We have also found that both nonesterified fatty acids (NEFA) and glucagon are important determinants of the peripheral effect of insulin on GP. However, in moderately hyperglycemic depancreatized dogs, suppression of GP appeared to be mediated by peripheral but not hepatic insulin. In this latter study, insulin concentrations were in the high postprandial range (approximately 300 pmol/L) and suppression of GP may have been close to maximum. The aim of the present study was to determine whether GP can be regulated by hepatic insulin in depancreatized dogs at low insulin concentrations in the postabsorptive range. Depancreatized dogs were maintained at moderately hyperglycemic levels (approximately 10 mmol/L) by subbasal insulin infusions. In paired experiments, additional low-dose equimolar insulin infusions (0.75 pmol/kg x min) were administered peripherally (PER, n = 6) or portally (POR, n = 6) during glucose clamps. This resulted in a minimal increase in peripheral insulin levels, which was greater in PER versus POR, 29.0 +/- 3.7 versus 11.7 +/- 2.2 pmol/L. Also, we infused insulin peripherally at half this rate (1/2 PER, n = 6) to match the increase in peripheral insulin levels in POR (1/2 PER, 14.6 +/- 2.2) and thus obtain a selective POR versus 1/2 PER difference in hepatic sinusoidal insulin levels. PER suppressed GP more than POR (45.4% +/- 4.0% v 35.3% +/- 6.8%, P < .001), whereas POR did not suppress GP more than 1/2 PER (35.6% +/- 6.3%). Therefore, suppression of GP was proportional to peripheral rather than hepatic sinusoidal insulin levels, as in our previous study at higher insulin concentrations. In conclusion, during glucose clamps in moderately hyperglycemic depancreatized dogs, (1) suppression of GP was dominated by insulin's peripheral effects not only at postprandial but also postabsorptive insulin levels, and (2) we found no evidence for a hepatic effect of insulin in suppressing GP. We hypothesize that this effect is reduced in the depancreatized dog model of diabetes due to hepatic insulin resistance and/or hyperglycemia.

Slower activation of insulin action in hypertension associated with obesity

OBJECTIVE

To determine whether kinetic abnormalities in the onset of insulin action contribute to the insulin resistance in obesity-associated hypertension.

DESIGN

We monitored the rate of increase in glucose infusion during 6 h of hyperinsulinemic (40 mU/m2 per min) euglycemic clamps in hypertensive and normotensive obese subjects. The two groups of hypertensive (n=9) and normotensive (n=9) subjects were matched for age (48+/-2 versus 45+/-5 years), sex (five males and four females versus four males and five females) and body mass index (42+/-3 versus 40+/-2 kg/m2).

RESULTS

In all subjects, the glucose infusion rate required to maintain euglycemia increased progressively during the clamp studies to achieve maximal, steady-state values within the fifth hour. During the first 2 h of the clamp, mean glucose infusion rate, the traditional approach to assessing insulin sensitivity, was lower in the hypertensive than in the normotensive obese patients (2.04+/-0.13 versus 3.29+/-0.41 mg/kg per min, respectively; P < 0.05). In contrast, the maximal steady-state glucose infusion rate, calculated as the mean value during the sixth hour of clamping, was similar in the hypertensive and in the normotensive obese patients (4.48+/-0.43 versus 4.81+/-0.45 mg/kg per min, respectively; NS). The time required to reach the half-maximal glucose infusion rate was greater in the hypertensive than normotensive obese patients (91+/-12 versus 38+/-5 min, respectively; P< 0.05).

CONCLUSION

In obesity, hypertension was associated with a slower rate of activation of the insulin effect on glucose metabolism, whereas the maximal steady-state insulin effects were not altered by elevated blood pressure. Thus, the link between obesity and hypertension may be associated with the kinetics of onset of insulin action.

Perioperative insulin and glucose infusion maintains normal insulin sensitivity after surgery

Elective surgery was performed after overnight fasting, a routine that may affect the metabolic response to surgery. We investigated the effects of insulin and glucose infusions before and during surgery on postoperative substrate utilization and insulin sensitivity. Seven patients were given insulin and glucose infusions 3 h before and during surgery (insulin group), and a control group of six patients underwent surgery after fasting overnight. Insulin sensitivity and glucose kinetics (D-[6,6-2H2]glucose) were measured before and immediately after surgery using a hyperinsulinemic, normoglycemic clamp. Glucose infusion rates and whole body glucose disposal decreased after surgery in the control group (-40 and -29%, respectively), whereas no significant change was found in the insulin group (+16 and +25%). Endogenous glucose production remained unchanged in both groups. Postoperative changes in cortisol, glucagon, fat oxidation, and free fatty acids were attenuated in the insulin group (vs. control). We conclude that perioperative insulin and glucose infusions minimize the endocrine stress response and normalize postoperative insulin sensitivity and substrate utilization.

Time course of insulin action on tissue-specific intracellular glucose metabolism in normal rats

We investigated the time course of insulin action in conscious rats exposed to constant physiological hyperinsulinemia (approximately 100 mU/l) while maintaining euglycemia (approximately 100 mg/dl) for 0, 0.5, 2, 4, 8, or 12 h. [3-3H]glucose was infused to quantitate whole body glucose disposal (rate of disappearance, Rd), glycolysis (generation of 3H2O in plasma), hepatic glucoses production (HGP), and skeletal muscle and liver glycogen synthesis ([3-3H]glucose incorporation into glycogen and time-dependent change in tissue glycogen concentration). The basal Rd, which equals HGP, was 6.0 +/- 0.3 mg.kg-1.min-1. With increased duration of hyperinsulinemia from 0 to 0.5 to 2 to 4 h, Rd increased from 6.0 +/- 0.3 to 21.0 +/- 1.1 to 24.1 +/- 1.5 to 26.6 +/- 0.6 mg.kg-1.min-1 (P < 0.05 for 2 and 4 h vs. 0.5 h). During the first 2 h the increase in Rd was explained by parallel increases in glycolysis and glycogen synthesis. From 2 to 4 h the further increase in Rd was entirely due to an increase in glycolysis without change in glycogen synthesis. From 4 to 8 to 12 h of hyperinsulinemia, Rd decreased by 19% from 26.6 +/- 0.6 to 24.1 +/- 1.1 to 21.6 +/- 1.8 mg.kg-1.min-1 (P < 0.05 for 8 h vs. 4 h and 12 h vs. 8 h). The progressive decline in Rd, in the face of constant hyperinsulinemia, occurred despite a slight increase (8-14%) in glycolysis and was completely explained by a marked decrease (64%) in muscle glycogen synthesis. In contrast, liver glycogen synthesis increased fourfold, indicating an independent regulation of muscle and liver glycogen synthesis by long-term hyperinsulinemia. In the liver, during the entire 12-h period of insulin stimulation, the contribution of the direct (from glucose) and the indirect (from C-3 fragments) pathways to net glycogen formation remained constant at 77 +/- 5 and 23 +/- 5%, respectively. HGP remained suppressed throughout the 12-h period of hyperinsulinemia.

Acute effects of blood pressure elevation on insulin clearance in normotensive healthy subjects

Reduced clearance of insulin from plasma contributes to the hyperinsulinemia associated with essential hypertension (EH); however, the association between impaired insulin clearance and EH remains unexplained. Whether elevated blood pressure (BP) affects insulin clearance is unknown; therefore, we used the hyperinsulinemic euglycemic clamp to determine the effects of BP elevation on insulin clearance and sensitivity in eight healthy volunteers. Placebo infusion increased mean BP by 2.6+/-1.6 mm Hg, which was significantly less than rises produced by phenylephrine, an alpha1-adrenoceptor agonist (+11+/-1.8 mmHg, P<.05), or by angiotensin II (+13+/-1.3 mmHg, P<.01). Although beta-adrenoceptor stimulation with isoproterenol did not change mean BP (+3.6 mm Hg, P=NS), it significantly increased systolic pressure (+23+/-2.8 mm Hg versus +2.3+/-4.6 mm Hg with placebo P<.01). Insulin secretion (ie, C-peptide concentrations) was not affected by any of the treatments; however, phenylephrine significantly reduced the metabolic clearance rate of insulin (MCRinsulin) (16.6+/-1.0 mL/kg per minute with placebo versus 13.6+/-0.7 mL/kg per minute with phenylephrine, P<.01) and thereby increased plasma insulin concentrations (66+/-5.1 microU/mL with placebo versus 79+/-4.1 microU/mL with phenylephrine, P<.05). Phenylephrine also increased glucose utilization (42+/-5.8 micromol/kg per minute during placebo versus 58+/-4.8 micromol/kg per minute during phenylephrine, P<.05); however, this was proportional to the increased insulin concentrations; therefore, insulin sensitivity was unchanged. MCRinsulin and plasma insulin concentrations were not affected by angiotensin II; however, glucose utilization increased to 51+/-2.7 micromol/kg per minute (P<.01 versus placebo), indicating insulin sensitivity was increased. MCRinsulin was unaffected by isoproterenol. Thus, alpha-adrenergic stimulation but not increased BP per se is a potent regulator of insulin clearance and plasma insulin concentrations.

The euglycaemic hyperinsulinaemic clamp: an evaluation of current methodology

1. The recognition of the role of insulin resistance in disease states and the recent development of new drugs that modify insulin-dependent metabolism has led to increased use of the euglycaemic hyperinsulinaemic clamp to measure in vivo insulin sensitivity, but several key aspects of the technique are poorly documented in the literature. 2. We have evaluated the reproducibility and intersubject variation of measurements of insulin sensitivity in groups of insulin-sensitive and insulin-resistant subjects and assessed the effects of hand warning on haemodynamic and metabolic responses. 3. Subjects participated in one of two protocols: (i) 18 healthy male volunteers and 18 patients with hypertension and glucose intolerance were clamped on two occasions, 1 week apart with measurements of insulin sensitivity (M) derived after 120 and 180 min of hyperinsulinaemia; and (ii) six healthy volunteers were clamped on one occasion with simultaneous sampling of antecubital and 'arterialized' (dorsal hand) venous blood for comparison of plasma glucose concentrations and oxygen saturation and a further six volunteers were clamped on two occasions with and without the use of hand warming. 4. Measurements of M derived after 120 min (M120) and 180 min (M180) of hyperinsulinaemia were reproducible: the coefficients of repeatability (mg/kg per min) of M120 and M180 were 1.0 and 0.9 for volunteers and 1.0 and 1.0 for the patient group, respectively. The intersubject variation in insulin stimulus was high: coefficients of variation for M180 were 22% for volunteers compared with 38% for the patient group. In volunteers compared with the patient group, hand warming significantly increased venous oxygen saturations (95 +/- 2 vs 79 +/- 18%, respectively) and glucose concentrations (5.2 +/- 0.2 vs 4.5 +/- 0.4 mmol/L, respectively) and measurements of M were significantly higher using arterialized compared with antecubital venous blood. However, local hand warming was associated with systemic vasodilatation: blood pressure decreased (e.g. 6 mmHg diastolic; P < 0.05) with a compensatory increase in heart rate (8 b.p.m.). 5. In conclusion, clamps of 120 and 180 min duration yielded measurements of M that were reproducible. The technique is much more robust when used in the context of a crossover design because of the significant (20-40%) intersubject variation in M, even among apparently homogeneous male volunteers. Hand warming effectively arterializes venous blood and gives significantly higher M values, but induces systemic vasodilation, which may confound measurements of M.

The day-to-day variation in insulin sensitivity in non-insulin-dependent diabetes mellitus patients assessed by the hyperinsulinemic-euglycemic clamp method

The objective was to study the day-to-day variation in insulin sensitivity in non-insulin-dependent diabetes mellitus (NIDDM) and to analyze within- and between-person variances in the glucose infusion rate during steady state (M value). Ten NIDDM patients attending the outpatient clinic at Aarhus Amtssygehus were studied three times under standardized conditions. Each time, a 120-minute hyperinsulinemic-euglycemic clamp was performed. Similar M values were found on the 3 study days, with difference between M values on the 3 days of (mean +/- SD) 0.3 +/- 1.8 mg glucose/kg lean body mass (LBM)/min. The total coefficient of variation (CV) for M values was 57% after the first clamp, 55% after the second, and 53% after the third. Ninety percent of the total day-to-day variation in M values could be ascribed to between-person variation and 10% to within-person variation. Within-person components of variance included all sources of variation other than between-person variation. The within-person CV for M values was 11.9% +/- 7.2% after two clamp studies and 12.1% +/- 7.3% after three (P < .55). In conclusion, under standardized conditions, a valid estimate of insulin sensitivity assessed by the hyperinsulinemic-euglycemic clamp in NIDDM patients is obtained after a single measurement. Because of large between-person variation, paired data should be used when comparing insulin sensitivity in NIDDM patients.

The acute impact of ethanol on glucose, insulin, triacylglycerol,and free fatty acid responses and insulin sensitivity in type 2 diabetes

The aim of the present study was to evaluate the acute effect of ethanol on insulin sensitivity, and glucose, insulin, free fatty acid (FFA), and triacylglycerol responses in ten patients with non-insulin-dependent (type 2) diabetes. In the test study an oral dose of 0.66 g ethanol/kg followed by continuous intravenous infusion of 0.1 g ethanol/kg per h was given to maintain a constant ethanol level in the blood. In the control study identical volumes of oral water and intravenous saline (9 g NaCl/l) were given. After 90 min insulin sensitivity was determined by the hyperinsulinaemic, euglycaemic clamp technique. Ethanol caused no change in blood glucose or insulin concentrations. The FFA level was suppressed by ethanol while the triacylglycerol level was unaffected. The insulin sensitivity was not affected by ethanol. No major acute effect of ethanol on the glycaemic control in fasting type 2 diabetic patients was found in comparison with what is seen in healthy people. The present study, along with the sparse literature, indicates that the ability of ethanol to induce hypoglycaemia is attenuated or absent in diet-treated type 2 diabetes. Furthermore, we found no change in insulin sensitivity. Consequently, the risk of acute ethanol-induced aberrations in carbohydrate metabolism in diet-treated type 2 diabetes seems to be less than previously expected, when alcohol is not taken as a part of a meal.

Interstitial insulin during euglycemic-hyperinsulinemic clamp in obese and lean individuals

Transcapillary insulin transport has been considered a rate-limiting step of insulin action. However, direct measurement of interstitial insulin levels during physiologic levels of insulinemia have not been performed. We determined changes in interstitial insulin in eight healthy non-obese men and seven healthy obese men by microdialysis during a euglycemic-hyperinsulinemic clamp. Interstitial insulin was determined in the subcutaneous tissue of the abdomen and thigh. Steady-state insulin concentrations were reached approximately 10 minutes after the start of insulin infusion in the subcutaneous tissue of the abdomen and thigh and returned to basal levels approximately 10 minutes after the infusion was discontinued. There was no difference in the rapidity of change in interstitial insulin between obese and lean individuals at either site studied, irrespective of the pattern of fat distribution. The relative change in dialysate insulin concentration during the euglycemic clamp did not differ between obese and lean individuals at either site studied. It was also unaffected by the waist to hip ratio. The rapid change in interstitial insulin concentration could be of physiologic significance in determining the effects of changes in circulating insulin concentration. We conclude that transcapillary insulin transport in adipose tissue is unaffected by obesity and the pattern of fat distribution in healthy men. It is also concluded that when interstitial insulin is determined directly, transcapillary insulin transport is rapid and does not demonstrate a significant lag phase.

Insulin sensitivity tested with a modified euglycemic technique in cats and rats

A new insulin sensitivity test (IST) is described using a modified euglycemic clamp in cats and rats. The IST uses the amount of glucose required to be infused to maintain euglycemia over a 30-min period in rats and 60 min in cats following a bolus administration of insulin as the index of insulin sensitivity. Glucose levels are determined at short time intervals (2-5 min), and variable glucose infusion is used to hold glucose levels within a few percentage points of the basal pre-test glucose level. A new blood sampling procedure is described that allows each IST to be carried out using a total of only 0.5 mL of blood. The IST is sensitive and allows clear insulin dose effects to be demonstrated with 100 mU/kg requiring 355.0 +/- 14.3 mg/kg over 30 min and 50 mU/kg requiring 198.7 +/- 11.1 mg/kg. Five consecutive tests were reproducibly carried out (%CV = 3.0 +/- 0.5) over a 12-hr period in the cat with insulin, glucagon, and glucose levels remaining stable prior to each IST. Glucagon and norepinephrine plasma concentrations do not change significantly during the IST. The IST is sufficiently sensitive to allow demonstration of dose-response relationships for atropine-induced insulin resistance. The IST is thus sensitive, reproducible, and able to demonstrate acute insulin resistance in anesthetized cats and rats. The test is demonstrated in fed (rats) and fasted (cats) state.

Insulin sensitivity, insulin secretion and glucose effectiveness in diabetic and non-diabetic cirrhotic patients

In cirrhotic patients with normal fasting glucose levels both insulin insensitivity and a blunted early insulin response to oral glucose are important determinants of the degree of intolerance to oral glucose. It is not known whether the ability of hyperglycaemia per se to enhance glucose disposal (glucose effectiveness) is also impaired. It is also unclear whether overt diabetes is due to: (1) more marked insulin insensitivity; (2) impaired insulin secretion; (3) reduced glucose effectiveness; or (4) a combination of these mechanisms. We used the "minimal model" to analyse the results of a 3-h intravenous glucose tolerance test to assess glucose effectiveness, insulin sensitivity and insulin responses in 12 non-diabetic cirrhotic patients, 8 diabetic cirrhotic patients and 10 normal control subjects. Fasting blood glucose levels were 4.8 +/- 0.2, 7.5 +/- 0.6 and 4.7 +/- 0.1 mmol/l, respectively. Fasting insulin and C-peptide levels were higher in both cirrhotic patient groups compared with control subjects. The glucose clearance between 6 and 19 min after i.v. glucose was lower in both cirrhotic groups (non-diabetic, 1.56 +/- 0.14, diabetic, 0.76 +/- 0.06, control subjects, 2.49 +/- 0.16 min-1%, both p < 0.001 vs control subjects). Serum insulin peaked at 3 and 23 min in the non-diabetic cirrhotic patients and control subjects; both peaks were higher in the non-diabetic cirrhotic patients and showed a delayed return to basal levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Dose-response characteristics of human proinsulin and insulin in non-insulin-dependent diabetic humans

We compared the actions of human proinsulin and insulin on glucose turnover and on intermediary carbohydrate and lipid metabolism in non-insulin-dependent diabetes mellitus (NIDDM). Six diet-controlled weight-matched (25.4 +/- 1.0 kg/m2) NIDDM subjects underwent six separate isoglycemic clamps. Glucose turnover was measured using a primed continuous infusion of [6',6'-2H2]glucose. Each subject received three low-dose intravenous infusions of both insulin and proinsulin. Blood glucose was maintained at 6.7 +/- 0.3 mM during proinsulin and insulin infusion. Insulin (I) infusions gave steady-state levels of 0.12 +/- 0.001 (I1), 0.18 +/- 0.01 (I2), and 0.33 +/- 0.01 nM (I3). Steady-state proinsulin (P) levels were 2.5 +/- 0.1 (P1), 4.3 +/- 0.2 (P2), and 8.8 +/- 0.9 nM (P3). Hepatic glucose production was suppressed equally by proinsulin and insulin at all doses. The metabolic clearance rate of glucose was significantly increased during the insulin infusion compared with proinsulin. The use of [6',6'-2H2]glucose resulted in a mean underestimation of the glucose infusion rate of 10.0 +/- 4.0 and 6.0 +/- 2.5% during the two highest insulin and proinsulin doses, respectively. Proinsulin had a significantly weaker effect than insulin, at the lowest infusion dose, in percent suppression of plasma nonesterified fatty acids, blood glycerol, and beta-hydroxybutyrate levels (all P less than 0.05). Blood lactate levels were lower during the P1 (628 +/- 43 microM) and P2 (657 +/- 93 microM) infusions compared with I1 (776 +/- 60 microM) and I2 (878 +/- 44 microM; P less than 0.05, P less than 0.02), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of angiotensin-I converting enzyme inhibition on insulin action in healthy volunteers

Acute hyperinsulinaemia, achieving insulin levels within the physiological range, induces sodium retention. At the same time an activation of the renin-angiotensin system occurs, with a rise in plasma renin activity (PRA) and angiotensin-II level but no change in plasma aldosterone. After administration of higher, pharmacological doses of insulin an increase in systolic blood pressure and heart rate can also be observed, while further increases in PRA and angiotensin-II are noted. To determine whether angiotensin-II is involved in observed insulin actions, we studied the renal and cardiovascular effects of three dosages of insulin (50 (Ins I), 300 (Ins II) and 500 (Ins III) mU kg-1 h-1) in healthy subjects after one week of treatment with the angiotensin-I converting enzyme inhibitor enalapril (10 mg twice a day), using the euglycaemic clamp technique. Control data were obtained from two previously conducted experiments in the same subjects, one with infusion of insulin and one with the insulin solvent only. The effect of insulin on fractional sodium excretion, blood pressure and heart rate was unaffected by enalapril, which precludes any involvement of the renin-angiotensin system with regard to these aspects of insulin action. Insulin sensitivity increased significantly during treatment with enalapril (with enalapril: Ins I: 11.3 +/- 3.0, Ins II: 20.0 +/- 3.4 and Ins III: 20.6 +/- 3.9 mg kg-1 min-1 glucose (mean +/- SD); without enalapril: Ins I: 8.7 +/- 2.3, Ins II: 13.7 +/- 3.0 and Ins III: 15.5 +/- 3.1 mg kg-1 min-1 glucose; P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Exogenous insulin augments in healthy volunteers the cardiovascular reactivity to noradrenaline but not to angiotensin II

Hyperinsulinemia has been implicated in the pathogenesis of the blood pressure elevation in patients with noninsulin-dependent diabetes mellitus, obesity, but also essential hypertension. In these conditions an increased cardiovascular reactivity to noradrenaline (NA) and angiotensin II (AII) can be observed. Using the euglycemic clamp technique, we determined the cardiovascular reactivity to graded infusions of NA and AII in nine healthy males before (Bas), and 1 and 6 h after infusion of insulin (50 mU/kg per h) was started. On separate days control experiments were carried out to control for any circadian variation. Insulin led to a decrease of the amount of circulating NA necessary to increase the diastolic blood pressure (DBP) 20 mmHg (actual experiment [mean +/- SEM]: Bas, 23.1 +/- 5.0; 1 h, 14.8 +/- 3.0; and 6 h, 12.3 +/- 3.1; and control experiment: Bas, 20.7 +/- 5.0; 1 h, 18.6 +/- 3.5; and 6 h, 17.3 +/- 3.3 nmol/liter; Bas vs. 1 and 6 h: P less than 0.05). Although the amount of NA infused to raise DBP 20 mmHg showed a similar decline after 1 h of insulin infusion, no such change from baseline could be observed at 6 h. This appeared to be due to an increase in NA clearance with more prolonged insulin infusion. Insulin exerted no effect on the amount of AII infused to increase DBP 20 mmHg (actual experiment: Bas, 27.6 +/- 6.4; 1 h, 28.8 +/- 10.0; and 6 h, 21.2 +/- 5.3; and control experiment: Bas, 33.6 +/- 5.7; 1 h, 34.2 +/- 6.1; and 6 h, 23.4 +/- 4.7 ng/kg/min; NS). We did observe a circadian variation in AII reactivity. Whether the increase in cardiovascular responsiveness to NA after administration of insulin contributes to the elevation in blood pressure frequently observed in patients with insulin resistance remains to be proven.

Insulin time-dependent effects on the leg exchange of glucose and amino acids in man

Time-dependent effects of insulin on the leg exchange of glucose, lactate, glycerol, free fatty acids (FFA) and amino acids were measured in relation to oxygen uptake (leg and whole body) and whole body glucose assimilation including oxidation. Seven healthy males (58 +/- 3 years of age) were investigated before operation of uncomplicated inguinal hernia or varicose veins. Euglycaemic glucose clamp investigations with systemic hyperinsulinaemia between 100-120 mU1(-1) were used. Metabolic measurements were performed before and during hyperinsulinaemia at 2 and 6 h following the start of glucose clamp to evaluate the time-dependency of insulin actions. Whole body glucose uptake increased continuously for up to 6 h (from 4.7 +/- 0.7 to 8.0 +/- 0.8 mg/kg/min, P less than 0.01) despite stable plasma concentrations of glucose and insulin. This was also true for glucose oxidation. Whole body oxygen uptake did not change significantly during the clamp while the leg exchange of oxygen uptake did (from 5.9 +/- 0.86 mumol/100 g/min to 11.6 +/- 2.4, P less than 0.01). Insulin effect on leg blood flow was time-dependent and increased two-fold (2.3 +/- 0.4 ml/100 g/min to 4.4 +/- 0.9, P less than 0.001) during clamp. The leg production of lactate increased continuously, accounting for approximately 15% of the glucose uptake across the leg, but the rise in arterial lactate did not reach the level of statistical significance. Plasma FFA concentrations decreased in a time-dependent manner during clamp, while the leg exchange of FFA switched rapidly to a stable net uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

Whole body and hepatic insulin action in normal, starved, and diabetic rats

In normal (N), 3-days starved (S), and streptozotocin-treated (65 mg/kg) 3-days diabetic (D) rats we examined the in vivo dose-response relationship between plasma insulin levels vs. whole body glucose uptake (BGU) and inhibition of hepatic glucose production (HGP) in conscious rats, as determined with the four-step sequential hyperinsulinemic euglycemic clamp technique, combined with [3-3H]glucose infusion. Twelve-hour fasting (basal) HGP was 3.0 +/- 0.2, 2.1 +/- 0.2, and 5.4 +/- 0.5 mg/min in N, S, and D rats, respectively. Next, all rats were clamped at matched glycemia (6 mM). Lowering plasma glucose in D rats from +/- 20 to 6.0 mM did not increase plasma norepinephrine, epinephrine, glucagon, and corticosterone levels. For BGU, insulin sensitivity was increased (70 +/- 11 microU/ml) in S and unchanged (113 +/- 21 microU/ml) in D compared with N rats (105 +/- 10 microU/ml). Insulin responsiveness was unchanged (12.4 +/- 0.8 mg/min) in S and decreased (8.5 +/- 0.8 mg/min) in D compared with N rats (12.3 +/- 0.7 mg/min). For HGP, insulin sensitivity was unchanged (68 +/- 10 microU/ml) in S and decreased (157 +/- 21 microU/ml) in D compared with N rats (71 +/- 5 microU/ml). Insulin responsiveness was identical among N, S, and D rats (complete suppression of HGP). In summary, 1) insulin resistance in D rats is caused by hepatic insensitivity and by a reduction in BGU responsiveness. 2) S rats show normal hepatic insulin action, but insulin sensitivity for BGU is increased. Therefore, S and D rats both suffering from a comparable catabolic state (10-15% body wt loss in 3 days) show opposite effects on in vivo insulin action. This indicates that in vivo insulin resistance in D rats is not caused by the catabolic state per se.

Amylin-induced in vivo insulin resistance in conscious rats: the liver is more sensitive to amylin than peripheral tissues

Amylin is a polypeptide of 37 amino acids, predominantly synthesized in pancreatic Beta cells. The peptide was suggested to be dysregulated in Type 2 (non-insulin-dependent) diabetes mellitus and it antagonized certain actions of insulin in vitro in rat muscle. This led to speculation that amylin is involved in the pathogenesis of Type 2 diabetes. We have examined the in vivo effects of rat amylin, amidated at the carboxy-terminus, on insulin-mediated carbohydrate metabolism in conscious rats, using the hyperinsulinaemic (+/- 1 nmol/l) euglycaemic (6 mmol/l) clamp technique combined with [3-3H]-glucose infusion. Basal plasma amylin levels were less than or equal to 75 pmol/l. Applied amylin levels of 220 +/- 75 pmol/l (infusion rate of 12.5 pmol/min) antagonized only the insulin action on liver, resulting in a 100% increase of hepatic glucose output. Amylin levels of 4750 +/- 750 pmol/l (infusion rate of 125 pmol/min) induced a 250% increase of insulin-inhibited hepatic glucose output and, in addition, a 30% decrease of insulin-stimulated peripheral glucose up-take. Amylin did not affect: 1) the metabolic clearance rate of insulin, 2) the levels of plasma glucagon, epinephrine, norepinephrine, and corticosterone, 3) in vitro insulin binding and insulin-stimulated receptor autophosphorylation. This suggests that amylin antagonizes insulin action via binding to a yet unknown receptor.

IN CONCLUSION

amylin causes in vivo insulin resistance and the liver seems the predominant organ regulated by this hormone. The in vivo effects of amylin mimic the pathophysiological abnormalities of insulin action in Type 2 diabetes.

Interaction of exercise and insulin action in humans

To assess the interaction of exercise and insulin action, healthy males were studied with saline infusion (n = 5) or with a hyperinsulinemic euglycemic clamp (0.5, 1.0, 2.0, or 15.0 mU.kg-1.min-1; n = 5 at each dose) during rest (40 min), moderate-intensity cycle exercise (100 min), and recovery (100 min). Metabolism was assessed using isotopic methods and indirect calorimetry. During rest, exercise, and recovery with saline infusion, plasma glucose was unchanged, total glucose utilization (Rd) was 2.4 +/- 0.4, 4.9 +/- 0.2, and 2.6 +/- 0.2 mg.kg-1.min-1, and carbohydrate (CHO) oxidation (OX) was 1.4 +/- 0.3, 10.6 +/- 1.1, and 0.5 +/- 0.2 mg.kg-1.min-1. The glucose infusion, insulin-dependent Rd, and CHO OX increased synergistically when exercise and insulin clamps were combined. Exercise decreased (P less than 0.05) the half-maximal doses (ED50) and increased the maximal responses (Vmax) for insulin-dependent Rd and CHO OX. Estimates of insulin-independent Rd were 1.3 +/- 0.7, 4.1 +/- 1.3, and 1.9 +/- 0.7 mg.kg-1.min-1 and insulin-independent CHO OX were 1.2 +/- 0.9, 10.4 +/- 1.3, and 0.6 +/- 0.3 mg.kg-1.min-1 during rest, exercise, and recovery. Estimates during exercise were greater than those at rest (P less than 0.05). The total suppression of free fatty acids (FFA) and fat OX by insulin were elevated by exercise (P less than 0.05). In summary, exercise and insulin interact synergistically in stimulating Rd and CHO OX.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors for development of secondary failure to sulfonylurea drugs in non-insulin-dependent diabetes mellitus

Thirty-five non-insulin-dependent diabetic subjects were divided into two groups, according to therapeutical approach. The first group consisted of 17 diabetics receiving sulfonylureas and maintaining a satisfactory metabolic control. The second group included 18 patients who were transferred from sulfonylureas to insulin treatment, i.e. patients developing secondary failure to sulfonylurea drugs. We established that the patients with secondary failure to sulfonylurea drugs show a significantly lower B-cell secretory response following stimulation with i.v. tolbutamide, a significantly lower peripheral insulin sensitivity by euglycemic hyperinsulinemic clamp, and an increased frequency of HLAB21 and HLADR1 antigens. This latter study was performed in 42 patients. We thus conclude that in these patients diabetes mellitus may be considered as a separate form of the disease, which needs reevaluation of the criteria concerning therapeutical approach, prognosis, and evolution.

Underestimation of glucose turnover determined using [6-3H]glucose tracer in non-steady state. The role of a tritiated tracer impurity

The use of tritiated glucose tracers may result in underestimation of glucose turnover during hyperinsulinaemic clamps giving paradoxical negative endogenous glucose production rates. While mathematical modelling errors in the analysis of tracer data are major determinants of this underestimate in the non-steady state, the relative importance of tracer contamination under these conditions remains in doubt. We have used high performance liquid chromatography to assess the possible contribution to this problem of a labelled tracer impurity found in [6-3H]glucose. In conventional 4 h hyperinsulinaemic clamps performed in six normal subjects, labelled impurity increased as a percentage of the neutral plasma radioactivity fraction from 5.3 +/- 0.9% after a 2 h equilibration period (0 min) to 13.5 +/- 2.2% at 120 min and 15.4 +/- 2.4% at 240 min, as plasma glucose specific activities fell following the infusion of insulin. Negative endogenous glucose production rates were observed both at 90-120 min (-8.8 +/- 1.6 mumol.kg-1min-1) and at 210-240 min (-8.5 +/- 1.4 mumol.kg-1min-1) implying a persistent underestimate in isotopically determined glucose appearance rate. Using chromatography data to correct for impurity increased glucose appearance rates by 7.9 +/- 2.1% at 120 min and 11.0 +/- 2.5% at 240 min. Purified tracer was then used for a further six clamps. When the conventional protocol was used with unlabelled glucose infusion an obvious negative error persisted only at 90-120 min. In contrast, labelled infusions gave exclusively positive values for endogenous glucose production.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic hyperinsulinemia decreases insulin action but not insulin sensitivity

Hyperinsulinemia and insulin resistance are commonly seen in obese and non-insulin-dependent diabetes mellitus (NIDDM) patients, suggesting a causal link exists between hyperinsulinemia and insulin resistance. In a previous study, we demonstrated that chronic (28 days) intraportal hyperinsulinemia (50% increase in basal insulin levels) resulted in a decrease in insulin action as assessed by a one-step euglycemic hyperinsulinemic clamp. Since only one dose of insulin was used during the clamp, it was not possible to determine if the decrease in insulin action was due to a change in insulin sensitivity and/or maximal insulin responsiveness. In the present study, insulin resistance was induced as before, but insulin action was assessed in overnight fasted conscious dogs using a four-step euglycemic hyperinsulinemic clamp (1, 2, 10, and 15 mU/kg/min). Insulin responsiveness was assessed before the induction of chronic hyperinsulinemia (day 0), and after 28 days of hyperinsulinemia (day 28). Transhepatic glucose balance and whole-body glucose utilization were measured to allow assessment of both the hepatic and peripheral effects of insulin. Chronic hyperinsulinemia increased basal insulin levels from 13 +/- 2 to 21 +/- 4 microU/mL. After 4 weeks of chronic hyperinsulinemia, maximal insulin-stimulated glucose utilization was decreased 23% +/- 4% (P less than .05) and insulin sensitivity (ED50) was not significantly altered. During the four-step clamp, the liver was a major site of glucose utilization. The liver was responsible for 13% of the total glucose disposal rate on day 0 (2.9 mg/kg/min) at the highest insulin infusion rate (15 mU/kg/min; 2,000 microU/mL).(ABSTRACT TRUNCATED AT 250 WORDS)

Decreased effect of insulin to stimulate skeletal muscle blood flow in obese man. A novel mechanism for insulin resistance

Obesity is characterized by decreased rates of skeletal muscle insulin-mediated glucose uptake (IMGU). Since IMGU equals the product of the arteriovenous glucose difference (AVGd) across muscle and blood flow into muscle, reduced blood flow and/or tissue activity (AVGd) can lead to decreased IMGU. To examine this issue, we studied six lean (weight 68 +/- 3 kg, mean +/- SEM) and six obese (94 +/- 3 kg) men. The insulin dose-response curves for whole body and leg IMGU were constructed using the euglycemic clamp and leg balance techniques over a large range of serum insulin concentrations. In lean and obese subjects, whole body IMGU, AVGd, blood flow, and leg IMGU increased in a dose dependent fashion and maximal rates of all parameters were reduced in obese subjects compared to lean subjects. The dose-response curves for whole body IMGU, leg IMGU, and AVGd were right-shifted in obese subjects with an ED50 two- to threefold higher than that of lean subjects for each parameter. Leg blood flow increased approximately twofold from basal 2.7 +/- 0.2 to 4.4 +/- 0.2 dl/min in lean, P less than 0.01, and from 2.5 +/- 0.3 to 4.4 +/- 0.4 dl/min in obese subjects, P less than 0.01. The ED50 for insulin's effect to increase leg blood flow was about fourfold higher for obese (957 pmol/liter) than lean subjects (266 pmol/liter), P less than 0.01. Therefore, decreased insulin sensitivity in human obesity is not only due to lower glucose extraction in insulin-sensitive tissues but also to lower blood flow to these tissues. Thus, in vivo insulin resistance can be due to a defect in insulin action at the tissue level and/or a defect in insulin's hemodynamic action to increase blood flow to insulin sensitive tissues.

Placental-fetal glucose exchange and placental glucose consumption in pregnant sheep

To determine the separate effects of changes in fetal glucose and insulin concentrations on uteroplacental glucose transfer (UPGT) and consumption (UPGC) we studied 24 late-gestation pregnant sheep during fetal insulin infusions alone and with simultaneous glucose clamp. Insulin infusion alone increased fetal glucose utilization rate (GUR) by 45% (P less than 0.001), decreasing fetal glucose concentration by 40% (P less than 0.01) and thereby increasing fetal glucose clearance (Clglu) by 150% (P less than 0.001). Maternal-fetal glucose gradient also increased, resulting in a 40% increase (P less than 0.02) in UPGT [measured as umbilical glucose uptake (UGU)] and a 30% decrease (P less than 0.05) in UPGC. Addition of a fetal glucose clamp returned fetal glucose concentration to base line and restored UPGC and UGU to control values with a further 2.25-fold increase in fetal GUR. Clglu did not change, as the increase in GUR was proportional to the increase in fetal glucose concentration. Similarly, in animals receiving an insulin infusion plus glucose clamp throughout, maternal glucose concentration, fetal glucose concentration, UPGC, and UGU did not change, whereas GUR and Clglu increased approximately 1.9-fold. These changes were noted at constant maternal glucose concentration and uterine glucose uptake. Thus variation in fetal glucose concentration rather than fetal insulin concentration directly regulates uteroplacental glucose transfer and consumption, whereas both fetal insulin and glucose affect, in separate ways, fetal glucose utilization and clearance.

Use of a variable tracer infusion method to determine glucose turnover in humans

The single-compartment pool fraction model, when used with the hyperinsulinemic glucose clamp technique to measure rates of glucose turnover, sometimes underestimates true rates of glucose appearance (Ra) resulting in negative values for hepatic glucose output (HGO). We focused our attention on isotope discrimination and model error as possible explanations for this underestimation. We found no difference in [3-3H] glucose specific activity in samples obtained simultaneously from the femoral artery and vein (2,400 +/- 455 vs. 2,454 +/- 522 dpm/mg) in 6 men during a hyperinsulinemic euglycemic clamp study where insulin was infused at 40 mU.m-2.min-1 for 3 h; therefore, isotope discrimination did not occur. We compared the ability of a constant (0.6 microCi/min) vs. variable tracer infusion method (tracer added to the glucose infusate) to measure non-steady-state Ra during hyperinsulinemic clamp studies. Plasma specific activity fell during the constant tracer infusion studies but did not change from base line during the variable tracer infusion studies. By maintaining a constant plasma specific activity the variable tracer infusion method eliminates uncertainty about changes in glucose pool size. This overcame modeling error and more accurately measures non-steady-state Ra (P less than 0.001 by analysis of variance vs. constant infusion method). In conclusion, underestimation of Ra determined isotopically during hyperinsulinemic clamp studies is largely due to modeling error that can be overcome by use of the variable tracer infusion method. This method allows more accurate determination of Ra and HGO under non-steady-state conditions.

Insulin transport across capillaries is rate limiting for insulin action in dogs

This study examined the relationship between transcapillary insulin transport and insulin action in vivo. During euglycemic clamps (n = 7) in normal conscious dogs we simultaneously measured plasma and thoracic duct lymph insulin and glucose utilization (Rd). Clamps consisted of an activation phase with constant insulin infusion (0.6 mU/kg per min) and a deactivation phase. [14C]Inulin was infused as a passively transported control substance. While [14C]inulin reached an equilibrium between plasma and lymph, steady-state (ss) plasma insulin was higher than lymph (P less than 0.05) and the ratio of 3:2 was maintained during basal, activation, and deactivation phases: 18 +/- 2 vs. 12 +/- 1, 51 +/- 2 vs. 32 +/- 1, and 18 +/- 3 vs. 13 +/- 1 microU/ml. In addition, it took longer for lymph insulin to reach ss than plasma insulin during activation and deactivation: 11 +/- 2 vs. 31 +/- 5 and 8 +/- 2 vs. 32 +/- 6 min (P less than 0.02). Rd increased from 2.6 +/- 0.1 to a ss of 6.6 +/- 0.4 mg/kg per min within 50 +/- 8 min. There was a remarkable similarity in the dynamics of insulin in lymph and Rd: the time to reach ss for Rd was not different from lymph insulin (P greater than 0.1), and the relative increases of the two measurements were similar, 164 +/- 45% and 189 +/- 29% (P greater than 0.05). While there was only a modest correlation (r = 0.78, P less than 0.01) between Rd and plasma insulin, the dynamic changes of lymph insulin and Rd showed a strong correlation (r = 0.95, P less than 0.01). The intimate relationship between lymph insulin and Rd suggests that the transcapillary insulin transport is primarily responsible for the delay in Rd. Thus, transcapillary transport may be rate limiting for insulin action, and if altered, it could be an important component of insulin resistance in obesity and diabetes mellitus.

The action profiles of human NPH insulin preparations

The complete time-action profiles of four subcutaneously injected human NPH insulin preparations (Protaphane HM/Novo; Insulatard Human/Nordisk; Huminsulin Basal/Eli Lilly; Basal H-Insulin/Hoechst) have been investigated by means of the euglycaemic clamp technique (blood glucose 5.0 mmol l-1). Six normal male subjects were connected to a Biostator on five occasions in randomized order including a control study without insulin injection. A stable basal insulin level of about 10 mU l-1 was established by means of a low dose insulin infusion (0.1 mU kg-1 min-1) which subsequently suppressed C-peptide by 35 +/- 19% (mean +/- SD) to levels of around 0.3 nmol l-1. Twelve units of NPH insulin were injected subcutaneously into the abdominal wall and glucose infusion rates were monitored for 19 h. In the control study, the mean glucose infusion rate was 1.11 +/- 0.60 (range 0.32-1.95) mg kg-1 min-1. Maximal glucose infusion rates, reached 5-7 h after injection, were comparable (4.3-4.9 mg kg-1 min-1) for the four different preparations used. Glucose infusion rates returned to basal rates within the 19 h study period. Mean plasma free insulin levels peaked at 17.5-18.6 mU l-1 3-4.5 h after injection and returned to basal levels within 16 h. The time ranges of greater than 90, greater than 75, greater than 50, and greater than 25% of maximal insulin action (as estimated from glucose infusion rates) revealed no significant differences between the four insulin preparations tested. No significant insulin action was observed beyond 17 h after insulin injection of any preparation.

Effects of short-term pulsatile and continuous insulin delivery on glucagon secretion and insulin secretion and action

In six normal nonobese subjects, hyperinsulinemic euglycemic clamps were performed during paired sequential two-hour intravenous (IV) insulin infusions separated by an hour washout period. Each infusion was either 32 mU/kg/h of continuous insulin (CI) or 75% of this dose as 40-second pulses delivered every 13 minutes (PI). Six studies were performed with each of the following sequences in random order: PI-CI, CI-PI, and CI-CI. Based on the initial infusions, the insulin-dependent fractional glucose disappearance rate (X) during pulsatile insulin delivery (3.0 +/- 0.4 min-1 X 10(2), n = 6) was 73% of that of the continuous infusions (4.1 +/- 0.3 min-1 X 10(2), n = 12). This ratio was similar to that of the measured time-averaged plasma insulin areas (PI = 24.7 +/- 3.8 v CI = 31.4 +/- 3.5 mU/L). There was an average 23% enhancement of insulin's hypoglycemic effect during the second 12 CI infusions compared with the 12 initial CI infusions (X = 5.1 +/- 0.5 v 4.1 +/- 0.3 min-1 X 10(2), P less than .05). There was no significant difference between the enhancing effects of PI and CI infusions on insulin action in the subsequent CI's (X = 4.9 +/- 0.9 for PI-CI v X = 5.3 +/- 0.2 min-1 X 10(2) for CI-CI). First infusion PI significantly (P less than .05) decreased plasma C-peptide levels (0.34 +/- 0.05 to 0.20 +/- 0.06 mumol/L), whereas CI did not (0.33 +/- 0.02 to 0.32 +/- 0.07).(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of streptozotocin on rates of glucose utilization, oxidation, and production in the sheep fetus

Streptozotocin was injected into chronically catheterized, late gestation fetal sheep to produce hypoinsulinemia and to investigate the effects of hypoinsulinemia on the rates of utilization and production of glucose. Each fetus received two IV doses of streptozotocin (100 mg/kg estimated fetal weight per dose). Experiments were conducted before and five to six days after giving the streptozotocin. Experiments consisted of direct measurement of fetal glucose utilization rate (using [U-14C]glucose tracer) and umbilical glucose uptake rate (Fick principle) during basal and glucose infusion periods. Fetal endogenous production rate was calculated as the difference between rates of fetal glucose utilization and umbilical glucose uptake. Following streptozotocin injections the rate of fetal glucose utilization was reduced (5.50 +/- 0.34 to 4.13 +/- 0.32 mg/kg/min) as was the rate of fetal CO2 production from fetal glucose carbon oxidation (91.7 +/- 5.3 to 71.7 +/- 6.0 mumol/kg/min) and the rate of fetal glucose oxidation (2.75 +/- 0.16 to 2.15 +/- 0.18 mg/kg/min). At the same time the rate of fetal endogenous glucose production was enhanced (0.31 +/- 0.18 to 2.06 +/- 0.28 mg/kg/min). These changes in glucose metabolism were accompanied by hypoinsulinemia (16 +/- 2 to 8 +/- 1 muU/mL), an inhibition of insulin secretion in response to glucose infusion (16 +/- 2 to 34 +/- 2 muU/mL control, 8 +/- 1 to 9 +/- 1 muU/mL after streptozotocin), hyperglycemia (19.5 +/- 0.7 to 30.4 +/- 1.7 mg/dL), and a reduction in the rate of umbilical glucose uptake (5.19 +/- 0.34 to 2.07 +/- 0.40 mg/kg/min). The disturbances in glucose metabolism could be alleviated only in part by insulin infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

A mixed meal potentiates the insulin sensitivity of glucose transport and metabolism in adipocytes from patients with type 2 diabetes mellitus

Post-glucose enhancement of insulin action may represent a physiological mechanism for the acute regulation of insulin sensitivity of target tissues. To clarify whether a similar mechanism is operative in the insulin-resistant diabetic state we have investigated the effects of a mixed meal on adipocyte insulin action in eight patients with Type 2 diabetes mellitus. Ninety minutes after ingestion of breakfast insulin binding to fat cells increased by 21% (p less than 0.05). In the fasting state 6 patients had a significant response of glucose transport and lipogenesis to insulin whereas two exhibited non-responsiveness. In the 6 responders insulin sensitivity, as estimated by the insulin concentration at which half-maximal effect was achieved, increased for glucose transport (before, 260 +/- 46 pmoll-1; after, 105 +/- 21 pmol l-1; p less than 0.05) and for lipogenesis (before, 36 +/- 9 pmol l-1; after, 9 +/- 2 pmol l-1; p less than 0.05). No significant changes occurred in basal or maximal glucose transport or lipogenesis. In the two primary non-responders intake of the meal was associated with average increase in maximal insulin responsiveness of 52% for glucose transport and 28% for lipogenesis. Intake of a mixed meal is associated with a slight increase of insulin binding to adipocytes from patients with Type 2 diabetes mellitus but a marked increase of adipocyte insulin sensitivity at the post-binding levels of glucose transport and metabolism.

Relationship between lipoprotein levels and in vivo insulin action in normal young white men

In epidemiologic studies, hyperinsulinemia has been found to be an independent risk factor for coronary heart disease (CHD). However, the mechanisms responsible for its role in atherogenesis remain unclear. We studied the relationship of in vivo insulin action and plasma lipids and lipoproteins in 44 normotriglyceridemic white men (aged 18 to 34 years). The euglycemic, hyperinsulinemic glucose clamp technique was used to quantitate insulin-mediated glucose disposal (M/I value) at a plasma insulin concentration of approximately 100 microU/mL. The M/I value correlated negatively with plasma triglycerides (r = -0.553, P less than .0001), as well as with fasting plasma insulin levels (r = -0.483, P less than .001), independent of age, body mass index, and fasting plasma glucose levels. A negative correlation of the M/I value was also observed with very low density lipoprotein (VLDL)-cholesterol (r = -0.347, P less than .05), VLDL-triglycerides (r = -0.474, P less than 0.005), and total cholesterol/high density lipoprotein (HDL)-cholesterol ratio (r = -0.431, P less than .01). The relationship between the M/I value and the total cholesterol/HDL-cholesterol ratio was independent of VLDL-cholesterol and VLDL-triglycerides, however, not independent of plasma triglycerides. No relationship was observed between insulin-mediated glucose uptake and total cholesterol, low density lipoprotein (LDL)-cholesterol, and HDL-cholesterol values. Individual differences in plasma triglycerides, fasting insulin concentration, and the total cholesterol/HDL-cholesterol ratio accounted for about half the variance observed in the M/I value.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxidative and non-oxidative glucose metabolism in non-obese type 2 (non-insulin-dependent) diabetic patients

Insulin resistance is a common feature of Type 2 (non-insulin-dependent) diabetes mellitus. This defect in insulin-mediated glucose metabolism could result from a defect in either glucose oxidation or non-oxidative glucose disposal. To examine this question, euglycaemic insulin clamp studies were performed in 16 normal weight Type 2 and 11 age-matched control subjects. In Type 2 diabetic patients the fasting plasma glucose concentration, 8.39 +/- 0.50 mmol/l, was allowed to decline (over 54 +/- 6 min) to 5.33 +/- 0.11 mmol/l before starting the insulin clamp. Total body glucose uptake was significantly decreased in Type 2 diabetic patients vs control subjects (148 +/- 15 vs 264 +/- 25 mg/min.m2, p less than 0.001). Both total glucose oxidation (59 +/- 6 vs 89 +/- 6 mg/min.m2, p less than 0.005) and non-oxidative glucose disposal (89 +/- 15 vs 179 +/- 24 mg/min.m2, p less than 0.005) were significantly reduced in the Type 2 diabetic patients. Basal glucose oxidation was also reduced in the Type 2 diabetic patients (22 +/- 3 vs 38 +/- 5 mg/min.m2, p less than 0.01). In conclusion, during the postabsorptive state and under conditions of euglycaemic hyperinsulinaemia, impairment of glucose oxidation and non-oxidative glucose disposal both contribute to the insulin resistance observed in normal weight Type 2 diabetic patients. Since lipid oxidation was normal in this group of diabetic patients, excessive non-esterified fatty acid oxidation cannot explain the defects in glucose disposal.