Modified protocols improve insulin sensitivity estimation using the minimal model

The Impact of Exogenous Insulin Input on Calculating Hepatic Clearance Parameters

OBJECTIVE

Model-based metabolic tests require accurate identification of subject-specific parameters from measured assays. Insulin assays are used to identify insulin kinetics parameters, such as general and first-pass hepatic clearances. This study assesses the impact of intravenous insulin boluses on parameter identification precision.

METHOD

Insulin and C-peptide data from two intravenous glucose tolerance test (IVGTT) trials of healthy adults (N = 10 × 2; denoted A and B), with (A) and without (B) insulin modification, were used to identify insulin kinetics parameters using a grid search. Monte Carlo analysis (N = 1000) quantifies variation in simulation error for insulin assay errors of 5%. A region of parameter values around the optimum was identified whose errors are within variation due to assay error. A smaller optimal region indicates more precise practical identifiability. Trial results were compared to assess identifiability and precision.

RESULTS

Trial B, without insulin modification, has optimal parameter regions 4.7 times larger on average than Trial A, with 1-U insulin bolus modification. Ranges of optimal parameter values between trials A and B increase from 0.04 to 0.12 min^-1 for hepatic clearance and from 0.07 to 0.14 for first-pass clearance on average. Trial B's optimal values frequently lie outside physiological ranges, further indicating lack of distinct identifiability.

CONCLUSIONS

A small 1-U insulin bolus improves identification of hepatic clearance parameters by providing a smaller region of optimal parameter values. Adding an insulin bolus in metabolic tests can significantly improve identifiability and outcome test precision. Assay errors necessitate insulin modification in clinical tests to ensure identifiability and precision.

Assessment of Insulin Secretion and Insulin Resistance in Human

The impaired insulin secretion and increased insulin resistance (or decreased insulin sensitivity) play a major role in the pathogenesis of all types of diabetes mellitus (DM). It is very important to assess the pancreatic β-cell function and insulin resistance/ sensitivity to determine the type of DM and to plan an optimal management and prevention strategy for DM. So far, various methods and indices have been developed to assess the β-cell function and insulin resistance/sensitivity based on static, dynamic test and calculation of their results. In fact, since the metabolism of glucose and insulin is made through a complex process related with various stimuli in several tissues, it is difficult to fully reflect the real physiology. In order to solve the theoretical and practical difficulties, research on new index is still in progress. Also, it is important to select the appropriate method and index for the purpose of use and clinical situation. This review summarized a variety of traditional methods and indices to evaluate pancreatic β-cell function and insulin resistance/sensitivity and introduced novel indices.

Glucose effectiveness: Lessons from studies on insulin-independent glucose clearance in mice

Besides insulin-mediated transport of glucose into the cells, an important role is also played by the non-insulin-mediated transport. This latter process is called glucose effectiveness (acronym SG ), which is estimated by modeling of glucose and insulin data after an intravenous glucose administration, and accounts for ≈70% of glucose disposal. This review summarizes studies on SG , mainly in humans and rodents with focus on results achieved in model experiments in mice. In humans, SG is reduced in type 2 diabetes, in obesity, in liver cirrhosis and in some elderly populations. In model experiments in mice, SG is independent from glucose levels, but increases when insulin secretion is stimulated, such as after administration of the incretin hormones, glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide. SG is reduced in insulin resistance induced by high-fat feeding and by exogenous administration of glucagon. Glucose-dependent (insulin-independent) glucose disposal is therefore important for glucose elimination, and it is also well regulated. It might be of pathophysiological relevance for the development of type 2 diabetes, in particular during insulin resistance, and might also be a target for glucose-reducing therapy. Measuring SG is essentially important when carrying out metabolic studies to understand glucose homeostasis.

When MINMOD Artifactually Interprets Strong Insulin Secretion as Weak Insulin Action

We address a problem with the Bergman-Cobelli Minimal Model, which has been used for 40 years to estimate S_I during an intravenous glucose tolerance test (IVGTT). During the IVGTT blood glucose and insulin concentrations are measured in response to an acute intravenous glucose load. Insulin secretion is often assessed by the area under the insulin curve during the first few minutes (Acute Insulin Response, AIR). The issue addressed here is that we have found in simulated IVGTTs, representing certain contexts, Minimal Model estimates of S_I are inversely related to AIR, resulting in artifactually lower S_I. This may apply to Minimal Model studies reporting lower S_I in Blacks than in Whites, a putative explanation for increased risk of T2D in Blacks. The hyperinsulinemic euglycemic clamp (HIEC), the reference method for assessing insulin sensitivity, by contrast generally does not show differences in insulin sensitivity between these groups. The reason for this difficulty is that glucose rises rapidly at the start of the IVGTT and reaches levels independent of S_I, whereas insulin during this time is determined by AIR. The minimal model in effect interprets this combination as low insulin sensitivity even when actual insulin sensitivity is unchanged. This happens in particular when high AIR results from increased number of readily releasable insulin granules, which may occur in Blacks. We conclude that caution should be taken when comparing estimates of S_I between Blacks and Whites.

Estimating individualized treatment regimes from crossover designs

The field of precision medicine aims to tailor treatment based on patient-specific factors in a reproducible way. To this end, estimating an optimal individualized treatment regime (ITR) that recommends treatment decisions based on patient characteristics to maximize the mean of a prespecified outcome is of particular interest. Several methods have been proposed for estimating an optimal ITR from clinical trial data in the parallel group setting where each subject is randomized to a single intervention. However, little work has been done in the area of estimating the optimal ITR from crossover study designs. Such designs naturally lend themselves to precision medicine since they allow for observing the response to multiple treatments for each patient. In this paper, we introduce a method for estimating the optimal ITR using data from a 2 × 2 crossover study with or without carryover effects. The proposed method is similar to policy search methods such as outcome weighted learning; however, we take advantage of the crossover design by using the difference in responses under each treatment as the observed reward. We establish Fisher and global consistency, present numerical experiments, and analyze data from a feeding trial to demonstrate the improved performance of the proposed method compared to standard methods for a parallel study design.

Glucose Effectiveness from Short Insulin-Modified IVGTT and Its Application to the Study of Women with Previous Gestational Diabetes Mellitus

BACKGROUND

This study aimed to design a simple surrogate marker (i.e., predictor) of the minimal model glucose effectiveness (S_G), namely calculated S_G (CS_G), from a short insulin-modified intravenous glucose tolerance test (IM-IVGTT), and then to apply it to study women with previous gestational diabetes mellitus (pGDM).

METHODS

CS_G was designed using the stepwise model selection approach on a population of subjects (n=181) ranging from normal tolerance to type 2 diabetes mellitus (T2DM). CS_G was then tested on a population of women with pGDM (n=57). Each subject underwent a 3-hour IM-IVGTT; women with pGDM were observed early postpartum and after a follow-up period of up to 7 years and classified as progressors (PROG) or non-progressors (NONPROG) to T2DM. The minimal model analysis provided a reference S_G.

RESULTS

CS_G was described as CS_G=1.06×10⁻²+5.71×10⁻²×K_G/G_peak, K_G being the mean slope (absolute value) of loge glucose in 10-25- and 25-50-minute intervals, and G_peak being the maximum of the glucose curve. Good agreement between CS_G and S_G in the general population and in the pGDM group, both at baseline and follow-up (even in PROG and NONPROG subgroups), was shown by the Bland-Altman plots (<5% observations outside limits of agreement), and by the test for equivalence (equivalence margin not higher than one standard deviation). At baseline, the PROG subgroup showed significantly lower S_G and CS_G values compared to the NONPROG subgroup (P<0.03).

CONCLUSION

CS_G is a valid S_G predictor. In the pGDM group, glucose effectiveness appeared to be impaired in women progressing to T2DM.

Central fat accretion and insulin sensitivity: differential relationships in parous and nulliparous women

BACKGROUND/OBJECTIVES

Childbearing is associated with a disproportionate accumulation of visceral fat and an increased risk of metabolic disease. However, it is unknown whether the visceral fat accretion associated with pregnancy modifies a woman's risk for metabolic disease. The purpose of this study was to test whether the association between abdominal fat and insulin sensitivity differs by parity status in healthy overweight women.

SUBJECTS/METHODS

Intra-abdominal adipose tissue (IAAT) via CT, body composition by DXA, insulin sensitivity via intravenous glucose tolerance test and minimal model (S_I), HOMA-IR, and cardiorespiratory fitness (VO_2max) were assessed in 212 non-diabetic, premenopausal, overweight non-Hispanic white and African-American women.

RESULTS

Nulliparous women (n=98) were younger, had less IAAT and higher VO_2max, but similar S_I, HOMA-IR and leg fat, compared to parous (n=114). In nulliparous women, IAAT was negatively associated with S_I, controlling for age, race and body fat mass (r=-0.40, P<0.001), but this relationship was attenuated in parous women (r=-0.15, P=0.16). In multiple linear regression analysis, leg fat and IAAT were significant predictors of S_I in nulliparous, but not parous women.

CONCLUSIONS

Results suggest that greater IAAT in parous women does not lead to greater insulin resistance; rather, transient insulin resistance during pregnancy may encourage intra-abdominal fat accumulation that is metabolically benign. This underscores the need to consider parity when assessing cardiometabolic risk.

Baseline insulin sensitivity affects response to high-amylose maize resistant starch in women: a randomized, controlled trial

BACKGROUND

Resistant starch (RS) is a type of dietary fiber that can improve glucose metabolism, but its effects may be modulated by sex or baseline insulin sensitivity. This study was designed to examine the effect of high-amylose maize resistant starch (HAM-RS2) on insulin sensitivity (SI) in women, and to determine if SI status affects the response to RS.

METHODS

This was a randomized, placebo-controlled, double-blind, cross-over study. Participants were 40 healthy, non-diabetic women aged 22-67 years in the normal-weight to obese BMI range (20.6-47.4 kg/m(2)). Two doses of HAM-RS2 were tested, 15 and 30 g per day, administered in the form of cookies. Participants were randomized to the order in which they received the experimental and placebo product. Each arm was 4 weeks, with a 4-week wash-out period in between. SI was assessed at the end of each 4-week arm of product consumption by frequently-sampled, insulin-modified, intravenous glucose tolerance test and minimal modeling. Participants were categorized as being insulin resistant (IR; SI < 7.8) or insulin sensitive (IS; SI ≥ 7.8) based on Gaussian analysis. The effect of treatment arm on SI was examined by mixed-model analysis within IR and IS sub-groups, using all available data. In addition, SI was examined by ANOVA among just those women who completed all three arms of the study with valid SI results.

RESULTS

Among IR participants, SI was on average ~16 % higher after the 30 g arm when compared to the control arm by mixed-model analysis (n = 40, P < 0.05), and tended to be 23 % higher by ANOVA among women who completed all arms (n = 23, P = 0.06). HAM-RS2 did not affect SI in IS women.

CONCLUSION

Consumption of HAM-RS2 at 30 g/day in the form of a snack food item was associated with improved insulin sensitivity in women with insulin resistance.

CLINICAL TRIALS REGISTRY NUMBER

NCT0152806.

Impact of PTBP1 rs11085226 on glucose-stimulated insulin release in adult Danes

BACKGROUND

The variant rs11085226 (G) within the gene encoding polypyrimidine tract binding protein 1 (PTBP1) was reported to associate with reduced insulin release determined by an oral glucose tolerance test (OGTT) as well as an intravenous glucose tolerance test (IVGTT). The aim of the present study was to validate the association of the rs11085226 G-allele of PTBP1 with previously investigated OGTT- and IVGTT-derived diabetes-related metabolic quantitative phenotypes, to conduct exploratory analyses of additional measures of beta-cell function, and to further investigate a potential association with type 2 diabetes.

METHODS

PTBP1 rs11085226 was genotyped in 20,911 individuals of Danish Caucasian ethnicity ascertained from 9 study samples. Case control analysis was performed on 5,634 type 2 diabetic patients and 11,319 individuals having a normal fasting glucose level as well as 4,641 glucose tolerant controls, respectively. Quantitative trait analyses were performed in up to 13,605 individuals subjected to an OGTT or blood samples obtained after an overnight fast, as well as in 596 individuals subjected to an IVGTT.

RESULTS

Analyses of fasting and OGTT-derived quantitative traits did not show any significant associations with the PTBP1 rs11085226 variant. Meta-analysis of IVGTT-derived quantitative traits showed a nominally significant association between the variant and reduced beta-cell responsiveness to glucose (β = -0.1 mmol · kg(-1) · min(-1); 95% CI: -0.200.20 - -0.024; P = 0.01) assuming a dominant model of inheritance, but failed to replicate a previously reported association with area under the curve (AUC) for insulin. Case control analysis did not show an association of the PTBP1 rs11085226 variant with type 2 diabetes.

CONCLUSIONS

Despite failure to replicate the previously reported associations of PTBP1 rs11085226 with OGTT- and IVGTT-derived measures of beta-cell function, we did find a nominally significant association with reduced beta-cell responsiveness to glucose during an IVGTT, a trait not previously investigated, leaving the potential influence of this variant in PTBP1 on glucose stimulated insulin release open for further investigation. However, the present study does not support the hypothesis that the variant confers risk of type 2 diabetes.

Macrophage gene expression in adipose tissue is associated with insulin sensitivity and serum lipid levels independent of obesity

OBJECTIVE

Obesity is linked to both increased metabolic disturbances and increased adipose tissue macrophage infiltration. However, whether macrophage infiltration directly influences human metabolism is unclear. The aim of this study was to investigate if there are obesity-independent links between adipose tissue macrophages and metabolic disturbances.

DESIGN AND METHODS

Expression of macrophage markers in adipose tissue was analyzed by DNA microarrays in the SOS Sib Pair study and in patients with type 2 diabetes and a BMI-matched healthy control group.

RESULTS

The expression of macrophage markers in adipose tissue was increased in obesity and associated with several metabolic and anthropometric measurements. After adjustment for BMI, the expression remained associated with insulin sensitivity, serum levels of insulin, C-peptide, high density lipoprotein cholesterol (HDL-cholesterol) and triglycerides. In addition, the expression of most macrophage markers was significantly increased in patients with type 2 diabetes compared to the control group.

CONCLUSION

Our study shows that infiltration of macrophages in human adipose tissue, estimated by the expression of macrophage markers, is increased in subjects with obesity and diabetes and associated with insulin sensitivity and serum lipid levels independent of BMI. This indicates that adipose tissue macrophages may contribute to the development of insulin resistance and dyslipidemia.

Population pharmacodynamic modeling of hyperglycemic clamp and meal tolerance tests in patients with type 2 diabetes mellitus

In this study, glucose and insulin concentration-time profiles in subjects with type 2 diabetes mellitus (T2DM) under meal tolerance test (MTT) and hyperglycemic clamp (HGC) conditions were co-modeled simultaneously. Blood glucose and insulin concentrations were obtained from 20 subjects enrolled in a double-blind, placebo-controlled, randomized, two-way crossover study. Patients were treated with palosuran or placebo twice daily for 4 weeks and then switched to the alternative treatment after a 4-week washout period. The MTT and HGC tests were performed 1 h after drug administration on days 28 and 29 of each treatment period. Population data analysis was performed using NONMEM. The HGC model incorporates insulin-dependent glucose clearance and glucose-induced insulin secretion. This model was extended for the MTT, in which glucose absorption was described using a transit compartment with a mean transit time of 62.5 min. The incretin effect (insulin secretion triggered by oral glucose intake) was also included, but palosuran did not influence insulin secretion or sensitivity. Glucose clearance was 0.164 L/min with intersubject and interoccasion variability of 9.57% and 31.8%. Insulin-dependent glucose clearance for the HGC was about 3-fold greater than for the MTT (0.0111 vs. 0.00425 L/min/[mU/L]). The maximal incretin effect was estimated to enhance insulin secretion 2-fold. The lack of palosuran effect coupled with a population-based analysis provided quantitative insights into the variability of glucose and insulin regulation in patients with T2DM following multiple glucose tolerance tests. Application of these models may also prove useful in antihyperglycemic drug development and assessing glucose-insulin homeostasis.

Insulin sensitivity affects propensity to obesity in an ethnic-specific manner: results from two controlled weight loss intervention studies

Background

Risk for obesity differs with ethnicity/race and is associated with insulin sensitivity (S_I), insulin responsiveness, and dietary glycemic load (GL). The objective of this study was to test the hypotheses that, 1) obesity-prone, normal weight, African-American (AA) women would be more insulin sensitive than BMI-matched, never overweight AA women; 2) increased adiposity over time would be associated with greater baseline S_I and higher dietary GL in AA but not European-American (EA) women; and 3) increased adiposity over time would be predicted by S_I in women with high but not low acute insulin response to glucose (AIRg).

Methods

Two controlled weight loss interventions were conducted involving overweight (BMI 25.0-29.9 kg/m²) premenopausal AA and EA women. The first included matching with normal-weight (BMI <25.0 kg/m²) controls following weight loss, and then comparing S_I. The second included a 1-year follow-up of weight-reduced participants to identify predictors of change in %body fat. Main outcome measure in the first study was insulin sensitivity (S_I) as assessed with intravenous glucose tolerance test (IVGTT), and in the second study was change in %fat, as assessed with DXA, over one year. AIRg was assessed during IVGTT, and free-living diet was determined by food record.

Results

In the first study, formerly overweight AA women were 43% more insulin sensitive than BMI-matched never overweight AA (P < 0.05). In the second study, S_I was positively associated with change in %fat over 1 year only in AA women (P < 0.05) and women with high AIRg (P < 0.05). In addition, AA who were insulin sensitive and who consumed a higher GL diet tended to gain greater %fat (P = 0.086 for diet x S_I interaction). In both studies, AA women had higher AIRg (P < 0.001) than EA women.

Conclusions

Formerly overweight (obesity-prone) AA women were more insulin sensitive than never overweight AA women, a quality that may predispose to adiposity, particularly when combined with a high GL diet. This ethnicity/race-specific effect may be due to high insulin responsiveness among AA.

Measurement of insulin resistance in chronic kidney disease

PURPOSE OF REVIEW

Insulin resistance is a known complication of end-stage renal disease that also appears to be present in earlier stages of chronic kidney disease (CKD). It is a risk factor for cardiovascular disease and an important potential therapeutic target in this population. Measurement of insulin resistance is reviewed in the context of known pathophysiologic abnormalities in CKD.

RECENT FINDINGS

Insulin resistance in CKD is due to a high prevalence of known risk factors (e.g. obesity) and to unique metabolic abnormalities. The site of insulin resistance in CKD is localized to skeletal muscle. Estimates based on fasting insulin concentration may not adequately capture insulin resistance in CKD because they largely reflect hepatic defects and because CKD impairs insulin catabolism. A variety of dynamic tests are available to directly measure insulin-mediated glucose uptake.

SUMMARY

Insulin resistance may be an important therapeutic target in CKD. Complementary methods are available to assess insulin resistance, and each method has unique advantages, disadvantages, and levels of complexity. These characteristics, and the likelihood that CKD alters the performance of some insulin resistance measurements, must be considered when designing and interpreting clinical studies.

Aerobic exercise training conserves insulin sensitivity for 1 yr following weight loss in overweight women

The objectives of this study were to 1) identify the independent effects of exercise (aerobic or resistance training) and weight loss on whole body insulin sensitivity and 2) determine if aerobic or resistance training would be more successful for maintaining improved whole body insulin sensitivity 1 yr following weight loss. Subjects were 97 healthy, premenopausal women, body mass index (BMI) 27-30 kg/m(2). Following randomized assignment to one of three groups, diet only, diet + aerobic, or diet + resistance training until a BMI <25 kg/m(2) was achieved, body composition, fat distribution, and whole body insulin sensitivity were determined at baseline, in the weight reduced state, and at 1-yr follow up. The whole body insulin sensitivity index (S(I)) was determined using a frequently sampled intravenous glucose tolerance test. Results of repeated-measures ANOVA indicated a significant improvement in S(I) following weight loss. However, there were no group or group×time interactions. At 1-yr follow up, there were no significant time or group interactions for S(I;) however, there was a significant group×time interaction for S(I). Post hoc analysis revealed that women in the aerobic training group showed a significant increased S(I) from weight reduced to 1-yr follow up (P < 0.05), which was independent of intra-abdominal adipose tissue and %fat. No significant differences in S(I) from weight reduced to 1-yr follow up were observed for diet only or diet + resistance groups. Additionally, multiple linear regression analysis revealed that change in whole body insulin sensitivity from baseline to 1-yr follow up was independently associated with the change in Vo(2max) from baseline to 1-yr follow up (P < 0.05). These results suggest that long-term aerobic exercise training may conserve improvements in S(I) following weight loss and that maintaining cardiovascular fitness following weight loss may be important for maintaining improvements in S(I).

Divergent effects of a combined hormonal oral contraceptive on insulin sensitivity in lean versus obese women

OBJECTIVE

To evaluate the effects of a commonly used combined hormonal oral contraceptive (OC) on carbohydrate metabolism in obese as compared with lean women.

DESIGN

6-month prospective study.

SETTING

Clinical research center at an academic medical center.

PATIENT(S)

Premenopausal nondiabetic women with body mass index <25 kg/m(2) (n = 15) or >30 kg/m(2) (n = 14).

INTERVENTION(S)

Ethinyl estradiol (35 μg) and norgestimate (0.18/0.215/0.25 mg) for 6 cycles.

MAIN OUTCOME MEASURE(S)

Insulin sensitivity by frequent sampling intravenous glucose tolerance test; other indices of insulin sensitivity (homeostatic model assessment of insulin sensitivity index [ISI HOMA], the Matsuda index); fasting lipid panel.

RESULT(S)

Insulin sensitivity changed from 6.62 ± 3.69 min(-1)/mIU/L (baseline) to 8.23 ± 3.30 min(-1)/mIU/L (6 months) in lean women, and from 4.36 ± 2.32 to 3.82 ± 2.32 min(-1)/mIU/L in obese women. Divergent effects on insulin sensitivity were also observed with ISI HOMA and the Matsuda index. Low-density lipoprotein increased by approximately 20 mg/dL in both the lean and obese groups.

CONCLUSION(S)

Lean and obese women exhibit differential changes in insulin sensitivity when given 6 months of a commonly used oral contraceptive. The mechanisms of these differences and whether these divergent effects persist in the long term require further investigation.

Fat distribution, aerobic fitness, blood lipids, and insulin sensitivity in African-American and European-American women

The purpose of this study was to determine independent relationships of intra-abdominal adipose tissue (IAAT), leg fat, and aerobic fitness with blood lipids and insulin sensitivity (S(i)) in European-American (EA) and African-American (AA) premenopausal women. Ninety-three EA and ninety-four AA with BMI between 27 and 30 kg/m(2) had IAAT by computed tomography, total fat and leg fat by dual-energy X-ray absorptiometry, aerobic fitness by a graded exercise test, African admixture (AFADM) by ancestry informative markers, blood lipids by the Ektachem DT system, and S(i) by glucose tolerance test. Independent of age, aerobic fitness, AFADM, and leg fat, IAAT was positively related to low-density lipoprotein-cholesterol (LDL-C), cholesterol-high-density lipoprotein (HDL) ratio, triglycerides (TGs), and fasting insulin (standardized beta varying 0.16-0.34) and negatively related to HDL-cholesterol (HDL-C) and S(i) (standardized beta -0.15 and -0.25, respectively). In contrast, independent of age, aerobic fitness, AFADM, and IAAT, leg fat was negatively related to total cholesterol, LDL-C, cholesterol-HDL ratio, TGs, and fasting insulin (standardized beta varying -0.15 to -0.21) and positively related to HDL-C and S(i) (standardized beta 0.16 and 0.23). Age was not independently related to worsening of any blood lipid but was related to increased S(i) (standardized beta for S(i) 0.25, insulin -0.31). With the exception of total cholesterol and LDL-C, aerobic fitness was independently related to worsened blood lipid profile and increased S(i) (standardized beta varying 0.17 to -0.21). Maintenance of favorable fat distribution and aerobic fitness may be important strategies for healthy aging, at least in premenopausal EA and AA women.

Effects of low- and high-glycemic index/glycemic load diets on coronary heart disease risk factors in overweight/obese men

Chronic insulin resistance contributes to subclinical inflammation, thrombosis/impaired fibrinolysis, and dyslipidemia. The effect of dietary carbohydrate, specifically of glycemic index (GI) and glycemic load (GL), on established and emerging coronary heart disease risk factors has not been elucidated fully. We conducted a randomized crossover feeding study of matched diets differing only in GI and GL in 24 overweight or obese but otherwise healthy men to investigate the effects on insulin sensitivity, inflammation, thrombosis/fibrinolysis, lipoproteins/lipids, and body composition. All meals for the high- and low-GI/GL diets were prepared in a metabolic kitchen. Each participant consumed both diets in random order for 4 weeks each, with a 4-week washout period in between. Each participant underwent a frequently sampled intravenous glucose tolerance test for assessment of insulin sensitivity; blood sampling for the measurement of inflammatory markers, coagulation factors, and lipoproteins/lipids; and dual-energy x-ray absorptiometry for assessment of body composition at the beginning and end of each dietary period. There were no statistically significant differences in glucose metabolism factors, inflammatory markers, or coagulation factors after 4 weeks on the high- and low-GI/GL diets. The high-GI/GL diet resulted in a slightly greater reduction in fat mass and a slightly greater increase in lean mass compared with the low-GI/GL diet. The high-GI/GL diet resulted in significant, but unexpected, reductions in total and low-density lipoprotein cholesterol, whereas high-density lipoprotein cholesterol concentration was significantly reduced on the high-GI/GL diet compared with the low-GI/GL diet. Overall, high- and low-GI/GL diets of 4 weeks' duration had no consistent effects on coronary heart disease risk factors in this group of overweight/obese men.

Optimization of the intravenous glucose tolerance test in T2DM patients using optimal experimental design

Intravenous glucose tolerance test (IVGTT) provocations are informative, but complex and laborious, for studying the glucose-insulin system. The objective of this study was to evaluate, through optimal design methodology, the possibilities of more informative and/or less laborious study design of the insulin modified IVGTT in type 2 diabetic patients. A previously developed model for glucose and insulin regulation was implemented in the optimal design software PopED 2.0. The following aspects of the study design of the insulin modified IVGTT were evaluated; (1) glucose dose, (2) insulin infusion, (3) combination of (1) and (2), (4) sampling times, (5) exclusion of labeled glucose. Constraints were incorporated to avoid prolonged hyper- and/or hypoglycemia and a reduced design was used to decrease run times. Design efficiency was calculated as a measure of the improvement with an optimal design compared to the basic design. The results showed that the design of the insulin modified IVGTT could be substantially improved by the use of an optimized design compared to the standard design and that it was possible to use a reduced number of samples. Optimization of sample times gave the largest improvement followed by insulin dose. The results further showed that it was possible to reduce the total sample time with only a minor loss in efficiency. Simulations confirmed the predictions from PopED. The predicted uncertainty of parameter estimates (CV) was low in all tested cases, despite the reduction in the number of samples/subject. The best design had a predicted average CV of parameter estimates of 19.5%. We conclude that improvement can be made to the design of the insulin modified IVGTT and that the most important design factor was the placement of sample times followed by the use of an optimal insulin dose. This paper illustrates how complex provocation experiments can be improved by sequential modeling and optimal design.

Uncoupling protein 2 Ala55Val polymorphism is associated with a higher acute insulin response to glucose

Recent evidence suggests that mitochondrial uncoupling protein 2 (UCP2) in pancreatic beta-cells plays a crucial role in insulin production and secretion. We hypothesized that 2 UCP2 polymorphisms, a -55C/T (Ala55Val) substitution in exon 4 and an exon 8 insertion, would alter the acute insulin response to glucose (AIRg). Subjects were 155 African American (AA) and European American (EA) women. Body composition was determined by dual-energy x-ray absorptiometry. Insulin sensitivity and AIRg were measured with an intravenous glucose tolerance test and minimal modeling. To account for the confounding effects of population stratification, estimates of African admixture were obtained from approximately 35 ancestry-informative markers. Uncoupling protein 2 genotyping was conducted with gel electrophoresis. Information was analyzed using mixed linear models. A positive association between the -55C/T homozygous mutation and AIRg was identified in the total sample (P < .01) and independently in EA women (P = .02) but not AA women. The exon 8 insertion did not significantly affect AIRg. No interaction effects of the 2 polymorphisms on AIRg were noted. These results indicate that AIRg is associated with the -55C/T UCP2 homozygous mutation and that the presence of this mutation could alter postchallenge insulin concentration.

Food intake patterns associated with incident type 2 diabetes: the Insulin Resistance Atherosclerosis Study

OBJECTIVE

Markers of hemostasis and inflammation such as plasminogen activator inhibitor-1 (PAI-1) and fibrinogen have been associated with risk of type 2 diabetes. We aimed to identify food intake patterns influencing this pathway and evaluate their association with incident diabetes.

RESEARCH DESIGN AND METHODS

The Insulin Resistance Atherosclerosis Study cohort included 880 middle-aged adults initially free of diabetes. At the 5-year follow-up, 144 individuals had developed diabetes. Usual dietary intake was ascertained with a 114-item food frequency questionnaire. Using reduced rank regression, we identified a food pattern maximizing the explained variation in PAI-1 and fibrinogen. Subsequently, the food pattern-diabetes association was evaluated using logistic regression.

RESULTS

High intake of the food groups red meat, low-fiber bread and cereal, dried beans, fried potatoes, tomato vegetables, eggs, cheese, and cottage cheese and low intake of wine characterized the pattern, which was positively associated with both biomarkers. With increasing pattern score, the odds of diabetes increased significantly (Ptrend < 0.01). After multivariate adjustment, the odds ratio comparing extreme quartiles was 4.3 (95% CI 1.7-10.8). Adjustment for insulin sensitivity and secretion and other metabolic factors had little impact (4.9, 1.8-13.7).

CONCLUSIONS

Our findings provide support for potential behavioral prevention strategies, as we identified a food intake pattern that was strongly related to PAI-1 and fibrinogen and independently predicted type 2 diabetes.

Insulin sensitivity in African-American and white women: association with inflammation

Whether the contribution of inflammation to risk for chronic metabolic disease differs with ethnicity is not known. The objective of this study was to determine: (i) whether ethnic differences exist in markers of inflammation and (ii) whether lower insulin sensitivity among African Americans vs. whites is due to greater inflammatory status. Subjects were African-American (n = 108) and white (n = 105) women, BMI 27-30 kg/m(2). Insulin sensitivity was assessed with intravenous glucose tolerance test and minimal modeling; fat distribution with computed tomography; body composition with dual-energy X-ray absorptiometry; markers of inflammation (tumor necrosis factor (TNF)-alpha, soluble tumor necrosis factor receptor (sTNFR)-1, sTNFR-2, C-reactive protein (CRP), and interleukin (IL)-6) with enzyme-linked immunosorbent assay (ELISA). Whites had greater intra-abdominal adipose tissue (IAAT), insulin sensitivity, and concentrations of TNF-alpha, sTNFR-1, and sTNFR-2 than African Americans. Greater TNF-alpha in whites vs. African Americans was attributed to greater IAAT in whites. Among whites, but not African Americans, CRP was independently and inversely associated with insulin sensitivity, after adjusting for IAAT (r = -0.29 P < 0.05, and r = -0.13 P = 0.53, respectively). Insulin sensitivity remained lower in African Americans after adjusting for CRP (P < 0.001). In conclusion, greater IAAT among whites may be associated with greater inflammation. Insulin sensitivity was lower among African Americans, independent of obesity, fat distribution, and inflammation.

Validity of the reduced-sample insulin modified frequently-sampled intravenous glucose tolerance test using the nonlinear regression approach

The disposition index, the product of the insulin sensitivity index (S(I)) and the acute insulin response to glucose, is linked in African Americans to chromosome 11q. This link was determined with S(I) calculated with the nonlinear regression approach to the minimal model and data from the reduced-sample insulin-modified frequently-sampled intravenous glucose tolerance test (Reduced-Sample-IM-FSIGT). However, the application of the nonlinear regression approach to calculate S(I) using data from the Reduced-Sample-IM-FSIGT has been challenged as being not only inaccurate but also having a high failure rate in insulin-resistant subjects. Our goal was to determine the accuracy and failure rate of the Reduced-Sample-IM-FSIGT using the nonlinear regression approach to the minimal model. With S(I) from the Full-Sample-IM-FSIGT considered the standard and using the nonlinear regression approach to the minimal model, we compared the agreement between S(I) from the Full- and Reduced-Sample-IM-FSIGT protocols. One hundred African Americans (body mass index, 31.3 +/- 7.6 kg/m(2) [mean +/- SD]; range, 19.0-56.9 kg/m(2)) had FSIGTs. Glucose (0.3 g/kg) was given at baseline. Insulin was infused from 20 to 25 minutes (total insulin dose, 0.02 U/kg). For the Full-Sample-IM-FSIGT, S(I) was calculated based on the glucose and insulin samples taken at -1, 1, 2, 3, 4, 5, 6, 7, 8,10, 12, 14, 16, 19, 22, 23, 24, 25, 27, 30, 40, 50, 60, 70, 80, 90, 100, 120, 150, and 180 minutes. For the Reduced-Sample-FSIGT, S(I) was calculated based on the time points that appear in bold. Agreement was determined by Spearman correlation, concordance, and the Bland-Altman method. In addition, for both protocols, the population was divided into tertiles of S(I). Insulin resistance was defined by the lowest tertile of S(I) from the Full-Sample-IM-FSIGT. The distribution of subjects across tertiles was compared by rank order and kappa statistic. We found that the rate of failure of resolution of S(I) by the Reduced-Sample-IM-FSIGT was 3% (3/100). For the remaining 97 subjects, S(I) for the Full- and Reduced-Sample-IM-FSIGTs were as follows: 3.76 +/- 2.41 L mU(-1) min(-1) (range, 0.58-14.50) and 4.29 +/- 2.89 L mU(-1) min(-1) (range, 0.52-14.42); relative error, 21% +/- 18%; Spearman r = 0.97; and concordance, 0.94 (both P < .001). After log transformation, the Bland-Altman limits of agreement were -0.29 and 0.53. The exact agreement for distribution of the population in the insulin-resistant tertile vs the insulin-sensitive tertiles was 92%, kappa of 0.82 +/- 0.06. Using the nonlinear regression approach and data from the Reduced-Sample-IM-FSIGT in subjects with a wide range of insulin sensitivity, failure to resolve S(I) occurred in only 3% of subjects. The agreement and maintenance of rank order of S(I) between protocols support the use of the nonlinear regression approach to the minimal model and the Reduced-Sample-IM-FSIGT in clinical studies.

Common variant in MTNR1B associated with increased risk of type 2 diabetes and impaired early insulin secretion

Genome-wide association studies have shown that variation in MTNR1B (melatonin receptor 1B) is associated with insulin and glucose concentrations. Here we show that the risk genotype of this SNP predicts future type 2 diabetes (T2D) in two large prospective studies. Specifically, the risk genotype was associated with impairment of early insulin response to both oral and intravenous glucose and with faster deterioration of insulin secretion over time. We also show that the MTNR1B mRNA is expressed in human islets, and immunocytochemistry confirms that it is primarily localized in beta cells in islets. Nondiabetic individuals carrying the risk allele and individuals with T2D showed increased expression of the receptor in islets. Insulin release from clonal beta cells in response to glucose was inhibited in the presence of melatonin. These data suggest that the circulating hormone melatonin, which is predominantly released from the pineal gland in the brain, is involved in the pathogenesis of T2D. Given the increased expression of MTNR1B in individuals at risk of T2D, the pathogenic effects are likely exerted via a direct inhibitory effect on beta cells. In view of these results, blocking the melatonin ligand-receptor system could be a therapeutic avenue in T2D.

Insulin-stimulated release of D-chiro-inositol-containing inositolphosphoglycan mediator correlates with insulin sensitivity in women with polycystic ovary syndrome

Some actions of insulin are mediated by inositolphosphoglycan (IPG) mediators. Deficient release of a putative D-chiro-inositol-containing (DCI) IPG mediator may contribute to insulin resistance in women with polycystic ovary syndrome (PCOS). Previously, we demonstrated that oral DCI supplementation improved ovulation and metabolic parameters in women with PCOS. However, whether oral DCI mediates an increase in the release of the DCI-IPG mediator and an improvement in insulin sensitivity in women with PCOS is unknown. We conducted a randomized controlled trial of DCI supplementation vs placebo in 11 women with PCOS who were assessed at 2 time points 6 weeks apart. Plasma DCI, DCI-IPG release during oral glucose tolerance test (AUC(DCI-IPG)), and insulin sensitivity (S(i)) by frequently sampled intravenous glucose tolerance test were assessed at baseline and end of study. The study was terminated early because of a sudden unavailability of the study drug. However, in all subjects without regard to treatment assignment, there was a positive correlation between the change in AUC(DCI-IPG)/AUC(insulin) ratio and the change in S(i) during the 6-week period (r = 0.69, P = .02), which remained significant after adjustment for body mass index (P = .022) and after further adjustment for body mass index and treatment allocation (P = .0261). This suggests that, in women with PCOS, increased glucose-stimulated DCI-IPG release is significantly correlated with improved insulin sensitivity. The significant relationship between DCI-IPG release and insulin sensitivity suggests that the DCI-IPG mediator may be a target for therapeutic interventions in PCOS.

Baseline inflammatory markers do not modulate the lipid response to weight loss

Recent studies have found that baseline inflammatory status affected the response of the lipid profile to diet intervention. The goal of this study was to determine whether baseline inflammatory status, as reflected in C-reactive protein, interleukin 6, and tumor necrosis factor alpha, affected the lipid and insulin response to a weight loss intervention. A second goal was to determine whether inflammatory markers were related to traditional metabolic risk factors, such as lipids and insulin, in our sample of 190 overweight (body mass index, 27-30 kg/m2) premenopausal women. Body composition, fat distribution, serum lipids, insulin sensitivity (Si), and markers of inflammation were assessed at baseline and after weight loss to body mass index<25 kg/m2. All measurements were taken after a 4-week period of weight maintenance. Mixed-model, repeated-measures analysis was used to determine whether the interaction of baseline inflammatory status and time was significant in determining the changes in metabolic risk factors (Si and lipids) with weight loss. Weight loss was associated with significant reductions in total cholesterol, low-density lipoprotein cholesterol, triglycerides, and insulin, and increases in high-density lipoprotein cholesterol and Si. Triglycerides were higher (P=.054) and Si lower (P=.057) with increasing C-reactive protein tertile. The interaction of baseline inflammatory status and time was not significant for any outcome variable of interest. These results do not support the hypothesis that baseline inflammatory status affects the lipid and insulin response to a weight loss intervention. However, in these young, healthy women, weight loss had a beneficial impact on both inflammatory status and risk factors for chronic metabolic disease.

Greek hyperinsulinemic women, with or without polycystic ovary syndrome, display altered inositols metabolism

BACKGROUND We have shown that American women with polycystic ovary syndrome (PCOS) have decreased glucose-stimulated release of a putative mediator of insulin action, D-chiro-inositol (DCI)-containing inositolphosphoglycan (DCI-IPG), and increased urinary clearance of DCI (uCl(DCI)), which was associated with hyperinsulinemia.

METHODS

DCI levels and the release of insulin and DCI-IPG during an oral glucose tolerance test (AUCs) were assessed in 27 Greek PCOS and 10 normal Greek women.

RESULTS

PCOS women were heavier than controls (BMI = 28.4 versus 23.7 kg/m(2), P = 0.05) with higher waist-to-hip ratios (WHR = 0.78 versus 0.71, P = 0.009) and increased free testosterone (P = 0.048) and AUC(insulin) (P = 0.04). In PCOS women, incremental AUC(DCI-IPG) was significantly decreased by 59% (2158 versus 5276%.min, P = 0.01), even after correction for BMI and WHR. Finally, increased uCl(DCI) (r = 0.35, P = 0.04) and decreased AUC(DCI-IPG) (r = 0.46, P = 0.004) were significantly associated with hyperinsulinemia in all women together, even after correction for BMI and WHR (Ps = 0.02 and 0.007), and regardless of PCOS status.

CONCLUSIONS

Greek women, with or without PCOS, display increased uCl(DCI) and decreased AUC(DCI-IPG) in association with higher insulin levels but independent of adiposity. Increased clearance of inositols might reduce tissue availability of DCI and decrease the release of DCI-IPG mediator, which could contribute to insulin resistance and compensatory hyperinsulinemia in Greek women, as previously described in American women.

Short-term exercise improves beta-cell function and insulin resistance in older people with impaired glucose tolerance

BACKGROUND

There is a high prevalence of diabetes and impaired glucose tolerance (IGT) in the older population. Normal aging is associated with insulin resistance and impaired insulin secretion, with greater defects in people with IGT. Short-term exercise has been found to increase insulin sensitivity, but little is known about acute exercise effects on beta-cell function in older people with IGT.

METHODS

We assessed the effects of 7 consecutive days of supervised aerobic exercise (1 h/d at 60-70% heart rate reserve) in 12 sedentary older people with IGT. Screening included oral glucose tolerance test, stress/maximal O(2) uptake test, and dual-energy x-ray absorptiometry scan. Participants had a frequently sampled iv glucose tolerance test at baseline and 15-20 h after the seventh exercise session. Insulin sensitivity (S(I)), glucose disappearance constant (Kg, a measure of iv glucose tolerance), acute insulin response to glucose (AIRg), and disposition index (AIRg x S(I)), a measure of beta-cell function in relation to insulin resistance, were calculated.

RESULTS

Exercise was well tolerated. Body weight, fasting glucose, fasting insulin, and iv glucose tolerance were unchanged with exercise. S(I) increased by 59%, AIRg decreased by 12%, and disposition index increased by 31%. There was no significant change in fasting lipid, catecholamine, leptin, or adiponectin levels.

CONCLUSIONS

Short-term exercise not only improved insulin resistance but also significantly enhanced beta-cell function in older people with IGT. These effects of short-term exercise on beta-cell function cannot be explained by changes in body weight or circulating levels of lipids, leptin, adiponectin, or catecholamines.

Current approaches for assessing insulin sensitivity and resistance in vivo: advantages, limitations, and appropriate usage

Insulin resistance contributes to the pathophysiology of diabetes and is a hallmark of obesity, metabolic syndrome, and many cardiovascular diseases. Therefore, quantifying insulin sensitivity/resistance in humans and animal models is of great importance for epidemiological studies, clinical and basic science investigations, and eventual use in clinical practice. Direct and indirect methods of varying complexity are currently employed for these purposes. Some methods rely on steady-state analysis of glucose and insulin, whereas others rely on dynamic testing. Each of these methods has distinct advantages and limitations. Thus, optimal choice and employment of a specific method depends on the nature of the studies being performed. Established direct methods for measuring insulin sensitivity in vivo are relatively complex. The hyperinsulinemic euglycemic glucose clamp and the insulin suppression test directly assess insulin-mediated glucose utilization under steady-state conditions that are both labor and time intensive. A slightly less complex indirect method relies on minimal model analysis of a frequently sampled intravenous glucose tolerance test. Finally, simple surrogate indexes for insulin sensitivity/resistance are available (e.g., QUICKI, HOMA, 1/insulin, Matusda index) that are derived from blood insulin and glucose concentrations under fasting conditions (steady state) or after an oral glucose load (dynamic). In particular, the quantitative insulin sensitivity check index (QUICKI) has been validated extensively against the reference standard glucose clamp method. QUICKI is a simple, robust, accurate, reproducible method that appropriately predicts changes in insulin sensitivity after therapeutic interventions as well as the onset of diabetes. In this Frontiers article, we highlight merits, limitations, and appropriate use of current in vivo measures of insulin sensitivity/resistance.

Acute exercise increases triglyceride synthesis in skeletal muscle and prevents fatty acid-induced insulin resistance

Fatty acid oversupply is a key mediator of skeletal muscle insulin resistance in obesity, primarily via accumulation of fatty acid metabolites and activation of proinflammatory pathways. Herein, we demonstrate that fatty acid-induced insulin resistance in humans is completely prevented the day after 1 session of endurance exercise. Because skeletal muscle is the primary site for systemic glucose disposal and is highly susceptible to impaired insulin action by elevated fatty acid availability, we obtained skeletal muscle samples to investigate possible mechanisms mediating this protective effect of exercise. Prevention of fatty acid-induced insulin resistance after exercise accompanied enhanced skeletal muscle protein expression of key lipogenic enzymes and an increase in muscle triglyceride synthesis. Partitioning more fatty acids toward triglyceride synthesis within muscle reduced the accumulation of fatty acid metabolites and suppressed the proinflammatory response in skeletal muscle, as evidenced by decreased phosphorylation and activation of JNK and increased abundance of inhibitor of NF-kappaB alpha (I kappa B-alpha) and I kappa B-beta. We believe this is the first study to demonstrate that 1 session of exercise completely reverses fatty acid-induced insulin resistance in humans. Reversal of insulin resistance accompanied enhanced lipogenic capacity within skeletal muscle, reduced accumulation of highly bioactive fatty acid metabolites, and suppressed activation of proinflammatory pathways known to impair insulin action.

Relationship between insulin sensitivity and in vivo mitochondrial function in skeletal muscle

Recent data have shown that individuals with low insulin sensitivity (S(I)) also have reduced whole body maximal oxygen uptake. The objectives of this study were to determine 1) whether muscle mitochondrial function was independently related to S(I) after being adjusted for known determinants of S(I) and 2) whether lower S(I) among African-American (AA) vs. Caucasian-American (CA) women was due to lower muscle mitochondrial function among AA women. Subjects were 37 CA and 22 AA premenopausal women (age: 33.6 +/- 6.3 yr). Mitochondrial function [time constant of ADP (ADP(tc))] was assessed during a 90-s unilateral isometric contraction using (31)P magnetic resonance spectroscopy, S(I) with an intravenous glucose tolerance test, body composition by dual-energy X-ray absorptiometry, and visceral adipose tissue (VAT) with computed tomography. ANOVA was used to compare AA and CA groups, and multiple linear regression modeling was used to identify independent predictors of S(I). Between-race comparisons indicated that muscle oxidative capacity was lower among AAs vs. CAs (ADP(tc): 25.6 +/- 9.8 vs. 21.4 +/- 9.9 s). Multiple linear regression models for the dependent variable S(I) contained 1) VAT and race and 2) VAT, race, and ADP(tc). Significant independent effects for all predictor variables were observed in both the first (r(2) = 0.345) and second (r(2) = 0.410) models. The partial correlation for race was lower in the second model (-0.404 vs. -0.300), suggesting that muscle mitochondrial function contributed to the racial difference in S(I). Lower muscle mitochondrial function among AAs may in part explain lower S(I) among them.

Dairy, magnesium, and calcium intake in relation to insulin sensitivity: approaches to modeling a dose-dependent association

Dairy intake has been inversely associated with insulin resistance, which may be partly due to the specific effects of calcium and magnesium. Data from the Insulin Resistance Atherosclerosis Study (1992-1999) for 1,036 US adults without diabetes at baseline were examined to evaluate the cross-sectional association of habitual dairy, magnesium, and calcium intake with insulin sensitivity at baseline and after 5 years of follow-up. Insulin sensitivity was directly measured with a validated, 12-sample, insulin-enhanced, intravenous glucose tolerance test with minimal model analysis. Dietary intake was assessed by a validated food frequency interview, and dietary supplement dose was confirmed by reviewing the supplement label. Several statistical approaches were used to ensure appropriate modeling of the dose-dependent association. No association was found between dairy intake and insulin sensitivity (p=0.41); however, associations were positive for magnesium and calcium intake (p=0.016) after adjusting for demographic, nondietary lifestyle and dietary factors, and food groups. Furthermore, magnesium intake was associated with insulin sensitivity in a threshold fashion, with a Bayesian method-estimated threshold (325 mg) (beta=0.0607/100 mg, p=0.0008 for <325 mg of magnesium/day; and beta=-0.001/100 mg, p=0.82 for >or=325 mg of magnesium/day). This study suggests that magnesium and calcium intake specifically, but not dairy intake, is associated with insulin sensitivity.

Evaluation of nonlinear regression approaches to estimation of insulin sensitivity by the minimal model with reference to Bayesian hierarchical analysis

Minimal model analysis of intravenous glucose tolerance test (IVGTT) glucose and insulin concentrations offers a validated approach to measuring insulin sensitivity, but model identification is not always successful. Improvements may be achieved by using alternative settings in the modeling process, although results may differ according to setting, and care must be exercised in combining results. IVGTT data (12 samples, regular test) from 533 men without diabetes was modeled by the traditional nonlinear regression (NLR) approach, using five different permutations of settings. Results were evaluated with reference to the more robust Bayesian hierarchical (BH) approach to model identification and to the proportion of variance they explained in known correlates of insulin sensitivity (age, BMI, blood pressure, fasting glucose and insulin, serum triglyceride, HDL cholesterol, and uric acid concentration). BH analysis was successful in all cases. With NLR analysis, between 17 and 35 IVGTTs were associated with parameter coefficients of variation (PCVs) for minimal model parameters S(I) (insulin sensitivity) and S(G) (glucose effectiveness) of >100%. Systematic use of each different approach in combination reduced this number to five. Mean (interquartile range) S(I)(NLR) was then 3.14 (2.29-4.63) min(-1).mU(-1).l x 10(-4) and 2.56 (1.74-3.83) min(-1).mU(-1).l x 10(-4) for S(I)(BH) (correlation 0.86, P < 0.0001). S(I)(NLR) explained, on average, 10.6% of the variance in known correlates of insulin sensitivity, whereas S(I)(BH) explained 8.5%. In a large body of data, which BH analysis demonstrated could be fully identified, use of alternative modeling settings in NLR analysis could substantially reduce the number of analyses with PCVs >100%. S(I)(NLR) compared favorably with S(I)(BH) in the proportion of variance explained in known correlates of insulin sensitivity.

Altered D-chiro-inositol urinary clearance in women with polycystic ovary syndrome

OBJECTIVE

Evidence suggests that some actions of insulin are effected by inositolphosphoglycan (IPG) mediators. We hypothesize that a deficiency in D-chiro-inositol (DCI) and/or a DCI-containing IPG (DCI-IPG) may contribute to insulin resistance in humans.

RESEARCH DESIGN AND METHODS

To assess this possibility in polycystic ovary syndrome (PCOS), we determined insulin sensitivity (Si by frequently sampled intravenous glucose tolerance test), plasma and urinary DCI and myo-inositol (MYO) levels (by gas chromatography/mass spectrometry), and the release of insulin and DCI-IPG during the oral glucose tolerance test (area under the curve [AUC]) in 23 women with PCOS and 26 normal women.

RESULTS

Women with PCOS were heavier than control subjects (P = 0.002 for BMI), but also had decreased Si (P < 0.001) and increased AUC(insulin) (P < 0.001) compared with normal women, even when corrected for BMI. The urinary clearance of DCI (uCl(DCI)) was increased almost sixfold in PCOS compared with normal women (P = 0.001), but not MYO clearance (P = 0.10). uCl(DCI) correlated inversely with Si when all women were analyzed together (n = 49, r = -0.50, P < 0.001) and was one of the three best independent parameters predicting Si. Finally, the ratio of AUC(DCI-IPG) to AUC(insulin) was decreased threefold in women with PCOS (P < 0.001).

CONCLUSIONS

uCl(DCI) is inversely correlated with insulin sensitivity in women and is a strong independent predictor of insulin resistance in multivariate models. PCOS, which is characterized by insulin resistance, is associated with a selective increase in uCl(DCI) and impaired DCI-IPG release in response to insulin. These findings are consistent with a defect in tissue availability or utilization of DCI in PCOS that may contribute to the insulin resistance of the syndrome.

Dietary glycemic index and glycemic load, carbohydrate and fiber intake, and measures of insulin sensitivity, secretion, and adiposity in the Insulin Resistance Atherosclerosis Study

OBJECTIVE

We studied the association of digestible carbohydrates, fiber intake, glycemic index, and glycemic load with insulin sensitivity (S(I)), fasting insulin, acute insulin response (AIR), disposition index, BMI, and waist circumference.

RESEARCH DESIGN AND METHODS

Data on 979 adults with normal (67%) and impaired (33%) glucose tolerance from the Insulin Resistance Atherosclerosis Study (1992-1994) were analyzed. Usual dietary intake was assessed via a 114-item interviewer-administered food frequency questionnaire from which nutrient intakes were estimated. Published glycemic index values were assigned to food items and average dietary glycemic index and glycemic load calculated per subject. S(I) and AIR were determined by frequently sampled intravenous glucose tolerance test. Disposition index was calculated by multiplying S(I) with AIR. Multiple linear regression modeling was employed.

RESULTS

No association was observed between glycemic index and S(I), fasting insulin, AIR, disposition index, BMI, or waist circumference after adjustment for demographic characteristics or family history of diabetes, energy expenditure, and smoking. Associations observed for digestible carbohydrates and glycemic load, respectively, with S(I), insulin secretion, and adiposity (adjusted for demographics and main confounders) were entirely explained by energy intake. In contrast, fiber was associated positively with S(I) and disposition index and inversely with fasting insulin, BMI, and waist circumference but not with AIR.

CONCLUSION

Carbohydrates as reflected in glycemic index and glycemic load may not be related to measures of insulin sensitivity, insulin secretion, and adiposity. Fiber intake may not only have beneficial effects on insulin sensitivity and adiposity, but also on pancreatic functionality.

Postexercise insulin sensitivity is not impaired after an overnight lipid infusion

High plasma fatty acid availability and a positive energy balance in sedentary individuals reduce insulin sensitivity. This study's purpose was to determine whether high plasma fatty acid availability and systemic caloric excess after exercise also impair insulin sensitivity. On two separate occasions, seven nonobese women performed 90 min of exercise at approximately 65% peak oxygen uptake. In one trial, a lipid + heparin emulsion (Lipid) was infused overnight to increase plasma fatty acid availability. In the other trial, saline was infused as control. The next morning, a muscle biopsy was taken to measure muscle glycogen and intramuscular triglyceride (IMTG) concentrations. Three hours after the overnight infusion was stopped, insulin sensitivity was assessed with an intravenous glucose tolerance test, using minimal model analysis (Si). During the overnight infusions, plasma fatty acid concentration was approximately fourfold higher [means (SD): 0.84 (0.36) vs. 0.22 (0.09) mmol/l; P = 0.003], and the next morning IMTG concentration was approximately 30% greater [49.2 (6.6) vs. 38.3 (7.7) mmol/kg dry wt; P = 0.036] in Lipid compared with saline. However, muscle glycogen concentration was not different between trials (P = 0.82). Lipid caused a 24-h surplus of approximately 1100 kcal above energy balance (P = 0.00001), whereas energy balance was maintained in saline. Despite these differences in fatty acid and energy availability, Si the morning after exercise was not different between trials (P = 0.72). Thus insulin sensitivity the morning after a single exercise session was not reduced despite overnight exposure to a fourfold increase in plasma fatty acid concentration, elevated IMTG concentration, and systemic delivery of approximately 1,100-kcal excess.

Effect of lowering postprandial hyperglycemia on insulin secretion in older people with impaired glucose tolerance

Glucose tolerance declines with age, resulting in a high prevalence of diabetes and impaired glucose tolerance (IGT) in the older population. Hyperglycemia per se can lead to impaired beta-cell function (glucose toxicity). We tested the role of glucose toxicity in age-related beta-cell dysfunction in older people (65 +/- 8 yr) with IGT treated with the alpha-glucosidase inhibitor acarbose (n = 14) or placebo (n = 13) for 6 wk in a randomized, double-blind study. Baseline and posttreatment studies included 1) an oral glucose tolerance test (OGTT), 2) 1-h postprandial glucose monitoring, 3) a frequently sampled intravenous glucose tolerance test (insulin sensitivity, or S(I)), and 4) glucose ramp clamp (insulin secretion rates, or ISR), in which a variable glucose infusion increases plasma glucose from 5 to 10 mM. The treatment groups had similar baseline body mass index; fasting, 2-h OGTT, and 1-h postprandial glucose levels; and S(I). In these carefully matched older people with IGT, both fasting (5.7 +/- 0.2 vs. 6.3 +/- 0.2 mM, P = 0.002) and 1-h postprandial glucose levels (6.9 +/- 0.3 vs. 8.2 +/- 0.4 mM, P = 0.02) were significantly lower in the acarbose than in the placebo group. Despite this reduction of chronic hyperglycemia in the acarbose vs. placebo group, measures of insulin secretion (ISR area under the curve: 728 +/- 55 vs. 835 +/- 81 pmol/kg, P = 0.9) and acute insulin response to intravenous glucose (329 +/- 67 vs. 301 +/- 54 pM, P = 0.4) remained unchanged and impaired. Thus short-term improvement of chronic hyperglycemia does not reverse beta-cell dysfunction in older people with IGT.

Cardiovascular disease risk factors predict the development of type 2 diabetes: the insulin resistance atherosclerosis study

OBJECTIVE

In a few previous studies, cardiovascular disease (CVD) risk factors (RFs) have been shown to predict diabetes. Our objective was to determine whether the presence of CVD RFs predict the eventual development of diabetes after controlling for known RFs, such as directly measured insulin resistance and obesity.

RESEARCH DESIGN AND METHODS

We studied 872 participants with normal or impaired glucose tolerance (IGT) who were enrolled at baseline in the Insulin Resistance Atherosclerosis Study (IRAS). Of these, 143 (16%) developed type 2 diabetes in 5 years. Using these participants, a series of logistic regression models were fit to address the question.

RESULTS

Significant RFs for developing type 2 diabetes included high plasminogen activator inhibitor-1, hypertension, high triglycerides, low levels of HDL cholesterol, and IGT. The 5-year cumulative incidence of type 2 diabetes by the number of RFs (0-5) was as follows: no RFs, 11 of 230 = 5%; one RF, 31 of 278 = 11%; two RFs, 36 of 202 = 18%; three RFs, 41 of 110 = 37%; four RFs, 19 of 42 = 45%; and five RFs, 5 of 10 = 50% (P < 0.001). The odds ratio (OR) for conversion to type 2 diabetes for each additional RF was 2.1 (95% CI 1.78-2.46) after adjusting for age, sex, ethnicity, and center. After further adjustment for insulin resistance, determined by the frequently sampled intravenous glucose tolerance test and waist circumference, each additional CVD RF increased the risk of type 2 diabetes significantly (OR 1.81, 95% CI 1.49-2.20).

CONCLUSIONS

Individuals with multiple CVD RFs are at increased risk of type 2 diabetes, which is only partially mediated by insulin resistance or central adiposity. This information should be useful for identifying high-risk patients for developing diabetes through RF assessments.

Assessment of single-dose benzodiazepines on insulin secretion, insulin sensitivity and glucose effectiveness in healthy volunteers: a double-blind, placebo-controlled, randomized cross-over trial [ISRCTN08745124]

BACKGROUND

The present study aimed at investigating in healthy volunteers the effects of diazepam and clonazepam on beta-cell function, insulin sensitivity and glucose effectiveness based on the frequently sampled intravenous (0.5 gkg-1) glucose tolerance test with minimal-model analysis.

METHODS

The study was designed as a double-blind, placebo-controlled, cross-over clinical trial. Diazepam (10 mg) and clonazepam (1 mg) were infused during 30 min to 15 male subjects with a mean age of 22 years (range: 20-29), after informed consent was given. Benzodiazepines were assayed by capillary gas chromatography with electron capture, insulin by radioimmunoassay and glucose by the enzymatic glucose oxidase method.

RESULTS

Both benzodiazepines induced significant psychotropic effects. The acute insulin responses (AIR) were significantly and negatively correlated with the clonazepam plasma concentrations (r = -0.609, P < 0.05, n = 14). However, the mean AIR was not significantly different between the benzodiazepine-treated subjects and the controls. In addition, the parameters of glucose assimilation were significantly decreased as compared with placebo in the subgroup of 7 subjects with plasma clonazepam concentrations higher than 6.0 ng ml-1 (median and lower limit of effective therapeutic concentrations): 1.37 +/- 0.3 versus 2.84 +/- 0.60 x 10(-2)min-1 (P = 0.028) for the coefficient of glucose tolerance (Kg), 2.18 +/- 0.29 versus 3.71 +/- 0.89 x 10(-4)microUml-1min-1 (P = 0.018) for insulin sensitivity (Si) and 1.80 +/- 0.39 versus 3.59 +/- 0.71 x 10(-2)min-1 (P = 0.028) for glucose effectiveness at basal insulin (Sg). These parameters were not significantly modified when diazepam was administered; plasma levels of this drug however, were below the effective therapeutic concentrations (300 ng ml-1) from min 15 after the end of the perfusion.

CONCLUSION

The present results suggest that a benzodiazepine, in particular clonazepam, may alter insulin secretion and insulin sensitivity after a single administration in healthy volunteers.

The effect of the PREMIER interventions on insulin sensitivity

OBJECTIVE

This ancillary study of PREMIER sought to determine the effects on insulin sensitivity of a comprehensive behavioral intervention for hypertension with and without the Dietary Approaches to Stop Hypertension (DASH) dietary pattern.

RESEARCH DESIGN AND METHODS

Participants were assigned to one of three nonpharmacologic interventions for blood pressure (group A, advice only; group B, established; and group C, established plus DASH). The established intervention included weight loss, reduced sodium intake, increased physical activity, and moderate alcohol intake; the DASH dietary pattern was added to the established intervention for those in group C. The DASH dietary pattern is high in fruits, vegetables, and low-fat dairy products while being lower in total fat, saturated fat, and cholesterol. It is abundant in nutrients such as magnesium, calcium, and protein, which have been associated with improved insulin sensitivity. Insulin sensitivity was measured at baseline and at 6 months using the frequently sampled intravenous glucose tolerance test with minimal model analysis.

RESULTS

Both intervention groups decreased total calories, percentage of calories from fat, and sodium intake to similar levels, with similar amounts of energy expenditure and weight loss. Covariate differences seen only in group C included increased intake of protein, potassium, calcium, and magnesium. Compared with control subjects, insulin sensitivity improved significantly only in group C, from 1.96 to 2.95 (P = 0.047). Group B did have a significant decrease in fasting insulin and glucose, but the changes in insulin sensitivity did not reach statistical significance when compared with control subjects.

CONCLUSIONS

These results suggest that including the DASH dietary pattern as part of a comprehensive intervention for blood pressure control enhances insulin action beyond the effects of a comprehensive intervention that does not include DASH.

Uncoupling protein 2 promoter polymorphism -866G/A affects its expression in beta-cells and modulates clinical profiles of Japanese type 2 diabetic patients

Common uncoupling protein 2 (UCP2) promoter polymorphism -866G/A is reported to be associated with its expression in adipose tissue and the risk of obesity in Caucasians. On the other hand, several studies suggested that UCP2 expression in beta-cells is an important determinant of insulin secretion. In the Japanese population, morbid obesity is very rare, and insulin secretion capacity is relatively low as compared with Caucasians. Because UCP2 would link to insulin secretion and obesity, it might explain this ethnic difference. Here, we report that the UCP2 promoter with the A allele showed higher promoter activity in the INS-1 beta-cell line. The frequency of the A allele is higher in our Japanese study than that in Caucasians. Type 2 diabetic patients with the A allele need insulin therapy earlier and showed higher frequency of insulin treatment. Moreover glucose-induced early insulin secretion is significantly lower in patients with the A allele. However, there was no difference in allele frequency between obese and lean type 2 diabetic patients. In conclusion, UCP2 promoter polymorphism -866G/A does not affect obesity in Japanese type 2 diabetic patients but affects its transcription in beta-cells and modulates glucose-induced insulin secretion and eventually insulin requirement in Japanese type 2 diabetic patients. Higher A allele frequency in the Japanese population might partly explain the ethnic difference of insulin secretion capacity.

Indexes of insulin resistance and secretion in obese children and adolescents: a validation study

OBJECTIVE

To assess the concurrent validity of fasting indexes of insulin sensitivity and secretion in obese prepubertal (Tanner stage 1) children and pubertal (Tanner stages 2-5) adolescents using estimates from the modified minimal model frequently sampled intravenous glucose tolerance test (FSIVGTT) as a criterion measure.

RESEARCH DESIGN AND METHODS

Eighteen obese children and adolescents (11 girls and 7 boys, mean age 12.2 +/- 2.4 years, mean BMI 35.4 +/- 6.2 kg/m(2), mean BMI-SDS 3.5 +/- 0.5, 7 prepubertal and 11 pubertal) participated in the study. All participants underwent an insulin-modified FSIVGTT on two occasions, and 15 repeated this test a third time (mean 12.9 and 12.0 weeks apart). S(i) measured by the FSIVGTT was compared with homeostasis model assessment (HOMA) of insulin resistance (HOMA-IR), quantitative insulin-sensitivity check index (QUICKI), fasting glucose-to-insulin ratio (FGIR), and fasting insulin (estimates of insulin sensitivity derived from fasting samples). The acute insulin response (AIR) measured by the FSIVGTT was compared with HOMA of percent beta-cell function (HOMA-beta%), FGIR, and fasting insulin (estimates of insulin secretion derived from fasting samples).

RESULTS

There was a significant negative correlation between HOMA-IR and S(i) (r = -0.89, r = -0.90, and r = -0.81, P < 0.01) and a significant positive correlation between QUICKI and S(i) (r = 0.89, r = 0.90, and r = 0.81, P < 0.01) at each time point. There was a significant positive correlation between FGIR and S(i) (r = 0.91, r = 0.91, and r = 0.82, P < 0.01) and a significant negative correlation between fasting insulin and S(i) (r = -90, r = -0.90, and r = -0.88, P < 0.01). HOMA-beta% was not as strongly correlated with AIR (r = 0.60, r = 0.54, and r = 0.61, P < 0.05).

CONCLUSIONS

HOMA-IR, QUICKI, FGIR, and fasting insulin correlate strongly with S(i) assessed by the FSIVGTT in obese children and adolescents. Correlations between HOMA-beta%, FGIR and fasting insulin, and AIR were not as strong. Indexes derived from fasting samples are a valid tool for assessing insulin sensitivity in prepubertal and pubertal obese children.

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.

Methods for clinical assessment of insulin sensitivity and beta-cell function

The quantitative assessment of insulin sensitivity (IS) and beta-cell function (BCF) is fundamental in the study of metabolic disorders. The most relevant experimental tests and data analysis methods for assessing both IS and BCF are described and their characteristic features discussed. Advantages and limitations of each method are comparatively reviewed to help investigators choose the most suitable test for their needs. The problem of properly relating BCF to IS is also addressed. Particular attention is paid to the oral glucose tolerance test, which has recently received considerable interest. The role of mathematical models in IS and BCF assessment is also emphasized.

Exercise-induced changes in insulin action are associated with ACE gene polymorphisms in older adults

We evaluated the association between insulin resistance and the angiotensin-converting enzyme (ACE) insertion (I)/deletion (D) gene polymorphism in a group of older hypertensive subjects (63 +/- 1 yr, n = 35) before and after a 6-mo aerobic exercise program (AEX). Insulin sensitivity index (S(I)), assessed by the frequently sampled intravenous glucose tolerance test, was significantly (P = 0.0001) increased following AEX. In addition, there was a significant (P = 0.001) interaction between AEX and ACE genotype. S(I) increased significantly (P < 0.05) more in those with the II (2.5 +/- 0.8 microU x 10(-4) x min(-1) x ml(-1)) ACE genotype compared with both the DD and ID (0.7 +/- 0.1 and 0.7 +/- 0.2 microU x 10(-4) x min(-1) x ml(-1), respectively) ACE genotypes. Similarly, there was a significant (P = 0.036) decrease in the acute insulin response to glucose (AIR(G)) and a significant (P = 0.05) interaction between AEX and ACE genotype. AIR(G) decreased significantly (P < 0.05) more in those with the II (-17.6 +/- 5.6 mU/ml) ACE genotype compared with both the DD and ID (-1.4 +/- 6.2 and -3.6 +/- 2.5 mU/ml) ACE genotypes. In conclusion, we demonstrated that those older hypertensives with the ACE II genotype have the greatest improvement in insulin action following AEX.

Is insulin sensitivity a causal intermediate in the relationship between alcohol consumption and carotid atherosclerosis?: the insulin resistance and atherosclerosis study

OBJECTIVE

A J-shaped association has been demonstrated between alcohol consumption and atherosclerosis. Insulin resistance, also a risk factor for atherosclerosis, has been shown to have a similar J-shaped association with alcohol intake. This raises the question of whether insulin sensitivity (S(I)) is a causal intermediate in the alcohol-atherosclerosis relationship.

RESEARCH DESIGN AND METHODS

The Insulin Resistance Atherosclerosis Study was a multicenter cohort study designed to investigate relationships among S(I), risk factors for cardiovascular disease, and carotid artery atherosclerosis. Using regression analysis, we tested whether adjustment for S(I) attenuated the alcohol-atherosclerosis relationship observed at baseline.

RESULTS

A J-shaped association was observed between alcohol consumption and common carotid artery intimal medial thickness. The protective aspect of the alcohol-atherosclerosis relationship was attenuated by 25% after the adjustment for S(I). However, an interaction was observed between alcohol consumption and glucose tolerance (GT) status. In comparison with never drinkers, all levels of alcohol consumption were associated with less atherosclerosis in participants with normal GT status. Participants with impaired GT status (but not diabetes) demonstrated a J-shaped alcohol-atherosclerosis association. All levels of alcohol consumption were associated with more atherosclerosis in participants with diabetes.

CONCLUSIONS

S(I) may be a causal intermediate at protective levels of alcohol intake, but an alcohol-GT interaction precluded a definitive conclusion. Moderate alcohol consumption may increase the risk of atherosclerosis in people with diabetes. These findings contrast with previous reports and do not support current recommendations regarding moderate alcohol consumption in people with diabetes. More research is needed to clarify this issue.

Development of a prediction equation for insulin sensitivity from anthropometry and fasting insulin in prepubertal and early pubertal children

OBJECTIVE

To test the utility of homeostasis model assessment (HOMA) in predicting insulin sensitivity [x10(- 4) min(-1)/(microIU/ml)] in children and to develop and compare two new prediction equations for insulin sensitivity in children using demographic and anthropometric measures in the presence or absence of fasting insulin.

RESEARCH DESIGN AND METHODS

We studied 156 white and African-American children with complete data (mean age 9.7 +/- 1.8 years, 87.8% Tanner Stage 1 or 2). For development of new equations, two-thirds of the children were randomly assigned to a development group, whereas the remaining children were assigned to a cross-validation group.

RESULTS

A modified HOMA equation accurately predicted insulin sensitivity, but its utility is similar to fasting insulin alone. Demographic and anthropometric measures alone did not predict insulin sensitivity accurately, even when precise measures of body composition were included in the prediction model. Ethnicity, calf skinfold, and fasting insulin together explained 73% of the variance in insulin sensitivity and accurately predicted insulin sensitivity. The regression of measured versus predicted insulin sensitivity in the cross-validation group was not significantly different from the line of identity (P > 0.05). Mean difference between measured and predicted insulin sensitivity was also not significant (P > 0.05). Some bias was apparent, particularly in white boys.

CONCLUSIONS

Ethnicity, calf skinfold, and fasting insulin can accurately predict insulin sensitivity with greater precision than HOMA or fasting insulin alone (R(2) = 0.73). Future studies, however, are needed to examine whether a universal equation is possible. A cross-validated prediction equation may be useful in population-based studies when complex measures of insulin sensitivity are not available.

Sympathetic activity and the heterogenous blood pressure response to exercise training in hypertensives

To test whether changes in sympathetic nervous system (SNS) activity or insulin sensitivity contribute to the heterogeneous blood pressure response to aerobic exercise training, we used compartmental analysis of [3H]norepinephrine kinetics to determine the extravascular norepinephrine release rate (NE2) as an index of systemic SNS activity and determined the insulin sensitivity index (S(I)) by an intravenous glucose tolerance test, before and after 6 mo of aerobic exercise training, in 30 (63 +/- 7 yr) hypertensive subjects. Maximal O2 consumption increased from 18.4 +/- 0.7 to 20.8 +/- 0.7 ml x kg(-1) x min(-1) (P = 0.02). The average mean arterial blood pressure (MABP) did not change (114 +/- 2 vs. 114 +/- 2 mmHg); however, there was a wide range of responses (-19 to +17 mmHg). The average NE2 did not change significantly (2.11 +/- 0.15 vs. 1.99 +/- 0.13 microg x min(-1) x m(-2)), but there was a significant positive linear relationship between the change in NE2 and the change in MABP (r = 0.38, P = 0.04). S(I) increased from 2.81 +/- 0.37 to 3.71 +/- 0.42 microU x 10(-4) x min(-1) x ml(-1) (P = 0.004). The relationship between the change in S(I) and the change in MABP was not statistically significant (r = -0.03, P = 0.89). When the changes in maximal O2 consumption, percent body fat, NE2, and S(I) were considered as predictors of the change in MABP, only NE2 was a significant independent predictor. Thus suppression of SNS activity may play a role in the reduction in MABP and account for a portion of the heterogeneity of the MABP response to aerobic exercise training in older hypertensive subjects.

The iterative two-stage population approach to IVGTT minimal modeling: improved precision with reduced sampling. Intravenous glucose tolerance test

The minimal model method is widely used to estimate glucose effectiveness (S(G)) and insulin sensitivity (S(I)) from intravenous glucose tolerance test (IVGTT) data. In the standard protocol (sIVGTT, 0.33 g/kg glucose bolus given at time 0), which allows the simultaneous assessment of beta-cell function, the precision of the individualized estimates often degrades and particularly so in the presence of reduced sampling schedules. Here, we investigated the use of a population approach, the iterative two-stage (ITS) approach, to analyze 16 sIVGTTs in healthy subjects and to obtain refined estimates of S(G) and S(I) in the population and in the individual subjects. The ITS is based on calculation of the population mean and standard deviation of the parameters at each iteration and then use of them as prior information for the individual analyses. Theoretically, the use of a prior in the ITS should improve the precision of the individual estimates. The customary approach (standard two stage, STS), where modeling is performed separately for each individual subject, does not take the population knowledge into account. We used both frequent (FSS, 30 samples) and (quasi-optimally) reduced (RSS, 14 samples) sampling schedules. For the FSS, STS gave estimates (mean +/- SD) for S(G) = 2.66 +/- 1.09 x 10(-2). min(-1) and S(I) = 6.46 +/- 6.99 10(-4). min(-1). microU(-1). ml, with an average precision of 51 (range 5-176) and 33% (3-91), respectively. RSS radically worsened the precision of both S(G) and S(I). However, RSS and ITS gave S(G) = 2.59 +/- 0.73 and S(I) = 6.06 +/- 7.28, with an average precision of 23 (12-42) and 27% (), respectively. In conclusion, population minimal modeling of sIVGTT data improves the precision of individual estimates of glucose effectiveness and insulin sensitivity, as the theory predicts, and, even with reduced sampling, the improvement is substantial.