Relationship between surrogate estimates and direct measurement of insulin resistance in women with polycystic ovary syndrome

PURPOSE

To evaluate the relationship between surrogate estimates of insulin resistance and a direct measurement of insulin-mediated glucose uptake women with and without PCOS.

METHODS

Retrospective cohort study of 75 PCOS and 118 controls. Fasting plasma glucose and insulin concentrations, insulin resistance as determined by the insulin suppression test, calculation of multiple surrogate estimates of insulin resistance, total and free testosterone concentrations, and correlations between the direct measure and surrogate estimates of insulin resistance were evaluated.

RESULT(S)

Surrogate markers of insulin resistance were correlated to a variable, but statistically significant degree with the direct measure of insulin resistance in control population and the women with PCOS. There was no correlation between the surrogate estimates of insulin resistance and total or free plasma testosterone concentrations.

CONCLUSION(S)

The surrogate estimates of insulin resistance evaluated were significantly related to a direct measure of insulin resistance, and this was true of both the control population and women with PCOS. The magnitude of the relationship between the surrogate estimates and the direct measurement was comparable and not significantly altered by androgen levels. Fasting plasma insulin concentration seems to be at least as accurate as any other surrogate estimate, and is by far the simplest.

Plasma triglyceride determination can identify increased risk of statin-induced type 2 diabetes: a hypothesis

OBJECTIVE

To evaluate the ability of plasma triglyceride (TG) measurements to identify statin-treated persons at accentuated risk of statin-induced type 2 diabetes (T2DM).

METHODS

The experimental population consisted of nondiabetic, statin-treated patients (n = 469), classified as being at high risk for T2DM, subdivided on the basis of a plasma TG concentration of 1.7 mmol/L. Comparisons were made of demographic characteristics, concentrations of fasting glucose, insulin, HbA1c, and hs-CRP, oral glucose tolerance tests, estimates of insulin action and secretion, and lipid/lipoprotein profiles.

RESULTS

Despite similar fasting glucose and HbA1c concentrations, patients with elevated TG concentrations displayed markers of increased risk of T2DM (insulin resistance and compensatory hyperinsulinemia), more adverse lipid/lipoprotein profiles, and increased prevalence of abnormal hs-CRP values.

CONCLUSION

These findings demonstrate that plasma TG concentrations ≥ 1.7 mmol/L identified a subset of individuals at enhanced risk of developing statin-induced diabetes within a population classified prior to statin treatment as being at high risk of T2DM.

The metabolic syndrome: useful concept or clinical tool? Report of a WHO Expert Consultation

This article presents the conclusions of a WHO Expert Consultation that evaluated the utility of the 'metabolic syndrome' concept in relation to four key areas: pathophysiology, epidemiology, clinical work and public health. The metabolic syndrome is a concept that focuses attention on complex multifactorial health problems. While it may be considered useful as an educational concept, it has limited practical utility as a diagnostic or management tool. Further efforts to redefine it are inappropriate in the light of current knowledge and understanding, and there is limited utility in epidemiological studies in which different definitions of the metabolic syndrome are compared. Metabolic syndrome is a pre-morbid condition rather than a clinical diagnosis, and should thus exclude individuals with established diabetes or known cardiovascular disease (CVD). Future research should focus on: (1) further elucidation of common metabolic pathways underlying the development of diabetes and CVD, including those clustering within the metabolic syndrome; (2) early-life determinants of metabolic risk; (3) developing and evaluating context-specific strategies for identifying and reducing CVD and diabetes risk, based on available resources; and (4) developing and evaluating population-based prevention strategies.

Inflammation in subcutaneous adipose tissue: relationship to adipose cell size

AIMS/HYPOTHESIS

Inflammation is associated with increased body mass and purportedly with increased size of adipose cells. We sought to determine whether increased size of adipose cells is associated with localised inflammation in weight-stable, moderately obese humans.

METHODS

We recruited 49 healthy, moderately obese individuals for quantification of insulin resistance (modified insulin suppression test) and subcutaneous abdominal adipose tissue biopsy. Cell size distribution was analysed with a multisizer device and inflammatory gene expression with real-time PCR. Correlations between inflammatory gene expression and cell size variables, with adjustment for sex and insulin resistance, were calculated.

RESULTS

Adipose cells were bimodally distributed, with 47% in a 'large' cell population and the remainder in a 'small' cell population. The median diameter of the large adipose cells was not associated with expression of inflammatory genes. Rather, the fraction of small adipose cells was consistently associated with inflammatory gene expression, independently of sex, insulin resistance and BMI. This association was more pronounced in insulin-resistant than insulin-sensitive individuals. Insulin resistance also independently predicted expression of inflammatory genes.

CONCLUSIONS/INTERPRETATION

This study demonstrates that among moderately obese, weight-stable individuals an increased proportion of small adipose cells is associated with inflammation in subcutaneous adipose tissue, whereas size of mature adipose cells is not. The observed association between small adipose cells and inflammation may reflect impaired adipogenesis and/or terminal differentiation. However, it is unclear whether this is a cause or consequence of inflammation. This question and whether small vs large adipose cells contribute differently to inflammation in adipose tissue are topics for future research.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00285844.

Persistence of improvement in insulin sensitivity following a dietary weight loss programme

AIM

Short-term dietary weight loss can improve insulin resistance but long-term studies are lacking. We sought to quantify the degree to which maintenance of weight loss after a short-term dietary intervention was associated with persistent metabolic benefits.

METHODS

Fifty-seven insulin-resistant obese subjects had insulin-mediated glucose disposal quantified through the steady-state plasma glucose (SSPG) test, and associated metabolic risk markers quantified at baseline, after a 16-week dietary weight loss intervention, and in 25 subjects, at follow-up of 28.8 +/- 13 months. Changes in metabolic variables over time were analysed and correlation with weight loss ascertained. Those with greatest vs. least long-term SSPG response (responders vs. non-responders) were compared. Multivariate analysis was performed for predictors of persistent SSPG response.

RESULTS

At follow-up, the 25 subjects who returned for metabolic testing had, on average, maintained their weight loss. Insulin-mediated glucose disposal remained significantly improved vs. baseline, as did plasma triglyceride and HDL cholesterol (HDL-C) concentrations, and improvement correlated with total amount of weight lost. Comparison of SSPG responders to non-responders showed no difference in amount of weight lost and SSPG change during the 16-week dietary intervention; however, SSPG non-responders regained 2.6% of weight lost, whereas responders lost an additional 1.5% at follow-up (p < 0.05 vs. non-responders). Non-responders had baseline characteristics consistent with more severe insulin resistance, including higher fasting plasma glucose (p = 0.03). Long-term SSPG change was independently predicted by both total weight loss (p = 0.005) and baseline fasting plasma glucose (p = 0.007).

CONCLUSIONS

Improvement in insulin sensitivity is maintained for 2-3 years following dietary weight loss if weight is not regained. Triglyceride and HDL-C concentrations also remain improved over time, consistent with improvement in insulin sensitivity. Fasting glucose and weight regain predict less long-term response in insulin sensitivity. These results highlight the potential long-term benefits of weight loss and importance of preventing weight regain among high-risk individuals.

Insulin resistance is associated with a modest increase in inflammation in subcutaneous adipose tissue of moderately obese women

AIMS/HYPOTHESIS

We have previously described differences in adipose cell size distribution and expression of genes related to adipocyte differentiation in subcutaneous abdominal fat obtained from insulin-sensitive (IS) and -resistant (IR) persons, matched for degree of moderate obesity. To determine whether other biological properties also differ between IR and IS obese individuals, we quantified markers of inflammatory activity in adipose tissue from overweight IR and IS individuals.

METHODS

Subcutaneous abdominal tissue was obtained from moderately obese women, divided into IR (n = 14) and IS (n = 19) subgroups by determining their steady-state plasma glucose (SSPG) concentrations during the insulin suppression test. Inflammatory activity was assessed by comparing expression of nine relevant genes and by immunohistochemical quantification of CD45- and CD68-containing cells.

RESULTS

SSPG concentrations were approximately threefold higher in IR than in IS individuals. Expression levels of CD68, EMR1, IL8, IL6 and MCP/CCL2 mRNAs were modestly but significantly increased (p < 0.05) in IR compared with IS participants. Results of immunohistochemical staining were consistent with gene expression data, demonstrating modest differences between IR and IS individuals. Crown-like structures, in which macrophages surround single adipocytes, were rarely seen in tissue from either subgroup.

CONCLUSIONS/INTERPRETATION

A modest increase in inflammatory activity was seen in subcutaneous adipose tissue from IR compared with equally obese IS individuals. Together with previous evidence of impaired adipose cell differentiation in IR vs equally obese individuals, it appears that at least two biological processes in subcutaneous adipose tissue characterize the insulin-resistant state independent of obesity per se.

Relationship between insulin resistance, weight loss, and coronary heart disease risk in healthy, obese women

Several popular books have recently been published stating that being insulin-resistant favors weight gain and/or prevents weight loss. Because this view seems to have gained widespread support in the general population, we thought it important to perform the current study testing the hypothesis that differences in insulin-mediated glucose disposal do not affect weight loss in response to calorie-restricted diets. For this purpose, we studied the change in weight and risk factors for coronary heart disease (CHD) in healthy women volunteers, defined as being obese on the basis of a body mass index (BMI) greater than 30.0 kg/m(2). The insulin suppression test was used to stratify obese women at baseline into insulin-resistant and insulin-sensitive subgroups on the basis of their steady-state plasma glucose (SSPG) concentration at the end of a 180-minute infusion of octreotide, exogenous insulin, and glucose. They were then instructed on a calorie-restricted diet plus sibutraminine (15 mg/day) for a total period of 4 months. Baseline measurements also included determination of fasting lipid and lipoprotein concentrations, and hourly (8 AM to 4 PM) determinations of plasma glucose and insulin concentrations before and after breakfast and lunch. Twenty-four women completed the 4-month period of calorie restriction: 13 classified as insulin-resistant (SSPG = 219 +/- 7 mg/dL) and 11 as insulin-sensitive (SSPG = 69 +/- 6 mg/dL). The insulin-resistant group also had higher (P =.03) plasma triglyceride (TG) concentrations and a higher ratio of total to high-density lipoprotein (HDL) cholesterol concentration (P =.02) at baseline. Both groups lost a significant amount of weight during the study, and there was no difference between the weight loss in the insulin-resistant (8.6 +/- 1.3 kg) and insulin-sensitive (7.9 +/- 1.4 kg) groups. Weight loss in the insulin-resistant group was also associated with a significant decrease in SSPG concentration (219 +/- 7 to 144 +/- 14 mg/dL), associated with significantly lower fasting TG concentrations (P <.001) and day-long concentrations of plasma glucose and insulin (P <.005). None of these variables changed in the insulin-sensitive group. These results indicate that: (1) CHD risk factors in obese women vary as a function of being insulin-resistant or insulin-sensitive; (2) dramatic variations in insulin-mediated glucose disposal do not modulate weight loss in response to calorie-restricted diets, and (3) weight loss is effective in reducing CHD risk in insulin-resistant, obese women. Given these data, it seems obvious that attempts to reduce CHD risk factors by weight loss should focus on obese individuals who are also insulin-resistant.

Metabolic abnormalities characteristic of dysmetabolic syndrome predict the development of transplant coronary artery disease: a prospective study

BACKGROUND

This study examines the hypothesis that metabolic abnormalities of dysmetabolic syndrome are risk factors for transplant coronary artery disease (TxCAD).

METHODS AND RESULTS

Sixty-six patients without overt diabetes, 2 to 4 years after surgery, underwent intracoronary ultrasound (ICUS), measurement of plasma glucose and insulin after oral glucose (75 g), and fasting lipid and lipoproteins. TxCAD incidence by angiography or autopsy was prospectively determined during subsequent follow-up (8 years). Coronary artery intimal thickness (IT) and subsequent outcomes were compared in patients stratified as having "high" versus "low" plasma glucose (>8.9 mmol/L) and insulin (>760 pmol/L) 2 hours after glucose challenge; and "abnormal" versus "normal" fasting lipid and lipoprotein concentrations as defined by the National Cholesterol Education

PROGRAM

Patients with high glucose or insulin concentrations had greater IT: 0.38+/-0.05 versus 0.22+/-0.02 mm, P</=0.05, and 0.39+/-0.05 versus 0.20+/-0.02 mm, P</=0.01, respectively. Freedom from TxCAD was 56+/-11% versus 81+/-6% (P<0.01) in patients with high versus low glucose and 57+/-10% versus 82+/-7% (P<0.05) in patients with high versus low insulin. Actuarial survival was 60+/-12% versus 92+/-5% (P<0.005) in patients with high versus low glucose and 72+/-9% versus 88+/-6% (P<0.05) in patients with high versus low insulin. Triglycerides and VLDL were higher and HDL was lower in patients with IT >0.3 mm than with IT </=0.3 mm. TxCAD incidence was higher in patients with high plasma TG and VLDL and low HDL.

CONCLUSIONS

These data suggest that insulin resistance plays a role in TXCAD:

Effect of orlistat-assisted weight loss in decreasing coronary heart disease risk in patients with syndrome X

This study describes the changes in risk factors for coronary heart disease in obese persons with syndrome X after orlistat-assisted weight loss. Data were available for 1,700 patients who completed 52 weeks of weight loss; 128 were defined as having syndrome X by being in the quintile with the highest plasma triglyceride levels (>2.2 mM/L) and the lowest high-density lipoprotein cholesterol (HDL, <1.0 mM/L) concentrations. Initial characteristics of those with syndrome X were similar to the 119 subjects (non-syndrome X) in the lowest quintile of plasma triglyceride (<0.975 mM/L) and highest quintile of HDL cholesterol (>1.5 mM/L). Subjects were placed on a calorie-restricted diet, and randomized to receive orlistat or placebo. Initial values were higher in those with syndrome X for diastolic blood pressure (p = 0.03), plasma insulin (p = 0.0001), triglyceride (p = 0.0001) concentrations, and ratio of low-density lipoprotein cholesterol to HDL cholesterol (p = 0.0001), and were lower for HDL cholesterol (p = 0.001) concentrations. Weight loss was greater in both groups of orlistat-treated patients (p = 0.026); in those with syndrome X, it was associated with a significant reduction in plasma insulin (p = 0.019) and triglyceride (p = 0.0001) concentrations, an increase in HDL cholesterol concentration, and a decrease in low-density lipoprotein/HDL cholesterol ratio (p = 0.0001). There were no significant changes in plasma insulin, triglycerides, or HDL cholesterol concentration in the non-syndrome X group. In conclusion, weight loss attenuates coronary heart disease risk factors in obese persons with syndrome X, and the risk factor reduction is enhanced with administration of orlistat.

Carbohydrate-induced hypertriglyceridemia: an insight into the link between plasma insulin and triglyceride concentrations

This study was initiated to test the hypothesis that endogenous hypertriglyceridemia results from a defect in the ability of insulin to inhibit the release of very low-density lipoprotein-triglyceride (TG) from the liver. To accomplish this goal, plasma glucose, insulin, free fatty acid (FFA), and TG concentrations were compared in 12 healthy volunteers, in response to diets containing either 40% or 60% of total calories as carbohydrate (CHO). The protein content of the two diets was similar (15% of calories), and the fat content varied inversely with the amount of CHO (45% or 25%). The diets were consumed in random order, and measurements were made of plasma glucose, insulin, FFA, and TG concentrations at the end of each dietary period, fasting, and at hourly intervals following breakfast and lunch. The results indicated that the 60% CHO diet resulted in higher fasting plasma TG concentrations associated with higher day-long plasma insulin and TG concentrations, and lower FFA concentrations. These results do not support the view that hypertriglyceridemia is secondary to a failure of insulin to inhibit hepatic TG secretion.

Alterations in nitric oxide/cyclic-GMP pathway in nondiabetic siblings of patients with type 2 diabetes

In this study, we have compared resistance to insulin-mediated glucose disposal and plasma concentrations of nitric oxide (NO) and cyclic-GMP in healthy volunteers with (n = 35) or without (n = 27) at least one sibling and one parent with type 2 diabetes. The 62 volunteers were further divided into groups of those with normal glucose tolerance or impaired glucose tolerance. Insulin-mediated glucose disposal was quantified by determining the insulin sensitivity index (ISI) in response to a low-dose, constant infusion of insulin (25 mU/kg x h) and glucose (4 mg/kg x min) for 150 min. The mean (+/-SEM) ISI [(mL kg(-1) min(-1)/pmol/L) x 10(3)] was significantly greater in those without a family history (30.3 +/- 2.3) as compared with nondiabetic volunteers with a family history of type 2 diabetes, whether they had normal glucose tolerance (17.0 +/- 7.2) or impaired glucose tolerance (9.5 +/- 1.4). In addition, basal NO levels, evaluated by the measurement of its stable end products [i.e. nitrite and nitrate levels (NO2-/ NO3-)], were significantly higher, and cyclic-GMP levels, its effector messenger, were significantly lower in those with a family history, irrespective of their degree of glucose tolerance, when compared with healthy volunteers without a family history of type 2 diabetes. Furthermore, when the 62 volunteers were analyzed as one group, there was a negative correlation between ISI and NO2-/NO3- levels (r = -0.35; P < 0.005) and a positive correlation between ISI and cyclic-GMP levels (r = 0.30; P < 0.02). These results have shown that alterations of the NO/cyclic-GMP pathway seem to be an early event in nondiabetic individuals with a family history of type 2 diabetes and these changes are correlated with the degree of insulin resistance.

Insulin resistance and hypertension. Patients in double jeopardy for cardiovascular disease

Essential hypertension is prevalent among older individuals, and approximately 50% of persons with hypertension can be considered to have insulin resistance and hyperinsulinemia. It appears likely that insulin resistance and hyperinsulinemia predispose to, rather than result from, hypertension. Insulin resistance is associated with abnormalities in lipoprotein metabolism, hypercoagulability, and endothelial function, which probably account in part for the increased cardiovascular risk among hypertensive patients. To identify this subset of patients, all hypertensive patients should be screened for diabetes and lipid abnormalities. The presence of impaired glucose tolerance, diabetes, or hypertriglyceridemia and low HDL suggest the presence of insulin resistance. Insulin resistant patients, in particular, will benefit from exercise and weight loss.

Differences in insulin resistance do not predict weight loss in response to hypocaloric diets in healthy obese women

The current study was initiated to determine whether insulin resistance and/or hyperinsulinemia affected the ability of obese individuals to lose weight in response to hypocaloric diets. Thirty-one obese, nondiabetic women, with values for body mass index ranging from 28.0-35.0 kg/m2, volunteered for this program. Resistance to insulin-mediated glucose disposal was assessed by determining their steady state plasma insulin and glucose concentration during the last 30 min of a 180-min infusion of somatostatin, insulin, and glucose. The total integrated insulin response to breakfast and lunch was also determined. After the baseline measurements, volunteers were placed on a hypocaloric diet calculated to lead to a minimum weekly loss of 1% of ideal body weight. Individuals who met the criteria after 30 days of dieting were defined as weight loss successes (n = 20) and continued on the diet for another 30 days. Individuals not meeting the criteria were designated as weight loss failures (n = 12) and were discharged from the study. There was a mean (+/-SEM) weight loss at 60 days of 9.2 +/- 0.4 kg in the 20 individuals defined as weight loss successes, but there was no correlation between weight loss and either steady state plasma glucose or the total integrated insulin response (r < 0.1; P > 0.83). Furthermore, using the same criteria to define insulin sensitivity and insulin resistance as those for therapeutic successes, the therapeutic failures comprised six insulin-sensitive and five insulin-resistant subjects. In summary, insulin-mediated glucose disposal varied widely in nondiabetic, obese women, and there was no relationship between baseline insulin resistance or total integrated insulin response and weight loss. It is concluded that the ability to lose weight on a calorie-restricted diet over a short time period does not vary in obese, healthy women as a function of insulin resistance or hyperinsulinemia.

Diabetes and dyslipidemia. A new model for transplant coronary artery disease

BACKGROUND

Clinical observations suggest that transplant coronary artery disease (TxCAD) is immunologically mediated but may be accelerated by metabolic derangements. We developed a rat model of heterotopic heart transplantation in the presence of diabetes and dyslipidemia to further study their role in TxCAD development.

METHODS AND RESULTS

Major histocompatibility complex-mismatched strains of inbred rats underwent heterotopic heart transplantation (ACI-to-Lewis allografts). Diabetes (DM) was induced by streptozotocin injection (80 mg/kg) after transplantation; dyslipidemia was worsened by feeding of a 60% high-fructose diet (+F). Allograft transplants were divided into four groups: (1) +DM/+F; (2) +DM/-F; (3) -DM/+F; and (4) -DM/-F. Isograft transplants (Lewis to Lewis, +DM/+/-F) were controls. All animals received daily cyclosporine (5 mg/kg). Grafts surviving > 30 days were evaluated for TxCAD on histological sections and graded 0 to 5 for intimal thickness. All streptozotocin-treated animals were diabetic within 2 weeks, with fourfold increases in plasma glucose concentrations versus nondiabetics. Severe TxCAD was observed in diabetic allografts only. The mean grade of TxCAD in diabetic allografts was 3.2 +/- 0.5 versus 1.1 +/- 0.4 in diabetic isografts (P < 0.03) and zero TxCAD in nondiabetic allografts (P < or = 0.0001). Fructose feeding resulted in a 1.5-fold higher triglyceride and a 1.3-fold higher cholesterol level versus the regular diet (-F) but showed no independent contribution to the development of TxCAD.

CONCLUSIONS

These findings suggest that metabolic derangements associated with diabetes play an important role in TxCAD development in heterotopic ACI-to-Lewis rat heart transplantation. In this model of TxCAD in major histocompatibility complex-mismatched, diabetic, and dyslipidemic rats, immunologic and metabolic mechanisms that contribute to TxCAD can be further delineated and approaches to its prevention assessed.

Effect of variations in plasma magnesium concentration on resistance to insulin-mediated glucose disposal in nondiabetic subjects

Eighteen nondiabetic volunteers were selected for these studies on the basis of their plasma magnesium (Mg) concentrations defined as being either high (> 0.83 mmol/L) or low (< 0.80 mmol/L). Although different in Mg concentration (0.90 +/- 0.02 vs. 0.73 +/- 0.01 mmol/L), the 2 groups were comparable in terms of age, gender distribution, body mass index, and waist to hip girth. Measurements were made of their plasma glucose and insulin concentrations in response to a 75-g oral glucose load and the steady state plasma insulin and glucose (SSPG) concentrations at the end of an 180-min infusion of octreotide, insulin, and glucose. The low Mg group had significantly higher plasma glucose (P < 0.001) and insulin (P < 0.002) concentrations after the oral glucose challenge. Although the steady state plasma insulin concentrations were similar during the infusion study, the SSPG concentration was significantly (P < 0.001) greater in the low Mg group (11.9 +/- 0.9 vs. 6.6 +/- 0.9 mmol/L). Finally, when the 18 patients were analyzed together, there were significant (P < 0.05 to P < 0.01) inverse correlations between Mg concentrations and glucose (r = -0.68) and insulin (r = -0.51) areas and SSPG concentrations (r = -0.60). Thus, a low Mg concentration in nondiabetic subjects was associated with relative insulin resistance, glucose intolerance, and hyperinsulinemia.

Similar weight loss with low- or high-carbohydrate diets

The goal of this study was to evaluate the effect of diets that were equally low in energy but widely different in relative amounts of fat and carbohydrate on body weight during a 6-wk period of hospitalization. Consequently, 43 adult, obese persons were randomly assigned to receive diets containing 4.2 MJ/d (1000 kcal/d) composed of either 32% protein, 15% carbohydrate, and 53% fat, or 29% protein, 45% carbohydrate, and 26% fat. There was no significant difference in the amount of weight loss in response to diets containing either 15% (8.9 +/- 0.6 kg) or 45% (7.5 +/- 0.5 kg) carbohydrate. Furthermore, significant decreases in total body fat and waist-to-hip circumference were seen in both groups, and the magnitude of the changes did not vary as a function of diet composition. Fasting plasma glucose, insulin, cholesterol, and triacylglycerol concentrations decreased significantly in patients eating low-energy diets that contained 15% carbohydrate, but neither plasma insulin nor triacylglycerol concentrations fell significantly in response to the higher-carbohydrate diet. The results of this study showed that it was energy intake, not nutrient composition, that determined weight loss in response to low-energy diets over a short time period.

Coronary artery intimal thickening in the transplanted heart. An in vivo intracoronary untrasound study of immunologic and metabolic risk factors

This study examined the hypothesis that immunologic factors are the major correlates of coronary artery intimal thickening and luminal stenosis. The study population included 116 adult heart transplant recipients with a mean age of 44.7 +/- 12.0 years (89 men and 27 women) undergoing annual coronary angiography and intracoronary ultrasound 3.4 +/- 2.7 (range, 1.0-14.6) years after transplantation. Mean intimal thickness was obtained from several distinct sites along the left anterior descending and/or left circumflex coronary artery by intracoronary ultrasound. Coronary artery stenosis defined by angiography was classified as mild (< 30% luminal stenosis), moderate (> or = 30-70% luminal stenosis), or severe (> 70% luminal stenosis or diffuse pruning of distal vessels). Prevalence of any transplant coronary artery disease (TxCAD) was 85% by intracoronary ultrasound and 15% by angiography. By multiple regression analysis, only average fasting plasma triglyceride level (P < 0.006) and average weight (P < 0.007) were significantly correlated with severity of intimal thickening (R = 0.54, P < 0.0001). Donor age (P < 0.006) and average fasting plasma triglyceride level (P < 0.009) were significantly correlated with stenosis by angiography. Correlation of multiple immunologic and metabolic factors with intimal thickness by univariate analysis suggests a multifactorial etiology for TxCAD. Among the multiple univariate correlates of TxCAD, higher fasting plasma triglyceride levels and body weight are the only independent correlates of TxCAD. The absence of acute rejection as an independent predictor of intimal thickening suggests that mechanisms beyond those mediating typical cellular rejection should be targeted for advancing our understanding of Tx-CAD.

Mechanism of hypertriglyceridemia in Dahl rats

Plasma triglyceride concentrations were shown to be higher in hypertensive (153 +/- 2 mm Hg) male Dahl salt-sensitive rats than in control Sprague-Dawley rats (122 +/- 2 mm Hg). These differences in triglyceride concentrations were seen when blood was drawn at 9 AM from unfasted animals (229 +/- 27 versus 111 +/- 8 mg/dL), at 1 PM after a 4-hour fast (186 +/- 13 versus 88 +/- 4 mg/dL), or at 9 AM after a 13-hour fast (151 +/- 6 versus 90 +/- 6 mg/dL), all p < 0.001. Total triglyceride secretion was also compared in groups of rats by determining the increment in plasma triglyceride concentration for 2 hours after blocking triglyceride removal from plasma by injecting Triton. Studies performed at 1 PM and 9 AM, after the 4- and 13-hour fast, demonstrated that total triglyceride secretion was greater (p < 0.05) in Dahl rats only when studied at 1 PM. Direct estimates of hepatic triglyceride secretion at 1 PM also demonstrated a significant (p < 0.02) increase in secretion rate by perfused livers from Dahl rats, due in part to their increased liver size. In addition, removal of prelabeled very low density lipoprotein-triglyceride in the intact rat was significantly (p < 0.05) decreased in Dahl rats. Lipoprotein lipase activity measured in skeletal muscle, heart, and adipose tissue was also significantly decreased at 9 AM and 1 PM (after 0 and 4 hours of fasting) in tissue from Dahl rats. These data confirm that Dahl rats have higher plasma triglyceride concentrations than Sprague-Dawley rats. Since both total and hepatic triglyceride secretion were somewhat greater in Dahl rats, in association with a decrease in both removal of very low density lipoprotein from plasma and decreased muscle and adipose tissue lipoprotein lipase activity, it seems likely that hypertriglyceridemia in Dahl rats results from a combination of increased triglyceride secretion and decreased triglyceride removal.

Effect of anatomical site on insulin action and insulin receptor phosphorylation in isolated rat adipocytes

The effects of insulin were evaluated on adipocytes isolated from three different anatomical sites in male, Sprague-Dawley rats: epididymal (EPI), retroperitoneal (RP), and dorsal subcutaneous (SC). The results indicated that maximal insulin-stimulated glucose transport was significantly lower (P less than 0.001) in cells from the SC region as compared to EPI and RP cells. In addition, the ED50 value for SC cells (259 +/- 34 pmol/l) was significantly higher than for EPI (66 +/- 5 pM) or RP adipocytes (111 +/- 32 pmol/l). Insulin inhibition of catecholamine-induced lipolysis was also significantly greater (P less than 0.001) in EPI cells as compared to RP or SC adipocytes, and that was true when expressed in absolute or relative terms. The decrease in the ability of insulin to either stimulate glucose transport or inhibit catecholamine induced lipolysis in SC cells was associated with a decrease in insulin receptor autophosphorylation and receptor tyrosine kinase activity. These data show that insulin action on isolated adipocytes varies as a function of anatomical site, and that these changes are associated with variations in insulin receptor autophosphorylation and insulin receptor tyrosine kinase activity.

Insulin-resistance and associated risk factors for coronary heart disease as seen in families

Recent reports have shown that resistance to insulin-stimulated glucose uptake, increased plasma glucose and insulin response to oral glucose, and hypertriglyceridemia can be seen in first degree relatives of patients with type 2 diabetes. We have recently shown that very similar metabolic changes can be seen in hyperinsulinemic individuals who have either normal or impaired glucose tolerance (IGT). Given these data, we thought it would be of interest to compare the plasma glucose and insulin response to an oral glucose challenge, plasma lipid concentrations, and blood pressure in offspring of parents with IGT as compared to offspring of parents with normal glucose tolerance. Parents with IGT had higher plasma insulin and triglyceride levels and blood pressure than those with normal glucose tolerance. The two groups of offspring were young, non-obese and similar in terms of age, gender distribution and body mass index. Statistically significant increases in plasma insulin response to oral glucose and in systolic and diastolic blood pressure were present in the offspring of parents with IGT. Demonstration of similar abnormalities in plasma insulin response to glucose and blood pressure regulation in patients with IGT and in their offspring is consistent with the view that individual differences in insulin metabolism and blood pressure are modulated by genetic factors and that both may be related to variations in insulin-stimulated glucose uptake and/or plasma insulin concentration.

Abnormal lipid metabolism in treated hypertensive patients with non-insulin-dependent diabetes mellitus

Plasma lipid, lipoprotein, and apoprotein concentrations were measured in 169 patients with non-insulin-dependent diabetes mellitus (NIDDM), 78 with normal blood pressure, and 91 diagnosed and receiving drug treatment for hypertension. Plasma triglyceride, cholesterol, low-density lipoprotein-cholesterol, and apoprotein B concentrations were significantly higher (p = less than 0.05 to less than 0.001) in the hypertensive group. In addition, the ratios of high-density to low-density lipoprotein-cholesterol and of apoprotein A-1 to apoprotein B were significantly reduced (p less than 0.01) in patients with hypertension. The changes noted were independent of differences in sex distribution, degree of obesity, and level of glycemic control. These results indicate that substantial differences in plasma lipid, lipoprotein, and apoprotein concentrations are seen when normotensive patients with NIDDM are compared with patients who are also being treated for hypertension, and that all of the changes noted would increase the risk of coronary artery disease in the hypertensive group. Since all patients with hypertension were receiving anti-hypertensive medications, it is not clear if it is hypertension per se, or its treatment, that is responsible for the observed changes in lipid metabolism.

Effect of a low fat diet on carbohydrate metabolism in patients with hypertension

Plasma glucose and insulin responses to both a 75-g oral glucose challenge and to conventional meals were determined in eight patients with hypertension and compared with values of a control population. The results indicated that patients with hypertension had significantly higher than normal plasma glucose and insulin concentrations in both situations. Furthermore, when dietary carbohydrate was increased by 16% of total calories (with a reciprocal reduction in dietary fat), the hyperglycemia and hyperinsulinemia present in patients with hypertension were accentuated. Since low fat-high carbohydrate diets are usually recommended for patients with hypertension, these data suggest that abnormalities of glucose and insulin metabolism associated with hypertension would be increased if patients with high blood pressure followed conventional dietary advice. Since hyperglycemia and hyperinsulinemia have been shown to be associated with an increased risk of developing coronary artery disease, it may be appropriate to reevaluate the clinical utility of low fat-high carbohydrate diets in the treatment of hypertension.

Comparison of glucose metabolism in adipocytes from Pima Indians and Caucasians

The present study was designed to compare various aspects of glucose metabolism of adipocytes isolated from 10 obese Pima Indians and 10 Caucasians. All 20 subjects had normal glucose tolerance, and the two groups were matched for sex, age, degree of obesity, and fasting plasma glucose and insulin concentrations. The results indicated that adipocytes from the two groups were comparable in average cell size, basal and maximum insulin-stimulated glucose transport, glucose metabolism at 5.5 mmol/L glucose, ED50 of insulin for glucose transport and the inhibition of lipolysis, basal lipolysis rates, and insulin binding. The similarity between the metabolic behavior of adipocytes isolated from Pimas and Caucasians suggests that the study of adipocytes from Pima Indians yields information that is relevant to the understanding of obesity in other populations.

Relationship between degree of obesity and in vivo insulin action in man

Previous studies have demonstrated reduced in vivo insulin action in obese subjects compared with lean controls. However, little data is available on the relationship between degree of obesity and insulin action, and this relationship has not been shown to be independent of individual differences in maximal aerobic capacity. We studied 55 male Pima Indians and 35 male Caucasians with normal glucose tolerance. In vivo insulin action was measured using the hyperinsulinemic, euglycemic clamp technique at a plasma insulin concentration of approximately 100 microU/ml. Body composition was determined by densitometry, and maximal aerobic capacity was estimated using a graded exercise test. The results showed that degree of obesity was nonlinearly related to in vivo insulin action. In both Indians and Caucasians there was a significant decline in insulin action with increasing obesity up to a percent body fat of approximately 28-30%. Further increases in obesity in the Indians were not associated with significant changes in insulin action. Maximal aerobic capacity was positively linearly correlated with insulin action over the entire range of insulin action in both racial groups. Degree of obesity and maximal aerobic capacity were each independently associated with insulin action although these independent relationships were of marginal significance in the Caucasians. Surprisingly, individual differences in obesity and maximal aerobic capacity accounted for only half the variability observed in insulin action in these glucose tolerant subjects.

Inhibition of lipolysis by adenosine is potentiated with age

The ability of a variety of hormones to activate cells declines with age. We have investigated the mechanism for the reduced ability of beta adrenergic stimulation to activate lipolysis in fat cells from older rats. Previously, we have found that these cells have an intact lipolytic response to a cAMP analogue but diminished cAMP accumulation after isoproterenol stimulation, suggesting that the blunted cAMP response is rate limiting. In the present study we have tested the hypothesis that enhanced inhibition of lipolysis by endogenously released adenosine accounts for the diminished lipolysis. Adenosine deaminase was added to media containing the adipocytes from older rats to remove endogenous adenosine. Under these conditions beta adrenergic stimulation of lipolysis is intact in fat cells from older rats. The adenosine analogue N6-phenylisopropyladenosine more effectively inhibited lipolysis in the older group (77 +/- 6%) than in the younger group (46 +/- 5%), suggesting that enhanced efficacy of endogenous adenosine may account for the reduced lipolytic response to catecholamines. When pertussis vaccine was used to functionally inactivate adenosine receptors in adipocytes from the younger and older rats, the ability of isoproterenol to activate lipolysis was restored in the older group. All the data are consistent with the hypothesis that enhanced inhibitory effects of adenosine explain the diminished ability of beta adrenergic agonists to activate lipolysis. It is possible that enhanced inhibitory pathways may be involved in blunting responses to stimulatory hormones in other tissues from older animals.

Relationships between insulin secretion, insulin action, and fasting plasma glucose concentration in nondiabetic and noninsulin-dependent diabetic subjects

The relationships between insulin secretion, insulin action, and fasting plasma glucose concentration (FPG) were examined in 34 southwest American Indians (19 nondiabetics, 15 noninsulin-dependent diabetics) who had a broad range of FPG (88-310 mg/100 ml). Fasting, glucose-stimulated, and meal-stimulated plasma insulin concentrations were negatively correlated with FPG in diabetics but not in nondiabetics. In contrast, fasting and glucose-stimulated plasma C-peptide concentrations did not decrease with increasing FPG in either group and 24-h urinary C-peptide excretion during a diet of mixed composition was positively correlated with FPG for all subjects (r = 0.36, P less than 0.05). Fasting free fatty acid (FFA) was correlated with FPG in nondiabetics (r = 0.49, P less than 0.05) and diabetics (r = 0.77, P less than 0.001). Fasting FFA was also correlated with the isotopically determined endogenous glucose production rate in the diabetics (r = 0.54, P less than 0.05). Endogenous glucose production was strongly correlated with FPG in the diabetics (r = 0.90, P less than 0.0001), but not in the nondiabetics. Indirect calorimetry showed that FPG was also negatively correlated with basal glucose oxidation rates (r = -0.61, P less than 0.001), but positively with lipid oxidation (r = 0.74, P less than 0.001) in the diabetics. Insulin action was measured as total insulin-mediated glucose disposal, glucose oxidation, and storage rates, using the euglycemic clamp with simultaneous indirect calorimetry at plasma insulin concentrations of 135 +/- 5 and 1738 +/- 59 microU/ml. These parameters of insulin action were significantly, negatively correlated with FPG in the nondiabetics at both insulin concentrations, but not in the diabetics although all the diabetics had markedly decreased insulin action. We conclude that decreased insulin action is present in the noninsulin-dependent diabetics in this population and marked hyperglycemia occurs with the addition of decreased peripheral insulin availability. Decreased peripheral insulin availability leads to increased FFA concentrations and lipid oxidation rates (and probably also increased concentrations of gluconeogenic precursors) that together stimulate gluconeogenesis, hepatic glucose production, and progressive hyperglycemia.

The effect of sucrose content in high and low carbohydrate diets on plasma glucose, insulin, and lipid responses in hypertriglyceridemic humans

To further understand the effect of high carbohydrate (CHO)-low fat diets and the role of variations in dietary sucrose on CHO and lipid metabolism, 10 patients with hypertriglyceridemia were fed 2 isocaloric, typical American diets, containing 40% and 60% CHO, for 15 days in random sequence. Each patient was their own control, and they were divided into 2 groups of 5 patients each. In one group, sucrose was held constant at 13% of total calories (40-13% and 60-13%), whereas the sucrose content was 9% of the total calories on a 40% CHO diet (40-9%), and 15% of total calories on a 60% CHO diet (60-15%) in the other group. Fasting and postprandial blood samples were analyzed for plasma glucose, insulin, cholesterol (Chol), and triglycerides (TG), as well as for Chol and TG in chylomicrons, very low density, low density, and high density lipoproteins (HDL). Fasting plasma TG levels were significantly increased in both groups on the 60% CHO diet, primarily due to increases in very low density-TG concentration. The magnitude of the elevation was attenuated when sucrose content was kept constant. Postprandial TG responses were qualitatively similar. There were no significant changes in plasma Chol concentrations, except for a modest fall in plasma HDL-Chol level after the 60-13% diet period (P less than 0.05). No significant differences were found in fasting plasma glucose or insulin concentration. However, postprandial glucose and insulin responses were increased on both high CHO diets. The results of these studies demonstrate that high CHO-low fat diets, in general, tend to elevate plasma glucose, insulin, and TG concentrations and reduce HDL-Chol concentration in patients with endogenous hypertriglyceridemia. In addition, these data illustrate the important role that small variations in dietary sucrose can play in modulation of CHO and lipid metabolism.

Glucose-induced insulin secretion by perfused pancreas of 2- and 12-mo-old Fischer 344 rats

Previous studies have shown that cells from older Sprague-Dawley rats secrete insulin less efficiently in response to a maximal glucose challenge than do beta-cells from young animals. In the current study we have asked whether this change in beta-cell response occurs in another strain of rat, and, if so, whether the secretory defect occurs at submaximal as well as maximal glucose stimulatory levels. Pancreas perfusions were carried out on 2- and 12-mo-old Fischer 344 rats at perfusate glucose concentrations of 150 and 300 mg/dl. The secretory data for each pancreas was subsequently corrected for differences in islet cell mass and expressed as insulin secretion per unit islet cell. The results show that 12-mo-old Fischer rats release more insulin per total pancreas than do 2-mo-old animals at both glucose concentrations. However when corrected for islet cell mass, the amount of insulin secretion per islet cell is actually reduced in the older Fischer rat. These data are comparable to those seen previously in the 12-mo-old Sprague-Dawley rat and indicate that the insulin secretory defect seen as rats grow older is not species specific.

Sex difference in insulin-stimulated glucose transport in rat and human adipocytes

In an effort to determine whether differences in basal and maximum insulin-stimulated glucose transport by isolated adipocytes are a function of donor sex, we measured glucose transport rates in the absence and presence of 8 nM insulin in adipocytes isolated from the abdominal subcutaneous fat tissue of nine male and ten female subjects with varying degrees of obesity and in adipocytes isolated from the abdominal subcutaneous and retroperitoneal fat tissue of (180-220 g) male and female rats. Because maximal insulin-stimulated glucose transport rate per cell of adipocytes isolated from subcutaneous abdominal tissue of male and female subjects was constant in each sex, the data have been normalized on the basis of transport per cell. The results demonstrated that basal and maximal insulin-stimulated glucose transport per cell was 53-75% higher per cell in the females versus males in adipocytes from human subcutaneous abdominal adipose tissue (P less than 0.01). A similar difference in glucose transport rate between males and females (P less than 0.001) was also found in rat abdominal subcutaneous adipose tissue. Adipocytes isolated from rat retroperitoneal adipose tissue had higher transport rates (approximately three-fold) and smaller sex differences (35% higher in females) than found in adipocytes from rat and human subcutaneous tissue. These results indicate that basal and maximum insulin-stimulated glucose transport is higher by adipocytes isolated from females and that this difference is independent of adipose cell size and species.

Improvement in in vitro insulin action after one month of insulin therapy in obese noninsulin-dependent diabetics. Measurements of glucose transport and metabolism, insulin binding, and lipolysis in isolated adipocytes

It has been previously reported that maximum insulin-stimulated glucose transport and utilization were both decreased, while basal lipolysis was increased in adipocytes from obese subjects with noninsulin-dependent diabetes mellitus (NIDDM). To determine whether these values can be returned towards those obtained in equally obese subjects with normal glucose tolerance, these measures of adipocyte metabolism were quantified in 10 NIDDM subjects before and after control of hyperglycemia with insulin. The results demonstrate that maximum insulin-stimulated glucose transport (P less than 0.02) and glucose incorporation into triglyceride (P less than 0.01) and CO2 (P less than 0.05) (at 5.5 mM glucose) increased and basal lipolysis decreased (P less than 0.05) after 4 wk of insulin treatment. In contrast, glucose incorporation into lactate and other glycolytic metabolites (at 5.5 mM glucose), and sensitivity of glucose transport to insulin, did not improve with insulin therapy. The latter occurred despite an increase in insulin binding (P less than 0.01). Finally, the improvement in maximal insulin-stimulated glucose transport correlated with the fall in fasting hyperglycemia (r = 0.77, P less than 0.01). These findings demonstrate that several of the abnormalities of carbohydrate and lipid metabolism recently noted to be present in adipocytes from patients with NIDDM can be shown to significantly improve with insulin treatment.

In vitro insulin resistance of human adipocytes isolated from subjects with noninsulin-dependent diabetes mellitus

To assess possible cellular mechanisms of in vitro resistance in noninsulin-dependent diabetes mellitus (NIDDM), maximum insulin-stimulated glucose transport and utilization and insulin binding were measured in adipocytes isolated from weight-matched normal glycemic subjects and patients with NIDDM. Glucose transport rate was determined by measuring the amount of [U-14C]-D-glucose taken up by incubating adipocytes at trace concentrations of glucose (300 nM), and glucose metabolism by estimating the amount of lactate, CO2, triglyceride, and total glucose carbons retained in the cells following incubating at 5.5 mM glucose. Insulin binding was measured at 50, 100, and 200 pM [mono125I-tyrosinyl A14]insulin. Both maximum insulin-stimulated glucose transport and utilization in adipocytes from diabetic subjects were 40% (P less than 0.01) and 32% (P less than 0.05) lower, respectively, than values obtained for subjects with normal glucose tolerance. In addition, the maximum capacity of glucose transport was correlated with the maximum capacity of glucose utilization (r = 0.81, P less than 0.001). Furthermore, fasting plasma glucose concentrations of diabetic subjects were negatively correlated with both maximum insulin-stimulated glucose transport (r = -0.56, P less than 0.05) and glucose utilization (r = -0.67, P less than 0.05). Since basal glucose transport in adipocytes from diabetic subjects was also 33% lower than in adipocytes from normal subjects, there was no change in the relative ability of insulin to stimulate glucose transport. However, there was a 64% decrease in the sensitivity of the glucose transport system to insulin (P less than 0.05), unrelated to concomitant changes in insulin binding. These results demonstrate that both maximal insulin-stimulated glucose transport and utilization, and the sensitivity of the glucose transport system to insulin, was decreased in adipocytes isolated from subjects with NIDDM. These in vitro defects were associated with impaired glucose metabolism in vivo, consistent with the view that the metabolic alterations observed at the cellular level may contribute to the in vivo insulin resistance of NIDDM.

Disparate effects of prazosin and propranolol on lipid metabolism in a rat model

The effects of 14 days of daily intraperitoneal injections of prazosin hydrochloride (3.0 or 0.3 mg/kg) or propranolol (5 mg/kg) on various aspects of the lipid metabolism of normal rats was studied. The results indicate that plasma triglyceride and cholesterol concentrations were lower and the ratio of plasma HDL-cholesterol to total cholesterol concentration higher in prazosin-treated rats compared with propranolol-treated rats. The decline in plasma triglyceride levels in prazosin-treated rats was associated with a commensurate reduction in triglyceride secretion rates. Plasma free fatty acid levels were also lower in prazosin-treated rats, and this change may have contributed to the fall in triglyceride secretion rates. These data demonstrate that the disparate effects of alpha and beta receptor antagonists, previously shown to occur in hypertensive humans, can be duplicated in normal rats.

Effect of age and environmental factors on insulin release from the perfused pancreas of the rat

In this study we examined the effect of age and various age-related environmental factors on maximal glucose-stimulated insulin release by the intact perfused pancreas. Male Sprague-Dawley rats were maintained from 40 d to 12 mo of age on standard chow, or on a sucrose-rich or calorie-restricted diet. At 12 mo, studies were carried out on the isolated pancreas of each animal to determine maximal (300 mg/ml) glucose-stimulated insulin secretion. After these studies were completed, each pancreas was perfused with formalin fixative and processed for morphometric estimation of the mass of the endocrine pancreas. Data from these older animals were compared with data from 2-mo-old control rats. The results indicate that maximal glucose-stimulated insulin secretion per unit endocrine pancreas was markedly reduced in all three groups of 12-mo-old rats, and was only 25-33% of that of 2-mo-old rats. Thus, aging led to a decline in insulin secretion per beta cell that was not modifiable by environmental manipulation. On the other hand, environmental factors can influence the development of endocrine tissue within the pancreas, and in so doing, modify total pancreatic insulin secretion. The mass of the endocrine pancreas of 12-mo-old rats fed either sucrose or chow was between three and four times that of 2-mo-old control rats, and these older rats were able to maximally secrete as much insulin per total pancreas as the young rats. In contrast, the endocrine cell mass of the calorie-restricted rats had not enlarged to this extent, and the maximally stimulated perfused pancreas from these rats secreted less insulin. These data suggest that the aging animal, challenged in vivo to secrete insulin, can overcome the loss of the beta cell response by expanding its pancreatic pool of beta cells. Although this compensation is successful in the 12-mo-old, obese, middle-aged rat, it is not yet clear what effect further aging would have on these events.

Effect of exercise and diet on triglyceride metabolism in rats with moderate insulin deficiency

The ability of exercise and diet to modify the effects of moderate streptozotocin-induced insulin deficiency on triglyceride metabolism has been studied in the rat. Insulin-deficient rats allowed to run spontaneously in exercise wheel cages had significantly lower (P less than 0.001) plasma glucose levels (187 +/- 19 mg/dl) than either sedentary (374 +/- 24 mg/dl) or sucrose-fed (450 +/- 13 mg/dl) diabetic rats, despite the fact that plasma insulin levels were comparable in all these groups. Plasma triglyceride (TG) levels in exercise-trained rats with diabetes (51 +/- 5 mg/dl) were actually lower than in control rats with normal glucose tolerance (90 +/- 14 mg/dl). In contrast, plasma TG levels were higher than control levels in diabetic sedentary rats (128 +/- 11 mg/dl), and severe hypertriglyceridemia developed in sucrose-fed diabetic rats (369 +/- 35 mg/dl). The ability of exercise training to attenuate diabetic hypertriglyceridemia, which was observed in both chow-fed and sucrose-fed rats, was secondary to a decrease in TG secretion, and appeared to be related to lower plasma FFA concentrations. In contrast, the accentuation of diabetic hypertriglyceridemia seen in sucrose-fed rats was related to a defect in TG catabolism. Adipose tissue lipoprotein lipase (LPL) activities were essentially identical in all diabetic rats, suggesting that the observed difference in TG kinetics could not be attributed to concomitant increases or decreases in adipose tissue LPL activity. These results emphasize the powerful impact of exercise and diet on TG metabolism in rats with moderate degrees of insulin deficiency.

Functional homogeneity of pancreatic islets of aging rats

Islest from different regions of pancreases of aging rats were compared for size and variations of response to glucose stimulation. The results show that pancreatic islets from the ventral-duodenal and splenic regions of 12-mo-old retired breeder. Spraque dawley rats are comparable in all respects measured: thus, pancreatic regional differences cannot explain the age-associated reduction in beta cell secretory response noted in previous studies.

Effect of variations in basal plasma glucose concentration on glucose utilization (M) and metabolic clearance (MCR) rates during insulin clamp studies in patients with non-insulin-dependent diabetes mellitus

Two insulin clamp studies were performed at different steady-state plasma glucose concentrations in 13 patients with non-insulin-dependent diabetes mellitus (NIDDM). Steady-state plasma insulin concentrations were comparable, with mean +/- SEM levels of 94 +/- 3 and 95 +/- 4 muU/ml being achieved during the two studies. Glucose utilization rate (M) varied directly with plasma glucose concentration in each subject. Thus, the mean +/- SEM value of M was 4.92 +/- 0.73 mg/kg/min when patients were studied at a mean +/- SEM plasma glucose concentration of 226 +/- 15 mg/dl, and M was 2.71 mg/kg/min when the same subjects were studied at a glucose concentration of 118 +/- 6 mg/dl. In contrast, the values for glucose metabolic clearance rate (MCR), which were 2.35 +/- 0.50 and 2.49 +/- 0.47 ml/kg/min, respectively, during the two studies, did not vary significantly with plasma glucose concentration. These data indicate that the glucose metabolic clearance rate (MCR), but not glucose utilization rate (M), can be used to compare in vivo insulin action when insulin clamp studies are performed in subjects with different basal plasma glucose concentrations.

Effect of age on plasma glucose and insulin responses to a test mixed meal

Plasma glucose and insulin responses to an oral dextrose tolerance test and to a mixed-meal test were determined in fully ambulatory residents of a retirement community. The study population consisted of 127 women and 79 men, whose ages ranged from 47 to 90 years. Progressive hyperglycemia and hyperinsulinemia with age could be demonstrated in the women. These changes were observed with either type of tolerance test and could not be attributed to age-related differences in measurements of body mass index or estimates of physical activity. In contrast, no significant changes with age in either glucose or insulin responses were noted in men. The ability to document increases in the plasma glucose or insulin responses were noted in men. The ability to document increases in the plasma glucose and insulin responses to a mixed meal suggests that aging, at least in women, is associated with day-long elevations of both plasma glucose and insulin concentrations. The possible relationship of these metabolic changes to the development of atherosclerosis merits further consideration.

Assessment of insulin resistance with the insulin suppression test and the euglycemic clamp

Insulin resistance was quantified with two different methods in 30 subjects with varying degrees of glucose tolerance. One method, the insulin suppression test, is performed by continuously infusing epinephrine, propranolol, insulin, and glucose. Epinephrine and propranolol suppress endogenous insulin release, and steady-state plasma levels of exogenous insulin and glucose are reached in all individuals. Because the steady-state insulin level is the same in all subjects, the height of the steady-state plasma glucose level provides a direct estimate of insulin resistance. The other method, the euglycemic clamp technique, produces a steady-state level of exogenous hyperinsulinemia by means of a primed and continuous insulin infusion. Glucose is also infused at a rate sufficient to prevent an insulin-induced fall in glucose concentration, and the amount of glucose required to maintain the basal plasma glucose level provides the estimates of insulin resistance. The results indicated that estimates of insulin resistance generated by the two methods were highly correlated (r = 0.93). Furthermore, both methods of assessing insulin resistance indicated that the greater the degree of glucose intolerance, the more severe the insulin resistance. These results serve to further emphasize the importance of insulin resistance in the pathogenesis of hyperglycemia in type II diabetes.