Nonketotic diabetes mellitus: insulin deficiency or insulin resistance?

Fatty acid inhibition of glucose-stimulated insulin secretion is enhanced in pancreatic islets from insulin-resistant rats

A study was initiated to test two hypotheses. The first was the postulate that glucose-stimulated insulin secretion would be enhanced in pancreatic islets isolated from normal non-obese rats made insulin-resistant by dietary means. The second, related hypothesis was that glucose-stimulated insulin secretion by pancreatic islets isolated from insulin-resistant rats would be more vulnerable to inhibition following culture in the presence of fatty acids. For this purpose, insulin resistance was induced in normal Sprague-Dawley rats by feeding fat-enriched and fructose-enriched diets. The results indicate that islets isolated from either fat-fed or fructose-fed rats secreted significantly more insulin at a glucose concentration of 2.5 to 10.0 mmol/L. In addition, the mean maximal glucose (27 mmol/L)-stimulated insulin secretion rate was significantly lower (15.3 +/- 2.5 ng/islet/h) in islets from fructose-fed rats versus chow-fed rats (25.2 +/- 3.1 ng/islet/h) following culture for 48 hours in the presence of palmitate (0.125 micromol/L). These results support the view that glucose-stimulated insulin secretion is enhanced in islets from insulin-resistant rats, and that these islets are more vulnerable to the inhibitory effects of free fatty acid (FFA) on insulin secretion.

Dose-response relationship of insulin to glucose fluxes in the awake and unrestrained mouse

The purpose of the study was to use the hyperinsulinemic-euglycemic clamp technique to generate insulin dose-response curves for insulin suppression of endogenous glucose output (EGO) and stimulation of the glucose disposal rate (GDR) in conscious unstressed mice. Five groups of male ICR (Institute for Cancer Research) mice were studied (N = 43). The animals underwent surgery for implantation of a jugular vein catheter 2 to 3 days before the clamp and were fasted 6 hours before the study. Each group was clamped at a different insulin infusion rate of 0, 2.5, 10, or 20 mU/kg/min. 3H-3-glucose was infused for measurement of the glucose turnover rate (rate of appearance [Ra]). Blood samples were collected by milking a severed tail-tip. EGO was calculated as the difference between the Ra and glucose infusion rate (GIR), and the glucose clearance rate (GCR) as the GDR divided by the plasma glucose concentration. From the curves generated, half-maximal EGO and GCR were obtained at a plasma insulin concentration of 20 to 30 microU/mL, which was achieved at an insulin infusion rate of about 4 to 5 mU/kg/min. Maximal suppression of EGO and stimulation of the GCR occurred at an insulin infusion rate of 10 mU/kg/min. The establishment of normative curves for insulin-stimulated glucose metabolism in conscious mice facilitates the evaluation of glucose metabolism in a variety of mouse models of insulin resistance.

Impaired glucose transport as a cause of decreased insulin-stimulated muscle glycogen synthesis in type 2 diabetes

BACKGROUND

Insulin resistance, a major factor in the pathogenesis of type 2 diabetes mellitus, is due mostly to decreased stimulation of glycogen synthesis in muscle by insulin. The primary rate-controlling step responsible for the decrease in muscle glycogen synthesis is not known, although hexokinase activity and glucose transport have been implicated.

METHODS

We used a novel nuclear magnetic resonance approach with carbon-13 and phosphorus-31 to measure intramuscular glucose, glucose-6-phosphate, and glycogen concentrations under hyperglycemic conditions (plasma glucose concentration, approximately 180 mg per deciliter [10 mmol per liter]) and hyperinsulinemic conditions in six patients with type 2 diabetes and seven normal subjects. In vivo microdialysis of muscle tissue was used to determine the gradient between plasma and interstitial-fluid glucose concentrations, and open-flow microperfusion was used to determine the concentrations of insulin in interstitial fluid.

RESULTS

The time course and concentration of insulin in interstitial fluid were similar in the patients with diabetes and the normal subjects. The rates of whole-body glucose metabolism and muscle glycogen synthesis and the glucose-6-phosphate concentrations in muscle were approximately 80 percent lower in the patients with diabetes than in the normal subjects under conditions of matched plasma insulin concentrations. The mean (+/-SD) intracellular glucose concentration was 2.0+/-8.2 mg per deciliter (0.11+/-0.46 mmol per liter) in the normal subjects. In the patients with diabetes, the intracellular glucose concentration was 4.3+/-4.9 mg per deciliter (0.24+/-0.27 mmol per liter), a value that was 1/25 of what it would be if hexokinase were the rate-controlling enzyme in glucose metabolism.

CONCLUSIONS

Impaired insulin-stimulated glucose transport is responsible for the reduced rate of insulin-stimulated muscle glycogen synthesis in patients with type 2 diabetes mellitus.

Cellular mechanisms of insulin resistance in humans

Carbon nuclear magnetic resonance (13C NMR) spectroscopy and phosphorus (31p) NMR spectroscopy have been used to help define the contribution of insulin-stimulated muscle glycogen synthesis to whole-body insulin-stimulated glucose metabolism in normal individuals and the extent to which this process is defective in patients with type 2 (non-insulin-dependent) diabetes. Assessments of the response to hyperglycemic-hyperinsulinemic clamping have shown that abnormalities of muscle glycogen synthesis, apparently mediated by a defect in GLUT-4 transport and/or hexokinase activity, play a major role in causing insulin resistance in type 2 diabetes. Studies of the mechanisms by which free fatty acids (FFA) cause insulin resistance in humans indicate that increased FFA levels inhibit glucose transport, which may be a consequence of decreased insulin receptor substrate (IRS-1)-associated phosphatidylinositol 3-kinase activity. 13C NMR spectroscopy studies have documented that liver glycogen concentrations are reduced and the rate of hepatic gluconeogenesis is increased in subjects with type 2 diabetes; thus, the higher rate of glucose production in type 2 diabetes can be attributed entirely to increased rates of hepatic gluconeogenesis. These cellular mechanisms of insulin resistance can be addressed through combination therapy with agents that reverse the principal pathophysiologic defects of type 2 diabetes. The biguanide metformin appears to lower glucose by suppressing hepatic glucose production, whereas the thiazolidinedione troglitazone appears to increase glucose clearance by peripheral tissues. The two agents together have been shown to provide better glucose control than either drug alone, without stimulating insulin secretion.

Changes in islet capillary angioarchitecture coincide with impaired B-cell function but not with insulin resistance in male Otsuka-Long-Evans-Tokushima fatty rats: dimorphism of the diabetic phenotype at an advanced age

The Otsuka-Long-Evans-Tokushima fatty (OLETF) rat is a genetic model of spontaneous development of non-insulin-dependent diabetes mellitus (NIDDM) established as an inbred strain after 20 generations of selective breeding. Although they are thought to be genetically homogeneous, they show a dimorphism regarding the diabetic phenotype at an advanced age, with one remaining obese and modestly diabetic while the other becomes lean and overtly diabetic. To clarify the causes for this divergence, we examined the physical, biochemical, and histopathological features in rats at 50 weeks of age, including an analysis of islet angioarchitecture. Sixty-one of 85 male OLETF rats lost weight, while the remainder remained obese. Mean nonfasting plasma glucose in the lean group was 21.8+/-4.6 mmol/L, significantly higher versus the obese group (10.5+/-1.4 mmol/L) and the age-matched control Long-Evans-Tokushima-Otsuka (LETO) group (7.1+/-0.6 mmol/L). Morphological studies of the pancreas from the lean group showed enlarged multilobulated fibrotic islets with a paucity of B cells, whereas islets from the obese group appeared slightly enlarged and showed a relative abundance of B cells. The fine capillaries that form a network in the islets were extremely sparse in the lean group, resulting in a defective glomerular-like configuration, whereas those from the obese group were dense, forming a nearly typical glomerular-like configuration. Increased plasma insulin responses to oral and intravenous (i.v.) glucose and i.v. glucagon loads were nearly absent in the lean group, while they were evident in the obese group, although to a lesser extent compared with the LETO group. Mean insulin secretory output from the perfused pancreas in response to 11.1 mmol/L glucose in the lean group (3.5+/-2.2 pmol/20 min) was significantly lower versus the obese group (8.8+/-6.5 pmol/20 min) and LETO group (22.0+/-10.8 pmol/20 min). Similarly, pancreatic insulin content was significantly lower in the lean group (9.3+/-6.1 microg) versus the others (26.1+/-17.3 microg for obese and 41.1+/-24.8 microg for LETO). In vivo insulin-stimulated glucose uptake measured by a euglycemic clamp technique was significantly higher in the lean group compared with the obese group. These results demonstrate that the dimorphism regarding the diabetic phenotype in male OLETF rats at 50 weeks of age was due to differences in the number of islet B cells, which could be the result of a variation in the capacity for B-cell proliferation among male OLETF rats.

Dephosphorylation increases insulin-stimulated receptor kinase activity in skeletal muscle of obese Zucker rats

Serine/threonine phosphorylation of insulin receptor has been implicated in the development of insulin resistance. To investigate whether dephosphorylation of serine/threonine residues of the insulin receptor may restore the decreased insulin-stimulated receptor tyrosine kinase activity in skeletal muscle of obese Zucker rats, insulin receptor tyrosine kinase activity was measured before and after alkaline phosphatase treatment. Compared to lean controls, insulin-stimulated glucose transport was depressed by 61% (p < 0.05) in obese Zucker rats. The insulin receptor and insulin receptor substrate-1 contents were decreased by 14% (p < 0.05) and 16% (p < 0.05), respectively, in skeletal muscle of obese Zucker rats. In vivo insulin-induced tyrosine phosphorylation of insulin receptor and insulin receptor substrate-1 was depressed by 82% (p < 0.05) and 86% (p < 0.05), respectively. In the meantime, in vitro insulin-stimulated receptor tyrosine kinase activity in obese rats was decreased by 39% (p < 0.05). Dephosphorylation of the insulin receptor by prior alkaline phosphatase treatment increased insulin-stimulated receptor tyrosine kinase activity in both lean and obese Zucker rats, but the increase was three times greater in obese Zucker rats (p < 0.05). These findings suggest that excessive serine/threonine phosphorylation of the insulin receptor in obese Zucker rats may be a cause for insulin resistance in skeletal muscle.

Insulin resistance in short children with intrauterine growth retardation

Scientific evidence is accumulating for an association between intrauterine growth retardation (IUGR) and an increased risk of developing adult degenerative diseases, such as essential hypertension, non-insulin-dependent diabetes mellitus and ischaemic heart disease. A possible underlying mechanism for these conditions is insulin resistance. In this paper, mechanisms and methods of measurement of insulin resistance are briefly reviewed, and recent studies on the evaluation of insulin resistance in short children with IUGR are summarized. In our experience, short prepubertal children with IUGR show consistent insulin resistance, which becomes particularly evident during pubertal development.

Antecedent protein restriction exacerbates development of impaired insulin action after high-fat feeding

The study investigated whether a persistent impairment of insulin secretion resulting from mild protein restriction predisposes to loss of glucoregulatory control and impaired insulin action after the subsequent imposition of the diabetogenic challenge of high-fat feeding. Offspring of dams provided with either control (20% protein) diet (C) or an isocaloric restricted (8%) protein diet (PR) were weaned onto the maintenance diet with which their mothers had been provided. At 20 wk of age, protein restriction enhanced glucose tolerance despite impaired insulin secretion and an augmented and sensitized lipolytic response to norepinephrine in adipocytes. C and PR rats were then transferred to a high-fat diet (HF, 19% protein, 22% lipid, 34% carbohydrate) and sampled after 8 wk. These groups are termed C-HF and PR-HF. Glucose tolerance was impaired in PR-HF, but not C-HF, rats. Insulin-stimulated glucose disposal rates were significantly lower (by 30%; P < 0.01) in the PR-HF group than in the C-HF group, and a specific impairment of antilipolytic response of insulin was unmasked in adipocytes from PR-HF, but not C-HF, rats. The study demonstrates that antecedent protein restriction accelerates and augments the development of impaired glucoregulation and insulin resistance after high-fat feeding.

Type 2 diabetes care: the role of insulin-sensitizing agents and practical implications for cardiovascular disease prevention

Millions of Americans are at risk for cardiovascular morbidity and mortality related to disorders of glucose intolerance--particularly type 2 diabetes and prediabetic conditions, including the insulin resistance, or "cardiovascular dysmetabolic," syndrome. The latter is apparently more intricately associated with macrovascular disease--myocardial infarction, stroke, and peripheral vascular disease. In some situations the risk of cardiovascular disease might be reduced by the prevention of diabetes and also by prevention or treatment of the cardiovascular dysmetabolic syndrome. Studies have shown that intensive glycemic control can delay the development of microvascular complications in type 1, and possibly type 2, diabetes. Several longitudinal observational studies have demonstrated a relationship between glycemic control and the development of cardiovascular disease. Prospective clinical intervention trials to address this issue are underway. Insulin may have a role in atherogenesis, both directly and by promoting development of such risk factors as hypertension and dyslipidemia. Genetic factors and mechanisms promoting or discouraging development of glucose intolerance are also under investigation. Lifestyle changes--dietary and exercise modification, weight loss, and smoking cessation--have been shown to have a positive effect on cardiovascular disease risk. Clinical trials suggest that oral antidiabetic agents--particularly the new noninsulin secretagogues (including troglitazone and metformin, which act on the liver and on skeletal muscle)--may be useful in delaying or preventing development of type 2 diabetes and the cardiovascular dysmetabolic syndrome, as well as in their treatment, when present. Both agents, acting primarily by different mechanisms of action, have also demonstrated potential beneficial effects on serum lipid profiles and other cardiovascular risk factors and may be useful in patients with cardiovascular dysmetabolic syndrome who do not yet meet the criteria for diabetes.

Troglitazone: review and assessment of its role in the treatment of patients with impaired glucose tolerance and diabetes mellitus

OBJECTIVE

To introduce troglitazone (CS-045, Rezulin), a new oral antidiabetic agent and discuss its pharmacology, therapeutics, pharmacokinetics, dosing guidelines, adverse effects, drug interactions, and clinical efficacy.

DATA SOURCES

A MEDLINE database search was completed to identify relevant articles including reviews, recent studies and abstracts, and data from Parke-Davis.

STUDY SELECTION

Due to the small number of published human studies available, some data are derived from animal studies and abstracts of human studies. Studies and abstracts chosen summarize the clinical action of troglitazone in healthy volunteers, in subjects with impaired glucose tolerance, and in patients with diabetes mellitus. Three of the six published human studies used subjects in a placebo-controlled, multicenter, randomized environment (type 2 diabetic patients or obese subjects with insulin resistance).

DATA EXTRACTION

All clinical trials available, including unpublished reports, were reviewed.

DATA SYNTHESIS

Troglitazone is the first member of a new class of medications, the thiazolidinediones, to be approved for clinical use. Troglitazone increases insulin sensitivity in skeletal muscle and in hepatic and adipose tissue. It has been shown to decrease hepatic glucose output while having no effect on stimulating insulin secretion from the pancreatic beta-cells. Its metabolic effects decrease fasting and postprandial hyperglycemia, insulin concentrations, and triglyceride concentrations, while increasing high-density lipoprotein concentrations. There is some evidence, based on short-term trials, that troglitazone causes only minimal decreases in glycosylated hemoglobin A1C (HbA1C) concentrations. Data suggest that troglitazone decreases impaired glucose tolerance in nondiabetic obese subjects and leads to a reduction in both systolic and diastolic blood pressure in hypertensive type 2 diabetes mellitus patients. Troglitazone has a mild adverse effect profile, with rare instances of abnormal liver function tests.

CONCLUSIONS

Troglitazone appears to be a safe, effective, and useful new agent in the treatment of insulin-requiring type 2 diabetes mellitus patients, although its HbA1C-lowering effects have been minimal in short-term trials, and its insulin dosage-reduction activity remains unclear. The Food and Drug Administration has also approved its use as monotherapy and in combination with sulfonylureas for patients with type 2 diabetes. It may have use in the treatment of patients with impaired glucose tolerance, but more clinical experience is needed before definitive conclusions can be made. The role of troglitazone therapy in diabetes mellitus and impaired glucose intolerance will continue to evolve as the results of studies and our clinical experience with this agent become available.

Evidence for a role of tumor necrosis factor alpha in disturbances of triglyceride and glucose metabolism predisposing to coronary heart disease

Elevated plasma levels of triglyceride-rich lipoproteins, a decreased high-density lipoprotein (HDL) cholesterol concentration, hyperinsulinemia, and impaired fibrinolytic function frequently aggregate in patients with premature coronary heart disease (CHD). Experimental studies suggest that the cytokine tumor necrosis factor alpha (TNFalpha) produced by adipocytes plays a part in the regulation of triglyceride and glucose metabolism. The present study examined whether TNFalpha is implicated in these metabolic and fibrinolytic disturbances in young postinfarction patients. TNFalpha levels were determined in two groups of young (age <45 years) male postinfarction patients (n = 92 and 60) and in matched, population-based control subjects (n = 63). Plasma TNFalpha was higher in patients than in controls (4.1 +/- 1.6 v2.5 +/- 0.4 pg/mL, P < .0001). In hyperlipidemic patients, TNFalpha levels correlated significantly with the concentrations of very-low-density lipoprotein (VLDL) triglyceride and cholesterol and negatively with HDL cholesterol. Treatment with bezafibrate decreased VLDL triglycerides and increased HDL cholesterol, but did not affect TNFalpha levels. The TNFalpha concentration also correlated significantly with fasting glucose and proinsulin concentrations, as well as glucose and proinsulin levels after glucose ingestion. In contrast, no relations were found with the insulin level or degree of insulin resistance. The present results provide clinical evidence for a basic role of TNFalpha in hypertriglyceridemia, glucose intolerance, and the etiology of premature CHD.

Common medical problems in sports

This article reviews the most common medical problems encountered in the day-to-day care of athletes at all levels of competition. Common medical conditions affecting the pulmonary, gastrointestinal, urological, and endocrine systems are reviewed, as well as common infectious diseases. Review of environmental factors affecting athletes, including sleep disorders, travel, and exposure to the environment during athletic competition, are discussed.

Long-term (12 months) treatment with an anti-oxidant drug (silymarin) is effective on hyperinsulinemia, exogenous insulin need and malondialdehyde levels in cirrhotic diabetic patients

BACKGROUND/AIMS

Several studies have demonstrated that diabetic patients with cirrhosis require insulin treatment because of insulin resistance. As chronic alcoholic liver damage is partly due to the lipoperoxidation of hepatic cell membranes, anti-oxidizing agents may be useful in treating or preventing damage due to free radicals. The aim of this study was to ascertain whether long-term treatment with silymarin is effective in reducing lipoperoxidation and insulin resistance in diabetic patients with cirrhosis.

METHODS

A 12-month open, controlled study was conducted in two well-matched groups of insulin-treated diabetics with alcoholic cirrhosis. One group (n=30) received 600 mg silymarin per day plus standard therapy, while the control group (n=30) received standard therapy alone. The efficacy parameters, measured regularly during the study, included fasting blood glucose levels, mean daily blood glucose levels, daily glucosuria levels, glycosylated hemoglobin (HbA1c) and malondialdehyde levels.

RESULTS

There was a significant decrease (p<0.01) in fasting blood glucose levels, mean daily blood glucose levels, daily glucosuria and HbA1c levels already after 4 months of treatment in the silymarin group. In addition, there was a significant decrease (p<0.01) in fasting insulin levels and mean exogenous insulin requirements in the treated group, while the untreated group showed a significant increase (p<0.05) in fasting insulin levels and a stabilized insulin need. These findings are consistent with the significant decrease (p<0.01) in basal and glucagon-stimulated C-peptide levels in the treated group and the significant increase in both parameters in the control group. Another interesting finding was the significant decrease (p<0.01) in malondialdehyde/levels observed in the treated group.

CONCLUSIONS

These results show that treatment with silymarin may reduce the lipoperoxidation of cell membranes and insulin resistance, significantly decreasing endogenous insulin overproduction and the need for exogenous insulin administration.

Impact of early growth retardation on glucoregulatory control and insulin action in mature rats

Glucoregulation and insulin action were examined in adult female progeny of dams fed an 8% protein diet during gestation and lactation. Progeny were provided with standard (20% protein) diet at weaning (24 days), at which time body weight was reduced by 21%. Basal (postabsorptive) endogenous glucose production (Ra) and glucose utilization by oxidative muscles was decreased in offspring that had experienced early growth retardation. The glucose disappearance rate after intravenous glucose and the glucose infusion rate required to maintain euglycemia during insulin infusion were both increased (by 35 and 24%, respectively) by early growth retardation. Insulin secretion was unimpaired. During euglycemic-hyperinsulinemic clamp, Ra was suppressed further, and there was a twofold greater increment in the stimulation of whole body glucose clearance rate in the offspring that experienced early growth retardation. Insulin-stimulated glucose utilization by peripheral tissues was unaffected.

Understanding the pathogenesis of type 2 diabetes: can we get off the metabolic merry-go-rounds?

The aetiology of non-insulin-dependent diabetes mellitus (NIDDM) is not known. The concordance of NIDDM in identical twins and differences in the prevalence rate of NIDDM between different racial groups suggest a genetic cause. Hyperglycaemia in established diabetes is caused by a combination of hepatic insulin resistance, impaired peripheral (muscle and fat) glucose uptake and a defect in glucose-mediated insulin secretion. However, it is not known if these defects are all inherited or if one can cause the others. This uncertainty is due to the fact that hyperglycaemia per se can cause defects in insulin action and insulin secretion that resemble those found in NIDDM. Furthermore the elevated free fatty acid (FFA) levels found when NIDDM is associated with obesity are known to cause both peripheral and hepatic insulin resistance. Recently we have demonstrated the mechanism by which elevated FFA levels can cause hepatic insulin resistance. However, we also have evidence that the converse holds in that genetically engineered hepatic insulin resistance in a transgenic rat model leads to obesity. Thus an understanding of the pathogenesis of NIDDM is complicated by the fact that hyperglycaemia and obesity can be both causes and consequences of insulin resistance. To overcome these difficulties, studies in young euglycaemic diabetes-prone subjects have been conducted. Results suggest that there may be different causes for NIDDM in different racial groups.

Insulin, intact and split proinsulin, and coronary artery disease in young men

BACKGROUND

Glucose intolerance and hyperinsulinemia are common disturbances in nondiabetic men with premature coronary artery disease (CAD). To investigate the relation between insulin-like molecules and severity of coronary atherosclerosis, 62 consecutive nondiabetic men presenting with a first myocardial infarction before the age of 45 were studied along with 41 healthy, age-matched, male, population-based control subjects.

METHODS AND RESULTS

Specific two-site immunoradiometric assays were used to distinguish intact proinsulin, (des 31,32) proinsulin, and "true" insulin in fasting plasma and during an oral glucose tolerance test (OGTT). Global coronary atherosclerosis and number and severity of distinct stenoses were determined in the patients in 15 proximal coronary arterial segments by use of separate semiquantitative classification systems. The patients had a two- to threefold increase in insulin and insulin propeptide concentrations in the fasting state as well as during the OGTT. Severity of coronary atherosclerosis correlated significantly (P < .05 to P < .01) with basal proinsulin (r = .40) and the proinsulin area under the curve (AUC) (r = .34), basal insulin (r = .31), basal C peptide (r = .30), and the glucose AUC (r = .30). In multiple stepwise regression analysis including insulin-like molecules, major plasma lipoproteins, and lipoprotein subfractions, basal proinsulin (increase in R2 = .09) and dense LDL triglycerides (increase in R2 = .10) predicted 19% of the variation of the global coronary atherosclerosis score after adjustment for age, body mass index, fasting insulin concentration, and VLDL triglycerides.

CONCLUSIONS

This study shows that young, nondiabetic, male survivors of myocardial infarction are truly hyperinsulinemic during an OGTT and suggests a close association between proinsulin and coronary atherosclerosis.

Effects on glucose tolerance, insulin secretion, insulin-like growth factor 1 and its binding protein, IGFBP-1, in a randomized controlled diet and exercise study in healthy, middle-aged men

OBJECTIVES

To study the effects of advice on diet, exercise and their combination on oral glucose tolerance (OGTT), insulin secretion, insulin-like growth factor-1 (IGF-1) and its binding protein, IGFBP-1.

DESIGN

A 6-month, randomized, controlled intervention study.

SETTING

Primary health care centres in Sollentuna, Stockholm and the Department of Medicine, Karolinska Hospital, Stockholm, Sweden.

SUBJECTS

One hundred and fifty-seven normoglycaemic healthy men, mean age 46 years, range 35-60 years, with slightly to moderately raised cardiovascular risk factors.

INTERVENTIONS

Advice on diet (D, n = 40), exercise (E, n = 39) a combination of both (DE, n = 39) and a control group (C, n = 39).

MAIN OUTCOME MEASURES

An OGTT, insulin secretion, IGF-1 and its binding protein, IGFBP-1.

RESULTS

The number of pathological OGTTs in the intervention groups decreased from 42/118 to 33/118 whilst the number in the control group did not change. Fasting insulin levels decreased in groups E and DE from 8.8-7.4 mU L-1 (P < 0.01) and from 8.3-6.7 mU L-1 (P < 0.01), respectively. Accordingly, the insulin area under the curve decreased from 5278 to 4828 (P < 0.05) in group E, and from 5482 to 4809 (P < 0.01) in group DE. IGF-1 only increased in group D. The most prominent changes were noted for IGFBP-1, which increased in all three intervention groups and to the highest degree in group DE (from 33.7-42.6 micrograms L-1, P < 0.001).

CONCLUSIONS

A combination of increased exercise and improved diet, as well as increased exercise alone, favourably affect glucose and insulin homeostasis in middle-aged men with moderately elevated cardiovascular risk factors. The most marked changes were noted for IGFBP-1, possibly suggesting a decreased insulin secretion and an enhanced insulin sensitivity.

Lipoprotein lipase mass and activity in plasma and their increase after heparin are separate parameters with different relations to plasma lipoproteins

Lipoprotein lipase (LPL) activity and mass in plasma and their increase after heparin administration were measured in 61 men who had suffered myocardial infarction before the age of 45 years and in 69 population-based age- and sex-matched control subjects without coronary heart disease to study the relations between these parameters in plasma and their correlations with plasma lipoproteins in subjects with a wide range of lipoprotein and LPL levels. There was a relatively large amount of LPL protein compared with LPL activity in preheparin plasma, indicating that the majority of circulating LPL is catalytically inactive. LPL mass and activity in postheparin plasma (postheparin minus preheparin values) were highly correlated, and the calculated mean specific activity (0.35 mU/ng) was in the range expected for catalytically active LPL. Hence, heparin releases mainly active LPL. The four LPL parameters (mass and activity in plasma and their increase after heparin administration) were not related to each other, except for postheparin plasma LPL mass and activity, and they showed different correlations with plasma lipoprotein lipid concentrations. There was a strong positive correlation between LPL mass in preheparin plasma and the HDL cholesterol level as well as weak negative relations to VLDL triglyceride and cholesterol concentrations in the patients. In contrast, preheparin LPL activity showed no correlation with the HDL cholesterol level but weak positive relations to VLDL triglyceride and cholesterol concentrations in the control subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of insulin action and glucose effectiveness in diabetic and nondiabetic humans

Insulin concentrations in humans continuously change and typically increase only when glucose also increases such as with eating. In this setting, it is not known whether the severity of hepatic and extrahepatic insulin resistance is comparable and whether the ability of glucose to regulate its own uptake and release is defective in non-insulin-dependent diabetes mellitus (NIDDM). To address this question, NIDDM and nondiabetic subjects were studied when glucose concentrations were clamped at either 5 mM (euglycemia) or varied so as to mimic the glucose concentrations observed in nondiabetic humans after food ingestion (hyperglycemia). Insulin was infused so as to simulate a "nondiabetic" postprandial profile. During euglycemia, insulin increased glucose disposal in nondiabetic but not diabetic subjects indicating marked extrahepatic resistance. In contrast, insulin-induced suppression of glucose release was only minimally less (P < 0.05) in diabetic than nondiabetic subjects (-1.06 +/- 0.09 vs. -1.47 +/- 0.21 nmol.kg-1 per 4 h). Hyperglycemia substantially enhanced disposal in both groups. Glucose effectiveness measured as the magnitude of enhancement of disposal (0.59 +/- 0.18 vs. 0.62 +/- 0.17 nmollkg-1 per 4 h) and suppression of release (-0.36 +/- 0.12 vs. -0.14 +/- 0.12 nmol.kg-1 per 4 h) did not differ in the diabetic and nondiabetic subjects. In conclusion, when assessed in the presence of a physiological insulin profile, people with NIDDM demonstrate: (a) profound extrahepatic insulin resistance, (b) modest hepatic insulin resistance, and (c) normal ability of glucose to stimulate its own uptake and suppress its own release.

Clinical and biochemical factors associated with prognosis after myocardial infarction at a young age

OBJECTIVES

This study examined the effect of metabolic disturbances, hemostatic function, coronary artery disease severity and left ventricular function on the long-term prognosis after myocardial infarction in men < 45 years old.

BACKGROUND

Heavy smoking; dyslipoproteinemias involving very low density lipoprotein (VLDL), low density lipoprotein (LDL) and high density lipoprotein (HDL); a family history of premature coronary artery disease; hyperinsulinemic responses to oral and intravenous glucose challenges; and defective fibrinolytic function characterize the young postinfarction patient, but the influence of these features on the long-term prognosis is virtually unknown.

METHODS

Measurements of hemostatic function and metabolic and angiographic indicators of risk were included in a prospective cohort study of variables predictive of reinfarction, cardiac death and major coronary events within 6 to 9 years in 108 unselected nondiabetic men with a first myocardial infarction before age 45 years.

RESULTS

During follow-up, 20 patients had sudden cardiac death, and 53 had a major coronary event (reinfarction, sudden cardiac death, bypass surgery or intervention by catheterization). In multivariate analysis, VLDL and global coronary atherosclerosis score predicted reinfarction; plasma plasminogen activator inhibitor-1 (PAI-1) activity and global coronary stenosis score predicted cardiac death; and VLDL triglyceride levels, global coronary atherosclerosis score and age predicted any major coronary event.

CONCLUSIONS

This prospective cohort study shows that hypertriglyceridemia, impaired fibrinolytic capacity secondary to plasma PAI-1 activity elevation and extensive coronary artery disease increase the risk of recurrences in men with a first myocardial infarction before age 45 and contribute to the relatively poor long-term prognosis in this patient group.

Evaluation of two insulin assays in insulin resistance syndrome (syndrome X)

Recent data suggest that proinsulin is associated with cardiovascular risk factors in nondiabetic and diabetic subjects. Since most conventional insulin assays cross-react with proinsulin, it has been suggested that the associations of insulin concentrations with dyslipidemia and hypertension could actually reflect associations with proinsulin. We examined these associations by using both a conventional immunoreactive insulin assay and a specific Linco insulin assay that does not cross-react with proinsulin in 623 nondiabetic and in 180 non-insulin-dependent diabetic subjects who participated in the San Antonio Heart Study, a population-based study of diabetes and cardiovascular disease. Both the immunoreactive insulin assay and the specific Linco insulin assay were equally correlated with cardiovascular risk factors in nondiabetic subjects. Insulin concentrations were moderately correlated with high triglyceride and low high-density lipoprotein cholesterol levels and were weakly correlated with increased blood pressure. In diabetic subjects there were only weak associations between insulin and cardiovascular risk factors using either assay. We conclude that the association of insulin concentrations with cardiovascular risk factors is not a function of using insulin assays that cross-react with proinsulin and that for epidemiological studies of cardiovascular risk factors, conventional immunoreactive insulin assays are as good as the newer specific insulin assays.

Disorders of carbohydrate and lipid metabolism in veterans with paraplegia or quadriplegia: a model of premature aging

One hundred veterans with paralysis due to spinal cord injury (SCI), equally divided between those with paraplegia and quadriplegia, and 50 able-bodied veteran controls underwent a 75-g oral glucose tolerance test (OGTT). In subjects with SCI, 22% were diabetic by criteria established by the World Health Organization (WHO), whereas only 6% of the control group were diabetic. Eighty-two percent of the controls had normal (NL) oral glucose tolerance, compared with 38% of those with quadriplegia and 50% of those with paraplegia. Subjects with diabetes mellitus (DM) were older in both the SCI and control groups, but those with SCI developed carbohydrate disorders at younger ages than did the control group. SCI subjects had significantly higher mean glucose and insulin values at several points during the OGTT when compared with controls, suggesting an accentuated state of insulin resistance in those with SCI. Mean fasting plasma glucose (FPG) values for both SCI and control groups were significantly higher in subjects with DM compared with those with NL glucose tolerance. When the FPG value was compared between SCI or control subjects with abnormalities in glucose tolerance, the subgroups with SCI and NL or impaired glucose tolerance (IGT) had significantly lower FPG levels than the respective control subgroups, suggestive of decreased hepatic glucose output in SCI.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for impaired pancreatic beta cell function in South African Indians with impaired glucose tolerance

In a prospective study of South African Indians with impaired glucose tolerance (IGT), the serum insulin response during a 75 g oral glucose tolerance test (OGTT) was examined in 128 subjects who were classified as IGT 1 year previously (year 0) and in 60 matched control subjects. Based on the results at year 1, study subjects were divided into three groups, using World Health Organization criteria for glucose tolerance: IGT (n = 47), diabetes (n = 41), and transient IGT (normal glucose tolerance) (n = 40). When compared with the control group, despite higher plasma glucose concentrations, the IGT group showed similar fasting insulin, but lower 30-min insulin response (57.4 +/- 1.9 mUl-1 vs 86.5 +/- 1.8, p < 0.001) and lower 30-min insulin/glucose ratio (7.4 +/- 5.2 vs 13.3 +/- 8.7, p < 0.001). The insulinogenic index was lower in the IGT group than in the control group at 30, 60, 90, and 120 min (p < 0.01, p < 0.001, p < 0.001, p < 0.001, respectively). The 2-h insulin response was higher in the IGT group (106.7 +/- 1.9 mUl-1 vs 59.2 +/- 1.9, p < 0.01). The IGT group displayed a delayed pattern of insulin response with maximum levels only at 2-h. Insulin area was similar in the two groups. In the transient IGT group, despite similar plasma glucose levels, the insulin responses at 0, 15, 30, and 60 min (p < 0.01, p < 0.001, p < 0.001, p < 0.001, respectively) were lower than in the control group; the 30-min insulin/glucose ratio (7.1 +/- 5.1 vs 13.3 +/- 8.7, p < 0.001) and 60-min insulinogenic index (46.9 +/- 86.3 vs 123.4 +/- 206.3, p < 0.001) were also lower in the transient IGT group.(ABSTRACT TRUNCATED AT 250 WORDS)

Loss of the first phase insulin response to intravenous glucose in subjects with persistent impaired glucose tolerance

Loss of the first phase insulin response to intravenous glucose is one of the earliest detectable defects of beta cell dysfunction in Type 2 diabetes mellitus. Impaired glucose tolerance (IGT) is considered a prediabetic condition, therefore loss of first phase insulin secretion in subjects with IGT would suggest beta cell dysfunction as an early lesion in the development of Type 2 diabetes. Three groups of subjects were studied, 7 subjects with persistent IGT (classified as having IGT at two 75 g oral glucose tolerance tests (OGTT) done 6 months apart), 6 subjects with transient IGT (IGT at the first OGTT, but normal glucose tolerance at a repeat OGTT 6 months later), and 7 normal controls. First phase insulin secretion was studied using an intravenous glucose tolerance test with arterialized blood sampling. Fasting, 3, 4 and 5 min samples were assayed for glucose and insulin (specific two-site immunoradiometric assay). The fasting insulin was similar in all three groups, however the 3 min insulin response was significantly lower in those with persistent impaired glucose tolerance (p < 0.02). Thus subjects with persistent impaired glucose tolerance demonstrated loss of the first phase insulin response as an early indicator of beta cell dysfunction while subjects with transient IGT had a normal insulin response to intravenous glucose. During the OGTT, the 30 min glucose was not significantly different (p = 0.1) but the 30 min insulin to glucose ratio was significantly lower in subjects with persistent IGT (p < 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

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

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

Impaired insulin sensitivity and maximal responsiveness in older hypertensive men

This study examines the relation between blood pressure and insulin resistance in obese, sedentary middle-aged and older men. Eleven hypertensive and 17 normotensive subjects of comparable age (58.6 +/- 1.0 years, mean +/- SEM), percent body fat (27.7 +/- 0.7%), and maximal aerobic capacity (30.2 +/- 0.9 mL.kg-1.min-1) participated in this study. Glucose disposal (M, milligrams per kilogram of fat-free mass per minute) determined during a three-dose hyperinsulinemic euglycemic clamp was lower in the hypertensive than normotensive subjects at the low (M at 120 pmol/m2.min: 2.3 +/- 0.2 versus 3.2 +/- 0.3, P = .06), intermediate (M at 600 pmol/m2.min: 8.0 +/- 0.6 versus 10.4 +/- 0.6, P = .02), and high (M at 3000 pmol/m2.min: 13.5 +/- 0.5 versus 15.5 +/- 0.7, P = .04) insulin infusion rates. The calculated insulin concentration necessary for a half-maximal effect (EC50) was greater in the hypertensive than normotensive subjects (1164 +/- 168 versus 864 +/- 66 pmol/L, P = .03). In this population of normotensive and hypertensive men, systolic, diastolic, and mean arterial blood pressures were related to glucose disposal at these insulin infusion rates (r = -.35 to -.46, P < .05) as well as the EC50 (r = .42 to .44, P < .05). Thus, hypertensive obese, sedentary older men have a reduction in both sensitivity and maximal responsiveness to insulin that is directly related to the severity of hypertension independent of obesity and physical fitness.

Postprandial lipoproteins and progression of coronary atherosclerosis

The relations between triglyceride-rich lipoproteins, alimentary lipaemia and coronary heart disease (CHD) have remained obscure and much debated. We studied the basal and postprandial plasma levels of chylomicron remnants and very low density lipoproteins (VLDL) of varying particle size in 32 male postinfarction patients (mean (S.D.) age 48.8 (3.2) years) and in 10 age-matched control men. The selective quantification of postprandial intestinal and hepatic lipoproteins was accomplished by determining apolipoproteins B-48 and B-100 in lipoprotein subfractions of Svedberg flotation (Sf) rates > 12 before and 3, 6 and 12 h after an oral fat load. Since all patients had undergone two coronary angiographies with an intervening time interval of around 5 years, lipoprotein fractions were examined in relation to the global severity as well as the rate of progression of coronary lesions. The postprandial plasma levels of small chylomicron remnants (Sf 20-60 apolipoprotein B-48) were found to relate distinctly to the rate of progression of coronary lesions between the angiographies (r = 0.51, P = 0.01). Adjustment for the possible confounding effect of the HDL cholesterol and dense LDL apolipoprotein B concentrations did not substantially alter the strength of this association. Neither the increment of plasma triglyceride during the postprandial period nor the concentrations of other lipoprotein fractions closely reflected the amount of small chylomicron remnants in the circulation or correlated with progression of coronary lesions. Our data suggest that small chylomicron remnants are implicated in the progression of coronary artery disease.

Thinness at birth and insulin resistance in adult life

Type 2 (non-insulin-dependent) diabetes mellitus may originate through impaired development in fetal life. Both insulin deficiency and resistance to the action of insulin are thought to be important in its pathogenesis. Although there is evidence that impaired fetal development may result in insulin deficiency, it is not known whether insulin resistance could also be a consequence of reduced early growth. Insulin resistance was therefore measured in 81 normoglycaemic subjects, and 22 subjects with impaired glucose tolerance, who were born in Preston, UK, between 1935 and 1943. Their birth measurements had been recorded in detail. Insulin resistance was measured by the insulin tolerance test which uses the rate of fall in blood glucose concentrations after intravenous injection of insulin as an index of insulin resistance. Men and women who were thin at birth, as measured by a low ponderal index, were more insulin resistant. The association was statistically significant (p = 0.01) and independent of duration of gestation, adult body mass index and waist to hip ratio and of confounding variables including social class at birth or currently. Thinness at birth and in adult life has opposing effects such that resistance fell with increasing ponderal index at birth but rose with increasing adult body mass index. It is concluded that insulin resistance is associated with impaired development in fetal life.

Improved beta cell function, with reduction in secretion of intact and 32/33 split proinsulin, after dietary intervention in subjects with type 2 diabetes mellitus

Diet in Type 2 diabetes often reduces both hyperglycaemia and weight and both these factors may contribute to improvement in beta cell function. Sixty-nine subjects with newly diagnosed Type 2 diabetes had their glucose, insulin, intact and 32/33 split proinsulin measured at diagnosis, and after 16 (12-20) weeks of conventional diet. In the whole group following diet there was reduction in weight (p < 0.0001), Haemoglobin A1 (p < 0.0001), and fasting glucose (p < 0.0001). There was a fall in fasting intact proinsulin (p < 0.03), 32/33 split proinsulin (p < 0.0001), and the percentage of fasting proinsulin to total insulin-like molecules (p < 0.0001). Subjects were separated according to weight loss (group 1 < 0.5 kg, group 2 0.5-4 kg, group 3 > 4 kg). Only subjects in group 3 (mean weight loss 6.2 kg) had a fall in fasting insulin (p < 0.04). The fasting glucose achieved following diet was positively correlated with the initial fasting glucose (r = 0.7) and negatively correlated with the degree of insulin deficiency at diagnosis (with the initial 30 min insulin r = -0.62). The effect of diet on the final concentration of insulin, 32/33 split proinsulin and intact proinsulin was examined using multiple regression. The final insulin concentration was determined by the initial BMI and absolute weight loss, 32/33 split proinsulin concentration by the initial fasting glucose and absolute glucose fall, and intact proinsulin concentration by a combination of both weight loss and glucose reduction.(ABSTRACT TRUNCATED AT 250 WORDS)

Importance of transcapillary insulin transport to dynamics of insulin action after intravenous glucose

Insulin action in vivo is determined by both transendothelial insulin transport (TET) across the capillary and subsequent insulin binding and postreceptor events. To examine TET under non-steady-state conditions, we performed intravenous glucose tolerance tests (IVGTT; 0.3 g/kg; n = 7) on conscious dogs. At basal, insulin in lymph was only 53 +/- 7% of plasma insulin (P < 0.001), whereas lymph glucose exceeded plasma levels (109 +/- 4 vs. 104 +/- 4 mg/dl, respectively; P < 0.02). On injection, dynamics of glucose in plasma and lymph were similar, suggesting rapid equilibration of glucose between compartments. In contrast, insulin appearance in lymph was delayed relative to plasma (5.1 +/- 1.3 vs. 2 +/- 0 min), peaked later (21 +/- 2 vs. 8 +/- 2 min), attained peak value of only 52 +/- 6% of plasma insulin (range, 35-76%), and remained lower than plasma insulin throughout the IVGTT (P < 0.05 or better). Minimal model-derived insulin sensitivity (SI) averaged 3.55 +/- 0.75 x 10(-4) min-1/(microU/ml). There was a strong linear relationship between lymph insulin and its effect on glucose disappearance [X(t), r = 0.95 +/- 0.01]. Determination of the relative contributions of TET and post-TET insulin-sensitive processes to overall SI revealed that cellular sensitivity to interstitial insulin dominated (r2 = 0.55), but was not the exclusive determinant of, overall SI, as insulin transport was also important (r2 = 0.21). TET is a previously unrecognized contributor to SI in vivo.

Relation of plasma levels and composition of apolipoprotein B-containing lipoproteins to angiographically defined coronary artery disease in young patients with myocardial infarction

BACKGROUND

Hypertriglyceridemia is a common metabolic disturbance in men < 45 years old with myocardial infarction. To further investigate the relation between triglyceride-rich lipoproteins and severity of coronary atherosclerosis in this subset of postinfarction patients, apolipoprotein B-containing lipoproteins of 64 consecutive patients were subfractionated in connection with coronary angiography.

METHODS AND RESULTS

Density-gradient ultracentrifugation of plasma and coronary angiography were performed 4 to 6 months after the myocardial infarction. Global coronary atherosclerosis and the number and severity of distinct stenoses were evaluated by semiquantitative analysis of 15 proximal coronary segments. The majority of the patients (60%) were hypertriglyceridemic and had higher coronary scores than normotriglyceridemic patients. Of the major plasma lipoproteins, triglycerides and cholesterol in the low-density lipoprotein (LDL) fraction were associated with global coronary atherosclerosis, whereas LDL triglycerides and high-density lipoprotein (HDL) cholesterol correlated directly and inversely, respectively, with the coronary stenosis score. Plasma apolipoprotein B correlated with both coronary scores. The plasma concentrations of lipid and protein in the very-low-density lipoprotein (VLDL) subfractions (VLDL1 through VLDL3) and intermediate-density lipoprotein (IDL) did not correlate with either of the coronary scores, whereas the concentration of triglycerides in dense LDL (density > 1.040 kg/L) was strongly associated with both coronary scores. Compositional analysis of the smallest VLDL particles (VLDL3) and IDL revealed a correlation between the number of cholesteryl ester molecules in small VLDL and global coronary atherosclerosis in hypertriglyceridemic patients.

CONCLUSIONS

Global coronary atherosclerosis and distinct stenoses in young postinfarction patients are associated with the number of apolipoprotein B-containing particles in plasma and the concentration of LDL triglyceride. Specifically, dense triglyceride-rich LDL particles and, in hypertriglyceridemic patients, small cholesteryl ester-rich VLDL particles relate to coronary artery disease severity.

Insulin resistance and risk factors for coronary heart disease

In this presentation an effort has been made to review the impact of resistance to insulin-mediated glucose uptake and/or hyperinsulinaemia on various metabolic end-points and clinical syndromes. Insulin resistance is present in the great majority of patients with states of glucose intolerance, but frank decompensation of glucose homoeostasis does not occur if individuals can maintain a state of compensatory hyperinsulinaemia. Although compensatory hyperinsulinaemia may prevent the development of NIDDM in insulin-resistant individuals, there is substantial evidence that insulin resistance and/or hyperinsulinaemia is associated with higher plasma concentrations of triglyceride, uric acid and plasminogen activator inhibitor 1 and with lower HDL cholesterol concentrations. Obesity, decreased physical activity and possibly cigarette smoking accentuate the degree of insulin resistance and its manifestations, and a genetic basis is also involved. Resistance to insulin-mediated glucose uptake and/or hyperinsulinaemia have been shown to be associated with high blood pressure, microvascular angina and CHD. Thus, resistance to insulin-mediated glucose uptake is a common phenomenon, which makes a major contribution to the aetiology and clinical course of common and serious diseases. Based on the above considerations, it is difficult to over-emphasize the health-related implication of a defect in insulin-mediated glucose uptake.

Insulin deficiency rather than hyperinsulinaemia in newly diagnosed type 2 diabetes mellitus

This paper reports beta cell function as assessed during OGTT using specific IRMAs for insulin, intact and 32/33 split proinsulin in subjects with newly diagnosed Type 2 diabetes matched to normal controls. The relationships between insulin and the proinsulins to risk factors for cardiovascular disease were also examined. Similar fasting insulin concentrations but lower 30-min post-glucose-load insulin concentrations were found in diabetic subjects (mean +/- SEM 143 +/- 12 pmol-1 vs 304 +/- 19 (p < 0.001). Subjects with diabetes had increased fasting intact (10.6 +/- 1.1 pmol-1 vs 3.3 +/- 0.2, p < 0.001) and 32/33 split proinsulin concentrations (8.1 +/- 0.9 pmol-1 vs 2.2 +/- 0.3, p < 0.0001). Beta cell dysfunction, as expressed by a reduction in the 30-min insulin to glucose ratio (9.4 +/- 1 vs 34.8 +/- 2.3, p < 0.0001) and an increase in the fasting percentage of total proinsulin-like to total insulin-like molecules (24.5 +/- 9% vs 11.6 +/- 5, p < 0.001), was present in subjects with diabetes. In diabetic subjects beta cell dysfunction and insulin deficiency increased relative to the degree of fasting hyperglycaemia. It seems clear that beta cell dysfunction and insulin deficiency are major features of Type 2 diabetes. Only the fasting concentration of 32/33 split proinsulin positively correlated with both the waist/hip ratio (r = 0.36, p < 0.001), diastolic blood pressure (r = 0.23, p < 0.01) in addition to plasma triglyceride concentration (r = 0.46, p < 0.001). It is questionable whether hyperinsulinaemia plays a pathogenic role in cardiovascular disease in subjects with glucose intolerance.

Insulin deficiency and increased plasma concentration of intact and 32/33 split proinsulin in subjects with impaired glucose tolerance

In order to determine insulin status and beta cell function during the oral glucose tolerance test (OGTT), in impaired glucose tolerance (IGT), 51 such subjects and matched controls, identified during a population survey for diabetes, underwent a 75 g OGTT. Fasting, 30 min and 2 h insulin and intact proinsulin, and fasting and 2 h 32/33 split proinsulin, were measured by specific two-site immunoradiometric assays. The subjects with IGT had higher fasting (geometric mean +/- SD, 5.0 +/- 4.0 pmol-1 vs 2.9 +/- 1.7, p < 0.02) and 2 h intact proinsulin (23 +/- 14 vs 14 +/- 12, p < 0.0001), and fasting (3.2 +/- 3 pmol-1 vs 1.8 +/- 1.8, p < 0.0007) and 2 h 32/33 split proinsulin (18.3 +/- 19 pmol-1 vs 6.6 +/- 15, p < 0.0001). Despite higher plasma glucose concentrations, the IGT group had similar fasting insulin, lower 30 min insulin (216 +/- 124 pmol-1 vs 278 +/- 130, p < 0.02), and a lower 30 min insulin/glucose ratio (23.7 +/- 2.1 vs 34.8 +/- 2.3, p < 0.002). The percentage of fasting proinsulin-like to total insulin-like molecules was higher in those with IGT (15.3 +/- 8% vs 11.6 +/- 8, p < 0.04). After 6 months, at repeat OGTT, the same subjects with IGT were classified as 'persisters' or 'reverters'. The persister (24/51 47.1%), at initial OGTT, had a higher 2 h glucose level, a greater BMI and higher systolic blood pressure, but other parameters were similar to the reverters.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin receptor isotype expression correlates with risk of non-insulin-dependent diabetes

Skeletal muscle insulin resistance plays a pivotal role in the pathogenesis of non-insulin-dependent diabetes mellitus (NIDDM), as individuals with this defect are at increased risk of developing the disease later in life. To assess whether the abnormal expression of the structurally distinct human insulin receptor isoforms, HIR-A and HIR-B, which has been found in skeletal muscle of NIDDM patients, is a feature of a prediabetic state, skeletal muscle biopsies from nondiabetic individuals ranging from high insulin sensitivity to insulin resistance were examined. Polymerase chain reaction analysis of mRNA from muscle biopsies detected exclusive or predominant expression of HIR-A in 13 patients with normal insulin sensitivity. In contrast, 7 subjects with various degrees of insulin resistance exhibited abnormally increased HIR-B RNA expression. This association suggests the abnormal expression of receptor isoforms as a characteristic of the prediabetic state and supports the notion of a connection of this aberration with the pathogenesis of NIDDM. Changes in HIR-A/B expression in the skeletal muscle may thus provide a prognostic criterion for the development of NIDDM.

Metabolism of triglyceride-rich lipoproteins during alimentary lipemia

The metabolism of chylomicron remnants and VLDL was studied in healthy controls and normo- (NTG) and hypertriglyceridemic (HTG) patients with coronary artery disease after intake of an oral fat load. Specific determination of apo B-48 and B-100 enabled separation of the respective contribution of the two lipoprotein species. The postprandial plasma levels of small (Sf 20-60) and large (Sf 60-400) chylomicron remnants increased in controls and NTG patients. In contrast, only large chylomicron remnants increased in the HTG patients. An increase of large VLDL was seen in response to the oral fat load in all groups, whereas small VLDL were either unchanged in the controls and the NTG patients, or decreased in the HTG patient group. The whole plasma concentration of C apolipoproteins was essentially uninfluenced by the oral fat load, whereas the content in large triglyceride-rich lipoproteins paralleled the apo B elevations in controls and NTG patients. An even more prominent increase of apo B in large triglyceride-rich lipoproteins in the HTG group was not accompanied by an increase of C apolipoproteins. These findings indicate that chylomicrons compete with VLDL for removal of triglycerides by lipoprotein lipase and that the postprandial metabolism of triglyceride-rich lipoproteins is severely defective in hypertriglyceridemia.

HDLs and alimentary lipemia. Studies in men with previous myocardial infarction at a young age

The plasma concentration, particle size, and chemical composition of high density lipoproteins (HDLs) are associated with the metabolism of triglyceride-rich lipoproteins (TGRLs). During alimentary lipemia there is active exchange of lipids and apolipoproteins between HDL and apolipoprotein B-containing lipoproteins. Whereas HDL has been assigned a protective role against the development of atherosclerosis, alimentary lipemia has been proposed to represent a potentially atherogenic state. We examined plasma HDL concentration, particle size, and composition and their relations to postprandial TGRLs in 32 postinfarction patients and 10 healthy control subjects after intake of a standardized oral fat load of a mixed-meal type. All patients had undergone coronary angiographies in connection with the myocardial infarction and around 5 years thereafter. The plasma HDL cholesterol concentration decreased significantly in response to the oral fat load, particularly in hypertriglyceridemic patients, with a concomitant increase of HDL triglycerides. A limited and reversible yet consistent increase of HDL particle size (1-2%) was seen 6 hours after intake of the oral fat load on nondenaturing gradient gel electrophoresis (GGE) in both patients and control subjects. Virtually no changes in the plasma concentration of HDL GGE subclasses, lipoproteins containing apolipoprotein A-I but no apolipoprotein A-II (LpA-I), or lipoproteins containing both apolipoproteins A-I and A-II (LpA-I:A-II) were induced in the postprandial state despite massive increases of large very low density lipoprotein (VLDL) and large chylomicron remnant levels (determined as apolipoproteins B-100 and B-48 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis). Strong inverse correlations with fasting plasma HDL cholesterol and the larger HDL GGE subspecies were found for large postprandial VLDL and large chylomicron remnants, whereas the corresponding relations for small VLDL and small chylomicron remnants were weaker. The relations of both large and small VLDL and chylomicron remnants to HDL cholesterol were confined to subjects in the lower fasting plasma HDL cholesterol range (< 1.2 mmol/l). None of the HDL parameters measured, either in the fasting or in the postprandial state (HDL cholesterol, HDL triglycerides, HDL GGE subclasses, LpA-I, and LpA-I:A-II), were related to the development of coronary atherosclerosis, whereas the postprandial plasma levels of small chylomicron remnants, which showed weak negative correlations with HDL, related positively to the progression of coronary atherosclerosis.(ABSTRACT TRUNCATED AT 400 WORDS)

Hyperglycemic athymic nude mice: factors affecting in vitro insulin secretion

The strain of athymic nude male mice (ANM) developed at the University of Southern California (USC) exhibits spontaneous hyperglycemia and relative hypoinsulinemia in vivo. To investigate factors that influence insulin secretion in this animal model of non-insulin-dependent diabetes mellitus, we utilized the isolated perfused mouse pancreas of the ANM-USC and control BALB/c mice. We compared in vitro glucose-induced insulin secretion in ANM-USC and control mice, inhibition of secretion by somatostatin, and variability of insulin secretion over the two-year period it took to complete these experiments. Glucose-induced insulin secretion from the isolated pancreas was biphasic in both ANM-USC and controls. Insulin secretion was quantitatively equal to or greater than control mice, depending on the phase of secretion analyzed and the source of the control mice. In contrast to pancreases of control mice, insulin secretion from ANM-USC pancreases was relatively resistant to inhibition of insulin secretion by somatostatin. Variability in insulin secretion over the two years in which these experiments were performed was greater from pancreases of control than that observed from pancreases of the ANM-USC. The hyperglycemic ANM-USC mouse does not demonstrate diminished insulin secretion in vitro yet is relatively hypoinsulinemic in vivo. Thus circulating factors other than somatostatin might contribute to the insulinopenic stage in this animal model.

The insulin receptor: signalling mechanism and contribution to the pathogenesis of insulin resistance

The insulin receptor is a heterotetrameric structure consisting of two alpha-subunits of Mr 135 kilodalton on the outside of the plasma membrane connected by disulphide bonds to beta-subunits of Mr 95 kilodalton which are transmembrane proteins. Insulin binding to the alpha-subunit induces conformational changes which are transduced to the beta-subunit. This leads to the activation of a tyrosine kinase activity which is intrinsic to the cytoplasmatic domains of the beta-subunit. Activation of the tyrosine kinase activity of the insulin receptor represents an essential step in the transduction of an insulin signal across the plasma membrane of target cells. Signal transduction on the post-kinase level is not yet understood in detail, possible mechanisms involve phosphorylation of substrate proteins at tyrosine residues, activation of serine kinases, the interaction with G-proteins, phospholipases and phosphatidylinositol kinases. Studies in multiple insulin-resistant cell models have demonstrated that an impaired response of the tyrosine kinase to insulin stimulation is one potential mechanism causing insulin resistance. An impairment of the insulin effect on tyrosine kinase activation in all major target tissues of insulin, in particular the skeletal muscle was demonstrated in Type 2 (non-insulin-dependent) diabetic patients. There is no evidence that the impaired tyrosine kinase response in the skeletal muscle is a primary defect, however, it is likely that this abnormality of insulin signal transduction contributes significantly to the pathogenesis of the insulin-resistant state in Type 2 diabetes.

Glucose intolerance in first-degree relatives of patients with Friedreich's ataxia is associated with insulin resistance: evidence for a closely linked inherited trait

Multiple and different genetic defects may be associated with the development of diabetes mellitus. Friedreich's ataxia (FA) is an autosomal recessively inherited neurologic disease associated with a high prevalence of diabetes. We previously demonstrated that patients with FA have insulin resistance prior to the development of overt diabetes mellitus. To determine if insulin resistance is an inherited characteristic in this group, we performed oral glucose tolerance tests (OGTT) on first-degree relatives, 21 parents and 17 siblings, of patients with FA. While fasting concentrations were normal, both glucose and insulin concentrations in response to oral glucose were significantly elevated compared with controls. Corrected insulin responses, CIR = I x 100/G (G-70) (I = insulin, G = glucose), were not different from controls, whereas peripheral insulin activities, A = 10(4)/Ip Gp (p = values of I and G at peak glucose concentration), were significantly decreased (FA, 0.66 +/- 0.11, P less than .001; parents, 0.63 +/- 0.06, P less than .001; siblings, 0.72 +/- 0.09, P less than .01; v controls, 1.52 +/- 0.19), indicating the presence of insulin resistance in patients and first-degree relatives. Multiple discriminant analysis was used to separate patients with FA from controls. The combination of GLUT (sum of glucose values 0 to 3 hours of the OGTT) and CIR achieved significant separation (P less than .0004). Subsequent assignment of the relatives showed that 17 of 18 parents and 11 of 16 siblings (69%) fell in the range of FA, rather than with controls. These data suggest that insulin resistance is an inherited trait in this group.(ABSTRACT TRUNCATED AT 250 WORDS)

High density lipoprotein turnover in patients with hypertension

Although hyperinsulinemia and decreased high density lipoprotein cholesterol concentration can occur in patients with hypertension, there is no information available concerning the dynamic state of high density lipoprotein metabolism. To address this issue, we quantified high density lipoprotein turnover in 12 patients with mild hypertension and 11 matched subjects with normal blood pressure. Patients with high blood pressure had lower high density lipoprotein cholesterol concentrations. Fractional catabolic rates of 125I-apolipoprotein AI (apoAI)/high density lipoprotein were faster in patients with hypertension (0.36 +/- 0.02 versus 0.26 +/- 0.02 l/day, p less than 0.001). Total synthetic rates of apoAI were also significantly greater in patients with high blood pressure (17.4 +/- 1.1 versus 13.2 +/- 0.6 mg/kg/day, p less than 0.001). Although significant correlation was observed between blood pressure and fractional catabolic rate of 125I-apoAI/high density lipoprotein in the experimental population (r = 0.52, p less than 0.01), no relation was found when patients with normal blood pressure or hypertension were considered separately. However, a highly significant positive correlation was found between 125I-apoAI/high density lipoprotein fractional catabolic rate and insulin concentration in the entire population (r = 0.72, p less than 0.001). In conclusion, the patients with mild hypertension studied were hyperinsulinemic, had a faster fractional catabolic rate of 125I-apoAI/high density lipoprotein, and a lower high density lipoprotein-cholesterol concentration. It is suggested that the changes seen in high density lipoprotein-cholesterol concentration and 125I-apoAI/high density lipoprotein fractional catabolic rates were secondary to the hyperinsulinemia and not due to the high blood pressure per se.

Insulin resistance in normal rats infused with glucose for 72 h

Insulin resistance is accentuated during periods of poor metabolic control in human non-insulin-dependent diabetes mellitus. The role of hyperglycemia in this suppression of insulin action is not clear. If glucose impairs insulin action, then the effect should be reproducible in vivo in tissues of normal intact rats. To test this possibility, normal rats were continuously administered 50% glucose in water (60-66 mg.kg-1.min-1) via an indwelling jugular catheter. After 72 h, these animals were hyperglycemic, hyperinsulinemic, and glucosuric compared with control rats infused for 72 h with normal saline (P less than 0.01). Basal glucose uptake in vivo was greater in muscle of glucose-infused rats. Insulin-stimulated glucose uptake in vivo and in vitro (by perfused hindquarters and isolated adipocytes) were suppressed in the glucose-infused group (P less than 0.01). Glycogen synthase activity was reduced 40% in extracts of muscle and adipose tissue of hyperglycemic rats. Basal and isoproterenol-stimulated lipolysis were increased, whereas insulin suppression of lipolysis was blunted in adipocytes from glucose-infused animals (P less than 0.01). Glucose infusion did not alter insulin binding by isolated adipocytes or solubilized skeletal muscle insulin receptors. These results suggest that a 72-h in vivo glucose infusion impaired insulin action in muscle and adipose tissue of normal rats by inducing postbinding defects similar to those observed in human diabetes mellitus during intervals of deteriorated metabolic control.