Study of the relationship between plasma insulin concentration and efficiency of glucose uptake in normal and mildly diabetic subjects

The Visceral Adiposity Syndrome in Japanese-American Men

Japanese-Americans have an increased prevalence of non-insulin-dependent diabetes mellitus and coronary heart disease when compared to native Japanese. This increase has been associated with fasting hyperinsulinemia, hypertriglyceridemia, and low plasma levels of high-density lipoprotein (HDL) cholesterol. The purpose of this study was to examine the relationship of both visceral adiposity and insulin resistance to this metabolic syndrome and to the presence of a predominance of small, dense low-density lipoprotein (LDL) particles (LDL subclass phenotype B) that has been associated with increased atherogenic risk. Six Japanese-American men with non-insulin-dependent diabetes, each receiving an oral sulfonylurea, were selected. One or 2 nondiabetic Japanese-American men, matched by age and body mass index, were selected for each diabetic subject, giving a total of 9 nondiabetic men. Diabetic subjects had significantly higher fasting plasma glucose (p=0.0007) and lower insulin sensitivity (SI, p=0.018) using the minimal model technique than nondiabetic subjects matched for body mass index. Six men (2 with diabetes) had LDL phenotype A and 8 (4 with diabetes) had phenotype B. One nondiabetic subject had an intermediate low-density lipoprotein pattern. Significantly greater amounts of intra-abdominal fat (p=0.045) measured by computed tomography were found in the men with phenotype B while fasting insulin (p=0.070) and triglycerides (p=0.051) tended to be higher. free fatty acids (r=0.677), LDL density (relative flotation rate, r=-0.803), and plasma HDL-cholesterol (r=-0.717). SI was significantly correlated only with plasma free fatty acids (r=-0.546) and tended to be correlated with hepatic lipase activity (r=-0.512, p=0.061). In conclusion, these observations indicate that in non-obese Japanese-American men, the metabolic features of the so-called insulin resistance syndrome, including LDL phenotype B, are more strongly correlated with visceral adiposity than with SI. It may therefore be more appropriate to call this the visceral adiposity syndrome. Although questions concerning mechanisms still remain, we postulate that visceral adiposity plays a central role in the development of many of the metabolic abnormalities, including LDL subclass phenotype B, that occur in this metabolic syndrome.

Short-term overfeeding induces insulin resistance in weight-stable patients after bariatric surgery

BACKGROUND

Short time overfeeding of rats rapidly leads to insulin resistance (IR). A study with healthy human volunteers, which we suggest are less susceptible for developing IR after short time overfeeding, did not show these effects on IR. Therefore a study population of weight-stable, former morbidly obese subjects (BMI 31.3 kg/m2), which were treated with bariatric surgery approximately 3 years ago was selected.

METHODS

Eleven subjects were submitted to a 7-day overfeeding study, resulting in a 53% increase in caloric intake (1,227 +/- 394.4 to 1,879.2 +/- 298.4 kcal/day). During normal diet and after overfeeding, insulin sensitivity was measured using steady state plasma glucose (SSPG) levels. At these time points, BMI and waist/hip ratio together with plasma levels of inflammatory markers (CRP, AGP, LBP, and TNF-alpha receptors) and plasma leptin values were also measured.

RESULTS

SSPG levels after overfeeding increased from 8.2 +/- 3.2 to 10.6 +/- 2.6 mmol/l (P < 0.05), indicating decreased insulin sensitivity after overfeeding. Fasting plasma insulin, glucose, circulating levels of inflammatory markers, BMI, and waist/hip ratio remained unchanged.

CONCLUSIONS

This study shows that overfeeding in a group of weight-stable, former morbidly obese subjects 3 years after bariatric surgery results in decreased insulin sensitivity. The mechanisms behind decreased insulin sensitivity induced by overfeeding are poorly understood, but the present results reveal that a unique human model is available to study these mechanisms, leading to a better understanding of the pathophysiology of IR.

[Relation between body fat distribution, insulin levels and glucose tolerance in obese females]

Relationship between body fat distribution, serum insulin, and glucose tolerance in obese, non-diabetic women. Recent studies suggest that hyperinsulinemia and upper body obesity are predictive factors for the development of non-insulin-dependent diabetes mellitus. To further characterize the relationship between body fat distribution, serum insulin, and glucose tolerance an oral glucose tolerance test was performed in 48 obese, non-diabetic women. Fasting insulin levels were correlated to both total body fat calculated as body mass index (r = 0.58, p less than 0.001) and upper body fat distribution expressed as waist-to-hip ratio (WHR, r = 0.47, p less than 0.01). In the women with upper body fat localization (WHR greater than 0.90) significantly higher basal and glucose-stimulated insulin concentrations were established than in the women with a lower body type of obesity (WHR less than 0.78) (basal insulin 27.4 +/- 11.5 vs. 15.4 +/- 8.8 mU/l, p less than 0.05, insulin area 779 +/- 320 vs. 468 +/- 237 U, p less than 0.05). They also had impaired glucose tolerance (glucose area 925 +/- 139 vs. 633 +/- 147 U, p less than 0.01). Fasting triglyceride concentrations were correlated both with WHR (r = 0.63, p less than 0.001) and fasting insulin (r = 0.33, p less than 0.05) but not with BMI (r = -0.02, n.s.). A positive association was found between systolic and diastolic blood pressure and both WHR (r = 0.43 and r = 0.44 resp., p less than 0.01) and BMI (each r = 0.35, p less than 0.05). Interestingly, basal insulin was also associated with blood pressure (r = 0.30, p less than 0.1, and r = 0.40, p less than 0.01 resp.).(ABSTRACT TRUNCATED AT 250 WORDS)

Physiologic and cellular insulin action in a glucose-intolerant model of type 2 (non-insulin-dependent) diabetes in rats

A B-cell-deficient model for Type 2 (non-insulin-dependent) diabetes mellitus has been investigated with regard to insulin action at the cellular level. Two-day-old male Sprague Dawley rats were injected with streptozotocin (90 mg/kg) or citrate buffer. At 6 weeks streptozotocin-treated animals were hyperglycaemic and exhibited glucose intolerance, e.g. at 45 min post-glucose (1.5 g/kg) the change in serum glucose level from baseline was 6 +/- 7 mg% in control rats vs. 212 +/- 18 mg% for the streptozotocin-treated rats. Basal activity and insulin action in isolated adipocytes, as estimated by 2-deoxyglucose uptake and glucose metabolism, were not influenced by streptozotocin treatment. For example, uptake of 0.1 mmol/1 2-deoxyglucose at 1000 microU insulin/ml was 58 +/- 8 pmol/10(5) cells min-1 vs 54 +/- 6 pmol for adipocytes isolated from experimental vs. control animals. Although serum insulin levels in streptozotocin-treated rats were significantly decreased (p less than 0.05), there was no difference in insulin receptor number or affinity. Glucose intolerance present in this model is similar to that in Type 2 diabetes. However, concomitant insulin intolerance was not observed. Taken together with our findings of unaltered insulin action at the cellular level, this suggests that the pathogenesis of insulin resistance is not dependent on glucose intolerance. Moreover, this hyperglycaemic model is responsive to oral hypoglycaemic agents and can be used to establish their direct effects on physiologic and cellular insulin action.

Impaired insulin action in newly diagnosed type 1 (insulin-dependent) diabetes mellitus

Hepatic and peripheral insulin sensitivity were investigated in five newly diagnosed Type 1 (insulin-dependent) diabetic subjects before and after 1 week of twice daily insulin therapy. Eight weight-matched control subjects were also studied. Hepatic glucose production and glucose utilization were measured basally and during two sequential 2-h insulin (25 and 40 mU X kg-1 X h-1)/ glucose infusion periods. In the untreated hyperglycaemic diabetic patients hepatic glucose production was 16.3 +/- 2.6, 8.1 +/- 1.1 and 3.6 +/- 2.8 mumol X kg-1 X min-1 respectively for each of the three periods (mean +/- SEM), and fell with treatment to 12.5 +/- 1.4, 0.5 +/- 0.5 and 0.5 +/- 0.5 mumol X kg-1 X min-1. Hepatic glucose production for normal subjects was 13.4 +/- 0.7, 2.3 +/- 0.8 and less than 0.1 mumol X kg-1 X min-1. Glucose utilization was 12.7 +/- 1.4, 18.2 +/- 0.7 and 22.1 +/- 3.4 mumol X kg-1 X min-1 before treatment in the diabetic subjects, and 11.8 +/- 1.7, 20.9 +/- 3.3 and 30.1 +/- 3.6 after treatment. These values compare with those in the euglycaemic control subjects (13.4 +/- 0.7, 18.7 +/- 1.6 and 36.3 +/- 2.7 mumol X kg-1 X min-1). The pre-treatment metabolic clearance rate of glucose in all diabetic studies with insulin levels greater than 30 mU/l was 2.6 +/- 0.4 and rose to 3.9 +/- 0.5 ml X kg-1 X min-1 following insulin therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of insulin therapy on hepatic and peripheral insulin sensitivity in Type 2 (non-insulin-dependent) diabetes

Hepatic glucose production and metabolic clearance rate of glucose were measured using (3-3H) glucose at steady state, basally and during two sequential 2 h insulin (25 and 40 mU . kg -1 . h -1)/glucose (2 and 3 mg. kg -1 . min -1) infusion periods. Eight diabetic subjects were studied before and after 1 week of twice daily insulin therapy; six control subjects matched for age, weight and degree of obesity were also studied. In the diabetic patients, pre-treatment hepatic glucose production was 20.0 +/- 2.2, 9.9 +/- 2.9, and 1.4 +/- 0.8 mu mol . kg -1 . min -1 respectively (+/- SEM) for each of the three periods, and fell significantly with treatment to 12.8 +/- 1.7, 4.0 +/- 1.5 and 1.9 +/- 1.0 mu mol . kg -1 . min -1. Hepatic glucose production in normal subjects was 13.2 +/- 0.6, 2.2 +/- 0.8 and less than 1 mu mol . kg -1 . min -1. The pre-treatment metabolic clearance rate in all diabetic studies with insulin levels greater than or equal to 30 mU/l was 1.10 +/- 0.14 ml . kg -1 . min -1 and remained virtually unchanged following insulin therapy; this was significantly lower than in the control subjects (6.83 +/- 1.02, p less than 0.001). Basal non-esterified fatty acid levels were higher (p less than 0.02) in the pre-treated diabetic patients compared to post-treated diabetic patients and control subjects. Non-esterified fatty acids in each group fell to similar levels during the insulin infusions, but the rate of fall was slower in the pre-treated diabetic patients. Insulin receptor binding to erythrocytes was normal in the diabetic subjects and unchanged by treatment. Therefore, following insulin treatment of uncontrolled Type 2 (non-insulin-dependent) diabetes, the initially increased basal hepatic glucose production, and decreased hepatic sensitivity, return towards normal. However, the glucose clearance remains low, despite good diabetic control, and appears to be a major factor in the continuing glucose intolerance. As insulin receptor binding is normal, the defect of glucose clearance in Type 2 diabetes appears compatible with a post-receptor defect of glucose metabolism.

Development of insulin resistance in normal dogs following alloxan-induced insulin deficiency

Insulin resistance was measured in 16 normal dogs by a method involving the continuous intravenous infusion of epinephrine, propranolol, glucose and insulin. With this approach, endogenous insulin secretin is inhibited, similar steady state levels of exogenous insulin are achieved in all doags, and the resultant steady state plasma glucose level provides a direct estimate of the ability of insulin to dispose of the infused glucose load. Thus, the higher the steady state plasma glucose level, the more the insulin resistance. Different amounts of alloxan were then administered to these dogs in order to produce insulin deficiency of varying degrees. Insulin resistance was then measured again in each dog. The results indicated that insulin resistance did not develop in dogs with only a moderate degree of insulin deficiency (fasting plasma glucose levels less than 150 mg/100 ml). On the other hand, a significant degree of insulin resistance developed in dogs with severe insulin deficiency (fasting plasma glucose greater than 150 mg/100 ml). Furthermore, the insulin resistance that developed in dogs with severe insulin deficiency could be returned to normal with insulin replacement for one week. These results indicate that insulin resistance can occur as a secondary manifestation of insulin deficiency.

Glucose turnover and disposal in maturity-onset diabetes

The glucose turnover rate in maturity-onset diabetes in man has been variously reported as increased, normal, and decreased. The present experiments suggest that these discrepancies may have been due to methodology, and to nonrecognition of a circadian cycle in the glucose turnover rate that is present in health, and marked in diabetes. During the early morning hours the glucose turnover rate in maturity-onset diabetes is increased in proportion to the fasting blood glucose level. It may reach three to four times the rate found in health. During the evening hours the increments are about one-half as great. The glucose outflow rate constant, k, lower in diabetes than in health, is also lower in both groups in the evening than in the morning. An analysis of the relative contributions of glucose overproduction and underutilization to the development of hyperglycemia in maturity-onset diabetes indicates that overproduction is the greater factor. The relative role of underutilization appears to increase as the fasting blood glucose level increases. The circulating glucose oxidation rate in maturity-onset diabetes is only slightly lower than in health, but the fraction oxidized is markedly lower, and only a small fraction is excreted. The principal conclusion is that in maturity-onset diabetes there is a hypertrophied flux of endogenous glucose, most of which is neither oxidized nor excreted. The precursors and the qualitative and quantitative metabolic fates of this excess glucose are unknown.