Showing papers by "Jerrold M. Olefsky published in 1975"

Effect of dexamethasone on insulin binding, glucose transport, and glucose oxidation of isolated rat adipocytes.

Abstract: We have studied the in vitro effects of dexamethasone on isolated rat adipocytes at concentrations of dexamethasone therapeutically achieved in man. Glucose oxidation, glucose transport, and insulin binding were assessed. In dexamethasone-treated cells, glucose oxidation was decreased by 30-40% both in the absence of insulin (basal state) and at low insulin levels (less than 25 mu/ML). At maximally effective insulin levels (over 100 muU/ml) no differences existed between control and treated cells. If glucose transport were the rate-limiting step for glucose oxidation in the basal state and at low (submaximal) insulin levels, but not at maximally effective insulin concentrations, then these data could be explained by postulating that dexamethasone has a direct affect on glucose transport and does not affect intracellular oxidative pathways. We tested this hypothesis by directly assessing glucose transport in dexamethasone-treated cells. Glucose transport was assessed by measuring the uptake of [14C]2-deoxy glucose. These studies demonstrated a 30-40% decrease in 2-deoxy glucose uptake by treated cells both in the basal state and at all insulin concentrations. Thus, a direct glucocorticoid effect on the glucose transport system seems to account for the decreased ability of dexamethasone-treated cells to oxidize glucose. Since dexamethasone treatment leads to decreased insulin binding to adipocytes in vivo, we examined the possibility that the in vitro decreases in insulin-mediated glucose transport could be due to decreased insulin receptors. Insulin binding to control and treated adipocytes was measured, and no differences were found. Therefore, in cntrast to previously reported in vivo studies, adipocytes treated in vitro with dexamethasone retain a normal ability to bind insulin. Thus, these studies suggest that all of the in vitro effects of dexamethasone on glucose oxidation are due to direct inhibition of the glucose transport system.

Demonstration of insulin resistance in untreated adult onset diabetic subjects with fasting hyperglycemia.

Abstract: We have used a continuous intravenous infusion of glucose (6 mg/kg/min), insulin (80 mU/min), epinephrine (6 mug/min), and propranolol (0.08 mg/min) to directly assess insulin resistance in 14 untreated adult onset diabetics with a mean (plus or minus SE) fasting plasma glucose level of 217 plus or minus 17 mg/100 ml. During the infusion endogenous insulin secretion is inhibited and steady-state plasma glucose and insulin levels are achieved after 90 min. Since similar steady-state levels of plasma insulin are achieved in all subjects, the plasma glucose concentration observed during the steady-state period is a measure of an individual's insulin resistance. Under these conditions, the mean (plus or minus SE) steady-state plasma glucose level of the 14 diabetic patients was 350 plus or minus 16 mg/100 ml, while that of 12 normal subjects was 121 plus or minus 4 mg/100 ml. Additional studies were performed in which control subjects and patients with diabetes had their fasting plasma glucose levels acutely raised or lowered to comparable levels before receiving the basic infusion mixture of glucose, insulin, epinephrine, and propranolol. The results of these studies indicated that differences in initial plasma glucose levels could not account for the different glucose responses of the two groups to the basic infusion. Finally, the mean (plus or minus SE) steady-state plasma glucose level of 104 plus or minus 17 mg/100 ml observed during the same basic infusion in five patients with fasting hyperglycemia (mean plus or minus SE, 142 plus or minus 12 mg/100 ml) secondary to chronic pancreatitis suggested that neither chronic hyperglycemia nor hypoinsulinemia per se necessarily lead to insulin resistance. These results demonstrate that marked insulin resistance exists in adult onset diabetics with fasting hyperglycemia. Since previous studies have documented the presence of insulin resistance in patients with chemical diabetes, the possibility exists that insulin resistance may be characteristic of adult onset diabetes mellitus.

The effects of acute and chronic dexamethasone administration on insulin binding to isolated rat hepatocytes and adipocytes

Abstract: In an effort to determine the possible relationship between changes in insulin-receptor binding and the glucocorticoid-induced insulin-resistant state, we studied insulin binding to specific receptors located on isolated adipocytes and hepatocytes obtained from dexamethasone (D)-treated rats. Three groups of D-treated rats were studied: (1) acute high-dose treatment (1.5 mgdekg6 days), (2) acute low-dose treatment (0.125 mgkg6days), and (3) chronic low-dose treatment (0.125 mgkg21days). When insulin binding to isolated hepatocytes was studied, we found that binding was only 30%–50% of control values when cells from the D-treated animals were used. This decrease in binding was greatest for cells from the acute high-dose group, indicating a dose-response effect, and least for cells from the chronic group, suggesting a tendency toward return of insulin-receptor binding during chronic treatment. When insulin binding to isolated adipocytes was studied, binding was 50%–60% of control values when cells from both acute D-treated groups were used. While the magnitude of the decrease in insulin binding was not as great as that seen with hepatocytes, the decrease was still greatest using cells from the acute high-dose group as compared to the acute low-dose group. Thus, a dose-response effect was suggested in both tissues. On the other hand, the effects of chronic D treatment on insulin binding were strikingly different in the two cell systems. After chronic D treatment, insulin binding to adipocytes returned to near-normal levels, while a 55% decrease in binding to hepatocytes persisted. Thus, the tendency toward return of insulin binding after chronic D treatment seen with hepatocytes was almost fully expressed by adipocytes. This might be related to the amelioration of the corticosteroid-induced insulin-resistant state which has been reported after chronic corticosteroid administration to humans. In conclusion, (1) a decrease in insulin binding is associated with corticosteroid excess, and it is possible that this decreased binding is related to the insulin resistance which results from corticosteroid administration; (2) the return of insulin binding toward normal after chronic D treatment could well be related to the improvement in insulin resistance seen during chronic corticosteroid administration to humans; and (3) the difference in effects of chronic D treatment on insulin binding to hepatocytes versus adipocytes indicates that changes in insulin binding can be tissue specific.

Effects of Age and Obesity on Insulin Binding to Isolated Adipocytes1212

Abstract: We have measured insulin binding to isolated adipocytes prepared from rats of varying ages and body weights. The ability of adipocytes to bind insulin progressively decreases as animals get older and fatter until about 70 days of age and 300 g body weight are reached. From this point on further decreases in insulin binding to adipocytes were not seen as rats got older and fatter. Analysis of the data indicated that this decrease in insulin binding could be accounted for by decreased numbers olf insulin receptor sites per cell. Further studies were conducted in which animals were allowed to age, but obesity was prevented or reversed by hypocaloric diets. In these experiments decreased insulin binding was either prevented or restored to normal by the negative caloric state, indicating that age had no appreciable effect on the ability of adipocytes to bind insulin. The influence of the obesity associated variables—hyperinsulinemia and increased fat cell size—on insulin binding was also examined. These latter...

Removal of insulin by perfused rat liver: effect of concentration.

Abstract: The kinetics of insulin removal by isolated rat liver were investigated by measuring the rate of disappearance of insulin from the perfusate during recycling perfusion and by comparing the extraction of insulin over a wide range of constant arterial hormone levels during nonrecycling perfusion. In the recycling studies, insulin was removed from the perfusing medium at a uniform rate between 5 and 45 min. The reaction velocity constant, or hepatic clearance, during this period of uniform disappearance averaged 1.8 ml/min and represented 34% of the volume flow through the liver. In the nonrecycling flow-through studies at constant arterial insulin concentration, an initial period of accelerated hepatic uptake of insulin was seen. This period lasted for 3 to 7 min, was seen at every level of arterial insulin concentration, and was followed by a period of constant hepatic insulin removal. The hepatic removal rate during the period of constant uptake increased in a linear fashion until arterial insulin concentration reached 500 muU/ml and attained a maximal value at concentrations over 800 muU/ml. These findings indicate that the time course of hepatic insulin uptake by the perfused rat liver consists of two phases-an initial rapid phase, possibly associated with insulin binding, followed by a sustained rate of insulin removal, which probably represents insulin utilization and degradation. The rate of hepatic insulin removal was found to be proportional to arterial insulin concentration overa range of 20 to 500 muU/ML. Above this concentration, hepatic removal processes became saturated, reaching a maximal value of 183 muU of insulin per gram of liver per minute.

Metabolic effects of increased caloric intake in man.

Abstract: In order to determine if increased caloric intake could be responsible for the insulin resistance and elevated plasma glucose, insulin, and triglyceride levels commonly associated with obesity, hypercaloric diets were fed for 3 wk to eight normal subjects, and the metabolic consequences of this diet were assessed before significant weight gain had occurred. One wk of increased caloric intake led to statistically significant increases in fasting plasma insulin (22%), glucose (5%), and triglyceride (30%) levels, as well as an increased insulin response (20%) to oral glucose. Since the average weight gain during this period was only 1.6 kg, the observed changes appear to be secondary to increased caloric consumption, not obesity. Most of these changes returned toward baseline values during the succeeding 2 wk of increased caloric intake, but statistically significant elevations of fasting plasma glucose (10%), insulin (8%), and cholesterol (15%) levels were still seen at the end of the hypercaloric dietary period. On the other hand, insulin resistance, as estimated by direct measurement of insulin responsiveness, did not change as a result of 3 wk of increased caloric intake. These results indicate that acute increases in caloric intake can lead to elevated plasma glucose, insulin, cholesterol, and triglyceride levels. These changes occurred before significant weight gain had taken place, and raised the possibility that at least some of the abnormalities of carbohydrate and lipid metabolism attributed to obesity may be due to increased caloric intake. However, this conclusion would not seem to apply to the insulin resistance associated with obesity, as 3 wk of increased caloric intake did not produce any change in the responsiveness of these subjects to insulin's action.

Comparison of 125-I-insulin binding and degradation to isolated rat hepatocytes and liver membranes.

Abstract: We have compared the ability of rat liver plasma membranes and isolated hepatocytes to bind and degrade insulin. Isolated cells were prepared in two different ways: by mechanical separation of cells and by coliagenase digestion of extracellular matrix. In all studies the binding and degradative characteristics of both types of hepatocyte preparations were identical. Furthermore, with one exception, the binding characteristics of membranes and cells were also quite similar. The only exception concerned the amount of insulin bound by hepatocytes as compared to liver membranes. Thus, at concentrations of cells (1.2 × 10 6 cells per milliliter) and membranes (150 µg. protein per milliliter) that gave equal binding at insulin concentrations 100 ng./ml. was greater with use of hepatocytes. Additional studies indicated that, in contrast to membranes, at the higher insulin concentration only 75 percent of the previously bound insulin could be recovered from hepatocytes. Thus, a nondissociable component exists, which probably represents intracellular radioactivity and appears to account for the higher specific insulin binding by cells at higher insulin concentrations. When insulin degradation was studied at the above hepatocyte and plasma membrane concentrations, cells degraded 30 per cent more insulin than did membranes. Kinetic analysis of these data revealed that the Km for insulin degradation (5 × 10 −7 M at 37°) was the same for both systems whereas the Vmax was greater with use of hepatocytes. In conclusion: (1) Preparation of hepatocytes by coliagenase digestion does not appear to alter insulin binding or degradation; (2) studies of liver membranes and isolated hepatocytes obtained from normal rats should yield similar information about insulin-receptor interaction as long as insulin concentrations

Evaluation of Insulin Resistance in Patients with Primary Hyperparathyroidism

Abstract: Increased plasma insulin levels, both in the fasting state and in response to glucose loads have been reported in patients with primary hyperparathyroidism (1). In this study surgical correction of the hyperparathyroidism was associated with a decrease in plasma insulin levels. However, since glucose tolerance in these patients was similar before and after surgery, it appears that a state of insulin resistance coexisted with the hyperparathyroidism. Documentation of these findings would add hyperparathyroidism to the list of pathologic states associated with antagonism to the action of insulin (2). Furthermore, since hyperin-sulinemia and insulin resistance are often associated with hypertriglyceridemia (3), patients with primary hyperparathyroidism might have an increased incidence of elevated plasma triglyceride levels. In order to evaluate these possibilities, we have measured plasma levels of glucose, insulin, triglyceride, and cholesterol, and directly estimated insulin resistance in a group of patie...

Insulin Sensitivity of Isolated Perfused Rat Liver

Abstract: The responsiveness of the isolated perfused rat liver to different metabolic effects of insulin was investigated during recycling perfusion. Infusion of porcine insulin at rates of 6,9,16 and 33 mU/hr. resulted in stable perfusate insulin levels averaging 41, 72, 120 and 229 μU/ml., respectively. Since the portal vein insulin concentration in the intact rat averaged 48 μU/ml. after a twenty-six-hour fast and 125 μU/ml. two hours after removal of food, the studies were conducted at insulin levels within the physiological range. The effect of each insulin concentration on the net accumulation of K+, amino acid nitrogen, urea nitrogen and glucose in the perfusing medium was assessed against the net accumulation of perfusate constituents during perfusion of control livers and livers perfused with perfusate insulin levels greater than 500 μU/ml. The results indicate that essentially maximal suppression of amino acid nitrogen outflow and retention of K+ occurred at insulin concentrations of 72 μU/ml., with lesser effects being noted at 41 μU/ml. Inhibition of ureogenesis was demonstrated at insulin levels above 120 μU/ml. However, significant effects of insulin on suppressing net glucose outflow was not observed until insulin levels had reached 500 μU/ml. due presumably to the absence of a sustained rate of glycogenolysis by control livers. The observation that perfused livers from normal rats are extremely sensitive to several metabolic effects of insulin at physiological concentrations suggests that this experimental approach can provide useful information as to the role of the liver in the pathogenesis of various insulin resistant states.