Failure of chronic experimental hyperinsulinism to alter insulin binding to hypothalamic receptors in the rat

1984 ◽  
Vol 107 (1) ◽  
pp. 86-90 ◽  
Author(s):  
Roman B. Melnyk ◽  
J. M. Martin
Keyword(s):  
Food Restriction ◽  
Insulin Treatment ◽  
Binding Capacity ◽  
Insulin Receptors ◽  
Insulin Binding ◽  
Insulin Concentration ◽  
Regulatory Mechanisms ◽  
Hypothalamic Region ◽  
Insulin Levels ◽  
Lateral Area

Abstract. We have previously shown that [125I]insulin binding to medial hypothalamic receptors is attenuated following 14 days of food restriction. Such rats are characterized by considerably reduced circulating insulin levels with unchanged hypothalamic insulin concentration. The present data demonstrate that, in contrast to the effects of starvation, [125I]insulin binding to hypothalamic receptors from rats made hyperinsulinaemic by daily injections of protamine zinc insulin (4–6 U/rat/day for 14 days) is unaffected by this manipulation, even though hypothalamic insulin concentration in insulininjected animals was significantly higher than in salineinjected controls. Insulin binding to partially purified membranes from the medial hypothalamic region was significantly greater than that from the lateral area, confirming a finding in our earlier study. Insulin treatment was associated with slight reductions in maximal insulin-binding capacity of medial hypothalamic receptors, a tendency which appeared to be compensated by reciprocal changes in receptor affinity for this hormone. The data indicate that hypothalamic insulin receptors are not regulated by peripheral or even central insulin levels per se; it appears, rather, that some other, as yet unidentified, correlate(s) of significantly altered food intake and/or body weight can modify hypothalamic insulin receptor function. Perhaps such modifications could, in turn, participate in the activation of regulatory mechanisms involved in correcting energy imbalance.

Starvation-induced changes in insulin binding to hypothalamic receptors in the rat

1984 ◽  
Vol 107 (1) ◽  
pp. 78-85 ◽  
Author(s):  
Roman B. Melnyk ◽  
J. M. Martin
Keyword(s):  
Food Restriction ◽  
Central Body ◽  
Binding Capacity ◽  
Insulin Binding ◽  
Insulin Concentration ◽  
Regulatory Mechanisms ◽  
Feedback Signal ◽  
Medial Region ◽  
The Central Nervous System ◽  
Induced Changes

Abstract. In order to determine whether insulin binding to receptors in the central nervous system can be modified by changes in energy balance, hypothalami from 48 h food deprived and 14 day food restricted (8 or 4 g chow/day) rats were removed and insulin binding to partially purified membranes from both medial and lateral hypothalamic regions was studied. Hypothalamic insulin concentration was measured in similarly treated animals. Although hypothalamic insulin concentration did not vary, insulin binding to lateral receptors was significantly lower than that obtained from the medial region. After prolonged food restriction, binding to medial receptors was significantly reduced in comparison to controls, whereas binding in the lateral region remained unchanged; differences were most pronounced at near-physiological insulin concentrations. Changes in per cent specific [125I]insulin binding were associated with corresponding changes in maximal insulin-binding capacity, the latter being inversely related to receptor affinity for this hormone. These results are consistent with the hypothesis that insulin, acting via hypothalamic receptors, may serve as a metabolic feedback signal linking the periphery with central body weight regulatory mechanisms.

Receptor and postreceptor insulin resistance induced by in vivo hyperinsuiinemia

1983 ◽  
Vol 61 (8) ◽  
pp. 802-807 ◽  
Author(s):  
C. Martin ◽  
K. S. Desai ◽  
G. Steiner
Keyword(s):  
Insulin Resistance ◽  
Glucose Oxidation ◽  
Binding Capacity ◽  
Insulin Receptors ◽  
Insulin Binding ◽  
Insulin Concentration ◽  
Fat Cell ◽  
And Control

We examined the effects of inducing hyperinsuiinemia in vivo in rats on the insulin receptors of, and the glucose oxidation by their adipocytes. Hyperinsulinemia was induced over a 2-week period by injecting NPH insulin subcutaneously. This was given in doses that were gradually increased to a final dose of 6 units/day. Profound hypoglycemia was avoided by providing supplemental sucrose to both the insulin-treated and control rats. The insulin concentration was eight times greater in the insulin-treated rats. However, they were not grossly obese and their adipocytes were not enlarged. The adipocytes of the hyperinsulinemic rats had a 25% lower maximal insulin binding capacity and were resistant to the effects of insulin on glucose oxidation. We felt that the hyperinsuiinemia was sufficient so that, despite their somewhat lower insulin binding capacity, these adipocytes would not bind less insulin in vivo than would adipocytes from control rats. Hence, we postulated that, this massive hyperinsulinemia not only down regulated the insulin receptor, but also led to a postreceptor resistance. This notion was supported by two lines of in vitro data. First, even at maximally effective medium concentrations of insulin, the maximum rate of glucose oxidation by the adipocytes from hyperinsulinemic rats reached a plateau which was less than that reached by cells from controls. Second, when this in vitro glucose oxidation was related not merely to the medium insulin concentration, but to the amount of insulin bound to adipocytes, the response of the hyperinsulinemic rats' cells was always lower than control. These changes occurred in the absence of any difference in fat cell size. Thus, in vivo hyperinsulinemia led to insulin resistance in adipocytes. This was associated both with down regulation of the insulin receptors and with a postreceptor defect.

Insulin and central regulation of spontaneous fattening and weight loss

1985 ◽  
Vol 249 (2) ◽  
pp. R203-R208
Author(s):  
R. B. Melnyk ◽  
J. M. Martin
Keyword(s):  
Weight Loss ◽  
Body Weight ◽  
Weight Gain ◽  
Energy Balance ◽  
Binding Capacity ◽  
Insulin Receptors ◽  
Insulin Binding ◽  
Strong Positive Correlation ◽  
Central Regulation ◽  
Isolated Pancreatic Islets

Insulin binding to receptors in a partially purified hypothalamic membrane preparation is altered by prolonged starvation. To define further the relationship between hypothalamic insulin binding and energy balance, we studied the Richardson's ground squirrel, a hibernator that exhibits spontaneous 6- to 8-mo body weight cycles when kept in constant conditions. Isolated pancreatic islets from squirrels killed during the weight gain phase had greater glucose-stimulated insulin secretion than those from weight loss phase animals, and adipocytes showed significantly greater glucose incorporation into total lipid in response to insulin. Differences in lipogenesis were not attributable to changes in insulin-binding capacity. Hypothalamic tissue from weight gain phase animals bound more insulin than that from weight loss phase animals. Maximal binding was correlated with pancreatic islet responsiveness and maximal insulin-stimulated lipogenesis. The strong positive correlation between peripheral metabolic events associated with spontaneous alterations in energy balance and the binding kinetics of hypothalamic insulin receptors suggests that insulin may play an important role in the central regulation of body weight.

scholarly journals High glucose and insulin in combination cause insulin receptor substrate-1 and -2 depletion and protein kinase B desensitisation in primary cultured rat adipocytes: possible implications for insulin resistance in type 2 diabetes

2003 ◽  
Vol 148 (1) ◽  
pp. 157-167 ◽  
Author(s):  
J Buren ◽  
HX Liu ◽  
J Lauritz ◽  
JW Eriksson
Keyword(s):  
Glucose Uptake ◽  
High Glucose ◽  
Insulin Treatment ◽  
Insulin Signalling ◽  
Binding Capacity ◽  
Insulin Binding ◽  
Rat Adipocytes ◽  
Glucose Levels ◽  
High Insulin ◽  
The Right

OBJECTIVE: The purpose of this study was to investigate the cellular effects of long-term exposure to high insulin and glucose levels on glucose transport and insulin signalling proteins. DESIGN AND METHODS: Rat adipocytes were cultured for 24 h in different glucose concentrations with 10(4) microU/ml of insulin or without insulin. After washing, (125)I-insulin binding, basal and acutely insulin-stimulated d-[(14)C]glucose uptake, and insulin signalling proteins and glucose transporter 4 (GLUT4) were assessed. RESULTS: High glucose (15 and 25 mmol/l) for 24 h induced a decrease in basal and insulin-stimulated glucose uptake compared with control cells incubated in low glucose (5 or 10 mmol/l). Twenty-four hours of insulin treatment decreased insulin binding capacity by approximately 40%, and shifted the dose-response curve for insulin's acute effect on glucose uptake 2- to 3-fold to the right. Twenty-four hours of insulin treatment reduced basal and insulin-stimulated glucose uptake only in the presence of high glucose (by approximately 30-50%). At high glucose, insulin receptor substrate-1 (IRS-1) expression was downregulated by approximately 20-50%, whereas IRS-2 was strongly upregulated by glucose levels of 10 mmol/l or more (by 100-400%). Insulin treatment amplified the suppression of IRS-1 when combined with high glucose and also IRS-2 expression was almost abolished. Twenty-four hours of treatment with high glucose or insulin, alone or in combination, shifted the dose-response curve for insulin's effect to acutely phosphorylate protein kinase B (PKB) to the right. Fifteen mmol/l glucose increased GLUT4 in cellular membranes (by approximately 140%) compared with 5 mmol/l but this was prevented by a high insulin concentration. CONCLUSIONS: Long-term exposure to high glucose per se decreases IRS-1 but increases IRS-2 content in rat adipocytes and it impairs glucose transport capacity. Treatment with high insulin downregulates insulin binding capacity and, when combined with high glucose, it produces a marked depletion of IRS-1 and -2 content together with an impaired sensitivity to insulin stimulation of PKB activity. These mechanisms may potentially contribute to insulin resistance in type 2 diabetes.

Insulin Binding Sites Induced in the Tetrahymena by Rat Liver Receptor Antibody

1984 ◽  
Vol 39 (1-2) ◽  
pp. 183-185 ◽  
Author(s):  
G. Csaba ◽  
P. Kovács ◽  
Ágnes Inczefi-Gonda
Keyword(s):  
Rat Liver ◽  
Concanavalin A ◽  
Binding Sites ◽  
Binding Capacity ◽  
Insulin Receptors ◽  
Insulin Binding ◽  
Receptor Antibody ◽  
Receptor Antibodies

Abstract Tetrahvmena cells treated with purified rabbit anti­ bodies to rat hepatocellular membrane exhibited a consider­ able increase in binding capacity on reexposure to the antibody 24 h later. Insulin binding was similarly enhanced by preexposure to the antibody, and vice versa, preex­ posure to insulin enhanced the later binding of rat liver receptor antibodies. This suggests that (1) the Tetrahymena and the rat possess similar insulin receptors, and (2) the receptor antibody is also able to induce imprinting for itself as well as for insulin. Concanavalin-A, noted for binding overlap with insulin, failed to induce imprinting either for insulin or for antibodies to receptors, whereas the latter did induce imprinting for Concanavalin-A.

Forearm insulin uptake in healthy subjects after oral glucose and intravenous glipizide

1981 ◽  
Vol 98 (3) ◽  
pp. 407-412 ◽  
Author(s):  
Arne Nygren ◽  
Lars Erik Lindblad ◽  
Lars Sundblad
Keyword(s):  
Healthy Subjects ◽  
Insulin Receptors ◽  
Random Order ◽  
Insulin Binding ◽  
Insulin Concentration ◽  
Oral Glucose ◽  
Healthy Individuals ◽  
Pre Treatment ◽  
Insulin Uptake ◽  
Arterial Insulin

Abstract. In six healthy subjects fasted overnight two different experiments were carried out on separate days and in random order: A. Oral glucose followed 60 min later by iv glipizide. B. Iv glipizide followed 60 min later by oral glucose. Each experiment was divided into two 60 min periods, and the fractionated insulin uptake by forearm tissue was calculated for each 60 min period. When the fractional insulin uptake values for these four 60 min periods were compared it was found that the uptake of insulin was significantly higher for the 60 min period that was obtained in response to glucose without glipizide pre-treatment, than it was for any of the other 60 min periods. Moreover, in some of the participants the venous insulin concentration occasionally exceeded the corresponding arterial insulin concentration after iv glipizide administration. These findings imply that glipizide may decrease insulin binding to peripheral insulin receptors in healthy individuals.

Insulin binding, internalization, and receptor regulation in cultured human fibroblasts

1981 ◽  
Vol 241 (3) ◽  
pp. E251-E260
Author(s):  
D. Baldwin ◽  
M. Prince ◽  
P. Tsai ◽  
C. Johnson ◽  
R. Lotan ◽  
...  
Keyword(s):  
Incubation Temperature ◽  
Degradation Products ◽  
Human Fibroblasts ◽  
Insulin Receptors ◽  
Insulin Binding ◽  
Insulin Concentration ◽  
Target Cells ◽  
Kinetic Properties ◽  
Insulin Degradation ◽  
Normal Human

Insulin binding to receptors was studied using monolayers of cultured normal human fibroblasts. Binding was rapid and inversely related to the incubation temperature; prolonged periods of steady-state binding were achieved at all temperatures studied and the amount of degradation of extracellular insulin was minimal. Competition curves demonstrated half-maximal inhibition of 125I-insulin binding at an unlabeled insulin concentration of 125I-insulin binding at an unlabeled insulin concentration of 7 ng/ml. Scatchard plots of the binding data were curvilinear and revealed that fibroblasts contained about 7,000 receptor sites per cell. Bound 125I-insulin dissociated from fibroblasts with a t 1/2 of 10 min at 30 degrees C and 35 min at 16 degrees C. After 60 min dissociation at 30 degrees C, 45% of the dissociated radioactivity consisted of 125I-insulin degradation products, whereas only 8% of the dissociated material was in the form of degraded products after 60 min of dissociation at 16 degrees C. This indicates that fibroblasts possess a temperature-sensitive receptor-mediated process for insulin degradation. Preincubation of the monolayers with insulin led to a hormone-induced loss of insulin receptors. Thus, incubating cells with 25 ng/ml insulin for 6 h at 37 degrees C caused a 50% reduction in subsequently measured 125I-insulin binding. This hormone-induced receptor loss was sensitive to physiologic insulin levels, with approximately 5 ng/ml causing a half-maximal receptor loss. When monolayers were treated with the lysosomotropic agent chloroquine and subsequently incubated with 5 X 10(-11) M 125I-insulin, a 130% increase in cell-associated radioactivity was observed after 120 min at 30 degrees C. In summary, 1) cultured normal human fibroblasts possess insulin receptors that exhibit kinetic properties and specificity identical to that of other insulin target cells; 2) incubation of fibroblasts with physiologic concentrations of insulin causes a marked loss of cell-surface insulin receptors; and 3) receptor-bound 125I-insulin is internalized through an energy-dependent endocytotic pathway and subsequently degraded by a chloroquine-sensitive reaction.

Insulin receptors in normal pregnant women and women with gestational diabetes

1986 ◽  
Vol 113 (3_Suppl) ◽  
pp. S27-S30 ◽  
Author(s):  
Ole Andersen ◽  
Claus Kühl ◽  
Inge Buch
Keyword(s):  
Gestational Diabetes ◽  
Pregnant Women ◽  
Receptor Binding ◽  
Insulin Receptors ◽  
Late Pregnancy ◽  
Insulin Binding ◽  
Normal Weight ◽  
Insulin Concentration ◽  
Isolated Adipocytes ◽  
Normal Controls

Abstract. In a serial study of insulin receptor binding to monocytes from normal pregnant women, a significant increase in insulin binding in mid pregnancy followed by a significant decrease in late pregnancy at tracer insulin concentration was found. No changes in the insulin concentration necessary to reduce tracer binding by 50% (ID50) were observed. At delivery, binding to isolated adipocytes was significantly lower in normal pregnant women than in non-pregnant normal controls while no difference in ID50 was observed. No differences in insulin binding at tracer insulin concentration to monocytes and adipocytes between normal weight women with gestational diabetes and healthy non-diabetic pregnant controls were found, but the ID50 was significantly lower in women with gestational diabetes diagnosed in late pregnancy than in pregnant controls at the same weeks of gestation.

Increased fetal insulin receptors and changes in membrane fluidity and lipid composition

1982 ◽  
Vol 243 (3) ◽  
pp. E246-E250
Author(s):  
N. D. Neufeld ◽  
L. Corbo
Keyword(s):  
Membrane Fluidity ◽  
Binding Capacity ◽  
Insulin Receptors ◽  
Fetal Lung ◽  
Insulin Binding ◽  
Maternal Diabetes ◽  
Fetal Membrane ◽  
Membrane Cholesterol ◽  
Membrane Microviscosity ◽  
Microsomal Membranes

Fetal tissues exposed to hyperinsulinemia in utero have significantly greater numbers of insulin receptors than do those of controls. We have studied this upregulation phenomenon using crude microsomal membranes from fetal rabbit litters exposed to varying degrees of hyperinsulinemia in diabetic pregnant rabbits. We have observed that insulin binding capacity of membranes increased directly with the severity of maternal diabetes, ranging from 8.5 ng in controls to 44.6 ng insulin/mg membrane protein in offspring of severely diabetic animals and related directly with increasing fetal insulin levels (r = 0.77, P less than 0.005). Lipid analyses of fetal lung membranes showed that reduction of phospholipid to protein ratios occurred in the presence of maternal diabetes. Membrane cholesterol-to-phospholipid ratios were also altered in the presence of maternal diabetes. Significantly, increases in plasma membrane microviscosity were noted in the membranes from diabetic offspring. The data suggest that reduction of membrane fluidity is associated with increases in fetal membrane insulin receptors in severely diabetic pregnancies.

Expression of insulin receptors and of 60-kDa receptor substrate in rat mature and immature enterocytes

1997 ◽  
Vol 273 (1) ◽  
pp. G217-G226 ◽  
Author(s):  
J. P. Buts ◽  
N. De Keyser ◽  
S. Marandi ◽  
A. S. Maernoudt ◽  
E. M. Sokal ◽  
...  
Keyword(s):  
Tyrosine Kinase ◽  
Radioligand Binding ◽  
Binding Capacity ◽  
Insulin Receptors ◽  
Insulin Binding ◽  
Scatchard Analysis ◽  
Binding Assays ◽  
Age Related ◽  
High Affinity Receptor

The mechanism(s) by which rat immature enterocytes exhibit increased responsiveness to insulin before weaning is unknown. Therefore, we have analyzed the distribution, ontogeny, and molecular properties of insulin receptors (IR) and of related substrates in immature and mature enterocytes. IR were studied by radioligand binding assays, cross-linking labeling, immunohistochemistry, and in vitro phosphorylated substrates by immunoprecipitation. Regardless of age, 125I-insulin binding to IR was five times higher in crypt cells than in villus cells and two times higher in the ileum than in the jejunum. Binding capacity to villus cells from sucklings (day 14) exceeded three times that of older animals (day 30 and day 60). Scatchard analysis of equilibrium binding data confirmed an age-related decrease in low- and high-affinity receptor classes without change in affinity constants. In concordance, both alpha- and beta-IR subunits were more abundant in immature than in mature membranes. In vitro, insulin elicited the phosphorylation of three membrane proteins (96, 60 and 42 kDa), whose signals were virtually inhibited by preincubating membranes with antireceptor monoclonal antibodies. By immunoprecipitation, the 60-kDa signal was rapidly detected as a tyrosine-phosphorylated protein, expressed in mature and immature membranes, and identified as a receptor substrate phosphorylated in vitro by the IR tyrosine kinase. In conclusion, 1) increased responsiveness of rat immature enterocytes to insulin could be related to high membrane concentrations of IR and 2) normal rat enterocytes express a 60-kDa phosphotyrosine protein identified as a direct substrate of the IR tyrosine kinase.

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