Effect of dexamethasone and cortisone on insulin receptors in normal human male

Effects of 11β-hydroxysteroid dehydrogenase-1 inhibition on hepatic glycogenolysis and gluconeogenesis

The aim of this study was to determine the effect of prolonged 11β-hydroxysteroid dehydrogenase-1 (11β-HSD1) inhibition on basal and hormone-stimulated glucose metabolism in fasted conscious dogs. For 7 days prior to study, either an 11β-HSD1 inhibitor (HSD1-I; n = 6) or placebo (PBO; n = 6) was administered. After the basal period, a 4-h metabolic challenge followed, where glucagon (3×-basal), epinephrine (5×-basal), and insulin (2×-basal) concentrations were increased. Hepatic glucose fluxes did not differ between groups during the basal period. In response to the metabolic challenge, hepatic glucose production was stimulated in PBO, resulting in hyperglycemia such that exogenous glucose was required in HSD-I (P < 0.05) to match the glycemia between groups. Net hepatic glucose output and endogenous glucose production were decreased by 11β-HSD1 inhibition (P < 0.05) due to a reduction in net hepatic glycogenolysis (P < 0.05), with no effect on gluconeogenic flux compared with PBO. In addition, glucose utilization (P < 0.05) and the suppression of lipolysis were increased (P < 0.05) in HSD-I compared with PBO. These data suggest that inhibition of 11β-HSD1 may be of therapeutic value in the treatment of diseases characterized by insulin resistance and excessive hepatic glucose production.

Evidence that autonomic mechanisms contribute to the adaptive increase in insulin secretion during dexamethasone-induced insulin resistance in humans

AIMS/HYPOTHESIS

This study examined whether autonomic mechanisms contribute to adaptively increased insulin secretion in insulin-resistant humans, as has been proposed from studies in animals.

METHODS

Insulin secretion was evaluated before and after induction of insulin resistance with or without interruption of neural transmission. Insulin resistance was induced by dexamethasone (15 mg given over 3 days) in nine healthy women (age 67 years, BMI 25.2+/-3.4 kg/m(2), fasting glucose 5.1+/-0.4 mmol/l, fasting insulin 46+/-6 pmol/l). Insulin secretion was evaluated as the insulin response to intravenous arginine (5 g) injected at fasting glucose and after raising glucose to 13 to 15 mmol/l or to >28 mmol/l. Neural transmission across the ganglia was interrupted by infusion of trimethaphan (0.3-0.6 mg kg(-1) min(-1)).

RESULTS

As an indication of insulin resistance, dexamethasone increased fasting insulin (to 75+/-8 pmol/l, p<0.001) without significantly affecting fasting glucose. Arginine-induced insulin secretion was increased by dexamethasone at all glucose levels (by 64+/-12% at fasting glucose, by 80+/-19% at 13-15 mmol glucose and by 43+/-12% at >28 mmol glucose; p <0.001 for all). During dexamethasone-induced insulin resistance, trimethaphan reduced the insulin response to arginine at all three glucose levels. The augmentation of the arginine-induced insulin responses by dexamethasone-induced insulin resistance was reduced by trimethaphan by 48+/-6% at fasting glucose, 61+/-8% at 13-15 mmol/l glucose and 62+/-8% at >28 mmol/l glucose (p<0.001 for all). In contrast, trimethaphan did not affect insulin secretion before dexamethasone was given.

CONCLUSIONS/INTERPRETATIONS

Autonomic mechanisms contribute to the adaptative increase in insulin secretion in dexamethasone-induced insulin resistance in healthy participants.

Serum glucose, insulin and C-peptide response to oral glucose after intravenous administration of hydrocortisone and methylprednisolone in man

Glucocorticoid-induced glucose intolerance and insulin resistance are dependent on the type of steroid, its dose and route of administration. Although the intravenous (i.v.) route is used mainly, the effects of different steroids have so far been compared using the oral route. The present study was therefore planned to compare the effects on glucose metabolism of hydrocortisone (HC) and methylprednisolone (MP) administered i.v. at equivalent antiinflammatory doses in healthy subjects. Eighteen healthy volunteers with normal glucose tolerance, divided into three groups (A,B,C) matched for age, sex and body mass index were subjected to oral glucose tolerance tests (oGTT) 12 h after HC or MP i.v. injection. The two tests were performed at a 1-month interval and in random sequence. Group A received low doses (HC 100 mg, MP 20 mg), group B intermediate doses (HC 200 mg, MP 40 mg) and group C high doses (HC 400 mg, MP 80 mg). Serum glucose, insulin and C-peptide were measured during both fasting and oGTT. Serum glucose values were not significantly different after HC or MP, during both fasting and oGTT. However, there was a positive correlation between fasting serum glucose or the area under the glucose curve and the dose.kg-1 body weight of HC (r = 0.748; r = 0.462) and MP (r = 0.708; r = 0.736). Serum insulin values were significantly higher after MP than after HC when fasting (A: 115 vs 223; B: 95 vs 215, C: 158 vs 268 pmol.l-1) and as area under the oGTT curve (A: 57.8 vs 87; B: 48.5 vs 92.1; C:57.8 vs 94.5 pmol.l-1 x 2 h).(ABSTRACT TRUNCATED AT 250 WORDS)

Change in glucose metabolism after long-term treatment with deflazacort and betamethasone

We have compared the long-term effects of different corticosteroids on glucose metabolism by carrying out a 75 g oral glucose tolerance test in 27 subjects before and after the administration of deflazacort or betamethasone for two months in random balanced sequence. Fasting plasma glucose and insulin concentrations were significantly higher after betamethasone, whereas deflazacort increased only fasting plasma insulin. After oral glucose there were significant increases in blood glucose and insulin after betamethasone compared with deflazacort. These results suggest that the degree of glucose intolerance and insulin resistance depends on the steroid used and on the dose given, although long-term treatment with deflazacort has a smaller effect on glucose metabolism than betamethasone.

Insulin action and insulin binding following pancreas transplantation

Insulin action and insulin specific binding to erythrocytes were examined in ten recipients of a pancreatic segment and renal graft (Group 1), in nine non-diabetic kidney recipients (Group 2) and in ten age- and weight-matched healthy control subjects (Group 3). All transplant recipients were normoglycaemic without need of insulin, received the same immunosuppression and had good renal graft function at 11-18 months post-transplantation, when the investigation was performed. Using the insulin clamp technique, insulin action was expressed as the metabolic clearance rate of glucose at insulin infusion rates of 1.0 (MCRsubmax) and 10.0 (MCRmax) mU.kg-1.min-1. In comparison with the healthy control subjects, fasting free insulin and C-peptide levels were significantly higher in Groups 1 and 2, but no differences between Groups 1 and 2 were found (p greater than 0.05). Mean values +/- SEM of MCRsubmax in Groups 1, 2 and 3 were 6.30 +/- 0.55, 6.09 +/- 0.69 and 10.52 +/- 1.10 ml.kg-1.min-1 respectively, and of MCRmax 12.65 +/- 0.78, 13.14 +/- 0.92 and 19.28 +/- 1.42 ml.kg-1.min-1 respectively. Insulin action was significantly decreased in Groups 1 and 2 at the low as well as the high insulin infusion rates but there was no difference between the two groups of recipients (p greater than 0.05). No differences in binding data (specific binding, number of binding sites per cell) were found. It is concluded that insulin resistance is common to all immunosuppressed organ recipient and is not related to the pancreas graft. The decrease maximal response to insulin and normal insulin binding to erythrocytes tend to suggest a post-receptor defect in insulin action.

Equine laminitis--another hypothesis for pathogenesis

Laminitis is an important condition in horses and ponies, not just because of the seriousness of the clinical signs and systemic changes involved, but because of the potentially poor prognosis and likelihood of recurrence. Laminitis is particularly prevalent in ponies and involves a multiplicity of aetiological factors. Fat ponies and those having previously suffered laminitis were found to be far more intolerant to oral glucose loading (1 g/kg bwt) than normal ponies or Standardbred horses. These ponies also exhibited a far greater response in plasma insulin levels after glucose loading. Insulin response tests (0.4 iu/kg bwt insulin intravenously) showed only a minimal and very protracted response in both the fat and laminitic ponies establishing the existence of an apparently innate insulin insensitivity in these animals. These findings are important in regulation of carbohydrate and lipid metabolism and play a role in the pathogenesis of laminitis. The reduction of insulin effectiveness leads to elevation in thromboxane A2 activity, predisposing the animal to peripheral vasoconstriction, compromisation of blood flow to the foot and the development of laminitis.

Dexamethasone effects on creatine kinase activity and insulin-like growth factor receptors in cultured muscle cells

We examined the effects of dexamethasone on creatine kinase (CK) activity and insulin-like growth factor I (IGF-I) binding in two skeletal muscle-derived cell lines (mouse, C2C12; rat, L6) and in one cardiac muscle-derived cell line (rat, H9c2). Dexamethasone treatment during differentiation of cultured cells caused a dose-dependent increase in CK activity as well as an increase in the degree of myotube formation in C2C12 and L6, whereas H9c2 cells did not exhibit significant CK activities during culture or dexamethasone treatment. Dexamethasone treatment of C2C12 did not stimulate proliferation in differentiating cultures, but a dose-dependent increase in the number of nuclei was observed for L6 concomitant with increased CK activity. In L6 the increased CK activity may therefore reflect a dose-dependent increase in proliferation. Short-term (48 hr) treatment of C2C12 with dexamethasone (20 nM) did not appear to alter myoblast fusion but reversibly increased CK activity. In C2C12 the observed increase in CK, alanine aminotransferase (ALT), and aspartate aminotransferase (AST) activities with dexamethasone treatment suggest modulation of protein expression and/or turnover. Although the data for dexamethasone effects on CK activities varied in each of the cell lines, consistent behavior was observed in all three cell lines when IGF-I binding was examined. IGF-I binding to dexamethasone-treated cells (50 nM for 24 hr the day prior to confluence) resulted in an increased number of available binding sites, with no effect on the binding affinities. Affinity cross linking and autoradiography indicated that the increase in IGF-I binding was the result of dexamethasone up-regulation of type I IGF receptors. Our data for all three muscle cell lines suggest that similar heterologous hormone receptor modulation of type I IGF receptor sites occurs with dexamethasone treatment.

Increased insulin binding of erythrocytes and insulin sensitivity in adrenal insufficiency

We have studied 125I-insulin binding to erythrocytes (RBC) in five patients with hypoadrenocortisolism, and compared to 17 normal subjects and in nine patients with Cushing's syndrome. In another study insulin sensitivity index (ISI) was measured by the IV insulin tolerance test in four patients with hypoadrenocortisolism (1.82 +/- 0.15 mg/dL/min), and compared to 19 normal subjects and 23 patients with Cushing's syndrome (1.56 +/- 0.1 mg/min/dL). Mean insulin binding in hypocortisolism was 17.9 +/- 0.7%, and was significantly higher (P less than .01) than in normal subjects (12.0 +/- 1.4%) and was significantly (P less than .001) decreased toward normal (11.8 +/- 1.47) during replacement therapy. Increased binding in untreated hypoadrenocortisolism was due to elevated high affinity site receptor concentration as compared to the treated patients (0.10 +/- 0.015 v 0.053 +/- 0.003 nmol/L,P less than .01). These results suggest that increased insulin binding in chronic hypoadrenocortisolism may be attributed to increased insulin binding to the receptor, which can revert to normal by replacement therapy. The role of increased insulin binding to increased insulin sensitivity in hypoadrenocortisolism is discussed.

Decreased insulin binding and antilipolytic response in adipocytes from patients with Cushing's syndrome

Human adipocytes from patients with chronic endogenous hypercortisolism (Cushing's syndrome) showed a statistically significant decrease in insulin binding at low unlabelled-insulin concentrations but no change in receptor numbers (Cushing's 180,000 +/- 48,000 (3) receptors/cell and controls 189,000 +/- 30,000 (7)) together with a fourfold decrease in apparent receptor affinity (ED50: Cushing's 2.25 x 10(-9) M and controls 0.57 x 10(-9) M) and a decreased sensitivity to the antilipolytic effect of insulin. These events could represent the final situation of a chronic and endogenous regulation by high levels of cortisol of insulin receptors in human adipose tissue.

Effects of gluconeogenic hormones on insulin binding in intact human red blood cells

The effects of gluconeogenic hormones, adrenaline and cortisol, on insulin binding were studied in intact human red blood cells. Insulin binding was significantly decreased when red blood cells were preincubated with 1.0 microgram . ml-1 adrenaline or cortisol respectively. The Scatchard plot suggested that this was due to a decrease in surface receptor concentration. Furthermore, it showed that adrenaline also increased insulin receptor affinity. The negative co-operativity affinity profile demonstrated that adrenaline caused a rise in only the upper limit average affinity, Ki, of the insulin receptor.

Characterization of differences in insulin receptors from young and old red blood cells

It has been demonstrated that young RBCs (reticulocytes and early mature erythrocytes) possess more insulin receptors than old RBCs (late mature erythrocytes) but it is not yet known whether insulin receptors on young and old RBCs are regulated similarly. In the present investigation insulin receptors on young and old RBCs have, therefore, been studied in five normal male subjects before and after 2 days dexamethasone ingestion (0.5 mg tablet every 6 h) and, in the same subjects, before and 5 h after ingestion of 75 g glucose. The results obtained clearly demonstrate that dexamethasone increases insulin receptor concentration while glucose ingestion increases both insulin receptor affinity and concentration on young RBCs. By contrast, neither stimuli modify insulin receptors on old RBCs. Studies on RBCs are usually performed on the whole RBC population not taking into account this differential responsiveness of receptors on young versus old RBCs; consequently, this phenomenon might be responsible of the fact that some data reported on RBCs are not in agreement with those reported on monocytes or adipocytes and it should be taken into consideration when using RBCs to evaluate insulin receptor regulation.

Mechanism of hyperglycemia induced by extensive wounds and generalized surgical infection

Significant differences were revealed in the mechanism of hyperglycemia in extensive wounds and generalized surgical infection. Hyperglycemia in extensive burn injuries is caused by the inhibition of insulin formation, decreased insulin binding to cellular receptors, which leads to decreased sensitivity of tissues to insulin. Hyperglycemia developing in generalized infection is a result of insufficient blood insulin levels consequent to inhibition of its secretion (while insulin biosynthesis is elevated) under the effects of hyperproduction of prostaglandins, and is also mediated by defects in insulin-receptor interaction. Correction of carbohydrate metabolism disorders in these surgical pathologies in spite of the different pathogenetic mechanisms might be achieved by exogenous insulin administration, and also by insulin administration together with indomethacin, a nonsteroid anti-inflammatory agent, inhibiting prostaglandin production.

The effect of glucocorticoid on 125I-insulin binding to human erythrocytes. Possible postreceptor modulation of receptor binding

To evaluate the role of insulin receptors in the pathogenesis of insulin resistance observed in glucocorticoid excess, we measured 125I-insulin binding to circulating erythrocytes in 7 patients with Cushing's syndrome and 7 patients with adrenal insufficiency. Insulin receptor binding was higher in Cushing's syndrome and was lower in adrenal insufficiency, compared to normal subjects. Insulin binding decreased after transsphenoidal surgery in 2 patients with Cushing's syndrome. In addition, glucocorticoid treatment in 6 patients with adrenal insufficiency resulted in the increase of insulin binding. The biological significance of this phenomenon must await further investigation, but it does suggest that insulin resistance in glucocorticoid excess should be interpreted as an alteration of cellular mechanisms of insulin at a step distal to the insulin receptor. Increased insulin binding to the receptor is probably modulated by postreceptor events.

Induction of the insulin proreceptor by hydrocortisone in cultured lymphocytes (IM-9 line)

Hydrocortisone increases the number of insulin receptors at the surface of human cultured lymphocytes (IM-9 line) without altering the degradation of the mature receptor subunits. To elucidate the effect of glucocorticoids on the biosynthesis of the insulin receptor of IM-9 cells, we preincubated cells in the presence or absence of hydrocortisone (1.4 X 10(-6) M) and measured the incorporation of radiolabeled sugars into the insulin receptor components. From 6 to 22 h, there was a progressive increase in the incorporation of [3H]mannose into the insulin proreceptor (190,000 mol wt) and the mature subunits (210,000, 135,000, and 95,000 mol wt). The amount incorporated into hydrocortisone-treated cells was always three to four times higher than in control cells, despite no change in cell number, viability, or radioactive sugar pool. To test directly the earliest effect of hydrocortisone, we undertook pulse-chase studies. The incorporation of [3H]mannose into the insulin receptor precursor and the mature subunits was detectable as early as 30 min of chase and was two to three times higher in hydrocortisone-treated cells at any time point of incubation. In both groups, the increase into the proreceptor (190,000 mol wt) peaked by 60 min and decreased rapidly thereafter (half disappearance rate, 45 min); there was a sustained increase of incorporation into the two major mature subunits (135,000 and 95,000 mol wt) throughout the 4-h chase. Hydrocortisone represents the first pharmacologic agent shown to induce the synthesis of the insulin proreceptor. Further, we present a model system designed to study other agents that may act at a very early step in insulin receptor biosynthesis.

Corticosteroids as long-term regulators of the insulin effectiveness in mouse 3T3 adipocytes

Since corticosteroid treatment is often accompanied by insulin resistance, we explored the role of corticosteroids in the regulation of the insulin effectiveness in cultured 3T3 (mouse) adipocytes. Exposure of the fat cells to dexamethasone or corticosterone (0-5 days) induced a time-, concentration-, and protein synthesis-dependent and reversible decrease in insulin binding and in basal and insulin-stimulated 2-deoxyglucose uptake. The decrease in binding (50%) was primarily due to a decrease in receptor affinity i.e. to an increase in the rate of dissociation of insulin from its receptors, and was independent from the effects of pH and temperature on the affinity. The reduction in the 2-deoxyglucose uptake (30-50%) was due to a decrease in the hexose transport capacity rather than to a decrease in the phosphorylation component of the 2-deoxyglucose uptake process. Lineweaver-Burk analysis revealed the dexamethasone induced a decrease in the apparent Vmax of the transport system i.e. in the number or activity of the hexose transporters. The effect of dexamethasone seemed to be superimposed on that of long-term insulin treatment, suggesting a different mechanism. It is concluded that corticosteroids act as long-term regulators of the insulin effectiveness by influencing the rate at which insulin dissociates from its receptors and by altering the number or activity of the hexose transporters by a common mechanism, which differs from that of the long-term regulatory effect of insulin.

Dexamethasone-induced insulin resistance enhances B cell responsiveness to glucose level in normal men

To determine whether islet adaptation during insulin resistance involves increased responsiveness to the level of plasma glucose, insulin resistance was induced in nine normal men by giving dexamethasone (Dex) (3 mg twice daily for 2 days). Plasma insulin and acute insulin responses (AIR) to isoproterenol were measured at three different glucose levels under control and Dex conditions. During Dex there were elevations above control levels of basal glucose (104 +/- 2 vs. 94 +/- 3 mg/dl) and insulin (21 +/- 3 vs. 13 +/- 2 microU/ml, both P less than 0.03). When glucose levels were raised stepwise by matching amounts using glucose clamps, AIR to isoproterenol rose as a linear function of glucose level under both conditions but rose more steeply during Dex. That is, the potentiating effect of glucose (delta AIR/delta glucose) was greater during Dex: 1.3 +/- 0.2 vs. 0.8 +/- 0.2 (P less than 0.01). Similarly, matched increments in glucose level produced greater increments in prestimulus insulin level during Dex (P less than 0.03). We conclude that 48 h of Dex raises the "gain" of the potentiating effect of glucose. Because the direct effect of glucocorticoids on B cell function has been reported to be inhibitory, the observed stimulation is likely to be a result of the insulin resistance caused by Dex.

Developmental changes in insulin receptors of pig red blood cells

Scatchard analysis of the insulin binding to pig reticulocytes, fetal red cells, and adult erythrocytes showed the maximum number of high-affinity binding sites per cell to be 274, 147, and 29, respectively. All three cell types displayed a practically identical dissociation constant of approximately 1.22 X 10(-8) M at the high-affinity region. A long-term in vitro incubation of the fetal red cells and reticulocytes under tissue culture conditions was accompanied by a significant loss of insulin-binding capacity without any appreciable alteration of the dissociation constant. The isolation and characterization of insulin-receptor complexes from these cell types were carried out to establish whether the difference in insulin-binding capacity was due to the difference in the amount of the same species or due to different species of insulin receptors. Membrane proteins were extracted with Triton X-102 and fractionated by DEAE-Sephacel ion-exchange column chromatography. Each peak sample was complexed with 125I-insulin, and the complexes were covalently crosslinked and then applied to a Sepharose CL-6B column. A 95,000-Da complex was obtained from adult pig erythrocyte membranes; 220,000- and and 95,000-Da complex was obtained from adult pig erythrocyte membranes; 220,000- and 95,000-Da complexes from pig reticulocyte membranes; and greater than 600,000-, 220,000-, and 95,000-Da complexes from pig fetal cell membranes. Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis under a nonreducing condition, the 95,000-Da complex was dissociated into a 53,000-Da component; the greater than 600,000-Da complex into greater than 320,000-, 130,000-, and 53,000-Da components; and the 220,000-Da complex was dissociated into 220,000-, 130,000-, and 53,000-Da components. These findings strongly suggest that the decrease in insulin binding during the developmental changes of red blood cells is due to a disappearance of high-molecular-weight insulin receptors rather than a decrease in the amount of the smaller receptor molecules.

Comparison of acute and subacute effects of deflazacort and prednisone on glucose metabolism in man

Corticosteroid treatment produces glucose intolerance with insulin resistance. Recent reports have indicated that deflazacort (DF) is significantly less diabetogenic than prednisone (PN). A euglycaemic hyperinsulinaemic (100 microU/ml) glucose clamp ( EHGC ) and 3H-glucose infusion for 240 min were performed in 6 healthy volunteers (HV) after administration of 15 mg PN or 18 mg DF, 12 h and 2 h before test. The glucose metabolic clearance rate (MCR) was significantly (p = 0.02) higher after DF (4.75 +/- 0.58 ml/min X kg) than after PN (3.31 +/- 0.27 ml/min X kg). Basal hepatic glucose production (HGP) was significantly (p = 0.003) lower after DF (3.58 +/- 0.33 mg/kg X min) than after PN (4.44 +/- 0.23 mg/kg X min). A similar pattern was obtained for glucose volume (GV) and glucose pool (GP). The kinetic parameters of insulin were not significantly different after the two drugs. After 7 day of PN 30 mg/day or DF 36 mg/day, EHGC and 3H-glucose infusion for 240 min were performed in 10 HV. Glucose MCR values were significantly (p = 0.03) higher after DF (5.03 +/- 0.91 ml/min X kg) than after PN (2.80 +/- 0.26 ml/min X kg). HGP values did not different significantly after the two drugs. GV (p = 0.001) and GP (p = 0.002) were significantly lower after DF than after PN. Insulin kinetics were not significantly different after the two drugs. It is concluded that on acute and 7-day administration to healthy subjects DF, in an anti-inflammatory dose equivalent to PN, shows significantly less influence on glucose metabolism.

An in vivo and in vitro study of the mechanism of prednisone-induced insulin resistance in healthy subjects

Prednisone-induced insulin resistance may depend on either reduced sensitivity (receptor defect) or reduced response to insulin (postreceptor defect). To clarify the mechanism of prednisone-induced insulin resistance, a [3H]glucose infusion (1 microCi/min) was performed for 120 min before and during a euglycemic clamp repeated at approximately 100, approximately 1,000, and approximately 10,000 microU/ml steady state plasma insulin concentration in 10 healthy, normal weight subjects, aged 35 +/- 7 yr. Each test was repeated after 7-d administration of placebo or prednisone (15 plus 15 mg/d per subject), in a randomized sequence with an interval of 1 mo between the two tests. Mean fasting blood glucose (89.5 +/- 2.1 vs. 83.7 +/- 1.9 mg/dl) and mean fasting plasma insulin values (17.8 +/- 1.2 vs. 14.3 +/- 0.8 microU/ml) were significantly higher (P less than 0.01) after prednisone. The insulin sensitivity index (glucose metabolic clearance rate in ml/kg per min) was significantly lower (P less than 0.001) after prednisone at all three steady state plasma insulin levels: 2.8 +/- 0.3 vs. 7.4 +/- 1.1 at approximately 100 microU/ml; 6.0 +/- 0.5 vs. 12.2 +/- 1.1 at approximately 1,000 microU/ml; 7.4 +/- 0.6 vs. 14.4 +/- 0.5 at approximately 10,000 microU/ml. Fasting glucose production (in mg/kg per min) was significantly higher after prednisone: 3.7 +/- 0.2 vs. 2.9 +/- 0.2, P less than 0.001. Suppression of glucose production at steady state plasma insulin level of approximately 100 microU/ml was less after prednisone (1.01 +/- 0.35 vs. 0.14 +/- 0.13, NS), and total at approximately 1,000 and approximately 10,000 microU/ml after both prednisone and placebo. The metabolic kinetic parameters of insulin after prednisone were not significantly different from those after placebo. In addition, insulin binding and 3-ortho-methyl-glucose transport were studied in vitro on fat cells from 16 normal-weight surgical candidates aged 40 +/- 8 yr (10 treated with placebo and 6 with prednisone as above). No significant difference was observed with regard to specific insulin binding (tested with 1 ng/ml hormone only), whereas significant transport differences were noted at the basal level (0.40 +/- 0.10 vs. 0.54 +/- 0.12 pmol/10(5) cells, P less than 0.05), and at increasing concentrations up to the maximum stimulation values (5 ng/ml): 0.59 +/- 0.04 vs. 0.92 +/- 0.12 pmol/10(5) cells, P less than 0.005. These results suggest that (a) administration of an anti-inflammatory dose of prednisone for 7 d induces insulin resistance in man; (b) this is more dependent on depressed peripheral glucose utilization than on increased endogenous production; (c) total insulin binding on isolated adipocytes is not significantly affected; (d) insulin resistance is primarily the outcome of postreceptor defect (impaired glucose transport).

Insulin receptors in normal and disease states

The binding of insulin to its receptor has been studied under various physiological and pathological conditions. Quantitative studies have involved human circulating cells such as monocytes and erythrocytes, adipocytes, placental cells, and cultured cells such as fibroblasts and transformed lymphocytes. In animals, other target tissues such as liver and muscle have been studied and correlated with the human studies. Various physiological conditions such as diurnal rhythm, diet, age, exercise and the menstrual cycle affect insulin binding; in addition, many drugs perturb the receptor interaction. Disease affecting the insulin receptor can be divided into five general categories: (1) Receptor regulation--this involves diseases characterized by hyper- or hypoinsulinaemia. Hyperinsulinaemia in the basal state usually leads to receptor 'down' regulation as seen in obesity, type II diabetes, acromegaly and islet cell tumours. Hypoinsulinaemia such as seen in anorexia nervosa or type I diabetes may lead to elevated binding. (2) Antireceptor antibodies--these immunoglobulins bind to the receptor and competitively inhibit insulin binding. They may act as agonists, antagonists or partial agonists. (3) Genetic diseases which produce fixed alterations in both freshly isolated and cultured cells. (4) Diseases of receptor specificity where insulin may bind with different affinity to its own receptor or related receptors such as receptors for insulin-like growth factors. (5) Disease of affinity modulation where physical factors such as pH, temperature, ions, etc. may modify binding. In this review, we have considered primarily abnormality in insulin receptor binding. There are numerous other functions of the receptor such as coupling and transmission of the biological signal. These mechanisms are frequently referred to as postreceptor events, but more properly should be referred to as postbinding events since the receptor subserves other functions in addition to recognition and binding of insulin.

Glucose tolerance, insulin release, and insulin binding to monocytes in kidney transplant recipients

In order to evaluate glucose tolerance following renal transplantation, intravenous glucose tolerance tests (IVGTT), with evaluation of hormonal responses to the intravenous glucose load and percent specific 125I-insulin binding to peripheral blood monocytes, were studied in eight clinically stable kidney transplant recipients. For comparison purposes, identical studies were done in eight control subjects and seven clinically stable hemodialysis patients. One transplant recipient was glucose intolerant, with fasting hyperglycemia, elevated HbA1C, and abnormal glucose decay constant. Impaired pancreatic insulin release appeared to be the major factor accounting for his glucose intolerance. The seven glucose-tolerant transplant recipients had significantly increased insulin release during IVGTT compared to control subjects, and significant correlations were found among insulin release, glucose decay constant, and fasting blood sugar in those patients. Insulin binding to monocytes was significantly greater in transplant recipients than control subjects due to an increase in insulin binding capacity per cell. A significant correlation was found between percent specific 125I-insulin binding and steroid dose, expressed as mg/kg body weight/day, in those patients. Thus, chronic steroid administration does not cause glucose intolerance in transplant recipients who manifest steroid-associated increases in pancreatic insulin release and cellular insulin binding capacity.

Acute effect of prednisone and deflazacort on glucose tolerance in prediabetic subjects

The diabetogenic effect of deflazacort (DF), an oxazolinic synthetic corticosteroid, was studied in 12 healthy adult subjects with a positive family history of diabetes mellitus. Three oral glucose tests (oGTT) were performed at 9.00 a.m., after a 12 h fast, following randomized administration of Placebo (PL), or Deflazacort (DF 36 +36 mg) or Prednisone (PN 30 + 30 mg) 12 and 2 h before the test. Plasma glucose (BG), insulin (IRI), non-esterified fatty acids, (NEFA), total cholesterol (CL), HDL-cholesterol (HDL-CL) and triglycerides (TG) were measured at time 0, and BG, IRI, NEFA were again measured 30, 60, 90 and 120 min after oGTT. PN was followed by a significant increase in BG over the PL values in accordance with the prediabetic state of these subjects, and there was also an increase in IRI values. No change in CL, HDL-CL and TG was found. AFter DF administration, there was a small increase only in BG and IRI over PL values. The differences between DF- PL were not significant, but those between PL-PN and DF-PN were significant at p less than 0.05 (Scheffe's test). The lesser metabolic effect of DF on glucose balance by comparison with PN, as shown by these results, is consistent with previous reports of its lower osteopaenic effect. Thus, DF may be more suitable than PN and similar corticosteroids for corticosteroid therapy in prediabetic and diabetic subjects.