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

Dexamethasone-Induced Mitochondrial Dysfunction and Insulin Resistance-Study in 3T3-L1 Adipocytes and Mitochondria Isolated from Mouse Liver

Dexamethasone is a glucocorticoid analog, which is reported to induce insulin resistance and to exacerbate diabetic symptoms. In this study, we investigated the association between mitochondrial dysfunction and the pathophysiology of dexamethasone-induced insulin resistance. An insulin resistance model in 3T3-L1 adipocyte was established by 48-h treatment of 1 μM dexamethasone, followed with the detection of mitochondrial function. Results showed that dexamethasone impaired insulin-induced glucose uptake and caused mitochondrial dysfunction. Abnormality in mitochondrial function was supported by decreased intracellular ATP and mitochondrial membrane potential (MMP), increased intracellular and mitochondrial reactive oxygen species (ROS) and mtDNA damage. Mitochondrial dynamic changes and biogenesis were suggested by decreased Drp1, increased Mfn2, and decreased PGC-1, NRF1, and TFam, respectively. The mitochondrial DNA (mtDNA) copy number exhibited no change while the mitochondrial mass increased. In agreement, studies in isolated mitochondria from mouse liver also showed dexamethasone-induced reduction of mitochondrial respiratory function, as suggested by decreased mitochondrial respiration controlling rate (RCR), lower MMP, declined ATP synthesis, opening of the mitochondrial permeability transition pore (mPTP), damage of mtDNA, and the accumulation of ROS. In summary, our study suggests that mitochondrial dysfunction occurs along with dexamethasone-induced insulin resistance in 3T3 L1 adipocytes and might be a potential mechanism of dexamethasone-induced insulin resistance.

Impact of Glucocorticoid Excess on Glucose Tolerance: Clinical and Preclinical Evidence

Glucocorticoids (GCs) are steroid hormones that exert important physiological actions on metabolism. Given that GCs also exert potent immunosuppressive and anti-inflammatory actions, synthetic GCs such as prednisolone and dexamethasone were developed for the treatment of autoimmune- and inflammatory-related diseases. The synthetic GCs are undoubtedly efficient in terms of their therapeutic effects, but are accompanied by significant adverse effects on metabolism, specifically glucose metabolism. Glucose intolerance and reductions in insulin sensitivity are among the major concerns related to GC metabolic side effects, which may ultimately progress to type 2 diabetes mellitus. A number of pre-clinical and clinical studies have aimed to understand the repercussions of GCs on glucose metabolism and the possible mechanisms of GC action. This review intends to summarize the main alterations that occur in liver, skeletal muscle, adipose tissue, and pancreatic islets in the context of GC-induced glucose intolerance. For this, both experimental (animals) and clinical studies were selected and, whenever possible, the main cellular mechanisms involved in such GC-side effects were discussed.

Antipsychotics-induced metabolic alterations: focus on adipose tissue and molecular mechanisms

The use of antipsychotic drugs for the treatment of mood disorders and psychosis has increased dramatically over the last decade. Despite its consumption being associated with beneficial neuropsychiatric effects in patients, atypical antipsychotics (which are the most frequently prescribed antipsychotics) use is accompanied by some secondary adverse metabolic effects such as weight gain, dyslipidemia and glucose intolerance. The molecular mechanisms underlying these adverse effects are not fully understood but have been suggested to involve a dysregulation of adipose tissue homeostasis. As such, the aim of this paper is to review and discuss the role of adipose tissue in the development of secondary adverse metabolic effects induced by atypical antipsychotics. Data analyzed in this article suggest that atypical antipsychotics may increase adipose tissue (particularly visceral adipose tissue) lipogenesis, differentiation/hyperplasia, pro-inflammatory mediator secretion and insulin resistance and decrease adipose tissue lipolysis. Consequently, patients receiving antipsychotic medication could be at risk of developing obesity, type 2 diabetes and cardiovascular disease. A better knowledge of the impact of these drugs on adipose tissue homeostasis may unveil strategies to develop novel antipsychotic drugs with less adverse metabolic effects and to develop adjuvant therapies (e.g. behavioral and nutritional therapies) to neuropsychiatric patients receiving antipsychotic medication.

Glucocorticoid treatment and endocrine pancreas function: implications for glucose homeostasis, insulin resistance and diabetes

Glucocorticoids (GCs) are broadly prescribed for numerous pathological conditions because of their anti-inflammatory, antiallergic and immunosuppressive effects, among other actions. Nevertheless, GCs can produce undesired diabetogenic side effects through interactions with the regulation of glucose homeostasis. Under conditions of excess and/or long-term treatment, GCs can induce peripheral insulin resistance (IR) by impairing insulin signalling, which results in reduced glucose disposal and augmented endogenous glucose production. In addition, GCs can promote abdominal obesity, elevate plasma fatty acids and triglycerides, and suppress osteocalcin synthesis in bone tissue. In response to GC-induced peripheral IR and in an attempt to maintain normoglycaemia, pancreatic β-cells undergo several morphofunctional adaptations that result in hyperinsulinaemia. Failure of β-cells to compensate for this situation favours glucose homeostasis disruption, which can result in hyperglycaemia, particularly in susceptible individuals. GC treatment does not only alter pancreatic β-cell function but also affect them by their actions that can lead to hyperglucagonaemia, further contributing to glucose homeostasis imbalance and hyperglycaemia. In addition, the release of other islet hormones, such as somatostatin, amylin and ghrelin, is also affected by GC administration. These undesired GC actions merit further consideration for the design of improved GC therapies without diabetogenic effects. In summary, in this review, we consider the implication of GC treatment on peripheral IR, islet function and glucose homeostasis.

Decreased gene expressions of insulin signal molecules in canine hyperadrenocorticism

Hyperadrenocorticism (HAC) is a common endocrine disorder in dogs, in which excess glucocorticoid causes insulin resistance. Disturbance of insulin action may be caused by multiple factors, including transcriptional modulation of insulin signal molecules which lie downstream of insulin binding to insulin receptors. In this study, gene expressions of insulin signal molecules were examined using neutrophils of the HAC dogs (the untreated dogs and the dogs which had been treated with trilostane). Insulin receptor substrate (IRS)-1, IRS-2, phosphatidylinositol 3-kinase (PI3-K), protein kinase B/Akt kinase (Akt)-2 and protein kinase C (PKC)-lambda were analyzed in the HAC dogs and compared with those from normal dogs. The IRS-1 gene expressions decreased by 37% and 35% of the control dogs in the untreated and treated groups, respectively. The IRS-2 gene expressions decreased by 61% and 72%, the PI3-K gene expressions decreased by 47% and 55%, and the Akt-2 gene expressions decreased by 45% and 56% of the control dogs, similarly. Collectively, gene expressions of insulin signal molecules are suppressed in the HAC dogs, which may partially contribute to the induction of insulin resistance.

Novel views on new-onset diabetes after transplantation: development, prevention and treatment

New-onset diabetes after transplantation (NODAT) is associated with increased risk of allograft failure, cardiovascular disease and mortality, and therefore, jeopardizes the success of renal transplantation. Increased awareness of NODAT and the prediabetic states (impaired fasting glucose and impaired glucose tolerance, IGT) has fostered previous and present recommendations, based on the management of type 2 diabetes mellitus (T2DM). Unfortunately, the idea that NODAT merely resembles T2DM is potentially misleading, because the opportunity to initiate adequate anti-hyperglycaemic treatment early after transplantation might be given away for 'tailored' immunosuppression in patients who have developed NODAT or carry personal risk factors. Risk factor-independent mechanisms, however, seem to render postoperative hyperglycaemia with subsequent development of overt or 'full-blown' NODAT, the unavoidable consequence of the transplant and immunosuppressive process itself, at least in many cases. A proof of the concept that timely preventive intervention with exogenous insulin against post-transplant hyperglycaemia may decrease NODAT was recently provided by a small clinical trial, which is awaiting confirmation from a multicentre study. However, because early insulin therapy aimed at beta-cell protection seems to contrast the currently recommended, stepwise approach of 'watchful waiting' prior to pancreatic decompensation, we here aim at reviewing recent concepts regarding the development, prevention and treatment of NODAT, some of which seem to challenge the traditional view on T2DM and NODAT. In summary, we suggest a novel, risk factor-independent management approach to NODAT, which includes glycaemic monitoring and anti-hyperglycaemic treatment in virtually everybody after transplantation. This approach has widespread implications for future research and is intended to tackle NODAT and also ultimately cardiovascular disease.

Transplant-associated hyperglycemia

As patient survival after solid organ transplantation continues to improve, comorbidites associated with chronic hyperglycemia will assume increasing importance in limiting outcomes and quality of life. New-onset diabetes mellitus commonly occurs in the posttransplant setting and is associated with multiple complications including graft loss, cardiovascular disease, infection, and death. Furthermore, recent studies have begun to highlight the very high posttransplant prevalence and the significant cardiovascular implications of the prediabetic states of impaired fasting glucose and impaired glucose tolerance, indicating that the overall burden of transplantation-associated hyperglycemia is far greater than previously appreciated. Shared and distinct pathogenic factors and clinical repercussions exist among the organ-specific transplant scenarios. Diabetogenic immunosuppressive agents are common to all organ transplant settings, whereas glucose regulation is also strained by the restoration of failed hepatic and renal function. The atherogenic properties of hyperglycemia are particularly significant in the kidney transplant population, which has a marked predisposition to cardiovascular disease, whereas accelerated cardiac allograft vasculopathy and liver fibrosis have been associated with hyperglycemia in the heart and liver transplant settings, respectively. Aggressive screening will effectively detect transplant-associated hyperglycemia, whereas risk factor modification, lifestyle intervention and, where appropriate, drug therapy, may decrease its impact. Topics of future investigation should include the use of emerging diabetes therapies and avenues for the prevention and reversal of transplant-associated hyperglycemia.

Transplant-associated hyperglycemia: a new look at an old problem

New-onset diabetes has long been recognized as a common complication of kidney transplantation, promoting cardiovascular disease, death, and graft failure. Studies in recent years have begun to highlight the very high posttransplantation prevalence of the prediabetic states of impaired fasting glucose and impaired glucose tolerance and the significant repercussions of these states on cardiovascular health. Therefore, the overall burden of transplant-associated hyperglycemia (TAH), which encompasses new-onset diabetes and the prediabetic states, is far greater than previously appreciated. The kidney transplant population is predisposed to insulin resistance and to additional insults of hypertension and hyperlipidemia that, together with hyperglycemia, compose the metabolic syndrome and promote atherosclerosis. When recipients with an underlying, frequently nonmodifiable predisposition to glucose dysregulation encounter transplant-specific, often modifiable, diabetogenic exposures, TAH manifests. Aggressive screening will effectively detect TAH, whereas risk factor modification, lifestyle intervention, and, when appropriate, drug therapy may decrease its impact. Topics of future investigation should include the use of emerging diabetes therapies and avenues for the prevention and reversal of TAH.

In vivo effects of corticotropin-releasing hormone on femoral adipose tissue metabolism in women

OBJECTIVE

To investigate whether i.v. injected corticotropin-releasing hormone (CRH) (1 microg/kg) has a direct effect on adipose tissue metabolism in humans.

DESIGN

Double-blinded, placebo-controlled, crossover study.

SUBJECTS

Twelve healthy normal weight female volunteers (age 20-37 years, body mass index: 22.75+/-1.33 kg/m(2))

MEASUREMENTS

Assessment of local generation of glycerol, and glucose in adipose tissue by microdialysis. Measurement of adipose tissue and skin blood flow by laser Doppler flowmetry.

RESULTS

Injection of CRH acutely increases interstitial concentrations of glycerol (19.0+/-5.4%, P<0.05) and glucose (13.5+/-5.8%, P<0.05) reaching peak levels after 15 min. Plasma glycerol increases in parallel (Delta=16.7+/-5.9% after 15 min (P<0.05)), whereas plasma glucose remains unaffected. Changes in tissue blood flow do not explain interstitial metabolite alterations. Initial CRH effects on adipose tissue metabolism are short lasting and disappear after 15 min.

CONCLUSIONS

The importance of CRH on human energy metabolism is underlined by the present in vivo study demonstrating peptidergic effects on lipolysis and glucose homeostasis in human subcutaneous adipose tissue.

Relationship between visceral adiposity and intramyocellular lipid content in two rat models of insulin resistance

High visceral adiposity and intramyocellular lipid levels (IMCL) are both associated with the development of type 2 diabetes. The relationship between visceral adiposity and IMCL levels was explored in diet- and glucocorticoid-induced models of insulin resistance. In the diet-induced model, lean and fa/fa Zucker rats were fed either normal or high-fat (HF) chow over 4 wk. Fat distribution, IMCL content in the tibialis anterior (TA) muscle (IMCL(TA)), and whole body insulin resistance were measured before and after the 4-wk period. The HF diet-induced increase in IMCL(TA) was strongly correlated with visceral fat accumulation and greater glucose intolerance in both groups. The increase in IMCL(TA) to visceral fat accumulation was threefold greater for fa/fa rats. In the glucocorticoid-induced model, insulin sensitivity was impaired with dexamethasone. In vivo adiposity and IMCL(TA) content measurements were combined with ex vivo analysis of plasma and muscle tissue. Dexamethasone treatment had minimal effects on visceral fat accumulation while increasing IMCL(TA) levels approximately 30% (P < 0.05) compared with controls. Dexamethasone increased plasma glucose by twofold and increased the saturated fatty acid content of plasma lipids [fatty acid (CH2)n/omegaCH3 ratio +15%, P < 0.05]. The lipid composition of the TA muscle was unchanged by dexamethasone treatment, indicating that the relative increase in IMCL(TA) observed in vivo resulted from a decrease in lipid oxidation. Visceral adiposity may influence IMCL accumulation in the context of dietary manipulations; however, a "causal" relationship still remains to be determined. Dexamethasone-induced insulin resistance likely operates under a different mechanism, i.e., independently of visceral adiposity.

Metabolic syndrome without obesity: Hepatic overexpression of 11beta-hydroxysteroid dehydrogenase type 1 in transgenic mice

In obese humans and rodents there is increased expression of the key glucocorticoid (GC) regenerating enzyme, 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1), in adipose tissue. This increased expression appears to be of pathogenic importance because transgenic mice overexpressing 11beta-HSD1 selectively in adipose tissue exhibit a full metabolic syndrome with visceral obesity, dyslipidemia, insulin-resistant diabetes, and hypertension. In this model, while systemic plasma GC levels are unaltered, GC delivery to the liver via the portal vein is increased. 11beta-HSD1 is most highly expressed in liver where inhibition or deficiency of its activity improves glucose and lipid homeostasis. To determine the potential contribution of elevated intrahepatic GCs alone toward development of insulin-resistant syndromes we generated transgenic mice expressing increased 11beta-HSD1 activity selectively in the liver under transcriptional control of hepatic regulatory sequences derived from the human apoE gene (apoE-HSD1). Transgenic lines with 2- and 5-fold-elevated 11beta-HSD1 activity exhibited mild insulin resistance without altered fat depot mass. ApoE-HSD1 transgenic mice exhibited fatty liver and dyslipidemia with increased hepatic lipid synthesis/flux associated with elevated hepatic LXRalpha and PPARalpha mRNA levels as well as impaired hepatic lipid clearance. Further, apoE-HSD1 transgenic mice have a marked, transgene-dose-associated hypertension paralleled by incrementally increased liver angiotensinogen expression. These data suggest that elevated hepatic expression of 11beta-HSD1 may relate to the pathogenesis of specific fatty liver, insulin-resistant, and hypertensive syndromes without obesity in humans as may occur in, for example, myotonic dystrophy, and possibly, the metabolically obese, normal-weight individual.

Neuroendocrinology of insulin resistance: metabolic and endocrine aspects of adiposity

Abdominal obesity is a major risk factor to attract the insulin resistance syndrome. It is proposed that abdominal obesity exposes the liver to elevated levels of free fatty acids, which activate a neuroendocrine reflex, leading to increased circulating levels of glucocorticoids. Besides directly attenuating peripheral insulin signaling, glucocorticoids oppose the activity of central nervous regulatory systems that stimulate insulin action. Among the factors that promote insulin action is leptin. Leptin regulates peripheral fuel partitioning and insulin action mainly through hypothalamic neuronal networks, which in turn, regulate endocrine activity of adipose tissue in a way comparable to thiazolidinediones. These are a class of insulin-sensitizing drugs, which exert their antidiabetic effects through the gamma isoform of peroxisome proliferator-activated receptor (PPAR-gamma). Since glucocorticoids oppose leptin action at several levels of control (including the central nervous system, CNS), it is argued that subjects easily develop obesity and associated metabolic disorders.

Subsensitivity to insulin in adipocytes from rats submitted to foot-shock stress

We examined the effect of three daily foot-shock stress sessions on glucose homeostasis, insulin secretion by isolated pancreatic islets, insulin sensitivity of white adipocytes, and glycogen stores in the liver and soleus muscle of rats. Stressed rats had plasma glucose (128.3 ± 22.9 mg/dL) and insulin (1.09 ± 0.33 ng/mL) levels higher than the controls (glucose, 73.8 ± 3.5 mg/dL; insulin, 0.53 ± 0.11 ng/mL, ANOVA plus Fisher's test; p < 0.05). After a glucose overload, the plasma glucose, but not insulin, levels remained higher (area under the curve 8.19 ± 1.03 vs. 4.84 ± 1.33 g/dL 30 min and 102.7 ± 12.2 vs. 93.2 ± 16.1 ng/mL 30 min, respectively). Although, the area under the insulin curve was higher in stressed (72.8 ± 9.8 ng/mL) rats than in control rats (34.9 ± 6.9 ng/mL) in the initial 10 min after glucose overload. The insulin release stimulated by glucose in pancreatic islets was not modified after stress. Adipocytes basal lipolysis was higher (stressed, 1.03 ± 0.14; control, 0.69 ± 0.11 µmol of glycerol in 60 min/100 mg of total lipids) but maximal lipolysis stimulated by norepinephrine was not different (stressed, 1.82 ± 0.35; control, 1.46 ± 0.09 µmol of glycerol in 60 min/100 mg of total lipids) after stress. Insulin dose-dependently inhibited the lipolytic response to norepinephrine by up to 35% in adipocytes from control rats but had no effect on adipocytes from stressed rats. The liver glycogen content was unaltered by stress, but was lower in soleus muscle from stressed rats than in control rats (0.45 ± 0.04 vs. 0.35 ± 0.04 mg/100 mg of wet tissue). These results suggest that rats submitted to foot-shock stress develop hyperglycemia along with hyperinsulinemia as a consequence of insulin subsensitivity in adipose tissue, with no alteration in the pancreatic sensitivity to glucose. Foot-shock stress may therefore provide a useful short-term model of insulin subsensitivity.Key words: glucose tolerance test, white adipocytes, lipolysis, pancreatic islets, insulin release, soleus muscle, liver glycogen.

Humoral regulation of resistin expression in 3T3-L1 and mouse adipose cells

Resistin is a hormone secreted by adipocytes that acts on skeletal muscle myocytes, hepatocytes, and adipocytes themselves, reducing their sensitivity to insulin. In the present study, we investigated how the expression of resistin is affected by glucose and by mediators known to affect insulin sensitivity, including insulin, dexamethasone, tumor necrosis factor-alpha (TNF-alpha), epinephrine, and somatropin. We found that resistin expression in 3T3-L1 adipocytes was significantly upregulated by high glucose concentrations and was suppressed by insulin. Dexamethasone increased expression of both resistin mRNA and protein 2.5- to 3.5-fold in 3T3-L1 adipocytes and by approximately 70% in white adipose tissue from mice. In contrast, treatment with troglitazone, a thiazolidinedione antihyperglycemic agent, or TNF-alpha suppressed resistin expression by approximately 80%. Epinephrine and somatropin were both moderately inhibitory, reducing expression of both the transcript and the protein by 30-50% in 3T3-L1 adipocytes. Taken together, these data make it clear that resistin expression is regulated by a variety of hormones and that cytokines are related to glucose metabolism. Furthermore, they suggest that these factors affect insulin sensitivity and fat tissue mass in part by altering the expression and eventual secretion of resistin from adipose cells.

Insulin resistance, impaired glucose tolerance and non-insulin-dependent diabetes, pathologic mechanisms and treatment: current status and therapeutic possibilities

Impaired glucose tolerance and non-insulin-dependent diabetes (NIDDM) are the pathologic consequence of two co-incident and interacting conditions, namely insulin resistance and relative insulin deficiency. Recognised by the World Health Authority as a global health problem there are at 1995 estimates at least 110 million diagnosed diabetics world wide with at least the same number undiagnosed. Diabetes is the 4th leading cause of death in developed countries and its management exerts a vast economic and social burden. Insulin resistance is established as the characteristic pathologic feature of patients with glucose intolerance and NIDDM describing a state in which insulin stimulated glucose uptake and utilisation in liver, skeletal muscle and adipose tissue is impaired and coupled to impaired suppression of hepatic glucose output. Although the biochemical mechanisms underpinning both defects are becoming better understood, the genetic and molecular causes remain elusive; and whether insulin resistance or relative insulin deficiency represents the primary defect in patients with NIDDM is the matter of some debate. In this article we review the biochemical and molecular nature of the defects in insulin sensitivity and glucose uptake, and discuss some of the potential causative mechanisms. The genetic and environmental basis of insulin resistance is reviewed and presented, and potential therapeutic targets including thiazolidinediones are discussed.

DHEA improves glucose uptake via activations of protein kinase C and phosphatidylinositol 3-kinase

We have examined the effect of adrenal androgen, dehydroepiandrosterone (DHEA), on glucose uptake, phosphatidylinositol (PI) 3-kinase, and protein kinase C (PKC) activity in rat adipocytes. DHEA (1 microM) provoked a twofold increase in 2-[3H]deoxyglucose (DG) uptake for 30 min. Pretreatment with DHEA increased insulin-induced 2-[3H]DG uptake without alterations of insulin specific binding and autophosphorylation of insulin receptor. DHEA also stimulated PI 3-kinase activity. [3H]DHEA bound to purified PKC containing PKC-alpha, -beta, and -gamma. DHEA provoked the translocation of PKC-beta and -zeta from the cytosol to the membrane in rat adipocytes. These results suggest that DHEA stimulates both PI 3-kinase and PKCs and subsequently stimulates glucose uptake. Moreover, to clarify the in vivo effect of DHEA on Goto-Kakizaki (GK) and Otsuka Long-Evans fatty (OLETF) rats, animal models of non-insulin-dependent diabetes mellitus (NIDDM) were treated with 0.4% DHEA for 2 wk. Insulin- and 12-O-tetradecanoyl phorbol-13-acetate-induced 2-[3H]DG uptakes of adipocytes were significantly increased, but there was no significant increase in the soleus muscles in DHEA-treated GK/Wistar or OLETF/Long-Evans Tokushima (LETO) rats when compared with untreated GK/Wistar or OLETF/LETO rats. These results indicate that in vivo DHEA treatment can result in increased insulin-induced glucose uptake in two different NIDDM rat models.

Effect of glucocorticoid receptor antagonist RU 38486 on acute glucocorticoid-induced insulin resistance in rat adipocytes

We examined the mechanism of acute glucocorticoid-induced insulin resistance in rat adipocytes using the glucocorticoid receptor antagonist RU 38486. Pretreatment with dexamethasone (DEX) and prednisolone for 60 minutes resulted in 50% inhibition of insulin-induced [3H]2-deoxyglucose (DOG) uptake at 10(-8) and 10(-7) mol/L, respectively, in rat adipocytes and 20% and 25% inhibition of insulin-induced [3H]2-DOG uptake, respectively, in soleus muscles. Our previous experiments indicated that DEX and prednisolone alone stimulate protein kinase C (PKC) in rat adipocytes. Accordingly, we examined [3H]DEX binding to PKC from MonoQ column-purified rat brain cytosol. Specific [3H]DEX binding to MonoQ column-purified PKC was observed (kd, 56.8 nmol/L; Bmax, 725 fmol/mg protein). Thus, insulin-induced PKC translocation from the cytosol to the membrane was suppressed by pretreatment with 10(-7) mol/L DEX and 10(-6) mol/L prednisolone for 80 minutes. During treatment with RU 38486 for 60 minutes, there was no change in the glucocorticoid-induced inhibitory effect on insulin-induced [3H]2-DOG uptake and PKC translocation from the cytosol to the membrane. Moreover, pretreatment with RU 38486 for 120 minutes slightly prevented the DEX-mediated inhibition of insulin-induced glucose uptake. These results suggest that acute glucocorticoid-induced insulin resistance may be mainly mediated through the other non-glucocorticoid receptor pathway.

Effect of lipectomy and long-term dexamethasone on visceral fat and metabolic variables in rats

Intraperitoneal (IP) fat accumulation in humans is a risk factor for a number of diseases. We tried to increase this particular adipose mass in rats by long-term administration of low-dose dexamethasone (Dex) and/or elimination of other fat depots. Male adult Wistar rats were lipectomized (Lip) or sham-operated (Sh). Bilateral lipectomy of retroperitoneal and inguinal fat pads was performed under anesthesia with Na pentobarbital 40 mg/kg supplemented with ether. After 8 days, half the animals of each group received Dex in their drinking water (0.1 microgram/mL) while the other half received water (W), for a total of four groups: Sh-W, Lip-W, Sh-Dex, and Lip-Dex. Body weight (BW) and food and water intake were measured throughout the treatment period. A glucose tolerance test was performed 34 days after starting Dex treatment, and then rats were killed, fat depots were weighed, and plasma and liver were obtained for metabolic determinations. Dex rats ate the same amount of food as W controls, but gained significantly less weight (2.02 +/- 0.18 v 3.82 +/- 0.10 g/d, P < .01). Mean daily W intake was approximately 40 mL/d in all groups, which means that Dex rats ingested approximately 4 micrograms/d Dex. Average glycemic values during the 180-minute glucose tolerance test were as follows: Sh-W, 162 +/- 13; Lip-W, 166 +/- 7; Sh-Dex, 118 +/- 6; and Lip-Dex, 229 +/- 27 mg/dL. These values show that glucose tolerance was improved by Dex treatment alone, but was impaired in Lip-Dex animals. The same trend was evident for the relative weights (percent of BW) of two intact adipose depots: IP and epididymal (EPI) (Sh-W, 2.08 +/- 0.13 and 1.35 +/- 0.11, respectively; Lip-W, 1.67 +/- 0.15 and 1.17 +/- 0.11; Sh-Dex, 1.66 +/- 0.10 and 1.28 +/- 0.07; Lip-Dex, 2.41 +/- 0.11 and 1.53 +/- 0.09). Average glycemia for all rats was significantly correlated with IP (r = .55, P < .01) but not with EPI; moreover it was correlated in the Sh-W control group (r = .81, P < .05), suggesting a normal relation between these variables. Liver triglycerides (LTG), which were elevated in Dex rats, were also correlated with IP (r = .51, P < .02 for all rats and r = .82, P < .05 for Sh-W rats). The results show that long-term administration of low-dose Dex has some different effects in normal versus Lip rats concerning mainly the IP fat depot, the relative mass of which seems to significantly affect glucose tolerance.

Glucocorticoids and insulin but not growth hormone modulate insulin binding to adipocyte membranes from sheep

Mechanisms by which the glucocorticoid analogue dexamethasone and growth hormone modulate insulin action in sheep adipose tissue have been investigated. Maintenance of sheep adipose tissue in culture for 48 hr in the absence of exogenous hormones resulted in a decrease in insulin binding to adipocyte membranes; this was prevented by the inclusion of 10 nM dexamethasone during culture. Tissue culture for 48 hr with insulin itself decreased insulin binding to adipocyte membranes, whereas tissue culture with growth hormone had no effect on insulin binding. Neither dexamethasone nor growth hormone altered the ability of insulin to decrease insulin binding to its receptor. The study shows that the insulin-antagonistic effects of growth hormone on sheep adipose tissue metabolism are due to an effect subsequent to insulin binding to its receptor, whereas some of the effects of dexamethasone may be due to an increase in the insulin-binding capacity of membranes.

Effect of dexamethasone and prednisolone on insulin-induced activation of protein kinase C in rat adipocytes and soleus muscles

We examined the effect of glucocorticoids on [3H]2-deoxyglucose ([3H]2-DOG) uptake, [125I]insulin binding, tyrosine kinase activity, and protein kinase C (PKC) activity in rat adipocytes and soleus muscles. In adipocytes, insulin-stimulated [3H]2-DOG uptake was decreased by prior 60-minute treatment with dexamethasone (DEX) or prednisolone (PSL), whereas [125I]insulin binding, insulin (INS) receptor autophosphorylation, and tyrosine kinase activity, as measured using exogenous substrate of poly(Glu80-Tyr20), were not significantly changed. Cytosolic PKC activity decreased and membrane-associated PKC activity increased during a 60-minute treatment of adipocytes and soleus muscles with DEX or PSL, indicating that both DEX and PSL stimulate the translocation and activation of PKC. However, pretreatment of adipocytes and soleus muscles with glucocorticoids resulted in reduced INS-stimulated translocation of PKC from cytosol to membrane. INS-induced decreases in cytosolic PKC activity (50% +/- 7% v 10% +/- 8% and 20% +/- 7%, P < .05 to .01, for nonpretreated [control], DEX pretreated, and PSL pretreated cells) and increases in membrane PKC (100% +/- 10% v 50% +/- 9% and 20% +/- 9%, P < .01, for control, DEX pretreated, and PSL pretreated cells) were larger in nonpretreated adipocytes than in adipocytes pretreated with glucocorticoids. These results raise the possibility that glucocorticoids, namely, DEX and PSL, stimulate the translocation and subsequent degradative downregulation of PKC, and that this may be pertinent to their inhibitory effects on INS-stimulated glucose transport.

Effect of glucocorticoid replacement therapy on glucose tolerance and intermediary metabolites in hypopituitary adults

BACKGROUND AND OBJECTIVES

Excess impaired glucose tolerance and diabetes mellitus have been reported in hypopituitary adults on conventional replacement therapy including glucocorticoids. We investigated the effect of the glucocorticoid component on glucose tolerance and intermediary metabolites in hypopituitary adults.

DESIGN

A 3-hour 75-g oral glucose tolerance test (OGTT) was performed on two study days, at least one week apart. On one study day, the glucocorticoid replacement morning dose was taken 60 minutes before the OGTT, and on the other it was left until after the OGTT. All other pituitary replacement therapies were kept unchanged on the two study days.

PATIENTS

Eight hypopituitary adults (3 males and 5 females; aged 46-76 years) on conventional replacement therapy were studied. Their duration of hypopituitarism was mean (range) 15 (5-31) years. Their mean body mass index (BMI) was 28.4 (24.1-35.1) kg/m2. Their total daily cortisol dose was 26 (15-30) mg.

MEASUREMENTS

Plasma glucose, insulin, non-esterified fatty acids (NEFA), glycerol and 3-hydroxybutyrate were measured at 30-minute intervals and plasma cortisol levels were measured hourly.

RESULTS

Fasting glucose and insulin concentrations were similar on the glucocorticoid day (GD) and the non-glucocorticoid day (NGD) (glucose (mean +/- SD) 4.9 +/- 0.9 vs 4.4 +/- 0.5 mmol/l; insulin (median (range)) 5 (1-17) vs 2 (1-15) mU/l, respectively). Post-glucose glycaemia was higher on the GD than on the NGD with a significantly higher glucose area under the curve (AUC) (45.0 +/- 8.2 vs 38.9 +/- 11.7 mmol/l h, P < 0.05). Post-glucose insulinaemia was also higher on the GD than on the NGD with significantly higher insulin AUC (270 (47-909) vs 207 (46-687) mU/l h, P < 0.02). Impaired glucose tolerance was found in three patients on the GD, one of whom continued to have impaired glucose tolerance on the NGD. The areas under the curves of NEFA, glycerol and 3-hydroxybutyrate were not significantly different on the two days. On the NGD, plasma cortisol levels were undetectable (< 50 nmol/l) in all patients and on the GD the median (range) peak was 500 (330-740) nmol/l dropping to 125 (60-330) nmol/l at 180 minutes. The difference in glucose AUC between the two days correlated with the maximal plasma cortisol levels (Spearman's p = 0.83, P < 0.01).

CONCLUSIONS

Glucocorticoid replacement therapy taken pre-prandially in hypopituitary adults induces mild elevations in circulating glucose and insulin levels even with acceptable plasma cortisol concentrations. Optimal regimens for glucocorticoid replacement require more study.

Modulation of insulin receptor, insulin receptor substrate-1, and phosphatidylinositol 3-kinase in liver and muscle of dexamethasone-treated rats

Insulin rapidly stimulates tyrosine kinase activity of its receptor resulting in phosphorylation of its cytosolic substrate, insulin receptor substrate-1 (IRS-1), which in turn associates with phosphatidylinositol 3-kinase (PI 3-kinase), thus activating the enzyme. Glucocorticoid treatment is known to produce insulin resistance, but the exact molecular mechanism is unknown. In the present study we have examined the levels and phosphorylation state of the insulin receptor and IRS-1, as well as the association/activation between IRS-1 and PI 3-kinase in the liver and muscle of rats treated with dexamethasone. After dexamethasone treatment (1 mg/kg per d for 5 d), there was no change in insulin receptor concentration in liver of rats as determined by immunoblotting with antibody to the COOH-terminus of the receptor. However, insulin stimulation of receptor autophosphorylation determined by immunoblotting with antiphosphotyrosine antibody was reduced by 46.7 +/- 9.1%. IRS-1 and PI 3-kinase protein levels increased in liver of dexamethasone-treated animals by 73 and 25%, respectively (P < 0.05). By contrast, IRS-1 phosphorylation was decreased by 31.3 +/- 10.9% (P < 0.05), and insulin stimulated PI 3-kinase activity in anti-IRS-1 immunoprecipitates was decreased by 79.5 +/- 11.2% (P < 0.02). In muscle, the changes were less dramatic, and often in opposite direction of those observed in liver. Thus, there was no significant change in insulin receptor level or phosphorylation after dexamethasone treatment. IRS-1 and PI 3-kinase levels were decreased to 38.6 and 65.6%, respectively (P < 0.01 and P < 0.05). IRS-1 phosphorylation showed no significant change in muscle, but insulin-stimulated IRS-1 associated PI 3-kinase was decreased by 41%. Thus, dexamethasone has differential effects on the proteins involved in the early steps in insulin action in liver and muscle. In both tissues, dexamethasone treatment results in a reduction in insulin-stimulated IRS-1-associated P I3-kinase, which may play a role in the pathogenesis of insulin resistance at the cellular level in these animals.

Glucocorticoid induction of epinephrine synthesizing enzyme in rat skeletal muscle and insulin resistance

Rat skeletal muscle contains two enzymes which can make epinephrine: phenylethanolamine N-methyltransferase (PNMT) and nonspecific N-methyltransferase. We studied the time-course and mechanism by which the glucocorticoid dexamethasone increases muscle PNMT activity. We also examined the hypothesis that increased muscle E synthesis may contribute to glucocorticoid-induced insulin resistance. Dexamethasone (1 mg/kg s.c. for 12 d) increased muscle PNMT activity seven-fold but did not change NMT activity. Immunotitration with an anti-PNMT antibody indicated that the PNMT elevation was due to increased numbers of PNMT molecules. Dexamethasone rapidly increased PNMT activity and this elevation was largely maintained 6 d after glucocorticoid treatment stopped. Muscle epinephrine levels were transiently elevated by dexamethasone. Dexamethasone-treated rats had elevated insulin levels after a glucose load, and chronic administration of the PNMT inhibitor SKF 64139 reversed this increase. Chronic SKF 64139 improved glucose tolerance in normal rats. Dexamethasone induced muscle synthesis of the epinephrine-forming enzyme PNMT. A PNMT inhibitor lowered insulin levels in glucocorticoid-treated rats and glucose levels in untreated rats. These findings are compatible with antagonism of insulin-mediated glucose uptake by epinephrine synthesized in skeletal muscle.

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.

Dehydroepiandrosterone: Antiglucocorticoid Action in Mice

The acute effect of dehydroepiandrosterone (DHEA) and its conjugate, DHEA-sulfate (DHEA-S) on glucocorticoid action was tested in vivo using male Swiss-Webster mice. The authors found that DHEA and DHEA-S significantly inhibited induction of hepatic tyrosine aminotransferase activity, although the former was more potent. This inhibition was dose- and time-dependent and was not demonstrable with other steroids. The same inhibitory effect of DHEA was seen with kidney tyrosine aminotransferase induction, as well as with liver and kidney ornithine decarboxylase enzyme activity, another glucocorticoid-induced enzyme. The conclusion is that DHEA acts acutely as an antiglucocorticoid and exerts its effect in different glucocorticoid-sensitive systems.

The effects of cortisol on insulin sensitivity in muscle

The effects of cortisol on insulin sensitivity were examined in rats with the euglycaemic, hyperinsulinaemic clamp technique. Uptake of 2-deoxyglucose and incorporation of glucose into glycogen was followed in the white gastrocnemius, extensor digitorum longus, red gastrocnemius and soleus muscles as well as the liver (only glycogen synthesis). Maximal velocity and fractional velocity of the insulin-sensitive part of glycogen synthase (FV %) was measured in the muscles, as well as muscle fibre composition and capillary density. After 24 h exposure to cortisol, insulin sensitivity was diminished in the clamp measurements. This was paralleled by a decrease in glycogen synthesis in the most insulin-sensitive red gastrocnemius and Soleus muscles, but not in the white gastrocnemius or extensor digitorum longus muscles or the liver, and no effect was seen on 2-deoxyglucose uptake in muscles. FV % was markedly inhibited in all muscles. After 48 h exposure to cortisol, glycogen synthesis was markedly inhibited in all muscles, and 2-deoxyglucose uptake in all except the least insulin-sensitive muscle, WG. No changes in muscle morphology were found. These results suggest that the insulin resistance caused by cortisol is elicited in a stepwise manner, starting with an inhibition in the glycogen synthesis system in insulin-sensitive muscles, later including all muscles as well as 2-deoxyglucose uptake. This occurs without changes in morphology.

Evolution of dexamethasone-induced insulin resistance in rats

Glucocorticoids are known to cause insulin resistance and glucose intolerance. Although there have been many studies investigating the mechanism of this effect, several aspects remain to be clarified. The aim of this study was to investigate the evolution and sites of insulin resistance in dexamethasone-treated rats. To achieve this, chronically catheterized nonstressed rats had glucose kinetics measured during an oral glucose tolerance test by means of a double isotope technique. Studies were performed after 6, 48, or 96 h of dexamethasone administration (10 micrograms.rat-1.day-1) and were compared with control rats not treated with the steroid. Total hepatic glucose production (HGP) was increased in the 6-h (166 +/- 8.3, P less than 0.05) and 48-h (198 +/- 21, P less than 0.03) treated groups but not in the 96-h treated rats (140 +/- 8, P = 0.99) compared with the controls (141 +/- 8 mg/55 min). This increased HGP was despite the presence of higher insulin levels in the steroid-treated rats (1,220 +/- 115, P less than 0.09; 1,732 +/- 197, P less than 0.005; 1,567 +/- 107, P less than 0.001 in 6-, 48-, and 96-h treated rats, respectively, compared with 937 +/- 99 mU.l-1 x 55 min-1 in control rats). The metabolic clearance rate of glucose was higher in the dexamethasone-treated rats (200 +/- 14, P less than 0.07; 227 +/- 18, P less than 0.01; 227 +/- 17, P less than 0.01 in 6-, 48-, and 96-h groups, respectively, compared with 165 +/- 10 ml/55 min in control rats).(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin induces a similar reduction in the concentrations of its own receptor and of an insulin-sensitive glycosyl-phosphatidylinositol in isolated rat hepatocytes

We have used isolated rat hepatocytes to study whether the insulin-induced reduction of its own receptors may modify the transduction of hormone signals by changes in the content of a glycosyl-phosphatidylinositol. Both subsequent insulin binding and glycosyl-phosphatidylinositol concentrations markedly decreased as a function of time and insulin concentration during preincubation of hepatocytes with insulin. The modifications observed in insulin binding were due to changes in receptor concentration. These results show that insulin regulates both the number of its own receptors and glycosyl-phosphatidylinositol concentrations in target cells, which may be of interest in many pathophysiological situations.

Effects of hypercortisolemia and diabetes on skeletal muscle insulin receptor function in vitro and in vivo

Activation of skeletal muscle insulin receptor tyrosine kinase in vitro and in vivo was studied in two rat models of insulin resistance: insulinopenic diabetes and hypercortisolemia. In control rats, intravenous insulin administration resulted in dose-dependent in vivo activation of the muscle insulin receptor kinase towards histone H2b. Half-maximal and maximal activation were observed 5 min after injecting 0.1 and 0.5 U insulin/100 g, respectively. Diabetes (7 days) induced with streptozotocin did not affect insulin binding affinity of solubilized muscle receptors but depressed receptor kinase activation in vivo by 52 or 40% after intravenous insulin administration (0.1 or 2 U/100 g, respectively). Cortisone treatment (5 days) resulting in weight loss, hyperglycemia, and hyperinsulinemia did not affect the number, insulin binding affinity, or kinase activity of solubilized receptors activated with insulin in vitro or in vivo. It is concluded that impaired insulin receptor tyrosine kinase activation was demonstrated in vivo in rats with insulinopenic diabetes and that glucocorticoid-induced insulin resistance probably reflects postreceptor defect(s) in muscle.

Changes of insulin effect on lipogenesis and insulin binding receptors during hypokinesia

The effect of hypokinesia on insulin action and insulin binding to specific receptors in fat cells was studied. Male Wistar rats were exposed to hypokinesia in special adjustable plastic cages for 1, 7, 21 and 60 days, and the stimulatory effect of insulin (10 and 100 mU) on the incorporation of radiocarbon labelled glucose into lipids of fat tissue and the binding of insulin to receptors of isolated adipocytes was estimated. The stimulation of lipogenesis by insulin was slightly diminished after hypokinesia for 1 day, however, an important increase of insulin action was found in rats exposed to hypokinesia for 60 days. The decrease of insulin binding capacity of the number of binding sites per cell and of the insulin receptor density was found after 1 day of hypokinesia. In rats exposed to hypokinesia for 60 days, in agreement with the higher stimulatory affect of insulin, an increase of insulin receptor density was observed. These results showed that hypokinesia has an important influence on stimulatory action of insulin and on insulin receptors in adipocytes.

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.

Dexamethasone-dependent expression of beta 1-24 corticotropin stimulated adenylate cyclase during adipose conversion of 3T3-F442A cells

When 3T3-F442A preadipocytes were grown in culture media supplemented with corticosteroid poor fetal calf serum and insulin they differentiated into adipocytes. Glycerophosphate dehydrogenase, a marker of terminal differentiation, developed a 600-fold increase of activity whereas the adenylate cyclase system remained unresponsive to the synthetic ACTH(1-24) analog. In contrast, 3T3-F442A adipocytes, differentiated in the presence of dexamethasone, exhibited an adenylate cyclase activity which was stimulated 4-fold by ACTH(1-24). The stimulation of the adenylate cyclase activity by GTP gamma S remained unchanged (about 20-25-fold) suggesting that the G regulatory coupling protein was not functionally modified by dexamethasone. Binding studies with 125I-ACTH revealed that specific cellular binding could be evidenced in dexamethasone-treated cells while control adipocytes did not exhibit any specific binding of 125I-ACTH. These findings lend support to the hypothesis that the setting off of this ACTH responsiveness in 3T3-F442A cells is regulated by dexamethasone after cells are committed to adipose differentiation.

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.

Effect of dexamethasone on hepatic glucose and insulin metabolism after oral glucose in conscious dogs

To examine whether hyperinsulinemia associated with glucocorticoid treatment results solely from hypersecretion of insulin or also involves altered fractional hepatic extraction, oral glucose (1 g/kg body wt) was administered to dogs with or without dexamethasone treatment (2 mg/d for 2 d). Dexamethasone significantly increased basal glucose and insulin concentrations in the portal vein, hepatic vein, and femoral artery, reduced basal fractional hepatic extraction of insulin from 43 +/- 4% to 22 +/- 4%, and, after oral glucose, increased retention by the liver of net glucose released into the portal system from 27 +/- 4% to 53 +/- 13%. Intraportal insulin infusion (1 and 2 mU/kg per min) after 7 d of dexamethasone treatment (2 mg/d) caused less suppression of endogenous glucose production, and less exogenous glucose was required to maintain an euglycemic clamp than in control animals. Dexamethasone treatment is associated with: decreased basal fractional hepatic insulin extraction contributing to hyperinsulinemia; and less suppression of endogenous glucose production and increase in peripheral uptake in response to insulin, but no reduction in net hepatic glucose uptake after oral glucose.

Insulin antagonises the growth hormone-mediated increase in the activity of phosphatidate phosphohydrolase in isolated rat hepatocytes

Rat hepatocytes were incubated in monolayer culture, under serum-free conditions for 8 h. Rat growth hormone (up to 100 nM) increased the activity of phosphatidate phosphohydrolase by up to 47%. Insulin (500 pM or 35 nM), cycloheximide or actinomycin D reversed this effect. The ability of growth hormone to modify the effects of insulin is discussed in relation to the control of the phosphohydrolase activity and glycerolipid synthesis.

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.

Hyperalimentation as cause of markedly worsened metabolic control in a patient with autoantibodies to the insulin receptor

Patients with type B insulin resistance and acanthosis nigricans have autoantibodies to their insulin receptors and usually have signs and symptoms of other autoimmune diseases. The first case demonstrating that hyperalimentation markedly disturbs blood glucose control in type B insulin-resistant patients is described. Neither prednisone, insulin (up to 240 units per hour), nor tolbutamide appeared to help this patient's metabolic control. After the addition of cyclophosphamide for one week, the anti-insulin receptor autoantibody titer dropped from greater than 1:1,000 to 1:1. Six months later, the patient had a complete remission, which is rare, with only three other reported remissions in these patients with type B insulin resistance.

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.

Clinical and biologic correlates of insulin binding by leukemia lymphoblasts

The percentage of total 125I-labeled insulin specifically bound to lymphoblasts was measured in 46 children with leukemia. Among 35 children with newly diagnosed acute lymphoblastic leukemia (ALL), specific insulin binding ranged from 0.09 to 14.8% per 10(6) blasts. A lower level of insulin binding was correlated with T-cell surface markers (P less than 0.003), higher hemoglobin level (P less than 0.005), presence of a mediastinal mass (P less than 0.01), lower glucocorticoid receptor level (P less than 0.02), higher platelet count (P less than 0.04), age less than 2 or greater than 10 yr (P less than 0.05), white blood cell count greater than or equal to 100 X 10(3)/mm3 (P less than 0.06) and higher labeling index (P less than 0.07). It was not correlated with the presence of central-nervous-system disease, FAB classification, or sex. With a follow-up of 24 to 33 + months, insulin binding was not correlated with treatment outcome. Six patients with relapsed ALL and three with acute nonlymphoblastic leukemia showed insulin binding levels similar to those in newly diagnosed ALL patients. Blasts from one patient with B-cell ALL and one with chronic myelogenous leukemia were characterized by lower insulin binding, while lymphoblasts from a patient with T-cell lymphoma bound insulin at marginally detectable levels. In vitro studies with IM-9, NALM-1 and NALM-16 cell lines showed that changes in insulin binding caused by dexamethasone treatment were not correlated with hormone-induced cell death. Although study of insulin binding by malignant lymphoid cells may be important in understanding the biology of leukemic cells, it does not appear to have any obvious clinical utility.

Effects of changes in serum insulin in response to dexamethasone and adrenalectomy on insulin-sensitive phosphodiesterase in rat fat cells

The effects of dexamethasone administration and adrenalectomy on insulin-sensitive phosphodiesterase were studied in rat fat cells. Isolated fat cells were incubated at 37 degrees C for ten minutes or without insulin. A crude microsomal fraction prepared by differential centrifugation was used for the determination of phosphodiesterase level. With dexamethasone treatment (400 micrograms/kg/day) for seven days, specific activity of the enzyme and its sensitivity (ED50) to insulin were decreased, as was the maximal responsiveness to insulin. Under conditions of adrenalectomy, the specific activity and the sensitivity (ED50) were increased while the maximal responsiveness to insulin was decreased. Following dexamethasone treatment specific insulin binding was decreased, and after adrenalectomy it increased. These findings were attributed to changes in the number of insulin receptors per cell rather than to changes in affinity. Alterations in insulin sensitivity (ED50) of the enzyme seemed to be due to alterations in insulin binding to the receptor. The reduction in maximal insulin responsiveness suggested postreceptor defects in both experimental groups. The mechanism related to alterations in the specific activity was not thoroughly clarified; however, serum insulin levels may specifically affect the enzyme activity.

Effects of glucocorticoids on endocrine function in the dog

There are a multitude of possible side effects when using high levels of or chronic administration of glucocorticoid treatment. Several of the studies referred to in this discussion used large amounts of glucocorticoids for rather lengthy periods. The endocrine, as well as nonendocrine, effects of glucocorticoids are minimized when the lowest effective doses are used, when treatment is terminated as soon as reasonably possible, and when an alternate-day therapy schedule is followed. However, an occasional individual may appear with a particular susceptibility to one or more of the side effects of glucocorticoid treatment even when these measures are followed.

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.

Cortisone-induced islet cell hyperplasia in hamsters

Pancreatic islet cell hyperplasia was studied in hamsters during one to eight weeks of cortisone treatment. Measurement of serum glucose and insulin; pancreatic insulin, glucagon, somatostatin, pancreatic polypeptide as well as islet tissue morphometry were performed. Serum glucose was highest at week 2, followed by mild to moderate hyperglycemia. Serum insulin was increasingly higher from week 1 to week 8. Pancreatic insulin was maximal at week 5 then declined through week 8 in the presence of beta cell neurosis in markedly hyperplastic islets. Pancreatic concentration of somatostatin and pancreatic polypeptide moderately increased more than the control levels; however, compared with the controls, glucagon was reduced by cortisone treatment. Effect of cortisone in the four types of islet cells is discussed, particularly on beta cell hyperplasia, which appears to be a response to decreased insulin binding to the target organs with no changes in receptor concentration.

Insulin resistance in uremia. Characterization of insulin action, binding, and processing in isolated hepatocytes from chronic uremic rats

We have developed a model in the rat that leads to a predictable degree of severe uremia to study the role of the liver in the insulin-resistant state of uremia. The uremic animals were euglycemic and had increased serum immunoreactive insulin when compared with their pair-fed controls. Insulin action, binding, internalization, and degradation were characterized in freshly isolated hepatocytes from uremic animals, sham-operated pair-fed, and ad lib.-fed controls. The basal rate of aminoisobutyric acid (AIB) uptake was increased in hepatocytes from both uremic and pair-fed control rats. However, while hepatocytes from uremic animals were refractory to insulin with regard to AIB uptake, there was no significant difference in the absolute increment above basal AIB uptake by hepatocytes from pair-fed and fed ad lib. animals at any insulin concentration studied. 125I-Insulin binding at 24 degrees C was higher in hepatocytes from uremic rats at every insulin concentration studied when compared with fed ad lib. controls. The time course of 125I-insulin binding to the cell and to the fractions that were membrane bound or internalized were studied at 37 degrees C. An increase in membrane-bound 125I-insulin at 37 degrees C was present also in hepatocytes from uremic animals. The same fraction of membrane-bound 125I-insulin was internalized in hepatocytes from all groups of animals. Extracellular and receptor-mediated 125I-insulin degradation at the plasma membrane and after internalization was studied at 37 degrees C by gel chromatography. There was a delayed and decreased rate of 125I-insulin degradation in hepatocytes from uremic rats in the three compartments. We conclude: (a) In chronic uremia the liver is refractory to insulin with regard to AIB uptake. (b) Insulin resistance in uremic rat liver is not due to defects in insulin binding or internalization. (c) Despite the high level of circulating immunoreactive insulin, hepatocytes from uremic rats did not show the expected "down regulation" of their insulin receptors or an increased rate of insulin degradation. These studies further emphasize the primary role of postbinding events in the regulation of insulin binding and degradation. The mechanism as to how the coordinated steps of insulin metabolism in the liver are disrupted in a pathological state is presently unknown.