Effects of glucocorticoid excess on the sensitivity of glucose transport and metabolism to insulin in rat skeletal muscle

Resistance training enhances components of the insulin signaling cascade in normal and high-fat-fed rodent skeletal muscle

Our laboratory recently reported that chronic resistance training (RT) improved insulin-stimulated glucose transport in normal rodent skeletal muscle, owing, in part, to increased GLUT-4 protein concentration (Yaspelkis BB III, Singh MK, Trevino B, Krisan AD, and Collins DE. Acta Physiol Scand 175: 315-323, 2002). However, it remained to be determined whether these improvements resulted from alterations in the insulin signaling cascade as well. In addition, the possibility existed that RT might improve skeletal muscle insulin resistance. Thirty-two male Sprague-Dawley rats were assigned to four groups: control diet (Con)-sedentary (Sed); Con-RT; high-fat diet (HF)-Sed; and HF-RT. Animals consumed their respective diets for 9 wk; then RT animals performed 12 wk of training (3 sets, 10 repetitions at 75% one-repetition maximum, 3x/wk). Animals remained on their dietary treatments over the 12-wk period. After the training period, animals were subjected to hindlimb perfusions. Insulin-stimulated insulin receptor substrate-1-associated phosphatidylinositol-3 kinase activity was enhanced in the red gastrocnemius and quadriceps of Con-RT and HF-RT animals. Atypical PKC-zeta/lambda and Akt activities were reduced in HF-Sed and normalized in HF-RT animals. Resistance training increased GLUT-4 protein concentration in red gastrocnemius and quadriceps of Con-RT and HF-RT animals. No differences were observed in total protein concentrations of insulin receptor substrate-1, Akt, atypical PKC-zeta/lambda, or phosphorylation of Akt. Collectively, these findings suggest that resistance training increases insulin-stimulated carbohydrate metabolism in normal skeletal muscle and reverses high-fat diet-induced skeletal muscle insulin resistance by altering components of both the insulin signaling cascade and glucose transporter effector system.

11beta-Hydroxysteroid dehydrogenase Type 1 in obesity and Type 2 diabetes

Obesity and Type 2 diabetes mellitus are associated with abnormal regulation of glucocorticoid metabolism that are highlighted by clinical similarities between the sequelae of insulin resistance and Cushing's syndrome, as well as glucocorticoids' functional antagonism to insulin. 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) activates functionally inert glucocorticoid precursors (cortisone) to active glucocorticoids (cortisol) within insulin target tissues, such as adipose tissue, thereby regulating local glucocorticoid action. Recent data, mainly from rodents, provide considerable evidence for a causal role of 11beta-HSD1 for the development of visceral obesity and Type 2 diabetes though data in humans are not unequivocal. This review summarizes current evidence on a possible role of 11beta-HSD1 for development of the metabolic syndrome, raising the possibility of novel therapeutic options for the treatment of Type 2 diabetes by inhibition or down-regulation of 11beta-HSD1 activity.

Insulin resistance and hyperglycemia in critical illness: role of insulin in glycemic control

Alterations in glucose metabolism, including hyperglycemia associated with insulin resistance, occur in critical illness. Acutely, such alterations result from normal, adaptive activation of endocrine responses, including increased release of catecholamines, cortisol, and glucagon and a reduced glucose uptake capacity. In prolonged critical illness, neuroendocrine changes lead to more extensive metabolic changes that may be associated with development of complications and poor prognosis. Until recently, hyperglycemia was not routinely controlled in intensive care units, except among patients with known diabetes mellitus. Studies have demonstrated that glycemic management in postmyocardial infarction in patients with diabetes is an effective practice. Recent investigation has extended this to demonstrate reduced morbidity and mortality in a surgical critically ill population with and without diabetes mellitus in later phases of critical illness. Although the mechanisms for improved patient outcomes need to be established, this novel approach to management of hyperglycemia in critical illness is a new and important concept for those working in critical care. This article reviews alterations in glucose metabolism which occur in critically ill patients and discusses potential mechanisms and mediators (e.g., hormones, cytokines) that may play a key role in hyperglycemia and insulin resistance during acute and prolonged phases of severe illness. The article addresses the application of insulin protocols and exogenous regulation of glucose concentration in critical illness based on a review of recent intervention studies.

Glucocorticoids and insulin sensitivity: dissociation of insulin's metabolic and vascular actions

Insulin sensitivity in tissues such as a skeletal muscle and fat is closely correlated with insulin action in the vasculature, but the mechanism underlying this is unclear. We investigated the effect of dexamethasone on insulin-stimulated glucose disposal and vasodilation in healthy males to test the hypothesis that a reduction in glucose disposal would be accompanied by a reduction in insulin action in the vasculature. We performed a double-blind, placebo-controlled, cross-over trial comparing insulin sensitivity (measured by the euglycemic hyperinsulinemic clamp) and vascular insulin action (measured by small vessel wire myography) in young healthy males allocated to placebo or 1 mg dexamethasone twice daily for 6 d, each in random order. Six days of dexamethasone therapy was associated with a 30% (95% confidence interval, 19.1-40.0%) fall in insulin sensitivity. Despite this, there was no difference in insulin-mediated vasodilation between phases. Dexamethasone had no effect on circulating markers of endothelial function, such as D-dimer, von Willebrand factor, and tissue plasminogen activator. By short-term exposure to high dose dexamethasone we were able to differentially affect the metabolic and vascular actions of insulin. This implies that, using this model, there is physiological uncoupling of the effects of insulin in different tissues.

Relationship of depression to diabetes types 1 and 2: epidemiology, biology, and treatment

This article reviews the rapidly accumulating literature on the relationship between mood disorders and diabetes mellitus. Recent studies have demonstrated that depression and its associated symptoms constitute a major risk factor in the development of type 2 diabetes and may accelerate the onset of diabetes complications. Since the mid-1980s, multiple longitudinal and cross-sectional studies have scrutinized the association of diabetes with depressive symptoms and major depression. Utilizing the search terms depressive disorders, psychiatry, diabetes, and pathophysiology in MEDLINE searches (1966-2003), this article reviews studies investigating pathophysiological alterations related to glucose intolerance and diabetes in depressed patients. The few randomized, controlled studies of treatment of depression in patients with diabetes are also described. Short-term treatment of depression in patients with diabetes improves their dysphoria and other signs and symptoms of depression. Future research will confirm whether response to psychotherapy and/or psychopharmacologic treatment improves glucose control, encourages compliance with diabetes treatment, and perhaps even increases longevity.

Effective use of thiazolidinediones for the treatment of glucocorticoid-induced diabetes

We evaluated the efficacy of a thiazolidinedione in the treatment of diabetes induced by glucocorticoids. We examined the effectiveness of troglitazone in seven patients with long-standing steroid-induced diabetes. Five of the seven subjects were treated with insulin alone, one was treated with both insulin and oral therapy and one was treated with oral therapy alone. The mean insulin dose in six of the seven subjects was 0.66+/-0.09 units/kg per day. Diabetes status was assessed by measuring serum fructosamine, HgbA1c, oral glucose and meal tolerance tests (OGTT and MTT) at baseline and after treatment for 5-8 weeks with troglitazone 400 mg/day. Troglitazone caused a significant decrease in fructosamine (274+/-32 vs. 217+/-22 mmol/l; P<0.01) and HgbA1C (7.8+/-0.4 vs. 7.2+/-0.4%; P<0.01) as well as decrements in the areas under the OGTT 2,308+/-156 vs. 1,937+/-127 mmol/l; P<0.05) and MTT glucose curves (4694+/-449 vs. 4057+/-437 mmol/l; P<0.05). In addition, the area under the insulin curve for the oral glucose tolerance test showed a significant increase from 27,438+/-4,488 to 41,946+/-6,048 pmol/l (P<0.05). Total and LDL cholesterol were also significantly decreased (6.4+/-0.9 vs. 5.0+/-0.6 mmol/l and 3.8+/-0.7 vs. 2.7+/-0.4 mmol/l, respectively, P<0.05). Fasting leptin values decreased by 23% despite an increase in body weight. Troglitazone is effective in the treatment of glucocorticoid-induced diabetes as manifested by lower measures of glycemia, HgbA1c, and post-prandial glucose values, while the doses of other diabetes medications remained unchanged or were reduced. The insulin-sensitizing drug also produced a marked increase in endogenous insulin secretion in response to glucose, lower total and LDL cholesterol, and decreased fasting leptin despite weight gain. Thiazolidinediones may improve diabetes-related parameters by antagonizing pathways of glucocorticoid-induced insulin resistance and by reversing adverse effects of glucocorticoids on beta cell function.

Troglitazone antagonizes metabolic effects of glucocorticoids in humans: effects on glucose tolerance, insulin sensitivity, suppression of free fatty acids, and leptin

Glucocorticoids induce insulin resistance in humans, whereas thiazolidinediones enhance insulin sensitivity. Although the effects of glucocorticoids and thiazolidinediones have been assessed in isolation, interaction between these drugs, which both act as ligands for nuclear receptors, has been less well studied. Therefore, we examined the metabolic effects of dexamethasone and troglitazone, alone and in combination, for the first time in humans. A total of 10 healthy individuals with normal glucose tolerance (age 40 +/- 11 years, BMI 31 +/- 6.1 kg/m(2)) were sequentially studied at baseline, after 4 days of dexamethasone (4 mg/day), after 4-6 weeks on troglitazone alone (400 mg/day), and again after 4 days of dexamethasone added to troglitazone. Key metabolic variables included glucose tolerance assessed by blood glucose and insulin responses to an oral glucose tolerance test (OGTT), insulin sensitivity evaluated via hyperinsulinemic-euglycemic clamp, free fatty acids (FFAs) and FFA suppressibility by insulin during the clamp study, and fasting serum leptin. Dexamethasone drastically impaired glucose tolerance, with fasting and 2-h OGTT insulin values increasing by 2.3-fold (P < 0.001) and 4.4-fold (P < 0.001) over baseline values, respectively. The glucocorticoid also induced a profound state of insulin resistance, with a 34% reduction in maximal glucose disposal rates (GDRs; P < 0.001). Troglitazone alone increased GDRs by 20% over baseline (P = 0.007) and completely prevented the deleterious effects of dexamethasone on glucose tolerance and insulin sensitivity, as illustrated by a return of OGTT glucose and insulin values and maximal GDR to near-baseline levels. Insulin-mediated FFA suppressibility (FFA decline at 30 min during clamp/FFA at time 0) was also markedly reduced by dexamethasone (P = 0.002). Troglitazone had no effect per se, but it was able to normalize FFA suppressibility in subjects coadministered dexamethasone. Futhermore, the magnitudes of response of FFA suppressibility and GDR to dexamethasone were proportionate. The same was true for the reversal of dexamethasone-induced insulin resistance by troglitazone, but not in response to troglitazone alone. Leptin levels were increased 2.2-fold above baseline by dexamethasone. Again, troglitazone had no effect per se but blocked the dexamethasone-induced increase in leptin. Subjects experienced a 1.7-kg weight gain while taking troglitazone but no other untoward effects. We conclude that in healthy humans, thiazolidinediones antagonize the action of dexamethasone with respect to multiple metabolic effects. Specifically, troglitazone reverses both glucocorticoid-induced insulin resistance and impairment of glucose tolerance, prevents dexamethasone from impairing the antilipolytic action of insulin, and blocks the increase in leptin levels induced by dexamethasone. Even though changes in FFA suppressibility were correlated with dexamethasone-induced insulin resistance and its reversal by troglitazone, a cause-and-effect relationship cannot be established. However, the data suggest that glucocorticoids and thiazolidinediones exert fundamentally antagonistic effects on human metabolism in both adipose and muscle tissues. By preventing or reversing insulin resistance, troglitazone may prove to be a valuable therapeutic agent in the difficult clinical task of controlling diabetes in patients receiving glucocorticoids.

C2C12 myocytes lack an insulin-responsive vesicular compartment despite dexamethasone-induced GLUT4 expression

Insulin regulates the uptake of glucose into skeletal muscle and adipocytes by redistributing the tissue-specific glucose transporter GLUT4 from intracellular vesicles to the cell surface. To date, GLUT4 is the only protein involved in insulin-regulated vesicular traffic that has this tissue distribution, thus raising the possibility that its expression alone may allow formation of an insulin-responsive vesicular compartment. We show here that treatment of differentiating C2C12 myoblasts with dexamethasone, acting via the glucocorticoid receptor, causes a >or=10-fold increase in GLUT4 expression but results in no significant change in insulin-stimulated glucose transport. Signaling from the insulin receptor to its target, Akt2, and expression of the soluble N-ethylmaleimide-sensitive factor-attachment protein receptor, or SNARE, proteins syntaxin 4 and vesicle-associated membrane protein are normal in dexamethasone-treated C2C12 cells. However, these cells show no insulin-dependent trafficking of the insulin-responsive aminopeptidase or the transferrin receptor, respective markers for intracellular GLUT4-rich compartments and endosomes that are insulin responsive in mature muscle and adipose cells. Therefore, these data support the hypothesis that GLUT4 expression by itself is insufficient to establish an insulin-sensitive vesicular compartment.

Adrenalectomy improves diabetes in A-ZIP/F-1 lipoatrophic mice by increasing both liver and muscle insulin sensitivity

The virtually fatless A-ZIP/F-1 mouse is profoundly insulin resistant, diabetic, and a good model for humans with severe generalized lipoatrophy. Like a number of other mouse models of diabetes, the A-ZIP/F-1 mouse has elevated serum corticosterone levels. Leptin infusion lowers the corticosterone levels, suggesting that leptin deficiency contributes to the hypercorticosteronemic state. To test the hypothesis that the increased glucocorticoids contribute to the diabetes and insulin resistance, we examined the effect of adrenalectomy on A-ZIP/F-1 mice. Adrenalectomy significantly decreased the blood glucose, serum insulin, and glycated hemoglobin levels. Hyperinsulinemic-euglycemic clamps were performed to characterize the changes in whole-body and tissue insulin sensitivity. The adrenalectomized A-ZIP/F-1 mice displayed a marked improvement in insulin-induced suppression of endogenous glucose production, indicating increased hepatic insulin sensitivity. Adrenalectomy also increased muscle glucose uptake and glycogen synthesis. These results suggest that the chronically increased serum corticosterone levels contribute to the diabetes of the A-ZIP/F-1 mice and that removal of the glucocorticoid excess improves the insulin sensitivity in both muscle and liver.

Increased glucocorticoid receptor expression in human skeletal muscle cells may contribute to the pathogenesis of the metabolic syndrome

Altered glucocorticoid hormone action may contribute to the etiology of the metabolic syndrome, but the molecular mechanisms are poorly defined. Tissue sensitivity to glucocorticoid is regulated by expression of the glucocorticoid receptor (GR)-alpha and 11beta-hydroxysteroid dehydrogenase type I (11beta-HSD1)-mediated intracellular synthesis of active cortisol from inactive cortisone. We have analyzed GRalpha and 11beta-HSD1 expression in skeletal myoblasts from men (n = 14) with contrasting levels of insulin sensitivity (euglycemic clamp measurements of insulin-dependent glucose disposal rate), blood pressure, and adiposity. Positive associations were evident between myoblast expression of GRalpha under basal conditions and levels of insulin resistance (r(2) = 0.34, P < 0.05), BMI (r(2) = 0.49, P < 0.01), percent body fat (r(2) = 0.34, P < 0.02), and blood pressure (r(2) = 0.86, P < 0.001). Similar associations were evident when myoblasts were incubated with physiological levels of cortisol (P < 0.01 for all). Importantly, GRalpha expression was unaffected by variations in in vivo concentrations of insulin, IGF-1, or glucose concentrations. In common with the GR, 11beta-HSD1 expression in myoblasts incubated with physiological concentrations of cortisol in vitro was positively associated with levels of insulin resistance (r(2) = 0.68, P < 0.001), BMI (r(2) = 0.63, P < 0.005), and blood pressure (r(2) = 0.27, P < 0.05). Regulation of GRalpha and 11beta-HSD1 by cortisol was abolished by the GR antagonist RU38486. In summary, our data suggest that raised skeletal muscle cell expression of GRalpha and 11beta -HSD1-mediated regulation of intracellular cortisol may play a fundamental role in mechanisms contributing to the pathogenesis of the metabolic syndrome.

Alterations of the circadian clock in the heart by streptozotocin-induced diabetes

The heart, like other organs, possesses an internal circadian clock. These clocks provide the selective advantage of anticipation, enabling the organ to prepare for a given stimulus, thereby optimizing the appropriate response. The heart in diabetes is associated with alterations in morphology, gene expression, metabolism and contractile performance. The present study investigated whether diabetes also alters the circadian clock in the heart. Insulin-dependent diabetes mellitus was induced in rats by treatment with streptozotocin (STZ; 65 mg/kg). STZ increased humoral (glucose and non-esterified fatty acids) and heart gene expression (myosin heavy chain beta, pyruvate dehydrogenase kinase 4 and uncoupling protein 3) markers of diabetes. The circadian patterns of gene expression of seven components of the mammalian clock (bmal1, clock, cry1, cry2, per1, per2 and per3), as well as three clock output genes (dbp, hlf and tef), were compared in hearts isolated from control and STZ-induced diabetic rats. All components of the clock investigated possessed circadian rhythms of gene expression. In the hearts isolated from STZ-induced diabetic rats, the phases of these circadian rhythms were altered (approximately 3 h early) compared to those observed for control hearts. The clock in the heart has therefore lost normal synchronization with its environment during diabetes. Whether this loss of synchronization plays a role in the development of contractile dysfunction of the heart in diabetes remains to be determined.

Alteration in phosphorylation of P20 is associated with insulin resistance

We have recently identified a small phosphoprotein, P20, as a common intracellular target for insulin and several of its antagonists, including amylin, epinephrine, and calcitonin gene-related peptide. These hormones elicit phosphorylation of P20 at its different sites, producing three phosphorylated isoforms: S1 with an isoelectric point (pI) value of 6.0, S2 with a pI value of 5.9, and S3 with a pI value of 5.6 (FEBS Letters 457:149-152 and 462:25-30, 1999). In the current study, we showed that P20 is one of the most abundant phosphoproteins in rat extensor digitorum longus (EDL) muscle. Insulin and amylin antagonize each other's actions in the phosphorylation of this protein in rat EDL muscle. Insulin inhibits amylin-evoked phosphorylation of S2 and S3, whereas amylin decreases insulin-induced phosphorylation of S1. In rats made insulin resistant by dexamethasone treatment, levels of the phosphoisoforms S2 and S3, which were barely detectable in healthy rats in the absence of hormone stimulation, were significantly increased. Moreover, the ability of insulin to inhibit amylin-evoked phosphorylation of these two isoforms was greatly attenuated. These results suggested that alterations in the phosphorylation of P20 might be associated with insulin resistance and that P20 could serve as a useful marker to dissect the cellular mechanisms of this disease.

The maternal diet during pregnancy programs altered expression of the glucocorticoid receptor and type 2 11beta-hydroxysteroid dehydrogenase: potential molecular mechanisms underlying the programming of hypertension in utero

Potential mechanisms underlying prenatal programming of hypertension in adult life were investigated using a rat model in which maternal protein intake was restricted to 9% vs. 18% casein (control) during pregnancy. Maternal low protein (MLP) offspring exhibit glucocorticoid-dependent raised systolic blood pressure throughout life (20-30 mm Hg above the control). To determine the molecular mechanisms underlying the role of alterations in glucocorticoid hormone action in the prenatal programming of hypertension in MLP offspring, tissues were analyzed for expression of the glucocorticoid receptor (GR), mineralocorticoid receptor (MR), 11betaHSD1, 11betaHSD2, and corticosteroid-responsive Na/K-adenosine triphosphatase alpha1 and beta1. GR protein (95 kDa) and messenger RNA (mRNA) expression in kidney, liver, lung, and brain was more than 2-fold greater in MLP vs. control offspring during fetal and neonatal life and was more than 3-fold higher during subsequent juvenile and adult life (P < 0.01). This was associated with increased levels of Na/K-adenosine triphosphatase alpha1- and beta1-subunit mRNA expression. Levels of MR gene expression remained unchanged. Exposure to the MLP diet also resulted in markedly reduced levels of 11betaHSD2 expression in the MLP placenta on days 14 and 20 of gestation (P < 0.001), underpinning similar effects on 11betaHSD2 enzyme activity that we reported previously. Levels were also markedly reduced in the kidney and adrenal of MLP offspring during fetal and postnatal life (P < 0.001). This programmed decline in 11betaHSD2 probably contributes to marked increases in glucocorticoid hormone action in these tissues and potentiates both GR- and MR-mediated induction of raised blood pressure. In contrast, levels of 11betaHSD1 mRNA expression in offspring central and peripheral tissues remained unchanged. In conclusion, we have demonstrated that mild protein restriction during pregnancy programs tissue-specific increases in glucocorticoid hormone action that are mediated by persistently elevated expression of GR and decreased expression of 11betaHSD2 during adult life. As glucocorticoids are potent regulators not only of fetal growth but also of blood pressure, our data suggest important potential molecular mechanisms contributing to the prenatal programming of hypertension by maternal undernutrition in the rat.

The maternal diet during pregnancy programs altered expression of the glucocorticoid receptor and type 2 11beta-hydroxysteroid dehydrogenase: potential molecular mechanisms underlying the programming of hypertension in utero

Potential mechanisms underlying prenatal programming of hypertension in adult life were investigated using a rat model in which maternal protein intake was restricted to 9% vs. 18% casein (control) during pregnancy. Maternal low protein (MLP) offspring exhibit glucocorticoid-dependent raised systolic blood pressure throughout life (20-30 mm Hg above the control). To determine the molecular mechanisms underlying the role of alterations in glucocorticoid hormone action in the prenatal programming of hypertension in MLP offspring, tissues were analyzed for expression of the glucocorticoid receptor (GR), mineralocorticoid receptor (MR), 11betaHSD1, 11betaHSD2, and corticosteroid-responsive Na/K-adenosine triphosphatase alpha1 and beta1. GR protein (95 kDa) and messenger RNA (mRNA) expression in kidney, liver, lung, and brain was more than 2-fold greater in MLP vs. control offspring during fetal and neonatal life and was more than 3-fold higher during subsequent juvenile and adult life (P < 0.01). This was associated with increased levels of Na/K-adenosine triphosphatase alpha1- and beta1-subunit mRNA expression. Levels of MR gene expression remained unchanged. Exposure to the MLP diet also resulted in markedly reduced levels of 11betaHSD2 expression in the MLP placenta on days 14 and 20 of gestation (P < 0.001), underpinning similar effects on 11betaHSD2 enzyme activity that we reported previously. Levels were also markedly reduced in the kidney and adrenal of MLP offspring during fetal and postnatal life (P < 0.001). This programmed decline in 11betaHSD2 probably contributes to marked increases in glucocorticoid hormone action in these tissues and potentiates both GR- and MR-mediated induction of raised blood pressure. In contrast, levels of 11betaHSD1 mRNA expression in offspring central and peripheral tissues remained unchanged. In conclusion, we have demonstrated that mild protein restriction during pregnancy programs tissue-specific increases in glucocorticoid hormone action that are mediated by persistently elevated expression of GR and decreased expression of 11betaHSD2 during adult life. As glucocorticoids are potent regulators not only of fetal growth but also of blood pressure, our data suggest important potential molecular mechanisms contributing to the prenatal programming of hypertension by maternal undernutrition in the rat.

Maternal undernutrition during early to midgestation programs tissue-specific alterations in the expression of the glucocorticoid receptor, 11beta-hydroxysteroid dehydrogenase isoforms, and type 1 angiotensin ii receptor in neonatal sheep

We have investigated the effects of maternal nutrient restriction in the sheep during the period of rapid placental growth (i.e. 28-77 days gestation; term = 147 days) on feto-placental growth and expression of the glucocorticoid receptor (GR), types 1 and 2 11beta-hydroxysteroid dehydrogenase (11betaHSD1, 11betaHSD2), and types 1 and 2 angiotensin II receptor (AT1, AT2) in fetal and neonatal offspring. Ewes (n = 63) of similar age, body weight, and body composition were randomly allocated to a nutrient-restricted (NR) group in which they consumed 3.2 MJ/day metabolizable energy (ME; equivalent to 50% of predicted requirements) or to a control group in which they consumed 6.7 MJ/day ME (equivalent to 110% of predicted requirements). After 77 days gestation, ewes from both dietary groups consumed close to 100% of ME requirements up to term. Newborn offspring of NR ewes were of similar body weight, but had increased crown-rump length, greater placental weight, and increased placental/body weight ratio (P < 0.01) compared with controls. Their kidneys were heavier (P < 0.05), but shorter in length, with increased ratios of transverse width to length (P < 0.001). GR messenger RNA (mRNA) expression in neonatal offspring from NR ewes was increased in adrenal, kidney, liver, lung, and perirenal adipose tissue (P < 0.01). Conversely, 11betaHSD1 mRNA expression was unaffected, except in perirenal adipose tissue, where it was higher in lambs born to NR ewes (P < 0.01). 11betaHSD2 mRNA expression was decreased in adrenals and kidney (P < 0.001). Maternal NR also resulted in significantly increased AT1 expression in those tissues in which expression of GR was increased and/or 11betaHSD2 was decreased, i.e. adrenals, kidney, liver, and lung. AT2 expression was unaffected by maternal NR. Although 11betaHSD2 mRNA was undetectable in term placenta, it was abundant in midgestation placenta and was lower after maternal NR (P < 0.001). There was close agreement between levels of 11betaHSD enzyme (i.e. 11beta-dehydrogenase and 11-oxoreductase) activities and abundance of 11betaHSD1 mRNA and 11betaHSD2 mRNA expression. The persistence of tissue-specific increases in the expression of GR, 11betaHSD1 and AT1 and decreases in the expression of 11betaHSD2 in adrenals and kidney in newborn offspring in response to a defined period of maternal nutrient restriction during early to midgestation suggests that gene expression has been programmed by nutrient availability to the fetus before birth. These data suggest key potential mechanisms by which maternal nutrition prenatally programs physiological pathways, such as the renin-angiotensin system, in the offspring that may lead to raised blood pressure and other cardiovascular disease risk factors in later life.

Corticosterone-aggravated ischemic neuronal damage in vitro is relieved by vanadate

Preischemic hyperglycemia-aggravated neuronal damage has been postulated to occur via enhanced lactic acidosis. We have hypothesized that preischemic glucose loading induces a short-lived elevation in glucocorticoid release which, when combined with ischemia, aggravates the postischemic outcome. This study tested this hypothesis in rat hippocampal slices exposed to 4 min in vitro ischemia of which 58% exhibited recovery of neuronal function. However, when corticosterone (CT) was present during ischemia, the recovery of neuronal function decreased in a concentration-dependent manner. At 5 microM, CT reduced the recovery rate to 40% while only 10% of slices recovered when exposed to 20 microM CT. Insulin could not block the effect of CT; however, vanadate improved the postischemic recovery of CT-treated (20 microM) slices to 43%. These results indicate that acute, short exposure to CT can significantly exacerbate postischemic outcome and that vanadate can antagonize CT action.

Stress-induced hyperglycemia

Stress hyperglycemia is common and likely to be associated with at least some of the same complications as hyperglycemia in true diabetes mellitus, such as poor wound healing and a higher infection rate. The predominant cause is the intense counterregulatory hormone and cytokine responses of critical illness, often compounded by excessive dextrose administration, usually as TPN. Although randomized data suggesting benefit of controlling hyperglycemia in hospitalized patients are paltry, prospective controlled trials are feasible and should be initiated. In the interim, the practice at the authors' institution is to use insulin to lower plasma glucose concentrations to a safe range of 150 mg/dL to 200 mg/dL in all patients.

BRL37344, but not CGP12177, stimulates fuel oxidation by soleus muscle in vitro

The beta(3)-adrenoceptor agonist, (RR+SS)-(+/-)-4-[2-)2-)3-chlorophenyl)-2-hydroxyethyl)amino)propyl]ph enoxyacetate (BRL37344), stimulated fuel utilisation by isolated mouse soleus muscle at concentrations 10- to 100-fold lower than those required to stimulate lipolysis in brown adipocytes. At 1x10(-10) M BRL37344, uptake and phosphorylation of 2-deoxyglucose was increased (40%), as was glucose-oxidation (50%), palmitate-oxidation (70%) and oxidation of [2-14C]pyruvate (2-fold), indicating stimulation of tricarboxylic acid cycle reactions. Oxidation of [1-14C]pyruvate was unaffected, indicating no stimulation of pyruvate dehydrogenase activity. Other beta(3)-adrenoceptor agonists, disodium(RR)-5-[2-[[2-(3-chlorophenyl)-2-hydroxyethyl]-amino]propyl]- 1,3-benzodioxazole-2,2-dicarboxylate (CL316,243, 1x10(-7) M) and (S)-4-¿2-[2-hydroxy-3-(4-hydroxyphenoxy)propylamino]ethyl¿pheno xymeth ylcyclohexylphosphiric acid lithium salt (SB226552, 1x10(-9) M), achieved similar stimulation of 2-deoxyglucose uptake and phosphorylation but (+/-)-4-(3-t-butylamino-2-hydroxypropoxy)benzimidazol-2-one (CGP12177A) had no effect. The inhibitor of protein kinase A, H-89 (isoquinolinesulfonamide), had little effect on the stimulation of pyruvate-oxidation by BRL37344, while the specific inhibitor of protein kinase C, bisindolylmaleimide IX, reduced the stimulated rate to slightly below basal values. We consider that these responses provide evidence of the presence of a novel beta-adrenoceptor in skeletal muscle, which we have termed beta(skel)-adrenoceptor.

Pharmacokinetics and metabolic effects of triamcinolone acetonide and their possible relationships to glucocorticoid-induced laminitis in horses

Experiments were performed to establish the pharmacokinetics of triamcinolone acetonide and the effects of the glucocorticoid on glucose metabolism in horses. The pharmacokinetics after intravenous (i.v.) dosing was best described by a three-compartment open model. There was rapid distribution from the central compartment followed by two phases of elimination. The half-life of the rapid elimination phase was 83.5 min and of the slower phase was 12 h. The term (Vss/Vc)-1was 12.3 indicating extensive distribution into the tissues. Triamcinolone acetonide given i.v. or intramuscularly (i.m. ) induced a prolonged period of hyperglycaemia, hyperinsulinaemia and hypertriglyceridaemia. Significant changes in plasma glucagon and serum non-esterified fatty acids were not observed. These observations suggest that the hyperglycaemia was a result of decreased glucose utilization by tissues and increased gluconeogenesis. The effects on glucose metabolism persisted for 3-4 days after triamcinolone was given i.m. at 0.05 mg/kg, the upper limit of the recommended dose range, and for 8 days when given at 0. 2 mg/kg. These observations, together with recent evidence implicating inhibition of glucose metabolism in the pathogenesis of equine laminitis, indicated that triamcinolone-induced laminitis may be associated with the long duration of action of the glucocorticoid when higher than recommended doses or when repeated doses are given.

Disposition of a mixed meal by conscious dogs after seven days of treatment with cyclosporine A and prednisone

BACKGROUND

Combination immunosuppressive therapy, that often includes prednisone and cyclosporine A (CyA), is commonly used in the treatment of organ transplant patients. We hypothesized that CyA and prednisone treatment would alter the roles of the liver and peripheral tissues in the disposal of carbohydrates from a meal.

METHODS

Using the arteriovenous difference technique, we examined the disposition of an intragastrically delivered mixed meal in eight 24-hour fasted conscious dogs that had received CyA 15 mg x kg(-1) daily and prednisone 5 mg twice daily for 7 consecutive days before study (CyA-prednisone group). The results were compared with those from a group of 13 dogs (control group) receiving the same meal but no drugs.

RESULTS

Neither arterial blood glucose concentrations nor arterial plasma insulin or glucagon concentrations differed significantly between the groups at any time. Cumulative net gut glucose output was equivalent to 43 +/- 9 vs 57% +/- 7% of the glucose in the meal in CyA-prednisone vs control (p = .12). The CyA-prednisone group exhibited greater (p < .05) mean net hepatic glucose uptakes (15.4 +/- 4.6 vs 4.3 +/- 2.2 micromol x kg(-1) x min(-1) and net hepatic fractional extractions of glucose (7.8 +/- 1.6 and 1.5% +/- 1.0%) than the control group. Arterial blood lactate concentrations and net hepatic lactate output were greater in the CyA-prednisone group than the control group (p < .05). Hepatic glycogen content at the end of the study was 2.5-fold greater in the CyA-prednisone group than in the control group (p < .05). The nonhepatic tissues disposed of approximately 91% of the absorbed glucose in the control group but only approximately 26% in the CyA-prednisone group (p < .05).

CONCLUSIONS

CyA-prednisone treatment caused a marked shift in the carbohydrate disposal from a meal, enhancing the hepatic glucose uptake and decreasing peripheral glucose disposal.

Troglitazone prevents and reverses dexamethasone induced insulin resistance on glycogen synthesis in 3T3 adipocytes

Troglitazone lowers blood glucose levels in Type II diabetic patients. To evaluate the insulin sensitizing action of troglitazone on glycogen synthesis we have used dexamethasone-treated 3T3 adipocytes as an in vitro model. Differentiated 3T3 adipocytes were incubated with 100 nM dexamethasone for 6 days. Troglitazone (1.0 microM) or metformin (1.0 mM) with or without 200 nM insulin was added during the last 4 days. At the end, insulin (100 nM) stimulated glycogen synthesis was determined using (14)C-glucose. Dexamethasone caused a 50% reduction in glycogen synthesis. Troglitazone caused an approximately 3 fold increase in glycogen synthesis from 43.9+/-3.4 to 120+/-16.2 nmols h(-1). Under identical conditions metformin had no significant effect. When cells were incubated with troglitazone and dexamethasone simultaneously for 6 days, troglitazone but not metformin completely prevented dexamethasone-induced insulin resistance. RU 486 (1.0 microM) also completely prevented the insulin resistance. Chronic incubation with dexamethasone and insulin resulted in a 73% reduction in glycogen synthesis. In these adipocytes, troglitazone was partially active with glycogen synthesis rising from 23.1+/-3.0 to 44.4+/-4.5 nmol h(-1), P<0.01 while metformin was inactive. Troglitazone stimulated 2-deoxyglucose uptake by 2 - 3 fold in dexamethasone-treated adipocytes. Metformin also increased glucose uptake significantly. Troglitazone did not affect insulin binding while a 2 fold increase was observed in normal adipocytes where it exhibited a modest effect. Since the effect of troglitazone was greater in dexamethasone-treated adipocytes, troglitazone is likely to act by preventing dexamethasone-induced alterations which may include (i) binding to glucocorticoid receptor and (ii) effect on glucose uptake. These data demonstrate the direct insulin sensitizing action of troglitazone on glycogen synthesis and suggest a pharmacological profile different from metformin.

How do glucocorticoids influence stress responses? Integrating permissive, suppressive, stimulatory, and preparative actions

The secretion of glucocorticoids (GCs) is a classic endocrine response to stress. Despite that, it remains controversial as to what purpose GCs serve at such times. One view, stretching back to the time of Hans Selye, posits that GCs help mediate the ongoing or pending stress response, either via basal levels of GCs permitting other facets of the stress response to emerge efficaciously, and/or by stress levels of GCs actively stimulating the stress response. In contrast, a revisionist viewpoint posits that GCs suppress the stress response, preventing it from being pathologically overactivated. In this review, we consider recent findings regarding GC action and, based on them, generate criteria for determining whether a particular GC action permits, stimulates, or suppresses an ongoing stress-response or, as an additional category, is preparative for a subsequent stressor. We apply these GC actions to the realms of cardiovascular function, fluid volume and hemorrhage, immunity and inflammation, metabolism, neurobiology, and reproductive physiology. We find that GC actions fall into markedly different categories, depending on the physiological endpoint in question, with evidence for mediating effects in some cases, and suppressive or preparative in others. We then attempt to assimilate these heterogeneous GC actions into a physiological whole.

The Greek contribution to diabetes research

Interest in diabetes mellitus research has escalated in Greece during the last decade. This may be attributed to the realization that diabetes is becoming a major problem for the Greek population, the effect of the St Vincent Declaration in passing specific government legislation, and the founding of the National Hellenic Center for the Prevention and Treatment of Diabetes and its Complications. Research areas include epidemiology, etiopathogenesis, glucose metabolism, complications, prevention and treatment of the disease.

Glucocorticoid-Induced Muscle Atrophy: Mechanisms And Therapeutic Strategies

OBJECTIVE

To analyze the mechanisms of action of glucocorticoids in causing muscle atrophy and to examine the therapeutic effect of testosterone as well as other treatment modalities in counteracting this adverse effect.

METHODS

We reviewed selected publications to analyze the mechanisms of glucocorticoid-induced muscle atrophy in animal models and in humans. The pathophysiologic features of glucocorticoid-induced hypogonadism and the possible relationship to the muscle atrophy in patients receiving glucocorticoids were assessed. The beneficial effects of testosterone on the muscles of hypogonadal and eugonadal men were also reviewed. Other measures such as exercise and glutamine and their possible therapeutic and preventive effects were examined in the context of hypercortisolemia.

RESULTS

Glucocorticoids induce rapid muscle breakdown and proximal muscle atrophy. The mechanism of glucocorticoid-induced muscle atrophy relies on the degradation of the myosin heavy chain (catabolic effect), the most important contractile protein in muscle, associated with a decrease of its synthesis (antianabolic effect). One of the contributing factors in the development of muscle atrophy is hypogonadism that is induced by long-term glucocorticoid use. Androgen possesses anabolic and anticatabolic effects in vitro and in animal models. Androgens can be used safely to counteract the catabolic effects of cortisol. Other measures such as exercise, glutamine, and alanyl-glutamine are promising in animal models of glucocorticoid-induced muscle atrophy.

CONCLUSION

This study suggests the possible efficacy of testosterone and glutamine on glucocorticoid-induced muscle atrophy. Testosterone and glutamine are natural biologic products with safe pharmacologic profiles, and their bioefficacy merits active research in humans.

Creatine uptake in isolated soleus muscle: kinetics and dependence on sodium, but not on insulin

The increased use of creatine by athletes as a dietary supplement to improve their physical performance assumes that increased serum creatine levels will increase intracellular skeletal muscle creatine. Despite this common assumption, skeletal muscle creatine uptake awaits full characterization. Consequently, we have investigated 14C-labelled creatine uptake in isolated, incubated rat soleus (type I) muscle preparations at 37 degrees C. We found that the apparent Km for creatine uptake was 73 microM and the Vmax was 77 nmol h-1 gww-1. Creatine uptake was 82% inhibited by 2 mM beta-guanidinopropionic acid, the structural analogue of creatine. In addition, a decrease in buffer Na+ concentration, from 145 to 25 mM, reduced the rate of 14C-labelled creatine uptake by 77%, indicating that uptake is largely Na+-dependent in soleus muscle. Insulin had no effect on the rate of creatine uptake in vitro. The total creatine content was 34% lower, but the rate of creatine uptake in the presence of 100 microM extracellular creatine was 45% higher, in soleus than in extensor digitorum longus (type II) muscle. However, at 1 mM extracellular creatine, the maximal rate of uptake was not significantly different for the two muscle types, implying that soleus muscle has a lower Km for creatine uptake. We suggest that intracellular creatine levels may play a role in the regulation of skeletal muscle creatine uptake.

Cellular mechanism of nutritionally induced insulin resistance: the desert rodent Psammomys obesus and other animals in which insulin resistance leads to detrimental outcome

Animal species with genetic or nutritionally induced insulin resistance, diabetes and obesity (diabesity) may be divided into two broad groups: those with resilient pancreatic beta-cells, e.g. ob/ob mice and fa/fa rats, capable of long-lasting compensatory insulin over-secretion, and those with labile beta-cells in which the secretion pressure leads to irreversible beta-cell degranulation, e.g. db/db mice, Macaca mulatta primates, ZDF diabetic rats. Prominent in this group is the Israeli desert gerbil Psammomys obesus (sand rat), which features low insulin receptor density in liver and muscle. On a diet of relatively high energy, the capacity of insulin to activate the receptor tyrosine kinase (TK) is reduced, in the face of hyperinsulinemia. With the following hyperglycemia, the rising insulin resistance imposes a vicious cycle of insulinemia and glycemia, accentuating the TK activation failure and the beta-cell failure. Among various factors affecting the insulin signaling pathway, multisite phosphorylation, including serine and threonine on the receptor beta-subunit, due to overexpression of certain protein kinase C isoforms, seems to be responsible for the inhibition of the critical step of TK phosphorylation activity. The compromised TK activation is reversible by diet restriction which restores to normal the glycemia and insulinemia. The beta-cell response to long-lasting stimulation and the receptor malfunction in diabesity have implications for a similar etiology in human insulin resistance syndrome and type 2 diabetes, particularly in populations emerging from a food scarce environment into nutritional affluence, inappropriate to the human metabolic capacity. It is suggested that the "thrifty gene" is characterized by a low threshold for insulin secretion and low capacity for insulin clearance. Thus, nutritionally-induced hyperinsulinemia is potentiated and becomes the primary phenotypic expression of the thrifty gene, linked to the insulin receptor signaling pathway malfunction.

Islet amyloid polypeptide decreases the effects of insulin-like growth factor-I on glucose transport and glycogen synthesis in skeletal muscle

Previous studies have shown that islet amyloid polypeptide (IAPP) is co-secreted with insulin from the beta-cell. IAPP reduces insulin-stimulated rates of glycogen synthesis in skeletal muscle but the mechanisms are unclear. Insulin-like growth factor I (IGF-I) is an important regulator of glucose metabolism in skeletal muscle and acts through its own receptor, which has many structural and functional similarities with the insulin receptor. Despite this, the effects of IGF-I on glucose utilization are not identical to those of insulin. The aim of the study was to determine the effects of IAPP on IGF-I-stimulated rates of glucose transport and metabolism (measured by 3-O-methyl[3H]glucose and [U-14C]glucose, respectively) in rat soleus muscle, and compare them with those simulated by insulin. IAPP (10 nM) decreased the sensitivity of 3-O-methylglucose transport, the flux of glucose to hexosemonophosphate and the sensitivity of glycogen synthesis to IGF-I. In contrast, IAPP had no effect on IGF-I-stimulated rates of lactate formation (i.e., glycolysis). IAPP decreased the sensitivity of 3-O-methylglucose transport and glycogen synthesis to insulin. It is concluded that IAPP blunts the stimulation of glucose uptake and deposition by IGF-I or insulin in skeletal muscle. These observations expand those made initially for IAPP and insulin and suggest that IAPP affects IGF-I- or insulin-stimulated glucose metabolism in muscle by a mechanism which is common for both hormones. These experiments may serve as a framework for future studies in order to clarify the mechanisms by which IAPP affects glucose metabolism in skeletal muscle.