Insulin release after acute hydrocortisone treatment in mice

Effects of prenatal dexamethasone exposure on adult C57BL/6J mouse metabolism and oxidative stress

Prenatal glucocorticoid exposure has been shown to alter hypothalamic-pituitary-adrenal axis function resulting in altered fetal development that can persist through adulthood. Fetal exposure to excess dexamethasone, a synthetic glucocorticoid, has been shown to alter adult behaviour and metabolism. This study investigated the effects prenatal dexamethasone exposure had on adult offspring cardiac and liver metabolism and oxidative stress. Pregnant C57BL/6 mice received a dose of 0.4 mg/kg dexamethasone on gestational days 15-17. Once pups were approximately 7 months old, glucose uptake was determined using positron emission tomography and insulin resistance (IR) was determined by homeostatic model assessment (HOMA) IR calculation. Oxidative stress was assessed by measuring 4-hydroxynonenal protein adduct formation and total reactive oxygen species. Female dexamethasone group had significantly increased glucose uptake when insulin stimulated compared to vehicle-treated mice. HOMA IR revealed no evidence of IR in either male or female offspring. There was also no change in oxidative stress markers in either cardiac or liver tissues of male or female offspring. These data suggest that prenatal dexamethasone exposure in male mice does not alter oxidative stress or metabolism. However, prenatal dexamethasone exposure increased glucocorticoids, cardiac glucose uptake, and pAkt signaling in female heart tissues in adult mice, suggesting there are sex differences in prenatal dexamethasone exposure.

Effects of Restraint Stress on Circulating Corticosterone and Met Enkephalin in Chickens: Induction of Shifts in Insulin Secretion and Carbohydrate Metabolism

This study examined the effects of acute restraint stress in the presence or absence of naltrexone on the circulating concentrations of insulin, glucose, Met-enkephalin and corticosterone in 14-week-old chickens [design: 2 sex × 2 stress/non-stress × 2 +/- naltrexone]. In chickens (five male and five females per treatment) subjected to restraint for 30 min, there were increases in the plasma concentrations of corticosterone and Met-enkephalin. The plasma concentrations of insulin and glucose were also increased in the chickens during restraint. Moreover, there were increases in the plasma concentrations of insulin and glucose in the chickens. The patterns of expression of the proenkephalin gene (PENK) in both the anterior pituitary gland and the adrenal gland were very similar to that of plasma Met-enkephalin. There were relationships between the plasma concentrations of corticosterone, Met-enkephalin, insulin and glucose after 30 min of restraint. The effects of naltrexone treatment on both untreated and stressed chickens were also examined, with naltrexone attenuating the stress-induced increases in the plasma concentrations of corticosterone, Met-enkephalin and glucose but not in those of insulin. The present study demonstrates that stress increases insulin secretion in chickens but also induces insulin resistance.

Diabetes in stiff-person syndrome

Anti-glutamic acid decarboxylase (GAD) autoantibodies are a hallmark of stiff-person syndrome (SPS) and insulin-dependent diabetes mellitus (IDDM). However, patients with concurrent IDDM and SPS often manifest insulin resistance, and SPS-associated IDDM probably has heterogeneous causes. Some patients manifest IDDM associated only with high titers of anti-GAD65 caused by SPS. By contrast, other patients develop IDDM only after being treated with high-dose corticosteroids or they progress to insulin dependency following their treatment with high-dose corticosteroids. The profile of autoantibodies differs markedly between type 1 diabetes mellitus (T1DM), late-onset diabetes mellitus, and SPS-associated IDDM. Therefore, as with new-onset diabetes after transplantation (NODAT), SPS-associated IDDM should be classified as a specific diabetes entity, the pathophysiology of which requires increased attention.

Glucocorticoid Receptor Signaling in Diabetes

Stress and depression increase the risk of Type 2 Diabetes (T2D) development. Evidence demonstrates that the Glucocorticoid (GC) negative feedback is impaired (GC resistance) in T2D patients resulting in Hypothalamic-Pituitary-Adrenal (HPA) axis hyperactivity and hypercortisolism. High GCs, in turn, activate multiple aspects of glucose homeostasis in peripheral tissues leading to hyperglycemia. Elucidation of the underlying molecular mechanisms revealed that Glucocorticoid Receptor (GR) mediates the GC-induced dysregulation of glucose production, uptake and insulin signaling in GC-sensitive peripheral tissues, such as liver, skeletal muscle, adipose tissue, and pancreas. In contrast to increased GR peripheral sensitivity, an impaired GR signaling in Peripheral Blood Mononuclear Cells (PBMCs) of T2D patients, associated with hyperglycemia, hyperlipidemia, and increased inflammation, has been shown. Given that GR changes in immune cells parallel those in brain, the above data implicate that a reduced brain GR function may be the biological link among stress, HPA hyperactivity, hypercortisolism and hyperglycemia. GR polymorphisms have also been associated with metabolic disturbances in T2D while dysregulation of micro-RNAs—known to target GR mRNA—has been described. Collectively, GR has a crucial role in T2D, acting in a cell-type and context-specific manner, leading to either GC sensitivity or GC resistance. Selective modulation of GR signaling in T2D therapy warrants further investigation.

Glucocorticoids, metabolism and brain activity

The review integrates different experimental approaches including biochemistry, c-Fos expression, microdialysis (glutamate, GABA, noradrenaline and serotonin), electrophysiology and fMRI to better understand the effect of elevated level of glucocorticoids on the brain activity and metabolism. The available data indicate that glucocorticoids alter the dynamics of neuronal activity leading to context-specific changes including both excitation and inhibition and these effects are expected to support the task-related responses. Glucocorticoids also lead to diversification of available sources of energy due to elevated levels of glucose, lactate, pyruvate, mannose and hydroxybutyrate (ketone bodies), which can be used to fuel brain, and facilitate storage and utilization of brain carbohydrate reserves formed by glycogen. However, the mismatch between carbohydrate supply and utilization that is most likely to occur in situations not requiring energy-consuming activities lead to metabolic stress due to elevated brain levels of glucose. Excessive doses of glucocorticoids also impair the production of energy (ATP) and mitochondrial oxidation. Therefore, glucocorticoids have both adaptive and maladaptive effects consistently with the concept of allostatic load and overload.

Glucocorticoid induces human beta cell dysfunction by involving riborepressor GAS5 LincRNA

OBJECTIVE

A widely recognized metabolic side effect of glucocorticoid (GC) therapy is steroid-induced diabetes mellitus (DM). However, studies on the molecular basis of GC-induced pancreatic beta cell dysfunction in human beta cells are lacking. The significance of non-coding RNAs in various cellular processes is emerging. In this study, we aimed to show the direct negative impact of GC on beta cell function and elucidate the role of riborepressor GAS5 lincRNA in the GC signaling pathway in human pancreatic beta cells.

METHODS

Patients undergoing two weeks of high-dose prednisolone therapy were monitored for C-peptide levels. Human pancreatic islets and the human beta cell line EndoC-βH1 were incubated in pharmacological concentrations of dexamethasone. The GAS5 level was modulated using anti-sense LNA gapmeR or short oligonucleotides with GAS5 HREM (hormone response element motif). Immunoblotting and/or real-time PCR were used to assess changes in protein and RNA expression, respectively. Functional characterization included glucose-stimulated insulin secretion and apoptosis assays. Correlation analysis was performed on RNAseq data of human pancreatic islets.

RESULTS

We found reduced C-peptide levels in patients undergoing high-dose GC therapy. Human islets and the human beta cell line EndoC-βH1 exposed to GC exhibited reduced insulin secretion and increased apoptosis. Concomitantly, reduced expression of important beta cell transcription factors, PDX1 and NKX6-1, as well as exocytotic protein SYT13 were observed. The expression of the glucocorticoid receptor was decreased, while that of serum and glucocorticoid-regulated kinase 1 (SGK1) was elevated. The expression of these genes was found to significantly correlate with GAS5 in human islet transcriptomics data. Increasing GAS5 levels using GAS5 HREM alleviated the inhibitory effects of dexamethasone on insulin secretion.

CONCLUSIONS

The direct adverse effect of glucocorticoid in human beta cell function is mediated via important beta cell proteins and components of the GC signaling pathway in an intricate interplay with GAS5 lincRNA, a potentially novel therapeutic target to counter GC-mediated beta cell dysfunction.

Dominance of the hypothalamus-pituitary-adrenal axis over the renin-angiotensin-aldosterone system is a risk factor for decreased insulin secretion

How the association between the hypothalamus-pituitary-adrenal (HPA) axis and the renin-angiotensin-aldosterone system (RAAS) affects glucose metabolism were not well examined in a general population. Participants of the population-based 2015 Iwaki study were enrolled (n: 1,016; age: 54.4 ± 15.1 years). Principal component (PC) analysis identified two PCs: PC1 represented levels of the HPA axis (serum cortisol) and the RAAS (plasma aldosterone) as a whole, and PC2 represented the HPA axis relative to the RAAS (HPA axis dominance). We examined the association between these PCs and glucose metabolism using homeostasis model assessment indices of reduced insulin sensitivity (HOMA-R) and secretion (HOMA-β). Univariate linear regression analyses showed a correlation between PC2 and HOMA-β (β = −0.248, p < 0.0001), but not between PC1 and HOMA-β (β = −0.004, p = 0.9048). The correration between PC2 and HOMA-β persisted after adjustment for multiple factors (β = −0.101, p = 0.0003). No correlations were found between the PCs and HOMA-R. When subjects were tertiled based on PC2, the highest tertile was at greater risk of decreased insulin secretion (defined as the lower one third of HOMA-β (≤68.9)) than the lowest tertile after adjustment for multiple factors (odds ratio, 2.00; 95% confidence interval, 1.35–2.97). The HPA axis dominance is associated with decreased insulin secretion in a Japanese population.

Association between Higher Serum Cortisol Levels and Decreased Insulin Secretion in a General Population

Glucocorticoids (GCs) are well known to induce insulin resistance. However, the effect of GCs on insulin secretion has not been well characterized under physiological conditions in human. We here evaluated the effect of GCs on insulin secretion/ß-cell function precisely in a physiological condition. A population-based study of 1,071 Japanese individuals enrolled in the 2014 Iwaki study (390 men, 681 women; aged 54.1 ± 15.1 years), those excluded individuals taking medication for diabetes or steroid treatment, were enrolled in the present study. Association between serum cortisol levels and insulin resistance/secretion assessed by homeostasis model assessment using fasting blood glucose and insulin levels (HOMA-R and HOMA-ß, respectively) were examined. Univariate linear regression analyses showed correlation of serum cortisol levels with HOMA-ß (ß = -0.134, p <0.001) but not with HOMA-R (ß = 0.042, p = 0.172). Adjustments for age, gender, and the multiple clinical characteristics correlated with HOMA indices showed similar results (HOMA-ß: ß = -0.062, p = 0.025; HOMA-R: ß = -0.023, p = 0.394). The correlation between serum cortisol levels and HOMA-ß remained significant after adjustment for HOMA- R (ß = -0.057, p = 0.034). When subjects were tertiled based on serum cortisol levels, the highest tertile was at greater risk of decreased insulin secretion (defined as lower one third of HOMA-ß (≤70)) than the lowest tertile, after adjustment for multiple factors including HOMA- R (odds ratio 1.26, 95% confidence interval 1.03–1.54). In conclusion, higher serum cortisol levels are significantly associated with decreased insulin secretion in the physiological cortisol range in a Japanese population.

Regulation of Glucose Homeostasis by Glucocorticoids

Glucocorticoids are steroid hormones that regulate multiple aspects of glucose homeostasis. Glucocorticoids promote gluconeogenesis in liver, whereas in skeletal muscle and white adipose tissue they decrease glucose uptake and utilization by antagonizing insulin response. Therefore, excess glucocorticoid exposure causes hyperglycemia and insulin resistance. Glucocorticoids also regulate glycogen metabolism. In liver, glucocorticoids increase glycogen storage, whereas in skeletal muscle they play a permissive role for catecholamine-induced glycogenolysis and/or inhibit insulin-stimulated glycogen synthesis. Moreover, glucocorticoids modulate the function of pancreatic α and β cells to regulate the secretion of glucagon and insulin, two hormones that play a pivotal role in the regulation of blood glucose levels. Overall, the major glucocorticoid effect on glucose homeostasis is to preserve plasma glucose for brain during stress, as transiently raising blood glucose is important to promote maximal brain function. In this chapter we will discuss the current understanding of the mechanisms underlying different aspects of glucocorticoid-regulated mammalian glucose homeostasis.

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.

Augmented β-Cell Function and Mass in Glucocorticoid-Treated Rodents Are Associated with Increased Islet Ir-β /AKT/mTOR and Decreased AMPK/ACC and AS160 Signaling

Glucocorticoid (GC) therapies may adversely cause insulin resistance (IR) that lead to a compensatory hyperinsulinemia due to insulin hypersecretion. The increased β-cell function is associated with increased insulin signaling that has the protein kinase B (AKT) substrate with 160 kDa (AS160) as an important downstream AKT effector. In muscle, both insulin and AMP-activated protein kinase (AMPK) signaling phosphorylate and inactivate AS160, which favors the glucose transporter (GLUT)-4 translocation to plasma membrane. Whether AS160 phosphorylation is modulated in islets from GC-treated subjects is unknown. For this, two animal models, Swiss mice and Wistar rats, were treated with dexamethasone (DEX) (1 mg/kg body weight) for 5 consecutive days. DEX treatment induced IR, hyperinsulinemia, and dyslipidemia in both species, but glucose intolerance and hyperglycemia only in rats. DEX treatment caused increased insulin secretion in response to glucose and augmented β-cell mass in both species that were associated with increased islet content and increased phosphorylation of the AS160 protein. Protein AKT phosphorylation, but not AMPK phosphorylation, was found significantly enhanced in islets from DEX-treated animals. We conclude that the augmented β-cell function developed in response to the GC-induced IR involves inhibition of the islet AS160 protein activity.

Twenty-four-hour profiles of plasma glucose, insulin, C-peptide and free fatty acid in subjects with varying degrees of glucose tolerance following short-term, medium-dose prednisone (20 mg/day) treatment: evidence for differing effects on insulin secretion and action

OBJECTIVE

To determine the time course and prandial effects of short-term, medium-dose prednisone on 24-h metabolic patterns under standardized conditions.

CONTEXT

Glucocorticoids (GCs) adversely affect glucose homoeostasis but 24-h profiles of glucose, insulin, C-peptide and free fatty acids (FFAs) following short-term, medium-dose prednisone treatment in persons with varying degrees of glucose tolerance are not well defined.

DESIGN

An open-label cross-sectional interventional study.

SUBJECTS

Three groups were prospectively studied: persons with type 2 diabetes (T2DM; n = 7), persons 'at risk' for T2DM (AR; n = 8) and persons with normal glucose tolerance (NGT; n = 5).

METHODS

Before and after 3-day treatment with prednisone 20 mg each morning, subjects underwent 24-h frequent blood sampling. Eucaloric mixed meals were provided at 08:00, 12:00 and 18:00 h. Insulin/glucose ratio provided an estimate of β-cell response to meal stimuli.

MEASUREMENTS

Plasma glucose, insulin, C-peptide, haemoglobin A1c and FFA.

RESULTS

Prednisone induced greater increases in glucose levels from midday (P = 0·001) to midnight (P = 0·02) in the T2DM than the AR and NGT groups. In contrast, insulin (P = 0·03) and C-peptide (P = 0·04) levels decreased postbreakfast in the T2DM group, whereas no changes in the morning but higher C-peptide levels (P = 0·03) from midday to midnight were observed in the AR group. In the T2DM group, insulin/glucose ratio decreased postbreakfast (P = 0·04) and increased postdinner (P = 0·03). Fasting glucose, insulin and C-peptide levels were unchanged in all groups, and FFA levels modestly increased postdinner (P = 0·03) in the NGT group.

CONCLUSION

Short-term, medium-dose prednisone treatment induces postprandial hyperglycaemia in T2DM and AR predominantly from midday to midnight because of suppression of insulin secretion followed by decreased insulin action that dissipates overnight. Effective treatment of prednisone-induced hyperglycaemia should target both rapid onset relative insulin deficiency and a less than 24-h total duration of effect.

Acute and 2-week exposure to prednisolone impair different aspects of beta-cell function in healthy men

OBJECTIVE

Glucocorticoids (GCs), such as prednisolone, are associated with adverse metabolic effects, including glucose intolerance and diabetes. In contrast to the well known GC-induced insulin resistance, the effects of GCs on beta-cell function are less well established. We assessed the acute and short-term effects of prednisolone treatment on beta-cell function in healthy men.

RESEARCH DESIGN AND METHODS

A randomised, double-blind, placebo-controlled trial consisting of two protocols was conducted. In protocol 1 (n=6), placebo and a single dose of 75 mg of prednisolone were administered. In protocol 2 (n=23), participants received 30 mg of prednisolone daily or placebo for 15 days. Both empirical and model-based parameters of beta-cell function were calculated from glucose, insulin and C-peptide concentrations obtained during standardised meal tests before and during prednisolone treatment (protocols 1 and 2), and 1 day after cessation of treatment (protocol 2).

RESULTS

Seventy-five milligrams of prednisolone acutely increased the area under the postprandial glucose curve (AUC(gluc); P=0.005), and inhibited several parameters of beta-cell function, including AUC(c-pep)/AUC(gluc) ratio (P=0.004), insulinogenic index (P=0.007), glucose sensitivity (P=0.02) and potentiation factor ratio (PFR; P=0.04). A 15-day treatment with prednisolone increased AUC(gluc) (P<0.001), despite augmented C-peptide secretion (P=0.05). beta-cell function parameters were impaired, including the fasting insulin secretory tone (P=0.02) and PFR (P=0.007).

CONCLUSIONS

Acute and short-term exposure to prednisolone impairs different aspects of beta-cell function, which contribute to its diabetogenic effects.

Novel insights into glucocorticoid-mediated diabetogenic effects: towards expansion of therapeutic options?

At pharmacological concentrations, glucocorticoids (GCs) display potent anti-inflammatory effects, and are therefore frequently prescribed by physicians to treat a wide variety of diseases. Despite excellent efficacy, GC therapy is hampered by their notorious metabolic side effect profile. Chronic exposure to increased levels of circulating GCs is associated with central adiposity, dyslipidaemia, skeletal muscle wasting, insulin resistance, glucose intolerance and overt diabetes. Remarkably, many of these side-effects of GC treatment resemble the various components of the metabolic syndrome (MetS), in which indeed subtle disturbances in the hypothalamic-pituitary-adrenal (HPA) axis and/or increased tissue sensitivity to GCs have been reported. Recent developments have led to renewed interest in the mechanisms of GC's diabetogenic effects. First, 'selective dissociating glucocorticoid receptor (GR) ligands', which aim to segregate GC's anti-inflammatory and metabolic actions, are currently being developed. Second, at present, selective 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) inhibitors, which may reduce local GC concentrations by inhibiting cortisone to cortisol conversion, are evaluated in clinical trials as a novel treatment modality for the MetS. In this review, we provide an update of the current knowledge on the mechanisms that underlie GC-induced dysmetabolic effects. In particular, recent progress in research into the role of GCs in the pathogenesis of insulin resistance and beta-cell dysfunction will be discussed.

The influence of sleep and sleep loss upon food intake and metabolism

The present review investigates the role of sleep and its alteration in triggering metabolic disorders. The reduction of the amount of time sleeping has become an endemic condition in modern society and the current literature has found important associations between sleep loss and alterations in nutritional and metabolic aspects. Studies suggest that individuals who sleep less have a higher probability of becoming obese. It can be related to the increase of ghrelin and decrease of leptin levels, generating an increase of appetite and hunger. Sleep loss has been closely associated with problems in glucose metabolism and a higher risk for the development of insulin resistance and diabetes, and this disturbance may reflect decreased efficacy of the negative-feedback regulation of the hypothalamic–pituitary–adrenal axis. The period of sleep is also associated with an increase of blood lipid concentrations, which can be intensified under conditions of reduced sleep time, leading to disorders in fat metabolism. Based on a review of the literature, we conclude that sleep loss represents an important risk factor for weight gain, insulin resistance, type 2 diabetes and dyslipidaemia. Therefore, an adequate sleep pattern is fundamental for the nutritional balance of the body and should be encouraged by professionals in the area.

Direct glucocorticoid inhibition of insulin secretion. An in vitro study of dexamethasone effects in mouse islets

The direct effects of glucocorticoids on pancreatic beta cell function were studied with normal mouse islets. Dexamethasone inhibited insulin secretion from cultured islets in a concentration-dependent manner: maximum of approximately 75% at 250 nM and IC50 at approximately 20 nM dexamethasone. This inhibition was of slow onset (0, 20, and 40% after 1, 2, and 3 h) and only slowly reversible. It was prevented by a blocker of nuclear glucocorticoid receptors, by pertussis toxin, by a phorbol ester, and by dibutyryl cAMP, but was unaffected by an increase in the fuel content of the culture medium. Dexamethasone treatment did not affect islet cAMP levels but slightly reduced inositol phosphate formation. After 18 h of culture with or without 1 microM dexamethasone, the islets were perifused and stimulated by a rise in the glucose concentration from 3 to 15 mM. Both phases of insulin secretion were similarly decreased in dexamethasone-treated islets as compared with control islets. This inhibition could not be ascribed to a lowering of insulin stores (higher in dexamethasone-treated islets), to an alteration of glucose metabolism (glucose oxidation and NAD(P)H changes were unaffected), or to a lesser rise of cytoplasmic Ca2+ in beta cells (only the frequency of the oscillations was modified). Dexamethasone also inhibited insulin secretion induced by arginine, tolbutamide, or high K+. In this case also the inhibition was observed despite a normal rise of cytoplasmic Ca2+. In conclusion, dexamethasone inhibits insulin secretion through a genomic action in beta cells that leads to a decrease in the efficacy of cytoplasmic Ca2+ on the exocytotic process.

Beta-cell activity and hepatic insulin extraction following dexamethasone administration in healthy subjects

Glucocorticoids induce an increase of hepatic glucose production and peripheral resistance to insulin action. It is further assumed that dexamethasone administration in humans causes insulin hypersecretion, although inferences on beta-cell activity have been made in absolute terms and mostly from observations of systemic insulin concentration. In fact, the role of hepatic insulin extraction in humans treated long-term with glucocorticoids has not been investigated. The aim of the present study was to factor out quantitatively the main components of the insulin pathway that are responsible for the peripheral hypersecretion observed after steroids. Frequently sampled intravenous (FSIGT) and oral (OGTT) glucose tolerance tests were performed in healthy subjects before and after 5 days of oral dexamethasone administration (4 mg/d). Insulin sensitivity, beta-cell secretion, and hepatic insulin extraction were estimated by means of mathematical modeling. After steroids, insulin sensitivity decreased from 6.00 +/- 1.29 to 4.23 +/- 1.04 min-1/(microU/mL) (P < .04). Basal beta-cell secretion increased from 45 +/- 7 to 104 +/- 26 pmol/L . min-1 (P < .004) during the FSIGT and from 40 +/- 6 to 88 +/- 21 (P < .05) during the OGTT; total insulin release increased from 19 +/- 5 to 36 +/- 7 nmol/L in 180 minutes (P < .005) and from 33 +/- 5 to 50 +/- 10 (P < .02), respectively, FSIGT data also showed that first-phase beta-cell sensitivity increased from 236 +/- 39 to 309 +/- 33 pmol/L . min-1/(mg/dL) (P < .04), and second-phase from 631 +/- 154 to 1,103 +/ 196 10(4) pmol/L . min-2/(mg/dL) (P < .03). Posthepatic insulin delivery increased only insignificantly during the FSIGT (from 3.4 +/- 0.6 to 4.5 +/- 0.5 nmol/L, P = .073) due to an augmented hepatic insulin extraction from 73.0% +/- 7.2% to 83.0% +/- 3.5% (P < .05). During the OGTT, posthepatic insulin delivery increased after treatment from 6.6 +/- 1.2 to 11.4 +/- 2.5 nmol/L (P < .035) due to an increase, although slight, of hepatic insulin extraction from 77.4% +/- 1.9% to 79.3% +/- 3.3% (P = .319). The increased overall beta-cell activity during both tests was observed also by analyzing OGTT profiles of islet amyloid polypeptide (IAPP), the secretion of which was higher after steroids (basal, 0.081 +/- 0.012 v 0.272 +/- 0.082 pmol/L/min, P < .02; total, 35 +/- 8 v 116 +/- 48 mpmol/L in 3 hours, P < .05). In conclusion, after dexamethasone administration, peripheral hyperinsulinemia due to marked prehepatic beta-cell insulin hypersecretion is partially ameliorated by a concomitant increase of hepatic insulin clearance, which is more evident during a FSIGT. Model-derived secretion parameters from the OGTT and FSIGT produced comparable results, indicating that both tests, when properly analyzed, are feasible tools to evaluate insulin secretion.

Effects of morning cortisol elevation on insulin secretion and glucose regulation in humans

The time course of the effects of an acute elevation in morning plasma cortisol on the daytime profiles of plasma glucose, serum insulin, and insulin secretion under constant glucose infusion was determined using a placebo-controlled design in two groups of eight normal men. In one group, the elevation of plasma cortisol was obtained by oral administration of 100 mg hydrocortisone. In the other group, the elevation was obtained by intravenous administration of 25 micrograms of corticotropin-releasing hormone. In both studies, the immediate effect of the increase in plasma cortisol, even when of very small amplitude, was an abrupt inhibition of insulin secretion without change in glucose concentration. Larger cortisol elevations, such as occurred after hydrocortisone administration, were additionally associated with the appearance of insulin resistance, which developed 4-6 h after the cortisol elevation and persisted for > 16 h. These observations support the concept that the 24-h cortisol rhythmicity is responsible, at least in part, for the normal diurnal variation in glucose tolerance.

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.

Effect of adrenal steroids on insulin release from cultured rat islets of Langerhans

The effect of additions to the culture medium of some natural or synthetic corticosteroid hormones was studied in cultured rat islets of Langerhans. The steroids decreased glucose-induced insulin release. The extent of inhibition by dexamethasone was 18-55%, prednisolone 23%, hydrocortisone 21% and aldosterone 18%. None of them affected the basal secretion of insulin or had any effect on diameter or insulin content of the islet. The inhibitory action of dexamethasone on insulin release was observed in the range 63 nmol/l to 6.3 mumol/l. At 6.3 mumol/l during two h, dexamethasone (a) inhibited insulin response to glucose concentrations above 5 mmol/l (b) caused a delay in the first phase and markedly reduced the second phase of insulin release of perifused islets, and (c) decreased the incorporation of [H3]-leucine into total islet proteins without affecting [H3]-leucine-incorporation into insulin plus proinsulin. It is suggested that steroids, by directly acting on the islets of Langerhans, may modulate the insulin-release response to secretagogues.

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

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

The effect of insulin and hydrocortisone on the in vivo tissue uptake of 2-deoxyglucose in mice

The purpose of this study was to assess the feasibility and limitations of using the uptake of 14C-2-deoxyglucose (14C-2DG) under nonsteady-state conditions in the conscious mouse as a screening model for detecting changes in glucose uptake. Male, Swiss--Webster mice were administered an i.v. dose of 2-deoxyglucose (2DG, 50-75 mg/kg) with 14C-2DG (20 microCi/kg, 44-66 microCi/mmole). The levels of 14C-2DG were measured in gastrocnemius muscle, retroperitoneal fat, liver, cerebral cortex, and blood. Insulin (2 U/kg) s.c. significantly reduced 2DG levels in blood and liver compared to saline controls but significantly increased 2DG levels in muscle and fat. There was no effect on cerebral cortex 2DG uptake. Hydrocortisone (HC) treatment (300 mg/kg, i.p.) significantly reduced brain and muscle 2DG uptake. The effect of HC on brain 2DG levels may be caused by an indirect effect since determination of the 14C-sorbitol space indicated that HC reduced sorbitol levels in the brain when compared to saline controls, a reduction not detected in muscle. The limitations of the model seem to involve the brain and liver. Increasing glucose concentrations (i.v. glucose challenge) lead to decreased 2DG brain levels. It also appears that 2DG may not be reflecting glucose assimilation in the liver. However, it appears that the in vivo 2DG uptake model is a useful screening method for detecting changes in 2DG assimilation in fat and muscle following drug treatment.