Dexamethasone-induced insulin resistance and pancreatic adaptive response in aging rats are not modified by oral vanadyl sulfate treatment

Ocimum gratissimum enhances insulin sensitivity in male Wistar rats with dexamethasone-induced insulin resistance

Purpose

The antidiabetic activities of Ocimum gratissimum (OG) leaf extract are well documented in experimental diabetes induced by beta cell destruction resulting in hypoinsulinemia. There is however paucity of data on its effect in conditions characterized by hyperinsulinemia. This study therefore investigated the effect of OG on insulin resistance induced by dexamethasone in male Wistar rats.

Method

Twenty male Wistar rats grouped as control, normal + OG, Dex and Dex + OG were used. Control and normal + OG received normal saline while Dex and Dex + OG received dexamethasone (1 mg/kg, i.p) followed by distilled water or OG (400 mg/kg) for 10 days. Levels of fasting blood glucose (FBG), insulin, HOMA-IR, liver and muscle glycogen, hexokinase activities, hepatic HMG CoA reductase activity were obtained. Histopathology of pancreas and liver tissues was carried out using standard procedures.

Results

Body weight reduced significantly in the Dex and Dex + OG groups compared with the control. FBG (147.8 ± 9.93 mg/dL), insulin (2.98 ± 0.49 µIU/ml) and HOMA-IR (1.11 ± 0.22) of Dex animals were higher than the control (FBG = 89.22 ± 6.53 mg/dL; insulin = 1.70 ± 0.49 µIU/ml; HOMA-IR = 0.37 ± 0.04). These were significantly reduced in the Dex + OG (FBG = 115.31 ± 5.93 mg/dL; insulin = 1.85 ± 0.11µIU/ml; HOMA-IR = 0.53 ± 0.08) compared with Dex. Glycogen content and hexokinase activities were increased in the Dex + OG. Increased pancreatic islet size, hepatic steatosis and HMG Co A reductase activity were observed in the Dex but reduced in Dex + OG.

Conclusion

OG promotes cellular glucose utilization and reduces hepatic fat accumulation in Wistar rats with insulin resistance induced by dexamethasone. Further study to identify the involved signal transduction will throw more light on the observed effects.

Immunomodulatory effect of melatonin supplementation in experimental diabetes

Aim: To investigate the effect of melatonin on the immunomodulatory response in experimental type 1 and 2 diabetes mellitus.

Methods: Experiments were performed on male rats (180–200 g), purchased from the Experimental Animal Holding,. Animals were maintained in standard diet conditions. Two pathological states were simulated on male rats: experimental type 1 and type 2 diabetes. Melatonin was introduced from 14 to 23 days of experiment intraperitoneally. Levels of immunoglobulin classes A, M and G (Ig A, M, G), circulating immune complexes (CIC), interleukin 1β (EE), interleukin 6 (IL-6), and tumor necrosis factor (TNF-a) were measured.

Results: We demonstrated that melatonin in case of immune hyperactivity, can, provide a suppressive effect and is able to enhance immune reactivity under conditions of its limitation, indicating the immunostimulating activity. Furthermore, we found that administration of melatonin decreased inflammatory responses by mediating the levels of immunomodulatory factors, including TNF-α, IL-1β and IL-6.

Conclusion: Melatonin is a positive regulator of immune system, may be a potential therapeutic agent, it has no reported side effects.

Hypoglycemic Properties of the Aqueous Extract from the Stem Bark of Ceiba pentandra in Dexamethasone-Induced Insulin Resistant Rats

Parts of Ceiba pentandra are wildly used in Africa to treat diabetes and previous works have demonstrated their in vivo antidiabetic effects on type 1 diabetes models. In addition, it has been recently shown that the decoction and the methanol extract from the stem bark of C. pentandra potentiate in vitro, the peripheral glucose consumption by the liver and skeletal muscle slices. But nothing is known about its effect on type II diabetes, especially on insulin resistance condition. We investigated herein the antihyperglycemic, insulin-sensitizing potential, and cardioprotective effects of the dried decoction from the stem bark of Ceiba pentandra (DCP) in dexamethasone-induced insulin resistant rats. DCP phytochemical analysis using LC-MS showed the presence of many compounds, including 8-formyl-7-hydroxy-5-isopropyl-2-methoxy-3-methyl-1,4-naphthaquinone, 2,4,6-trimethoxyphenol, and vavain. Wistar rats were given intramuscularly (i.m.) dexamethasone (1 mg/kg/day) alone or concomitantly with oral doses of DCP (75 or 150 mg/kg/day) or metformin (40 mg/kg/day) for 9 days. Parameters such as body weight, glycemia, oral glucose tolerance, plasma triglycerides and cholesterol, blood pressure, and heart rate were evaluated. Moreover, cardiac, hepatic and aortic antioxidants (reduced glutathione, catalase, and superoxide dismutase), malondialdehyde level, and nitric oxide content were determined. DCP decreased glycemia by up to 34% and corrected the impairment of glucose tolerance induced by dexamethasone but has no significant effect on blood pressure and heart rate. DCP reduced the total plasma cholesterol and triglycerides as compared to animals treated only with dexamethasone. DCP also increased catalase, glutathione, and NO levels impaired by dexamethasone, without any effect on SOD and malondialdehyde. In conclusion, the decoction of the stem bark of Ceiba pentandra has insulin sensitive effects as demonstrated by the improvement of glucose tolerance, oxidative status, and plasma lipid profile. This extract may therefore be a good candidate for the treatment of type II diabetes.

Experimental model of glucocorticoid-induced insulin resistance

PURPOSE:

To evaluate metabolic effects in experimental model of glucocorticoid-induced insulin resistance.

METHODS:

Twenty Wistar male rats were randomly divided into two groups, which were treated with intraperitoneally injected dexamethasone 1mg/Kg/day for ten days consecutively (Group D; n=10) and placebo (Group C; n=10). The variables analyzed were: from the first to the 10th day - body weight (before and after treatment); food and water daily consumption; on the 10th day - glycemia, insulinemia, HOMA-beta and HOMA-IR. The blood samples for laboratory analysis were obtained by intracardiac puncture. Also on the 10th day liver fragments were taken for analyzing glycogen and fattty.

RESULTS:

Group D animals compared to group C had: weight reduction (g), (D=226.5±24.7 vs C=295.0±25.4; p=0.001); increased glycemia (mmol/l) (D=19.5±2.1 vs C=14.2±3.1; p=0.0001); diminished insulinemia (mU/l) (D=0.2±0.1 vs C=2.0±0.4; p=0.0001); reduced HOMA-β (D=0.2±0.1 vs C=4.2±1.7; p=0.0002); diminished HOMA-IR (D=0.2±0.1 vs C=1.3±0.4; p=0.0002). Histological examination of the liver showed that 100% of group D and none of group C had moderate fatty. (p=0.2).

CONCLUSION:

Animals treated with glucocorticoid, in this experimental model, expressed hyperglycemia, hypoinsulinism and decreased peripheral insulin sensitivity.

The Metabolic Implications of Glucocorticoids in a High-Fat Diet Setting and the Counter-Effects of Exercise

Glucocorticoids (GCs) are steroid hormones, naturally produced by activation of the hypothalamic-pituitary-adrenal (HPA) axis, that mediate the immune and metabolic systems. Synthetic GCs are used to treat a number of inflammatory conditions and diseases including lupus and rheumatoid arthritis. Generally, chronic or high dose GC administration is associated with side effects such as steroid-induced skeletal muscle loss, visceral adiposity, and diabetes development. Patients who are taking exogenous GCs could also be more susceptible to poor food choices, but the effect that increasing fat consumption in combination with elevated exogenous GCs has only recently been investigated. Overall, these studies show that the damaging metabolic effects initiated through exogenous GC treatment are significantly amplified when combined with a high fat diet (HFD). Rodent studies of a HFD and elevated GCs demonstrate more glucose intolerance, hyperinsulinemia, visceral adiposity, and skeletal muscle lipid deposition when compared to rodents subjected to either treatment on its own. Exercise has recently been shown to be a viable therapeutic option for GC-treated, high-fat fed rodents, with the potential mechanisms still being examined. Clinically, these mechanistic studies underscore the importance of a low fat diet and increased physical activity levels when individuals are given a course of GC treatment.

Hierarchical glucocorticoid-endocannabinoid interplay regulates the activation of the nucleus accumbens by insulin

Here we asked if insulin activation of the nucleus accumbens in vitro is reflected by an increase in (3)H-deoxyglucose ([(3)H]DG) uptake, thus subserving a new model to study molecular mechanisms of central insulin actions. Additionally, we investigated the dependence of this insulin effect on endocannabinoids and corticosteroids, two major culprits in insulin resistance. We found that in acute accumbal slices, insulin (3 and 300nM but not at 0.3nM) produced an increase in [(3)H]DG uptake. The synthetic cannabinoid agonist, WIN55212-2 (500nM) and the glucocorticoid dexamethasone (10μM), impaired insulin (300nM) action on [(3)H]DG uptake. The glucocorticoid receptor (GcR) antagonist, mifepristone (10μM) prevented dexamethasone from inhibiting insulin's action. Strikingly, this anti-insulin action of dexamethasone was also blocked by two CB1 cannabinoid receptor (CB1R) antagonists, O-2050 (500nM) and SR141716A (500nM), as well as by tetrahydrolipstatin (10μM), an inhibitor of diacylglycerol lipases-the enzymes responsible for the synthesis of the endocannabinoid, 2-arachidonoyl-glycerol (2-AG). On the other hand, the blockade of the post-synaptic 2-AG metabolizing enzymes, α,β-serine hydrolase domain 6/12 by WWL70 (1μM) also prevented the action of insulin, probably via increasing endogenous 2-AG tone. Additionally, an anti-insulin receptor (InsR) antibody immunoprecipitated CB1Rs from accumbal homogenates, indicating a physical complexing of CB1Rs with InsRs that supports their functional interaction. Altogether, insulin stimulates glucose uptake in the nucleus accumbens. Accumbal GcR activation triggers the synthesis of 2-AG that in turn binds to the known CB1R-InsR heteromer, thus impeding insulin signaling.

Deleterious effects of prepubertal corticosterone treatment on rat prostate

PURPOSE

To investigate the structural and functional changes induced by corticosterone (CORT) in the ventral prostrate (VP) of rats in order to study chronic stress effects in the prepubertal phase.

METHODS

Wistar rats received daily saline or CORT injections during the pubertal period from the 5th to 25th day of postnatal life. The animals were distributed into four groups: 1 - Control (n=5); 2 - Control 99mTc-P (n=5); 3 - Treated with CORT (n=14); 4 - Treated with CORT and 99mTc-P (n=10). All rats were sacrificed at two months of age. Technical tissue uptakes of 99mTc-P were used to evaluate the functional and stereological methods for morphological analysis.

RESULTS

Acini distribution in the group treated with CORT differed significantly (p<0.0001) from the control. The control group's epithelial average height (10.01±0.24 microns) was statistically significant (p<0.0001) from rats treated with CORT (19.27±0.73microns). The collagen distribution was lower in the treated group (2.79%) when compared to control (3.97%). The radioactivity percentage in the groups marked with 99mTc-P (%Ati/g) did not demonstrate a statistically significant difference (p=0.285897).

CONCLUSION

Chronic administration of corticosterone in prepubertal rats causes changes in their acinar structure and their ventral prostate stroma, indicating possible deleterious effects of this hormone.

Age-related impairment of pancreatic Beta-cell function: pathophysiological and cellular mechanisms

The incidence of type 2 diabetes significantly increases with age. The relevance of this association is dramatically magnified by the concomitant global aging of the population, but the underlying mechanisms remain to be fully elucidated. Here, some recent advances in this field are reviewed at the level of both the pathophysiology of glucose homeostasis and the cellular senescence of pancreatic islets. Overall, recent results highlight the crucial role of beta-cell dysfunction in the age-related impairment of pancreatic endocrine function and delineate the possibility of new original therapeutic interventions.

Dynamic modeling of methylprednisolone effects on body weight and glucose regulation in rats

Influences of methylprednisolone (MPL) and food consumption on body weight (BW), and the effects of MPL on glycemic control including food consumption and the dynamic interactions among glucose, insulin, and free fatty acids (FFA) were evaluated in normal male Wistar rats. Six groups of animals received either saline or MPL via subcutaneous infusions at the rate of 0.03, 0.1, 0.2, 0.3 and 0.4 mg/kg/h for different treatment periods. BW and food consumption were measured twice a week. Plasma concentrations of MPL and corticosterone (CST) were determined at animal sacrifice. Plasma glucose, insulin, and FFA were measured at various times after infusion. Plasma MPL concentrations were simulated by a two-compartment model and used as the driving force in the pharmacodynamic (PD) analysis. All data were modeled using ADAPT 5. The MPL treatments caused reduction of food consumption and body weights in all dosing groups. The steroid also caused changes in plasma glucose, insulin, and FFA concentrations. Hyperinsulinemia was achieved rapidly at the first sampling time of 6 h; significant elevations of FFA were observed in all drug treatment groups; whereas only modest increases in plasma glucose were observed in the low dosing groups (0.03 and 0.1 mg/kg/h). Body weight changes were modeled by dual actions of MPL: inhibition of food consumption and stimulation of weight loss, with food consumption accounting for the input of energy for body weight. Dynamic models of glucose and insulin feedback interactions were extended to capture the major metabolic effects of FFA: stimulation of insulin secretion and inhibition of insulin-stimulated glucose utilization. These models of body weight and glucose regulation adequately captured the experimental data and reflect significant physiological interactions among glucose, insulin, and FFA. These mechanism-based PD models provide further insights into the multi-factor control of this essential metabolic system.

Hypoglycaemic and anti-diabetic activity of stem bark extracts Erythrina indica in normal and alloxan-induced diabetic rats

The objective of the study is to investigate the alcoholic (AlcE) and aqueous (AqsE) extracts of stem bark of Erythrina indica (Papilionaceae) for hypoglycaemic effects in normal and diabetic rats. Diabetes was induced in rats by a single dose administration of alloxan (120 mg/kg, i.p.) or by injecting dexamethasone (10 mg/kg, i.p.) for 10 days. In normal rats, AlcE and AqsE had significantly decreased the blood glucose level (BGL) in a dose dependent manner after repeated administration for 7 days. In alloxan-induced diabetic rats, both the extracts decreased blood sugar levels with significant improvement in glucose tolerance and body weight at the end of 1st, 2nd and 3rd week after test extract treatment. In case of dexamethasone induced insulin resistant diabetic rats, repeated administration of AlcE and AqsE inhibited the increase in blood glucose level and improved glucose tolerance induced by dexamethasone as compared to dexamethasone induced diabetic rats. These results suggest that both extracts possess hypoglycaemic activity in normal as well as in diabetic rats. Among AlcE and AqsE, AqsE possesses better hypoglycaemic activity than AlcE in all the models. Preliminary phytochemical investigations revealed that alcoholic extracts contain carbohydrates, alkaloids, flavonoids, saponins, phytosterols, phenolics and tannins. Aqueous extract contains carbohydrates, alkaloids, flavonoids, glycosides, phytosterols and triterpenoids. These phytoconstituents may be responsible for the hypoglycaemic activity of the plant.

Involvement of the cholinergic pathway in glucocorticoid-induced hyperinsulinemia in rats

AIMS

We investigated the contribution of the cholinergic nervous system to dexamethasone-induced insulin resistance and hyperinsulinemia in rats.

METHODS

Seventy-day-old Wistar male rats were distributed in groups: control (CTL), vagotomized (VAG), and sham operated (SHAM). On the 90th day of life, half of the rats were treated daily with 1mg/kg of dexamethasone for 5 days (CTL DEX, VAG DEX, and SHAM DEX).

RESULTS

In the presence of 8.3mM glucose plus 100microM carbachol (Cch), isolated islets from CTL DEX secreted significantly more insulin than CTL. Cch-enhancement of secretion was further increased in islets from VAG CTL and VAG DEX than SHAM CTL and SHAM DEX, respectively. In CTL DEX islets, M3R and PLCbeta1 and phosphorylated PKCalpha, but not PKCalpha, protein content was significantly higher compared with each respective control. In islets from VAG DEX, the expression of M3R protein increased significantly compared to VAG CTL and SHAM DEX. Vagotomy per se did not affect insulin resistance, but attenuated fasted and fed insulinemia in VAG DEX, compared with SHAM DEX rats.

CONCLUSION

These data indicate an important participation of the cholinergic nervous system through muscaric receptors in dexamethasone-induced hyperinsulinemia in rats.

Effects of decavanadate and insulin enhancing vanadium compounds on glucose uptake in isolated rat adipocytes

The effects of different vanadium compounds namely pyridine-2,6-dicarboxylatedioxovanadium(V) (V5-dipic), bis(maltolato) oxovanadium(IV) (BMOV) and amavadine, and oligovanadates namely metavanadate and decavanadate were analysed on basal and insulin stimulated glucose uptake in rat adipocytes. Decavanadate (50 microM), manifest a higher increases (6-fold) on glucose uptake compared with basal, followed by BMOV (1 mM) and metavanadate (1 mM) solutions (3-fold) whereas V5 dipic and amavadine had no effect. Decavanadate (100 microM) also shows the highest insulin like activity when compared with the others compounds studied. In the presence of insulin (10 nM), only decavanadate increases (50%) the glucose uptake when compared with insulin stimulated glucose uptake whereas BMOV and metavanadate, had no effect and V5 dipic and amavadine prevent the stimulation to about half of the basal value. Decavanadate is also able to reduce or eradicate the suppressor effect caused by dexamethasone on glucose uptake at the level of the adipocytes. Altogether, vanadium compounds and oligovanadates with several structures and coordination spheres reveal different effects on glucose uptake in rat primary adipocytes.

Fat feeding potentiates the diabetogenic effect of dexamethasone in Wistar rats

Background

The role of cortisol and its increased action/availability is implicated in the pathogenesis of insulin resistance associated with obesity and metabolic syndrome but the mechanism of increased action/availability is not known. Availability of several other lipophilic hormones, drugs and pollutants are also reported to be increased in obesity. Increased lipids in the circulation are reported to alter the fluidity and permeability of membranes. Hyperlipidemia is also reported to alter the pharmacokinetics and pharmacodynamics of lipophilic molecules and also membrane fluidity and permeability. In this context we assumed that the hyperlipidemia associated with human obesity might play a role in the altered action/availability of cortisol and this in turn might have initiated the metabolic complications. To evaluate our assumption we have administered dexamethasone [low [50 μg/kg/day] or high [250 μg/kg/day] dose] to high-fat [coconut oil & vanaspati] fed rats and the results were compared with rats administered with either dexamethasone or high-fat.

Results and Discussion

Within two weeks, the rats co-administered with high-fat and dexamethasone developed severe hyperglycemia, hyperlipidemia and insulin resistance compared to rats treated either of them alone. High-fat fed rats treated with higher dose of dexamethasone were presented with severe hyperglycemia, insulin resistance and also severe glycosuria. The hyperlipidemia caused by high-fat feeding might have altered the transport and distribution of dexamethasone, probably by altering the physical state of membranes and transport proteins.

Conclusion

From the results obtained, it can be speculated that the altered lipid and cortisol metabolism could affect one another, forming a vicious cycle.

Dexamethasone treatment in vivo counteracts the functional pancreatic islet alterations caused by malnourishment in rats

The effects of dexamethasone (Dex) on the metabolic parameters, peripheral insulin, and glucose sensitivity in vivo as well as on islet function ex vivo of rats submitted to low-protein diet were analyzed. Dexamethasone (1.0 mg/kg body weight) was administered intraperitoneally daily to adult Wistar rats fed on a normal-protein diet or low-protein diet (LPD) for 5 days, whereas control rats fed on a normal-protein diet or low-protein diet (LP) received saline alone. At the end of the experimental period, LP rats showed a significant reduction in serum insulin, total serum protein, and serum albumin levels compared with rats fed on a normal-protein diet (P<.05). All these parameters tended to be normalized in LPD rats (P<.05); furthermore, these rats exhibited increased serum glucose and nonesterified fatty acid levels compared with LP rats (P<.05). Rats submitted to the low-protein diet demonstrated normal peripheral glucose sensitivity and improved peripheral insulin sensitivity, which was reversed by Dex treatment. A reduced area of islets from LP rats was partially recovered in LPD rats (P<.05). At 16.7 mmol/L glucose, insulin secretion from LPD islets was also partially recovered and was significantly higher than that from LP islets (P<.05). In conclusion, induction of insulin resistance by Dex treatment reverses most of the metabolic alterations in rats submitted to a low-protein diet. In addition, several islet functions were also improved by Dex, confirming the plasticity of pancreatic islets in adverse conditions.

Increased pancreatic islet mass is accompanied by activation of the insulin receptor substrate-2/serine-threonine kinase pathway and augmented cyclin D2 protein levels in insulin-resistant rats

It is well known that glucocorticoids induce peripheral insulin resistance in rodents and humans. Here, we investigated the structural and ultrastructural modifications, as well as the proteins involved in beta-cell function and proliferation, in islets from insulin-resistant rats. Adult male Wistar rats were made insulin resistant by daily administration of dexamethasone (DEX; 1mg/kg, i.p.) for five consecutive days, whilst control (CTL) rats received saline alone. Structure analyses showed a marked hypertrophy of DEX islets with an increase of 1.7-fold in islet mass and of 1.6-fold in islet density compared with CTL islets (P < 0.05). Ultrastructural evaluation of islets revealed an increased amount of secreting organelles, such as endoplasmic reticulum and Golgi apparatus in DEX islets. Mitotic figures were observed in DEX islets at structural and ultrastructural levels. Beta-cell proliferation, evaluated at the immunohistochemical level using anti-PCNA (proliferating cell nuclear antigen), showed an increase in pancreatic beta-cell proliferation of 6.4-fold in DEX islets compared with CTL islets (P < 0.0001). Increases in insulin receptor substrate-2 (IRS-2), phosphorylated-serine-threonine kinase AKT (p-AKT), cyclin D(2) and a decrease in retinoblastoma protein (pRb) levels were observed in DEX islets compared with CTL islets (P < 0.05). Therefore, during the development of insulin resistance, the endocrine pancreas adapts itself increasing beta-cell mass and proliferation, resulting in an amelioration of the functions. The potential mechanisms that underlie these events involve the activation of the IRS-2/AKT pathway and activation of the cell cycle, mediated by cyclin D(2). These adaptations permit the maintenance of glycaemia at near-physiological ranges.

Functional alterations in endocrine pancreas of rats with different degrees of dexamethasone-induced insulin resistance

OBJECTIVES

We have analyzed the peripheral insulin and glucose sensitivity in vivo, and islet function ex vivo in rats with different degrees of insulin resistance induced by dexamethasone (DEX).

METHODS

Dexamethasone, in the concentrations of 0.1 (DEX 0.1), 0.5 (DEX 0.5), and 1.0 mg/kg body weight (DEX 1.0) was administered daily, intraperitoneally, to adult Wistar rats for 5 days, whereas controls received saline.

RESULTS

Dexamethasone treatment induced peripheral insulin resistance in a dose-dependent manner. At the end of the treatment, only DEX 1.0 rats showed significant increase of postabsorptive blood glucose and serum triglycerides, and nonesterified fatty acids levels. Incubation of pancreatic islets in increasing glucose concentrations (2.8-22 mM) led to an augmented insulin secretion in all DEX-treated rats. Leucine, carbachol, and high KCl concentrations induced the insulin release in DEX 0.5 and DEX 1.0, whereas arginine augmented secretion in all DEX-treated groups.

CONCLUSIONS

We demonstrate that in DEX 0.5 and, especially in DEX 0.1 groups, but not in DEX 1.0, the adaptations that occurred in the endocrine pancreas are able to counteract metabolic disorders (glucose intolerance and dyslipidemia). These animal models seem to be interesting approaches for the study of degrees of subjacent effects that may mediate type 2 diabetes (DEX 1.0) and islet function alterations, without collateral effects (DEX 0.1 and DEX 0.5).

Cellular changes in the prostatic stroma of glucocorticoid-treated rats

Glucocorticoid hormones (GCs) have been widely used for the treatment of prostate cancer because of their inhibitory property against tumour growth. However, their mechanism of action in the prostate has received little attention. Excess GCs can lead to peripheral insulin resistance resulting in hyperglycaemia and hyperinsulinaemia. Insulin plays an important role as a cellular stimulant and high levels are related to low levels of androgens. Our objective has been to describe the effects of insulin resistance induced by dexamethasone treatment on the morphology of rat ventral prostate. Male adult Wistar rats received daily intraperitoneal injections of dexamethasone or saline for five consecutive days after which the rats were killed and the ventral prostate was removed, weighed and prepared for conventional and transmission electron microscopy (TEM). Dexamethasone treatment resulted in atrophy and decreased proliferative activity of prostatic epithelial cells. TEM analysis revealed changes in the epithelium-stroma interface, with some interruptions in the basement membrane. Fibroblasts showed a secretory phenotype with dilated endoplasmic reticulum. Smooth muscle cells exhibited a contractile pattern with 50% atrophy, an irregular membrane and twisted nuclei. Mitochondrial alterations, such as enlarged size and high electron density in the mitochondrial matrix, were also detected in smooth muscle cells. Insulin resistance induced by dexamethasone is thus associated with epithelial atrophy similar to that described for diabetic rats. However, GCs are responsible for morphological changes in the stromal cell population suggesting the activation of fibroblasts and atrophy of the smooth muscle cells.

Effects of dexamethasone on insulin receptor in aging

The aim of this study was to examine the effects of dexamethasone (Dex) on functional properties of the rat insulin receptor (IR). Male Mill Hill hooded rats, 3, 6, 12, 18 and 21 months old, were injected with Dex (4 mg/kg) and rat liver and erythrocytes were used for experiments 18 h after Dex administration. Treatment with Dex lowered the specific binding (SB) of insulin (INS) in the liver of 3- and 18-month-old rats and concentration of INS binding sites (N1, N2) and the dissociation constant of low-affinity binding sites (Kd2) in the liver of 6- and 18-month-old rats. In addition, Dex treatment lowered the liver IR protein level in all analyzed groups, except 21-month-old rats where it remained unchanged, but raised the IR mRNA level in 18-month-old rats. In erythrocytes, treatment with Dex decreased SB and Kd2 (in animals 3 and 6 months old) and N1 (in ones 3 and 18 months old). Following Dex treatment, the INS plasma level increased (in rats 3, 18 and 21 months old), while glucose (Glu) concentration increased in 3 and 12 months old, but decreased in 6- and 21-month-old rats. In summary, Dex exerts the strongest effect on the erythrocyte IR of 3- and 6-month-old rats and the hepatic IR of 18-month-old rats. IR in both tissues is almost insensitive to Dex in 12- and 21-month-old rats. The pattern of age-related changes of IR induced by Dex does not correlate with changes of plasma Glu and INS.

Free fatty acids as mediators of adaptive compensatory responses to insulin resistance in dexamethasone-treated rats

BACKGROUND

Chronic low-dose dexamethasone (DEX) treatment in rats is associated to insulin resistance with compensatory hyperinsulinaemia and reduction in food intake. We tested the hypothesis that the elevation in circulating free fatty acids (FFAs) induced by DEX is the common mediator of both insulin resistance and insulin hyperproduction.

METHODS

For this purpose, an anti-lipolytic agent was administered during DEX treatment to lower lipacidaemia for several hours prior to glucose and insulin tolerance tests. Leptin expression in adipose tissue (by Northern blot) and plasma leptin levels (by radioimmunoassay) were also investigated to verify whether a rise in circulating leptin could be responsible for the anorectic effect of DEX.

RESULTS

Our data show that a transient pharmacological reduction of elevated plasma FFA levels abates the post-loading hyperinsulinaemia and counteracts the insulin resistance induced by DEX, supporting the hypothesis that the chronic elevation in FFAs is the common mediator of DEX-induced changes. Despite enhanced leptin expression in white adipose tissue, DEX-treated rats show no significant increase in plasma leptin levels. This suggests that the anorectic effect of DEX should be mediated, at least partially, by other factors, possibly related to the influence of concomitantly elevated plasma FFA and insulin levels on the hypothalamic centers regulating feeding.

CONCLUSIONS

Our results sustain the idea that a prolonged increase in plasma FFA levels plays an important role in the adaptive regulation of glucose and energy homeostasis, not only by potentiating insulin secretion but also by providing a signal of 'nutrient abundance' capable of restraining food intake.

Dexamethasone-induced insulin resistance is associated with increased connexin 36 mRNA and protein expression in pancreatic rat islets

Augmented glucose-stimulated insulin secretion (GSIS) is an adaptive mechanism exhibited by pancreatic islets from insulin-resistant animal models. Gap junction proteins have been proposed to contribute to islet function. As such, we investigated the expression of connexin 36 (Cx36), connexin 43 (Cx43), and the glucose transporter Glut2 at mRNA and protein levels in pancreatic islets of dexamethasone (DEX)-induced insulin-resistant rats. Study rats received daily injections of DEX (1 mg/kg body mass, i.p.) for 5 days, whereas control rats (CTL) received saline solution. DEX rats exhibited peripheral insulin resistance, as indicated by the significant postabsorptive insulin levels and by the constant rate for glucose disappearance (KITT). GSIS was significantly higher in DEX islets (1.8-fold in 16.7 mmol/L glucose vs. CTL, p < 0.05). A significant increase of 2.25-fold in islet area was observed in DEX vs. CTL islets (p < 0.05). Cx36 mRNA expression was significantly augmented, Cx43 diminished, and Glut2 mRNA was unaltered in islets of DEX vs. CTL (p < 0.05). Cx36 protein expression was 1.6-fold higher than that of CTL islets (p < 0.05). Glut2 protein expression was unaltered and Cx43 was not detected at the protein level. We conclude that DEX-induced insulin resistance is accompanied by increased GSIS and this may be associated with increase of Cx36 protein expression.

Effect of chronic psychological stress on insulin release from rat isolated pancreatic islets

Despite documented studies, the exact role of stress on diabetes is still unclear. The present study investigates the effect of chronic psychological stress on insulin release from isolated rat pancreatic islets. Male Wistar rats were divided into two groups of control and stressed (n=8/group). The animals of the stressed group were exposed to restraint stressors (1 h twice daily) for 15 or 30 consecutive days. At the beginning and end of the experimental periods, the animals were weighed and blood samples taken to determine the fasting plasma levels of glucose, insulin and corticosterone. On the following day the pancreatic islets of 5/group of the above animals were isolated and the static release of insulin in the presence of different glucose concentrations (2.8, 5.6, 8.3, 16.7 mM) was assessed. The results showed that in the stressed group, fasting plasma glucose levels were increased significantly on the 15th day as compared to the control group. However there was no significant increase on the 30th day. Fasting plasma insulin was significantly decreased on the 15th and 30th days of the experiment in the stressed group. Stressed rats showed significantly higher fasting plasma corticosterone levels, only on the 15th day, as compared to the control rats. In response to increasing concentrations of glucose, insulin release from islets of the stressed group was increased significantly on the 30th day of the experiment as compared to the control group. We conclude that chronic psychological stress could increase responsiveness of pancreatic beta cells to glucose, in vitro, and thus, low insulin levels of the stressed animals, in vivo, may be due to reason(s) other than the reduction of insulin releasing capacity of pancreatic beta cells.

Glucocorticoid administration and brief occlusion of the main pancreatic duct are likely to increase islet mass by a similar mechanism

OBJECTIVES

Both glucocorticoid (GC) administration and brief occlusion of the main pancreatic duct result in an increase in total islet mass. Consequently, it was questioned whether these 2 stimuli would produce similar islet growth, indicating commonality in the mechanism of expansion. To test this, we assessed the effects on morphology after single and dual stimulation of the pancreas.

METHODS

Rat pancreata were harvested 56 days after (1) brief occlusion of the main pancreatic duct, (2) daily GC administration, (3) GC administration and brief occlusion, or (4) sham operation without GC administration or occlusion. The pancreata were weighed, fixed, wax embedded, and sectioned for morphologic analysis. The endocrine to exocrine ratio, endocrine mass, and the contribution that small, medium, and large islets made to increased pancreatic endocrine mass were assessed. Blood was taken immediately before termination, after overnight fasting, for analysis of serum glucose, amylase, and insulin.

RESULTS

GC treatment resulted in increased total pancreatic mass and exocrine mass, which were dissimilar to increases elicited by brief occlusion. However, there was no significant difference in the increase in the total endocrine mass or the increased mass of small, medium, or large islets between the GC, occluded, and dually stimulated pancreata. There were also no significant differences in the mean number of cells per islet between these groups. GC administration increased both circulating glucose and insulin in both occluded and nonoccluded groups, whereas occlusion alone had no effect on these parameters.

CONCLUSIONS

Glucocorticoid administration and brief occlusion of the main pancreatic duct result in a similar expansion of islet mass. This is reflected in nonsignificant increases in endocrine mass/body weight and the percentage contribution of small, medium, and large islets to this increase. The majority of additional islet mass is from the expansion of the large islet population, although extra large islets are not found after either pancreatic treatment. The effects of GC treatment and occlusion are not additive, indicating that there is commonality in the mechanism of expansion. Because occlusion does not result in elevated glucose or insulin levels and gives rise to increased islet mass equivalent to GC administration and dual stimulation, it is unlikely that the increased islet mass after GC treatment is caused by the accompanying hyperinsulinemia as previously hypothesized.

The genomic response of skeletal muscle to methylprednisolone using microarrays: tailoring data mining to the structure of the pharmacogenomic time series

High-throughput data collection using gene microarrays has great potential as a method for addressing the pharmacogenomics of complex biological systems. Similarly, mechanism-based pharmacokinetic/pharmacodynamic modeling provides a tool for formulating quantitative testable hypotheses concerning the responses of complex biological systems. As the response of such systems to drugs generally entails cascades of molecular events in time, a time series design provides the best approach to capturing the full scope of drug effects. A major problem in using microarrays for high-throughput data collection is sorting through the massive amount of data in order to identify probe sets and genes of interest. Due to its inherent redundancy, a rich time series containing many time points and multiple samples per time point allows for the use of less stringent criteria of expression, expression change and data quality for initial filtering of unwanted probe sets. The remaining probe sets can then become the focus of more intense scrutiny by other methods, including temporal clustering, functional clustering and pharmacokinetic/pharmacodynamic modeling, which provide additional ways of identifying the probes and genes of pharmacological interest.