Glucocorticoids in vivo induce both insulin hypersecretion and enhanced glucose sensitivity of stimulus-secretion coupling in isolated rat islets

Although glucocorticoids are widely used as antiinflammatory agents in clinical therapies, they may cause serious side effects that include insulin resistance and hyperinsulinemia. To study the potential functional adaptations of the islet of Langerhans to in vivo glucocorticoid treatment, adult Wistar rats received dexamethasone (DEX) for 5 consecutive days, whereas controls (CTL) received only saline. The analysis of insulin release in freshly isolated islets showed an enhanced secretion in response to glucose in DEX-treated rats. The study of Ca2 2+ signals by fluorescence microscopy also demonstrated a higher response to glucose in islets from DEX-treated animals. However, no differences in Ca2 2+signals were found between both groups with tolbutamide or KCl, indicating that the alterations were probably related to metabolism. Thus, mitochondrial function was explored by monitoring oxidation of nicotinamide dinucleotide phosphate autofluorescence and mitochondrial membrane potential. Both parameters revealed a higher response to glucose in islets from DEX-treated rats. The mRNA and protein content of glucose transporter-2, glucokinase, and pyruvate kinase was similar in both groups, indicating that changes in these proteins were probably not involved in the increased mitochondrial function. Additionally,weexplored the status of Ca2 2+-dependent signaling kinases. Unlike calmodulin kinase II, we found an augmented phosphorylation level of protein kinase Cα as well as an increased response of the phospholipase C/inositol 1,4,5-triphosphate pathway in DEX-treated rats. Finally, an increased number of docked secretory granules were observed in the β-cells of DEX animals using transmission electron microscopy. Thus, these results demonstrate that islets from glucocorticoid-treated rats develop several adaptations that lead to an enhanced stimulus-secretion coupling and secretory capacity. Copyright © 2010 by The Endocrine Society.

Exercise at anaerobic threshold intensity and insulin secretion by isolated pancreatic islets of rats

To evaluate the effect of acute exercise and exercise training at the anaerobic threshold (AT) intensity on aerobic conditioning and insulin secretion by pancreatic islets, adult male Wistar rats were submitted to the lactate minimum test (LMT) for AT determination. Half of the animals were submitted to swimming exercise training (trained), 1 h/day, 5 days/week during 8 weeks, with an overload equivalent to the AT. The other half was kept sedentary. At the end of the experimental period, the rats were submitted to an oral glucose tolerance test and to another LMT. Then, the animals were sacrificed at rest or immediately after 20 minutes of swimming exercise at the AT intensity for pancreatic islets isolation. At the end of the experiment mean workload (% bw) at AT was higher and blood lactate concentration (mmol/L) was lower in the trained than in the control group. Rats trained at the AT intensity showed no alteration in the areas under blood glucose and insulin during OGTT test. Islet insulin content of trained rats was higher than in the sedentary rats while islet glucose uptake did not differ among the groups. The static insulin secretion in response to the high glucose concentration (16.7 mM) of the sedentary group at rest was lower than the sedentary group submitted to the acute exercise and the inverse was observed in relation to the trained groups. physical training at the AT intensity improved the aerobic condition and altered insulin secretory pattern by pancreatic islets. © 2010 Landes Bioscience.

Agelaia MP-I: A peptide isolated from the venom of the social wasp, Agelaia pallipes pallipes, enhances insulin secretion in mice pancreatic islets

Peptides isolated from animal venoms have shown the ability to regulate pancreatic beta cell function. Characterization of wasp venoms is important, since some components of these venoms present large molecular variability, and potential interactions with different signal transduction pathways. For example, the well studied mastoparan peptides interact with a diversity of cell types and cellular components and stimulate insulin secretion via the inhibition of ATP dependent K + (K ATP) channels, increasing intracellular Ca 2+ concentration. In this study, the insulin secretion of isolated pancreatic islets from adult Swiss mice was evaluated in the presence of synthetic Agelaia MP-I (AMP-I) peptide, and some mechanisms of action of this peptide on endocrine pancreatic function were characterized. AMP-I was manually synthesized using the Fmoc strategy, purified by RP-HPLC and analyzed using ESI-IT-TOF mass spectrometry. Isolated islets were incubated at increasing glucose concentrations (2.8, 11.1 and 22.2 mM) without (Control group: CTL) or with 10 μM AMP-I (AMP-I group). AMP-I increased insulin release at all tested glucose concentrations, when compared with CTL (P < 0.05). Since molecular analysis showed a potential role of the peptide interaction with ionic channels, insulin secretion was also analyzed in the presence of 250 μM diazoxide, a K ATP channel opener and 10 μM nifedipine, a Ca 2+ channel blocker. These drugs abolished insulin secretion in the CTL group in the presence of 2.8 and 11.1 mM glucose, whereas AMP-I also enhanced insulin secretory capacity, under these glucose conditions, when incubated with diazoxide and nifedipine. In conclusion, AMP-I increased beta cell secretion without interfering in K ATP and L-type Ca 2+ channel function, suggesting a different mechanism for this peptide, possibly by G protein interaction, due to the structural similarity of this peptide with Mastoparan-X, as obtained by modeling. © 2012 Elsevier Ltd.

Short communication: Acute but transient increase in serum insulin reduces messenger RNA expression of hepatic enzymes associated with progesterone catabolism in dairy cows

The objective of this experiment was to evaluate the effects of glucose infusion on serum concentrations of glucose, insulin, and progesterone (P4), as well as mRNA expression of hepatic CYP2C19 and CYP3A4 in nonlactating, ovariectomized cows in adequate nutritional status. Eight Gir × Holstein cows were maintained on a low-quality Brachiaria brizantha pasture with reduced forage availability, but they individually received, on average, 3. kg/cow daily (as fed) of a corn-based concentrate from d -28 to 0 of the experiment. All cows had an intravaginal P4-releasing device inserted on d -14, which remained in cows until the end of the experiment (d 1). On d 0, cows were randomly assigned to receive, in a crossover design containing 2 periods of 24. h each (d 0 and 1), (1) an intravenous glucose infusion (GLUC; 0.5. g of glucose/kg of BW, over a 3-h period) or (2) an intravenous saline infusion (SAL; 0.9%, over a 3-h period). Cows were fasted for 12. h before infusions, and they remained fasted during infusion and sample collections. Blood samples were collected at 0, 3, and 6. h relative to the beginning of infusions. Liver biopsies were performed concurrently with blood collections at 0 and 3. h. After the last blood collection of period 1, cows received concentrate and returned to pasture. Cows gained BW (16.5 ± 3.6. kg) and BCS (0.08 ± 0.06) from d -28 to 0. Cows receiving GLUC had greater serum glucose and insulin concentrations at 3. h compared with SAL cohorts. No treatment effects were detected for serum P4 concentrations, although mRNA expression of CYP2C19 and CYP3A4 after the infusion period was reduced for cows in the GLUC treatment compared with their cohorts in the SAL treatment. In conclusion, hepatic CYP3A4 and CYP2C19 mRNA expression can be promptly modulated by glucose infusion followed by acute increases in circulating insulin, which provides novel insight into the physiological mechanisms associating nutrition and reproductive function in dairy cows. © 2013 American Dairy Science Association.

Acute exercise decreases PTP-1B protein level and improves insulin signaling in the liver of old rats

It is now commonly accepted that chronic inflammation associated with obesity during aging induces insulin resistance in the liver. In the present study, we investigated whether the improvement in insulin sensitivity and insulin signaling, mediated by acute exercise, could be associated with modulation of protein-tyrosine phosphatase 1B (PTP-1B) in the liver of old rats. Aging rats were subjected to swimming for two 1.5-h long bouts, separated by a 45 min rest period. Sixteen hours after the exercise, the rats were sacrificed and proteins from the insulin signaling pathway were analyzed by immunoblotting. Our results show that the fat mass was increased in old rats. The reduction in glucose disappearance rate (Kitt) observed in aged rats was restored 16 h after exercise. Aging increased the content of PTP-1B and attenuated insulin signaling in the liver of rats, a phenomenon that was reversed by exercise. Aging rats also increased the IRβ/PTP-1B and IRS-1/PTP-1B association in the liver when compared with young rats. Conversely, in the liver of exercised old rats, IRβ/PTP-1B and IRS-1/PTP-1B association was markedly decreased. Moreover, in the hepatic tissue of old rats, the insulin signalling was decreased and PEPCK and G6Pase levels were increased when compared with young rats. Interestingly, 16 h after acute exercise, the PEPCK and G6Pase protein level were decreased in the old exercised group. These results provide new insights into the mechanisms by which exercise restores insulin signalling in liver during aging. © 2013 Moura et al; licensee BioMed Central Ltd.

Maternal periodontal disease in rats decreases insulin sensitivity and insulin signaling in adult offspring

Background: Periodontal disease during pregnancy has been recognized as one of the causes of preterm and lowbirth- weight (PLBW) babies. Several studies have demonstrated that PLBW babies are prone to developing insulin resistance as adults. Although there is controversy over the association between periodontal disease and PLBW, the phenomenon known as programming can translate any stimulus or aggression experienced during intrauterine growth into physiologic and metabolic alterations in adulthood. The purpose of the present study is to investigate whether the offspring of rats with periodontal disease develop insulin resistance in adulthood. Methods: Ten female Wistar rats were divided into periodontal disease (PED) and control (CN) groups. All rats were mated at 7 days after induction of periodontal disease. Male offspring were divided into two groups: 1) periodontal disease offspring (PEDO; n = 24); and 2) control offspring (CNO; n = 24). Offspring body weight was measured from birth until 75 days. When the offspring reached 75 days old, the following parameters were measured: 1) plasma concentrations of glucose, insulin, fructosamine, lipase, amylase, and tumor necrosis factor-α (TNF-α); 2) insulin sensitivity (IS); and 3) insulin signal transduction (IST) in insulin-sensitive tissues. Results: Low birth weight was not detected in the PEDO group. However, plasma concentrations of glucose, insulin, fructosamine, lipase, amylase, and TNF-α were increased and IS and IST were reduced (P <0.05) in the PEDO group compared with the CNO group. Conclusion: Maternal periodontal disease may induce insulin resistance and reduce IST in adult offspring, but such alterations are not attributable to low birth weight.

Periapical lesions decrease insulin signal and cause insulin resistance

Introduction: Inflammatory cytokines are associated with decreased insulin signal transduction. Moreover, local oral inflammation, such as that accompanying periodontal disease, is associated with insulin resistance and type 2 diabetes mellitus. The aim of this study was to evaluate the effect of periapical lesions (PLs) on insulin signaling and insulin sensitivity in rats. We hypothesized that PLs alter systemic insulin signaling and insulin sensitivity via elevated plasmatic tumor necrosis factor α (TNF-α). Methods: Wistar rats were divided into control (CN) and PL groups. PLs were induced by exposing pulpal tissue to the oral environment. After 30 days, insulin sensitivity was measured using the insulin tolerance test. After euthanization, maxillae were processed for histopathology. Plasmatic concentrations of tumor necrosis factor α (TNF-α) were determined via the enzyme-linked immunosorbent assay. Insulin signal transduction was evaluated using insulin receptor substrate tyrosine phosphorylation status and serine phosphorylation status in periepididymal white adipose tissue via Western blotting. For insulin signaling and insulin tolerance tests, the analyses performed were analysis of variance followed by the Tukey post hoc test. For TNF-α analysis, the Student's t test was used. In all tests, P <.05 was considered significant. Results: The rats with PLs showed higher plasmatic TNF-α, lower constant rate for glucose disappearance values, and reduced pp185 tyrosine phosphorylation status but no change in serine phosphorylation status in white adipose tissue after insulin stimulation. Conclusions: PLs can cause alterations to both insulin signaling and insulin sensitivity, probably because of elevation of plasmatic TNF-α. The results from this study emphasize the importance of the prevention of local inflammatory diseases, such as PLs, with regard to the prevention of insulin resistance. Copyright © 2013 American Association of Endodontists.

Effects of propiogenic ingredients on serum concentration of insulin and progesterone in non-lactating cows

Three experiments evaluated serum insulin and progesterone (P4) concentrations in grazing Gir×Holstein cows supplemented with monensin (MON) or propylene glycol (PPG; 2.5mL/kg of live weight0.75 per drench). Cows were non-lactating, ovariectomized, and received an intravaginal drug-releasing device containing 1.9g of P4 to estimate treatment effects on hepatic P4 degradation. In Exp. 1, 15 cows received, in a crossover design containing 2 periods of 21d, 0.1kg/d of corn in addition to 2g/d of kaolin (CON) or 0.2g/d of MON. Blood samples were collected on d 13 and 20 of each period. Cows receiving CON had greater (P<0.05) serum insulin concentrations compared with MON prior to and 6h after feeding. However, MON cows had greater (P=0.01) serum P4 concentrations compared with CON 18h after feeding. In experiment 2, 15 cows received, in a replicated crossover design containing 2 periods of 24h, a single drench of PPG or water (WT). Cows receiving PPG had greater (P<0.01) serum insulin concentrations compared with WT from 0.5 to 3h after drench. However, PPG cows had reduced (P<0.05) serum P4 concentrations compared with WT at 1 and 2h after drench. In experiment 3, 13 cows received, in a replicated 3×3 Latin square design containing 3 periods of 24h, 3 PPG drenches administered 1h apart (PPG3x), 3 WT drenches administered 1h apart, or 1 PPG drench+2 WT drenches administered 1h apart (PPG1x). Serum insulin concentrations increased proportionally to PPG dosage (treatment×hour; P<0.01). However, mean serum P4 concentration was greater (P<0.01) in WT cows compared with PPG1x and PPG3x, but similar (P=0.25) between PPG1x and PPG3x cows. In conclusion, feeding propiogenic ingredients to grazing cows failed to substantially increase serum P4 concentrations. © 2013 Elsevier B.V.

Insulin concentrations in cerebellum and body balance in diabetic male rats: Aerobic training effects

Brain insulin has had widespread metabolic, neurotrophic, and neuromodulatory functions and has been involved in the central regulation of food intake and body weight, learning and memory, neuronal development, and neuronal apoptosis. Purpose: The present study investigated the role of swimming training on cerebral metabolism on insulin concentrations in cerebellum and the body balance performance of diabetic rats. Methods: Forty Male Wistar rats were divided in four groups: sedentary control (SC), trained control (TC), sedentary diabetic (SD), and trained diabetic (TD). Diabetes was induced by alloxan (32 mg kg b.w.), single dose injection. The mean blood glucose of diabetic groups was 367 ± 40 mg/dl. Training program consisted in swimming 5 days/week, 1 h/day, 8 weeks, supporting a workload corresponding to 90% of maximal lactate steady state (MLSS). For the body balance testing rats were trained to traverse for 5 min daily for 5-7 days. All dependent variables were analyzed by one-way analysis of variance (ANOVA) and a significance level of p < 0.05 was used for all comparisons. Results: The body balance testing scores were different between groups. Insulin concentrations in cerebellum were not different between groups. Conclusion: It was concluded that in diabetic rats, aerobic training does not induce alterations on cerebellum insulin but induces important metabolic, hormonal and behavioral alterations which are associated with an improvement in glucose homeostasis, serum insulin concentrations and body balance. © 2013 Elsevier Inc.

Insulin Suppresses Atrophy- and Autophagy-related Genes in Heart Tissue and Cardiomyocytes Through AKT/FOXO Signaling

Insulin is an important regulator of the ubiquitin-proteasome system (UPS) and of lysosomal proteolysis in cardiac muscle. However, the role of insulin in the regulation of the muscle atrophy-related Ub-ligases atrogin-1 and MuRF1 as well as in autophagy, a major adaptive response to nutritional stress, in the heart has not been characterized. We report here that acute insulin deficiency in the cardiac muscle of rats induced by streptozotocin increased the expression of atrogin-1 and MuRF1 as well as LC3 and Gabarapl1, 2 autophagy-related genes. These effects were associated with decreased phosphorylation levels of Akt and its downstream target Foxo3a; this phenomenon is a well-known effect that permits the maintenance of Foxo in the nucleus to activate protein degradation by proteasomal and autophagic processes. The administration of insulin increased Akt and Foxo3a phosphorylation and suppressed the diabetes-induced expression of Ub-ligases and autophagy-related genes. In cultured neonatal rat cardiomyocytes, nutritional stress induced by serum/glucose deprivation strongly increased the expression of Ub-ligases and autophagy-related genes; this effect was inhibited by insulin. Furthermore, the addition of insulin in vitro prevented the decrease in Akt/Foxo signaling induced by nutritional stress. These findings demonstrate that insulin suppresses atrophy- and autophagy-related genes in heart tissue and cardiomyocytes, most likely through the phosphorylation of Akt and the inactivation of Foxo3a. © Georg Thieme Verlag KG.

Resveratrol reduces chronic inflammation and improves insulin action in the myocardium of high-fat diet-induced obeserats

OBJETIVO: Avaliar o efeito do resveratrol sobre a via de sinalização da insulina e melhora do quadro inflamatório no miocárdio de ratos Wistar obesos induzidos por dieta.MÉTODOS: Ratos Wistar foram divididos em grupos: controle (dieta padrão para roedores), obeso (dieta hiperlipídica) e obeso suplementado com resveratrol (20 mg/kg/dia), por 8 semanas (n=10). Ao final do período experimental, realizou-se o teste de tolerância à insulina, nos tempos 0 (sem insulina), 5, 10, 15, 20, 25 e 30 minutos após injeção intraperitoneal de insulina (2 U/kg). O peso corporal e o tecido adiposo epididimal foram mensurados. Fragmentos do miocárdio foram extraídos para análises da via da insulina e moléculas pró-inflamatórias através de Western blot.RESULTADOS: Os resultados indicam que a intervenção com resveratrol aumenta a constante de decaimento da glicose, fosforilação do receptor de insulina, substrato do receptor de insulina e da proteína quinase B. A suplementação de resveratrol também reduziu os níveis proteicos do fator de necrose tumoral alfa e de moléculas envolvidas com a transdução do sinal pró-inflamatório (quinase indutora do kappa B e fator nuclear kappa B). Os resultados ainda sugerem que a melhora na sensibilidade à insulina e a redução das moléculas pró-inflamatórias ocorreram independentemente da perda de peso corporal e da redução do tecido adiposo epididimal.CONCLUSÃO: A suplementação de resveratrol aumenta a sensibilidade à insulina, o que está relacionado à redução de fatores inflamatórios no miocárdio.

Effects of different intensities of physical exercise on insulin sensitivity and protein kinase B/Akt activity in skeletal muscle of obese mice

Objetivo: Investigar os efeitos do exercício físico agudo com diferentes intensidades sobre a sensibilidade à insulina e a atividade da proteína quinase B/Akt no músculo esquelético de camundongos obesos. Método: Foram utilizados camundongos Swiss, divididos aleatoriamente em quatro grupos, que receberam dieta padrão (grupo controle) ou dieta hiperlipídica (grupos obeso sedentário e grupos obesos exercitados 1 e 2), por período de 12 semanas. Dois diferentes protocolos de exercício foram utilizados: natação durante 1 hora com ou sem sobrecarga de 5% da massa corporal. O teste de tolerância à insulina foi realizado para estimar a sensibilidade à insulina. E os níveis protéicos da proteína quinase B/Akt e de sua fosforilação foram determinados no músculo esquelético dos camundongos, através da técnica de Western blot. Resultado: Uma sessão de exercício físico foi capaz de inibir a resistência à insulina em decorrência de uma dieta hiperlipídica. Foi possível demonstrar um aumento na fosforilação da proteína quinase B/Akt, melhora da sinalização da insulina e redução da glicemia de jejum nos camundongos que realizaram 1 hora de natação sem sobrecarga adicional e nos camundongos que realizaram 1 hora de natação com sobrecarga adicional de 5% de sua massa corporal. Entretanto, não houve diferença significativa entre os grupos que realizaram o exercício em diferentes intensidades. Conclusão: Independente da intensidade, o exercício físico aeróbio conseguiu aumentar a sensibilidade à insulina e a fosforilação da proteína quinase B/Akt, revelando ser uma boa forma de tratamento e prevenção do diabetes tipo 2.

Glucose, Cholesterol, Total Protein and Growth Factor Insulin-like Type I in Follicular Fluid of River Buffaloes (Bubalus bubalis)

In order to establish the concentrations of glucose, cholesterol, total protein and growth factor insulin-like type I (IGF-I) in the follicular fluid, 26 Murrah breed river buffaloes, between 45 and 70 days postpartum, empty, multiparous, with average live weight of 675 +/- 56 kg and average body condition of 3.5 points on a scale of 1-5, were used in this study. The fluid was collected from dominant follicles with diameters between 8 and 12 mm by OPU, and was not taken into account the stage of the estrous cycle. Using this technique, the wave of follicular development was synchronized six days prior to collection. Biochemical analysis was performed to glucose and cholesterol through the enzymatic colorimetric method using commercial kit glicose CHOLESTEROL GOD-PAP and CHOD-PAP (Kovalent), respectively. Determination of total protein was carried out by using total protein commercial kit (Kovalent) Biuret method, and the readings were performed using absorption spectrophotometry with visible light. Concentration of IGF-I was measured by Radioimmunoassay (RIA) technique using commercial IRMA Kit IGF-I (INMUNOTECH). Descriptive statistics were developed using the PROC MEANS procedure of SAS (2009). Concentration of glucose (4.0 +/- 0.75 mmol / L-1) and IGF-I (340 +/- 129.83 ng / mL (-1)) were higher than those reported by other authors in river buffaloes and cows, respectively. However, cholesterol levels (0.51 +/- 0.12 mmol / L (-1)) and total protein (58.4 +/- 4.43 g / L (-1)) behaved inferior to other studies in same species. The results indicated that there is relationship among the nutritional aspects, diameter of follicles aspirated and productive period in the concentration of biochemical indicators.