Maria Lúcia Bonfleur

Insulin Secretion and Acetylcholinesterase Activity in Monosodium L-Glutamate-Induced Obese Mice

Objective: Pancreatic islets isolated from mice treated neonatally with monosodium L-glutamate (MSG) were used to study insulin secretion. Material and Methods: Total acetylcholinesterase (AchE) activity of tissue extract was measured as a cholinergic activity marker. Obesity recorded in 90-day-old MSG mice (OM) by Lee index reached 366.40 ± 1.70, compared to control mice (CM) 324.40 ± 1.10 (p < 0.0001). Glucose 5.6 mM induced insulin secretion of 36 ± 5 pg/15 min from islets of CM and 86 ± 13 from OM (p < 0.001). When glucose was raised to 16.7 mM, islets from OM secreted 1,271 ± 215 and 1,017 ± 112 pg/30 min to CM. AchE activity of pancreas from OM was 0.64 ± 0.02 nmol of substrate hydrolyzed/min/mg of tissue and 0.52 ± 0.01 to CM (p < 0.0001). Liver of obese animals also presented increase of AchE activity. Results: These indicate that OM insulin oversecretion in low glucose may be attributed, at least in part, to an enhancement of parasympathetic tonus.

Pancreatic islets from hypothalamic obese rats maintain K+ATP channel-dependent but not -independent pathways on glucose-induced insulin release process.

One of the main features of obesity is hyperinsulinemia, which is related to insulin oversecretion. Glucose is by far the major physiological stimulator of insulin secretion. Glucose promotes an increase in the ATP/ADP ratio, which inactivates ATP-sensitive K+ channels (K+ATP) and induces beta cell depolarization with consequent calcium influx. Increased intracellular calcium concentration triggers insulin exocytosis. K+ATP channel function is important for K+ATP channel-dependent pathways involved in glucose-stimulated insulin secretion (GSIS). However, K+ATP channel-independent pathway has been identified and it has been found that this pathway sustains GSIS. Both pathways are critical to better GSIS control. GSIS was studied in pancreatic islets from hyperinsulinemic adult obese rats obtained by monosodium l-glutamate (MSG) neonatal treatment. Islets from MSG-obese rats were more glucose responsive than control ones. Diazoxide, a drug which maintains the K+ATP channels open without interfering with cell metabolism, blocked GSIS in islets from both groups. High extracellular potassium concentration plus diaz-oxide was used to study an alternative to the K+ATP channel pathway; in these conditions islets from MSG-obese rats did not respond, while islets from control animals showed enhanced GSIS. Results indicate that MSG-obese rats oversecreted insulin, even though the K+ATP channel-independent pathway is impaired in their beta cells.

Duodenal jejunal bypass attenuates non-alcoholic fatty liver disease in western diet-obese rats

PURPOSE To evaluate the effects of duodenal-jejunal bypass (DJB) on serum and hepatic profiles of obese rats fed on a western diet (WD). METHODS Twenty eight male Wistar rats were fed a standard rodent chow diet (CTL group) or WD ad libitum. After 10 weeks, WD rats were submitted to sham (WD SHAM) or duodenal-jejunal bypass (WD DJB). Body weight, fat pad depots, glycemia, insulinemia, HOMA-IR, TyG, lipids profile and hepatic analyses were evaluated two months after surgery. RESULTS The WD SHAM group presented greater obesity, hyperglycemia, hyperinsulinemia, insulin resistance, hypertriglyceridemia and hepatic steatosis than the CTL group. WD DJB rats presented decreased serum glucose and insulin resistance, when compared to WD SHAM animals, without changes in insulinemia. In addition, DJB surgery normalized serum TG and attenuated TG accumulation and steatosis in the liver of the WD DJB group. Hepatic ACC and FAS protein expressions were similar in all groups. CONCLUSION Duodenal-jejunal bypass attenuates hepatic parameters of non-alcoholic fatty liver disease in obese rats fed on a western diet.

Decreased TNF-α gene expression in periodontal ligature in MSG-obese rats: A possible protective effect of hypothalamic obesity against periodontal disease?

The prevalence of obesity is increasing globally. There is evidence that the uncontrolled energetic metabolism in obese patients can accelerate periodontal disease. Therefore, the aim of this study was evaluate the possible relationship between hypothalamic obesity induced by neonatal treatment with MSG and experimental periodontal disease. Newborn male Wistar rats received subcutaneous injections in the cervical region, of 4g/Kg/day of body weight (BW) of MSG (MSG group) or hypertonic saline solution, 1.25/kg/day BW (control group, CTL). At 70 days of life periodontal disease was induced in these animals. After they were sacrificed, radiographic analyses of alveolar bone resorption and Tumor Necrosis Factor α (TNFα) gene expression in gingival tissue were performed. The neonatal treatment with MSG did not affect the concentration of plasma glucose and cholesterol (CHOL). However, plasma insulin, non-esterified fatty acids (NEFA) and triglycerides (TG) leves were higher in MSG compared with CTL group. The alveolar bone resorption was 44% lower in MSG-obese rats compared with CTL rats. In the presence of periodontal ligature, there was an increase in this parameter in all groups. The TNFα gene expression, an inflammatory marker, in periodontal tissue was similar in obese and CTL rats. The presence of ligature increased TNFα gene expression in both groups, but in a lower extension in MSG-obese rats. In conclusion these results suggested that hypothalamic obesity may produce a protective effect against periodontal disease, however further research is needed to understand the mechanisms involved in this process.

Vagotomy Reduces Insulin Clearance in Obese Mice Programmed by Low-Protein Diet in the Adolescence

The aim of this study was to investigate the effect of subdiaphragmatic vagotomy on insulin sensitivity, secretion, and degradation in metabolic programmed mice, induced by a low-protein diet early in life, followed by exposure to a high-fat diet in adulthood. Weaned 30-day-old C57Bl/6 mice were submitted to a low-protein diet (6% protein). After 4 weeks, the mice were distributed into three groups: LP group, which continued receiving a low-protein diet; LP + HF group, which started to receive a high-fat diet; and LP + HFvag group, which underwent vagotomy and also was kept at a high-fat diet. Glucose-stimulated insulin secretion (GSIS) in isolated islets, ipGTT, ipITT, in vivo insulin clearance, and liver expression of the insulin-degrading enzyme (IDE) was accessed. Vagotomy improved glucose tolerance and reduced insulin secretion but did not alter adiposity and insulin sensitivity in the LP + HFvag, compared with the LP + HF group. Improvement in glucose tolerance was accompanied by increased insulinemia, probably due to a diminished insulin clearance, as judged by the lower C-peptide : insulin ratio, during the ipGTT. Finally, vagotomy also reduced liver IDE expression in this group. In conclusion, when submitted to vagotomy, the metabolic programmed mice showed improved glucose tolerance, associated with an increase of plasma insulin concentration as a result of insulin clearance reduction, a phenomenon probably due to diminished liver IDE expression.

AVALIAÇÃO MORFOMÉTRICA DA INFLUÊNCIA DA OBESIDADE SOBRE O TECIDO GENGIVAL DE RATOS COM PERIODONTITE EXPERIMENTAL

Objetivo: O objetivo desse trabalho foi avaliar o comportamento do tecido gengival de ratos apos a inducao experimental de obesidade e doenca periodontal. Material e Metodos: Vinte e quatro ratos machos (n=24) foram divididos inicialmente em 2 grupos, que foram submetidos a injecoes intradermicas na regiao cervical de 4g/kg/dia de solucao glutamato monossodico (MSG) (grupo OBS) e 1,25g/kg/dia de solucao salina (grupo CTL), nos primeiros 5 dias de vida. Aos 70 dias foi induzida a doenca periodontal com a colocacao de ligadura nos dentes posteriores dos ratos, apos esse procedimento 4 grupos, com 6 ratos cada, foram originados: grupo controle sem ligadura (CTL); grupo controle com ligadura (LIG); obeso sem ligadura (OBS), obeso com ligadura (OBSLIG). Aos 100 dias os ratos foram sacrificados, e a hemimandibula direita de cada rato foi retirada para a analise morfometrica do tecido gengival. Resultados: A altura do epitelio da crista gengival foi significativamente (p<0,05) maior nos grupos com periodontite induzida (LIG 44,26±0,69; OBSLIG 43,30±1,23). A altura do tecido conjuntivo na regiao media mostrou-se menor nos grupos CTL (237,44±7,38) e OBS (238,17±0,73), sendo estas diferencas estatisticamente significativas (p<0,05) em relacao aos demais grupos. Conclusao: A obesidade induzida pelo glutamato monossodico nao alterou as caracteristicas dos tecidos epitelial e conjuntivo da regiao gengival de ratos. DESCRITORES Doenca Periodontal. Obesidade. Gengiva.

Effects of duodenal-jejunal bypass on structure of diaphragm in western diet obese rats

Purpose: To evaluate the effects of duodenal-jejunal bypass (DJB) on the diaphragm muscle of obese rats fed on a western diet (WD) . Methods: Eighteen male Wistar rats were fed a standard rodent chow diet (CTL group) or WD ad libitum. After 10 weeks, WD rats were submitted to sham (WD SHAM) or duodenal-jejunal bypass (WD DJB). The structure, ultrastructure, collagen content and the morphometry of the neuromuscular junctions (NMJs) were analyzed two months after surgery. Results: WD SHAM rats displayed an increase in body weight, the Lee index and retroperitoneal and peri-epididymal fat pads compared to the CTL group. DJB did not alter these parameters. The muscle fiber structure and NMJs were similar in the WD SHAM and CTL groups. However, the WD SHAM group showed alterations in the fiber ultrastructure, such as loosely arranged myofibrils and Z line disorganization. In addition, WD SHAM animals presented a considerable amount of lipid droplets and a reduction in the percentage of collagen compared to the CTL group. DJB did not affect the structure or ultrastructure of the muscle fibers or the NMJs in the diaphragm of the WD DJB animals. Conclusion: Duodenal-jejunal bypass did not improve the alterations observed in the diaphragm of western diet obese-rats.

Effects of Decrease of Extracellular Sodium in Carbachol-Evoked Catecholamine Secretion in Isolated Adrenal Medullae of Rats

The effect of extracellular Na+ deprivation on the carbachol-evoked catecholamine secretion was evaluated in chromaffin cells. Isolated adrenal medullae of male Wistar rats were incubated in solutions with different sodium concentrations (144,0; 75,0; 25,0 and ømM). Catecholamine secretions inversely increased as a response to fall of extracellular concentration of sodium. The magnitude of response to cholinergic stimulus (carbachol 100 μM) was decreased in low extracellular sodium concentration. Atropine (100 μM) inhibited secretion of catecholamine induced by carbachol in the presence and in the absence of extracellular sodium. Results suggest that in isolated adrenal medullae of rats (1) decrease in concentration of extracellular sodium increases