RESUMEN
Several reports have demonstrated that high-protein diets may have beneficial effects on experimental models of diabetes and have raised the possibility that branched-chain amino acids could play a role in these protective effects. We investigated the effect of a normoproteic, branched-chain amino acid-enriched diet (experimental diet) on insulin secretion from C57BL/6N mice transferred with splenocytes from diabetic syngeneic donors. Mice previously fed with the experimental or control diet received three intraperitoneal injections, every other day, of 5 x 107 viable mononuclear splenocytes obtained from control or diabetic donors. Results showed that mice fed with the experimental diet and transferred with "diabetic" splenocytes presented: i) normoglycemia, and (ii) significantly higher levels in both phases of glucose-induced insulin secretion and normal values of arginine-glucose-induced insulin secretion. To evaluate the in vitro cellular immune aggression, dispersed mouse islet cells were co-cultured with splenocytes from syngeneic diabetic mice. First, dispersed islet cells from mice on the experimental or control diet were co-cultured with splenocytes from control or diabetic mice on a commercial diet. In the presence of "diabetic splenocytes, dispersed islet cells from mice on the experimental diet presented a significantly lower in vitro cellular immune aggression. On the other hand, "diabetic" splenocytes from mice fed with the experimental diet produced a significantly reduced cellular immune aggression on dispersed islet cells. Our results showed that feeding branched-chain amino acids increased the capacity of beta cells to withstand a functional assault and diminished the extent of in vitro cellular immune aggression.
Asunto(s)
Aminoácidos de Cadena Ramificada/farmacología , Diabetes Mellitus Experimental/inmunología , Suplementos Dietéticos , Insulina/metabolismo , Islotes Pancreáticos/metabolismo , Transfusión de Linfocitos , Linfocitos/inmunología , Bazo/inmunología , Animales , Células Cultivadas , Técnicas de Cocultivo , Glucosa/farmacología , Inmunidad Celular/efectos de los fármacos , Secreción de Insulina , Islotes Pancreáticos/efectos de los fármacos , Islotes Pancreáticos/inmunología , Masculino , Ratones , Ratones Endogámicos C57BL , Trasplante Isogénico/inmunología , Trasplante Isogénico/fisiologíaRESUMEN
We studied the effect on in vitro glucose-induced insulin secretion of in vivo administration of L-Ng-monomethyl-arginine (L-NMMA), a competitive inhibitor of nitric oxide (NO) synthase, to mice injected with multiple low-dose streptozotocin (mld-SZ). In addition, the effect of L-NMMA treatment on the capacity of mononuclear spleen cells (MS) from mld-SZ mice to transfer alterations in insulin secretion from normal syngeneic receptors was also investigated. We also studied the effect of in vivo treatment with L-NMMA on anti-beta-cell cellular immune aggression (CIA) by coculturing MS from mld-SZ mice with rat dispersed islet cells. Our results show that mld-SZ mice treated with 0.25 mg L-NMMA/g body weight had normoglycemia, first and second-phase glucose-stimulated insulin secretion similar to those obtained in nondiabetic mice-effects not observed with a lower dose of L-NMMA (0.17 mg/g body weight)-and a diminished anti-beta-cell CIA. We also demonstrate that mice injected with MS from syngeneic donors treated with mld-SZ plus 0.25 mg L-NMMA/g had normal levels for first-phase glucose-stimulated insulin secretion and an absence of CIA. Taken together, these findings seem to indicate that prevention of in vivo NO production may block the onset of diabetes in mld-SZ mice, and that L-NMMA administration to diabetic donor mice prevents inhibition of first-phase insulin secretion and CIA in the transferred recipient mice. Although a nonimmunological mechanism or mechanisms of diabetes prevention by L-NMMA cannot be excluded, these results suggest that L-NMMA treatment could also be acting on T-cell-dependent immune reactions.
Asunto(s)
Trasplante de Células , Diabetes Mellitus Experimental/metabolismo , Insulina/metabolismo , Óxido Nítrico/biosíntesis , Bazo/patología , Animales , Glucemia/análisis , Diabetes Mellitus Experimental/inmunología , Diabetes Mellitus Experimental/patología , Inmunidad Celular , Secreción de Insulina , Masculino , Ratones , Ratones Endogámicos C3H , Óxido Nítrico Sintasa/antagonistas & inhibidores , Ratas , Ratas Wistar , Valores de Referencia , omega-N-Metilarginina/farmacologíaRESUMEN
We report here our study of the in vitro glucose-induced insulin secretion from mice fed with a high-protein diet and injected with mononuclear splenocytes from streptozotocin-diabetic syngeneic donors. Results show that transfer of "diabetic" splenocytes caused significant diminutions in first phase of stimulated-insulin secretion. Nevertheless, insulin secretory levels attained in recipient mice fed with the high-protein diet were significantly higher than in mice fed with control diets. We also evaluated the effect of high-protein feeding on the capacity of "diabetic" splenocytes to transfer an impaired insulin secretion in recipient mice. For this purpose, splenocytes donor mice were fed with high-protein or control diets and injected with multiple low doses of streptozotocin. "Diabetic" splenocytes from high-protein, or control diets fed donors caused in recipient mice similar impairments in glucose-stimulated insulin secretion. Taken together, these results seem to support the hypothesis of a protective effect of a high-protein diet on the beta-cell function.
Asunto(s)
Diabetes Mellitus Experimental/inmunología , Proteínas en la Dieta/administración & dosificación , Insulina/metabolismo , Animales , Secreción de Insulina , Masculino , Ratones , Ratones Endogámicos C57BL , EstreptozocinaRESUMEN
In the present study we have investigated the effect of a high-protein feeding on glucose induced-insulin secretion patterns from high dose streptozotocin (SZ) injected rats and mice, and from mice given multiple low doses of SZ. For this purpose male rats and mice were fed either a high-protein, carbohydrate-free diet, or control diets, before and after i.p. injections of SZ, or citrate buffer only. Our results show that when SZ was given as a single diabetogenic dose, rats and mice kept on the high-protein diet presented lower serum glucose levels, normal basal insulin values, and higher first and second phases of stimulated insulin release, when compared with diabetic animals on control diets. Furthermore, when rats prolonged their high-protein feeding from 4 to 11 days after SZ injection, there was an additional increment in insulin secretory capacity with a further diminution in serum glucose levels. We also show that high-protein feeding in mice given multiple low doses of SZ (a model of autoimmune diabetes), produced a diminution in serum glucose values, and an improvement in both phases of stimulated insulin release. Thus, in the two models of experimental diabetes used here, high-protein feeding exerts beneficial effects in beta cell responsiveness to glucose.
Asunto(s)
Diabetes Mellitus Experimental/sangre , Proteínas en la Dieta/administración & dosificación , Insulina/sangre , Animales , Glucemia/metabolismo , Dieta , Carbohidratos de la Dieta/administración & dosificación , Glucosa/farmacología , Concentración de Iones de Hidrógeno , Masculino , Ratones , Ratones Endogámicos C57BL , Ratas , Ratas WistarRESUMEN
We have used a model of experimental protein-energy malnutrition induced in weaned rats by administration of a protein free diet during 2 weeks. Some malnourished rats were then refed with a control diet for 4, 9 or 30 days. Control rats were fed for the same periods with the balanced control diet. Malnourished rats showed a loss in body weight of approximately 25%. After 30 days of refeeding, the animals gained weight reaching values higher than that of control rats. Insulin secreted by perifused pancreatic slices from malnourished rats, was impaired in first and second glucose-induced secretory phases. Basal secretion was also diminished in incubation of pancreatic slices. When malnourished rats were refed for 4 days, basal insulin secretion reached control values. Stimulated insulin secretion was normalized at 9 and 30 days of refeeding. Our result on somatostatin (SRIF) secretion in malnourished rats showed basal hypersecretion and diminished first and second glucose-induced secretory phases. During refeeding basal SRIF secretion was normalized from day 4. On the contrary stimulated secretion was significantly increased at 4 and 9 days of refeeding, and on day 30 values did not differ from controls. In protein energy malnutrition, the disturbed hormonal state can represent adaptative mechanisms to the protein depletion and hormonal changes have also an essential role in refeeding.
Asunto(s)
Proteínas en la Dieta/administración & dosificación , Insulina/metabolismo , Desnutrición Proteico-Calórica/fisiopatología , Somatostatina/metabolismo , Animales , Dieta , Femenino , Alimentos , Glucosa/farmacología , Técnicas In Vitro , Insulina/sangre , Secreción de Insulina , Páncreas/efectos de los fármacos , Páncreas/metabolismo , Radioinmunoensayo , Ratas , Ratas Wistar , Somatostatina/sangre , Pérdida de PesoRESUMEN
In the present study we have investigated the effect of a high-protein feeding on glucose induced-insulin secretion patterns from high dose streptozotocin (SZ) injected rats and mice, and from mice given multiple low doses of SZ. For this purpose male rats and mice were fed either a high-protein, carbohydrate-free diet, or control diets, before and after i.p. injections of SZ, or citrate buffer only. Our results show that when SZ was given as a single diabetogenic dose, rats and mice kept on the high-protein diet presented lower serum glucose levels, normal basal insulin values, and higher first and second phases of stimulated insulin release, when compared with diabetic animals on control diets. Furthermore, when rats prolonged their high-protein feeding from 4 to 11 days after SZ injection, there was an additional increment in insulin secretory capacity with a further diminution in serum glucose levels. We also show that high-protein feeding in mice given multiple low doses of SZ (a model of autoimmune diabetes), produced a diminution in serum glucose values, and an improvement in both phases of stimulated insulin release. Thus, in the two models of experimental diabetes used here, high-protein feeding exerts beneficial effects in beta cell responsiveness to glucose.
RESUMEN
We have used a model of experimental protein-energy malnutrition induced in weaned rats by administration of a protein free diet during 2 weeks. Some malnourished rats were then refed with a control diet for 4, 9 or 30 days. Control rats were fed for the same periods with the balanced control diet. Malnourished rats showed a loss in body weight of approximately 25
. After 30 days of refeeding, the animals gained weight reaching values higher than that of control rats. Insulin secreted by perifused pancreatic slices from malnourished rats, was impaired in first and second glucose-induced secretory phases. Basal secretion was also diminished in incubation of pancreatic slices. When malnourished rats were refed for 4 days, basal insulin secretion reached control values. Stimulated insulin secretion was normalized at 9 and 30 days of refeeding. Our result on somatostatin (SRIF) secretion in malnourished rats showed basal hypersecretion and diminished first and second glucose-induced secretory phases. During refeeding basal SRIF secretion was normalized from day 4. On the contrary stimulated secretion was significantly increased at 4 and 9 days of refeeding, and on day 30 values did not differ from controls. In protein energy malnutrition, the disturbed hormonal state can represent adaptative mechanisms to the protein depletion and hormonal changes have also an essential role in refeeding.
RESUMEN
In the present study we have investigated the effect of a high-protein feeding on glucose induced-insulin secretion patterns from high dose streptozotocin (SZ) injected rats and mice, and from mice given multiple low doses of SZ. For this purpose male rats and mice were fed either a high-protein, carbohydrate-free diet, or control diets, before and after i.p. injections of SZ, or citrate buffer only. Our results show that when SZ was given as a single diabetogenic dose, rats and mice kept on the high-protein diet presented lower serum glucose levels, normal basal insulin values, and higher first and second phases of stimulated insulin release, when compared with diabetic animals on control diets. Furthermore, when rats prolonged their high-protein feeding from 4 to 11 days after SZ injection, there was an additional increment in insulin secretory capacity with a further diminution in serum glucose levels. We also show that high-protein feeding in mice given multiple low doses of SZ (a model of autoimmune diabetes), produced a diminution in serum glucose values, and an improvement in both phases of stimulated insulin release. Thus, in the two models of experimental diabetes used here, high-protein feeding exerts beneficial effects in beta cell responsiveness to glucose.
RESUMEN
We have used a model of experimental protein-energy malnutrition induced in weaned rats by administration of a protein free diet during 2 weeks. Some malnourished rats were then refed with a control diet for 4, 9 or 30 days. Control rats were fed for the same periods with the balanced control diet. Malnourished rats showed a loss in body weight of approximately 25
. After 30 days of refeeding, the animals gained weight reaching values higher than that of control rats. Insulin secreted by perifused pancreatic slices from malnourished rats, was impaired in first and second glucose-induced secretory phases. Basal secretion was also diminished in incubation of pancreatic slices. When malnourished rats were refed for 4 days, basal insulin secretion reached control values. Stimulated insulin secretion was normalized at 9 and 30 days of refeeding. Our result on somatostatin (SRIF) secretion in malnourished rats showed basal hypersecretion and diminished first and second glucose-induced secretory phases. During refeeding basal SRIF secretion was normalized from day 4. On the contrary stimulated secretion was significantly increased at 4 and 9 days of refeeding, and on day 30 values did not differ from controls. In protein energy malnutrition, the disturbed hormonal state can represent adaptative mechanisms to the protein depletion and hormonal changes have also an essential role in refeeding.
RESUMEN
In previous studies in C57BL/KsJ mdb/mdb mice, we observed alterations in glucose-induced insulin secretion in vitro, and a defective inhibitory effect of somatostatin on insulin secretion. In this work we studied glucagon secretion patterns under arginine-glucose stimulation, in perifused pancreatic slices from genetically diabetic mice aged 20 to 90 days. We also explored whether alpha-cells present a diminished sensitivity to somatostatin. Results showed that: a) in mdb/mdb mice aged 20 to 90 days, glucagon secretion patterns exhibited basal hypersecretion and a diminished first peak; b) somatostatin inhibited stimulated-glucagon secretion below baseline values in mdb/mdb mice aged 20 to 30 days. In later stages (40 to 90 days), somatostatin exerted a lower inhibitory effect since glucagon levels remain above basal values. This could indicate a progressive impairment in alpha-cell sensitivity to somatostatin, as it was previously observed in beta-cells.
Asunto(s)
Diabetes Mellitus Experimental/fisiopatología , Glucagón/metabolismo , Islotes Pancreáticos/efectos de los fármacos , Somatostatina/farmacología , Factores de Edad , Animales , Femenino , Masculino , Ratones , Ratones Endogámicos C57BL , Páncreas/metabolismo , PerfusiónRESUMEN
In a previous study in C57BL/KsJ mdb/mdb mice aged 4 to 12 days we observed a diminished first phase of glucose-induced insulin secretion in vitro, and alterations in the inhibitory effect of somatostatin on insulin secretion. This study explores, using perifused pancreatic slices, whether the reduced B-cell responsiveness to somatostatin in mdb/mdb mice can be overcome upon induction of a biphasic insulin release by using theophylline. Under these conditions our results show: (1) in mdb/mdb mice aged 4 to 6 days, the restoration of the first peak of insulin secretion overcomes the reduced B-cell sensitivity to somatostatin; and (2) in mdb/mdb mice aged 7 to 12 days, the addition of theophylline only causes a partial restoration of B-cell responsiveness to somatostatin, suggesting that other mechanisms could be involved in the progressive impairement of B-cell sensitivity to somatostatin inhibitory effect.
Asunto(s)
Diabetes Mellitus Experimental/fisiopatología , Glucosa/farmacología , Insulina/metabolismo , Islotes Pancreáticos/metabolismo , Somatostatina/farmacología , Teofilina/farmacología , Envejecimiento , Animales , Femenino , Tamización de Portadores Genéticos , Homocigoto , Técnicas In Vitro , Secreción de Insulina , Islotes Pancreáticos/efectos de los fármacos , Islotes Pancreáticos/crecimiento & desarrollo , Masculino , Ratones , Ratones MutantesRESUMEN
In a previous study in C57BL/KsJ (mdb) mice aged 12 to 90 days, we observed alterations in the secretion of insulin and somatostatin and in the inhibitory effect of the latter upon insulin secretion. This study explores whether hormonal alterations are to be found in the very early stages of the diabetic syndrome, i.e. between ages 4 and 12 days. The results demonstrate two distinct phases in the development of the syndrome: up to age 6 days, the perifused slices of pancreata of control animals present biphasic glucose-induced patterns of insulin and somatostatin secretion, whereas the diabetic animals show a diminished first peak of insulin secretion, but a similar pattern of somatostatin secretion, to that of the control animals; between ages 7 and 12 days, the pancreata of diabetic mice exhibit insulin hypersecretion in basal conditions, and an absence of the first secretion peak and insulin hypersecretion in the second phase in response to glucose stimulation. The glucose-induced pattern of somatostatin secretion presents hormonal hypersecretion in both phases. B-cell sensitivity to the inhibitory effect of somatostatin is diminished in mdb mice of the above-mentioned groups, an alteration which becomes more evident as diabetes evolves. The results show that, in very early stages of the evolution of the diabetic syndrome in C57BL/KsJ (mdb) mice, there are already alterations in insulin and somatostatin secretion patterns and in the inhibitory effect of the latter on insulin secretion.