The Effect Of Prolonged Activation Of NMDA Receptor On The Function Of Pancreatic Beta Cell

[Objectives]N-methyl-D-aspartate (NMDA) receptors are ionotropic glutamate receptor subtype in the central nervous system (CNS) and peripheral non-neural tissues. Since NMDA receptors play a major role in many acute and chronic nervous system diseases, people have payed extensive attention on them, however, the influence of activation of the NMDA receptors on the peripheral organs and tissues is still poorly understood at present.In this study, we investigated the effect of prolonged application of NMDA on the function of pancreatic islets andβcells in vivo and in vitro. The function of a long-term activation of NMDA receptors in pancreas was then preliminarily discussed to further understand the significance of glutamate and NMDA receptors on pancreatic tissue andβcells and to provide new ideas for Prevention and Treatment of diabetes mellitus.[Methods]1. animal experiment NMDA was applied by intraperitoneal injection to C57 mice and Wistar rats, the body weight of animal, blood glucose, insulin concentrations and NMDA receptor subtypes mRNA expression were examined. The number and area of pancreatic islets were counted, and the proportion of pancreaticβcells of pancreas tissue sections were observed. Diabetes rat model were established with streptozotocin (STZ) to studyed the effect of NMDA receptor onβcell injury by STZ.2. cell test The effect of NMDA on apoptosis rate and glucose-stimulated insulin secretion function in MIN-6 cells were studyed. To study the mechanism of the effect of long-term activation of NMDA receptors on the function of pancreaticβcells, the intracellular ATP contents in MIN-6 cells were detected, and the mRNA expression of insulin, caspase-3, glucose-stimulated insulin secretion related genes in the process (KATp channel,glucose kinase,voltage-dependent calcium channel) were also examined by real-time PCR technique.[Result]1. Continual administration of NMDA for 5 days (20 mg/kg, ip) significantly increased food intake (P<0.01) and body weight (P<0.05), obviously rised fasting blood glucose (FBG) (P<0.01), decreased glucose tolerance (P<0.05), obviously increased fasting serum insulin concentration (P<0.01), decreased HOMA-βcell index (P<0.01) in C57 mice, while all the effects caused by NMDA were improved by the combined treatment of NMDA and MK-801 (P<0.01). The tissue microarray analysis data suggested NMDA application reduced the number of pancreatic islets per unit area (P<0.05), the area of pancreatic islets in per unit pancreas area (P<0.05), and the number of cell in one islet (P<0.05), the ratio of insulin positive cell (P<0.05).2. After Wistar rats received a single Intraperitoneal injection of STZ (60 mg/kg, ip), the amount of water drinking and food intake increased significantly (P<0.01), body weight decreased dramaticly (P<0.001), fasting blood glucose was far higher than those in non-STZ group (P <0.001), glucose tolerance was significantly lower (P<0.001). While, MK-801 did not significantly improve those change, when intraperitoneal injection of MK-801 on the STZ treated rats. After administration of NMDA on Wistar rats for 5 days (15 mg/kg, ip), the area under the glucose tolerance curve and fasting serum insulin concentration significantly increased (P<0.05), while after combined NMDA and MK-801 were applied to rats (MK-801 0.lmg/kg, ip 30 min before NMDA applicationfor 7 days), the area under the glucose tolerance curve and fasting serum insulin concentration significantly decreased (P<0.01, P<0.05). By using HE staining, we observed the decreased number of pancreatic islets per unit area in STZ group and STZ+MK-801 group rats (P<0.01).Compared with the control group, STZ group, STZ+MK-801 group and NMDA group showed decreased pancreatic islets area in per unit pancreas area (P<0.01, P<0.01 and P<0.05 respectively), pancreaticβcells of STZ group and STZ+MK-801 group significantly reduced, or there were a large number of non-functioning Pancreaticβcells.Real-time PCR results showed that, there is no differences of the expression of NMDA receptor subtypes between STZ and control group.3. Application of 1mmol/1 NMDA to MIN-6 cells for 96 hours reduced the glucose stimulate insulin secretion form MIN-6βcells. After Stimulation of 25 mmol/1 glucose, the accumulation of ATP in MIN-6 cells has no change.[Conclusion]1. Prolonged activation of NMDA receptors might play a role in promoting the injury of function of pancreatic islets of the C57 mice, which may be caused by the induction of apoptosis of pancreaticβcells, the peripheral insulin resistance, and the glucose metabolism disorders.2. NMDA receptors were not involved in the damage process of Wistar rat pancreaticβcells caused by STZ.15 mg/kg NMDA might cause mild glucose metabolism disorders, which may be due to the dose of NMDA can damage the normal function of pancreaticβcells and induce their apoptosis.3. Prolonged NMDA application might make the ATP level inβcells fail to increase, thereby reduce the response of pancreaticβcells to glucose.