Chronic Exposure To Elevated Epinephrine Reprogrammed Insulin Secretion In Rat Islets

With the high intensification of livestock production,animals are often in the abnormal environmental conditions and abnormal physiological function of the state,cause by livestock and poultry stress.A large number of studies show that stress can limit the growth and development of animals,reduce the production performance and immunity of animals,and cause death seriously.In stress state,the body stress hormone at a sustained high level,leading to endocrine disorders,energy metabolism imbalance.Typical examples can be seen in the development of fetal stress in the maternal uterus caused by heat stress,epinephrine(Epi)and norepinephrine(NE)in the fetal sheep,and the function of insulin secretion damage,and then reduce the use of glucose.Further studies have shown that continuous injection of norepinephrine on fetal sheep also reduces insulin secretion,and removal of NE,found that glucose stimulation,pancreatic β-cell secretion of insulin compensatory enhancement.The current phenomenon of hormonal changes caused by stress and thus change the function of pancreatic islet has been general y recognized,but still lack of stress hormone to reduce insulin secretion function of the direct argument.Therefore,in this study,the effect of high concentration of Epi on pancreatic islet secretion was explored in vitro.The test content is divided into three parts.First,Epi inhibited the half-inhibitory concentration of insulin secretion in primary islets of rat was measured at 20 mM glucose stimulated with Epi at concentrations of 0.1 nM,1 nM,10 nM,100 nM,1 μM and 10 μM.And this concentration was used as a longterm culture concentration for late test.Second,the experimental group: Epi(IC50)cultured for 3 days transfer to the common culture medium for 2 days.Control group: in the common culture medium for 5 days.Insulin secretion and total insulin were measured at 20 mM glucose with the concentration of 0.1 nM,1 nM,10 nM,100 nM,1 μM,10 μM Epi.Last,through regular PCR and RT-PCR to determine the glucose stimulation of insulin secretion pathway-related regulatory molecules expression.The results of this research:First,Epi inhibited the half-inhibitory concentration of insulin secretion in the primary islet cel s with 100 nM.Second,Insulin release was no difference between the chronic Epi treatment and the controls.But total insulin was 42% greater(P < 0.05).Moreover,the IC50 was 2.9-fold(P < 0.05)greater for chronic Epi treatment than controls.Finally,the expression patterns of GLUT2,adrenergic receptor(ARs),G protein subunit,Kir6.2,SUR1,CACNA1 D,UCP2 and PDX-1 in the islets were measured by regular PCR.The results showed that all ARs and G protein isoforms in addition to α1AAR,α1B-AR,β3-AR and Gβ3 were expressed in rat islets.mRNA expression was confirmed by RT-PCR analysis.All mRNA concentration of adrenergic receptors no difference in islets compared controls.But Gs,Gz,Gβ1 and Gβ2 was lower(P < 0.05)and mRNA concentration of UCP2 was significantly decreased(P < 0.05).According to the above results,chronic exposure to elevated Epi induce adrenergic receptor desensitization.We suppose that adrenergic receptor was phosphorylated lead to the mRNA concentration of Gβ1 and Gβ2 was decreased,and adrenergic receptor sensitivity was decreased.The results suggest that chronic exposure to high Epi reduce receptor desensitization may be due to down-regulation of Gβ to reduce receptor sensitivity,rather than reduce the number of receptor.Next,intracel ular cAMP concentration decreased was explained by Gs mRNA concentration decreased,indicating that sustained adrenergic inhibition by reducing G protein expression,inhibition of insulin secretion.In the end,the decrease of UCP2 expression in the Epi treatment indicated that the increase of intracel ular ATP synthesis and induced insulin secretion enhancement.However,the decrease of Gz indicating that it mediated exocytosis is weakened,inuslin granules release extracel ular content decreased.Consequently,intracel ular total insulin were augmented.In summary,chronic high concentration of Epi inhibition can reprogram the primary pancreatic islets secretion function,resulting in increased total insulin,but also induced adrenergic receptor desensitization.The process of reprogramming islet function may be related to UCP2-mediated regulation of the insulin secretion pathway and the function of the G protein subunit in the insulin secretion pathway.