Effect Of Ghrelin On Glucagon Secretion Of Islet Alpha Cells And Its Mechanism

Background and objective:Diabetes mellitus is characterized by chronic increase in fasting glucose levels and a significant and persistent increase in postprandial glucose levels.Insulin deficiency and insulin resistance are two major pathogenesis of diabetes mellitus.Insulin and glucagon are two major pancreatic hormones involved in regulating the homeostasis of glucose.It is generally believed that glucagon secreted by islet alpha cells plays an important role in the pathogenesis of diabetes mellitus.Ghrelin is an endogenous ligand of growth hormone secretin receptor(GHSR).Ghrelin binds to its receptor GHSR to promote feeding,growth hormone release,gastrointestinal motility,cardiovascular function and energy balance.Several studies have confirmed that ghrelin can increase glucose and inhibit insulin secretion by regulating the function of islet beta cells.Currently,only one paper has suggested that ghrelin can directly promote the secretion of glucagon by pancreatic islet cells,and ghrelin-glucagon axis is introduced as an important mechanism to control blood glucose under fasting conditions.In order to clarify the effect of ghrelin on glucagon secretion,clinical and animal experiments were combined,and the inhibitor EX527,which is a silent information regulator 1(SIRT1)in mammalian cells,was used to intervene to determine whether SIRT1 exists in the pathway through which ghrelin affects glucagon secretion.The results of this experiment lays a theoretical foundation for a new treatment of diabetes mellitus.Methods:1.Detection and clinical significance of serum glucagon in patients with type 2 diabetes mellitusTwenty patients with T2DM admitted to the Affiliated Hospital of Yangzhou University from January 2019 to March 2019 were selected and 20 healthy controls were collected from the Health Examination Center of the Affiliated Hospital of Yangzhou University.All subjects were excluded from infection,stress,severe cardiovascular and cerebrovascular diseases and acute complications of diabetes mellitus,severe gastrointestinal diseases or history of gastrointestinal surgery,liver and kidney dysfunction,positive serum insulin-related antibodies and other metabolic diseases possibly related to sugar metabolism.All subjects were fasting for 12 hours.Fasting venous blood was drawn early the next morning to measure serum glucose,ghrelin,glucagon and insulin levels.Meanwhile,the height and weight of the subjects were measured,and the gender and age were recorded.Data were analyzed by SPSS 19.0 statistical software.2.The effect of ghrelin on pancreatic hyperglycemia in miceFifty healthy male C57BL/6J mice aged 6 weeks were randomly divided into 5 groups,namely saline control group(NS group),DMSO solvent control group(DMSO group),low concentration ghrelin experimental group(LG group),high concentration ghrelin experimental group(HG group),high concentration ghrelin+EX527 experimental group(HG+E group),with 10 mice in each group.Maintain a 12-hour day/night rhythm and fed adaptively for 1 week.All groups were fasting for 12 hours before the experiment.On the day of the experiment,the control group was injected with normal saline and DMSO,and the experimental group was injected with ghrelin 0.2ug/g,ghrelin 0.5ug/g,ghrelin 0.5ug/g+ex52710ug/g respectively.One hour after injection,blood was collected from the retro-orbital venous plexus of mice and the serum was frozen at-20 degrees Celsius.One-Touch Ultra stable blood glucose meter was used to monitor the fasting blood glucose level of mice in each group and the blood glucose level 1 hour after intraperitoneal injection of drugs.Serum insulin and glucagon levels were measured by Mouse Insulin/Glucagon Elisa kit,and pancreatic H&E staining was performed to observe the morphological changes in different experimental groups.All data were analyzed by SPSS 19,0 statistical software.Result1.General situation of subjects in type 2 diabetes mellitus group and healthy control groupThere was no significant difference in gender,age and body mass index between the two groups.2.Fasting serum glucose level,glucagon concentration,insulin concentration and ghrelin concentration in subjects of type 2 diabetes mellitus group and healthy control groupFasting blood sugar in type 2 diabetes group was significantly higher than that in healthy control group(P<0.01);insulin concentration in type 2 diabetes group was higher than that in healthy control group(P<0.05);pancreatic hyperglycemia concentration in type 2 diabetes group was higher than that in healthy control group,but there was no significant difference;ghrelin concentration in type 2 diabetes group was significantly higher than that in healthy control group(P<0.01).3.Body weight,fasting blood glucose level,serum glucose level,glucagon and insulin concentration in C57BL/6J mice 1 hour after intraperitoneal injection of drugsThere was no significant difference in body weight and fasting blood glucose levels among the groups.Result of serum glucose level of mice in each group after intraperitoneal injection of ghrelin for 1 hour:HG and LG groups were significantly higher than NS group and DMSO group(P<0.01);HG group was higher than LG group(P<0.05);HG+E group was higher than NS group(P<0.05),DMSO group(P<0.05);HG group was higher than HG+E group(P<0.01);there was no significant difference between LG group and HG+E group;there was no significant difference between NSG and DMSO group.Schooling differences;The results of serum glucagon concentration of mice in each group after intraperitoneal injection of ghrelin for 1 hour showed that HG and LG groups were significantly higher than NS group and DMSO group(P<0.01);HG group was higher than LG group(P<0.01);HG+E group was higher than NS group(P<0.05),DMSO group(P<0.05);HG group was higher than HG+E group(P<0.01);there was no significant difference between LG group and HG+E group;Significant statistical difference;There was no significant difference in serum insulin concentration after intraperitoneal injection of ghrelin for 1 hour in each group.4.Contrastive results of histopathological examination of pancreas in C57BL/6J mice 1 hour after intraperitoneal injection of drugsThere was no significant difference in the number,density and morphology of pancreatic islet cells between groups by H&E staining.ConclusionGhrelin can promote the secretion of glucagon of islet alpha cells,and SIRT1 may exist in the pathway.