Effect Of Obesity On Islet Function,GLP-1 And GC Plasma Concentration In T2DM

Objective: To investigate the effect of obesity on islet function,GLP-1 and GC plasma concentration after 75 g oral glucose tolerance test（OGTT）in T2DM patients.Methods: A total of 85 T2DM patients were divided into three groups according to BMI: normal BMI group,overweight group,obesity group.Otherwise,according to the WC,they were divided into abdominal obesity group（AO group）and non-abdominal obesity group（NAO group）.OGTT experiment was carried out to all subjects after fasting for 8¹2hours,then the blood samples at 0,0.5h and 2h were collected respectively.Plasma glucose,insulin,C-peptide,GLP-1 and GC level of each sample were measured.HOMA-IR,ISI,HOMA-β,△I30/△G30 and AUC_ins/AUCg were calculated.Results: Comparison of different BMI groups: AUC_ins,AUC_cp,△I30/△G30,AUC_ins/AUCg and HOMA-IR of overweight group and obesity group were higher than control group（P<0.05）,while ISI was lower（P<0.05）.There was no significant difference between overweight group and obesity group.Within each group,INS,CP concentrations after OGTT were higher than basic level（P<0.05）,while the GC was increase accordingly（P>0.05）.GLP-1 concentration was highest in 30 min after OGTT,then back to basic level within 2hours,the difference at each time point was significant（P<0.05）.Comparison of different WC group: AUC_ins,AUC_cp and HOMA-IR of AO group were higher than NAO group（P<0.05）,while ISI was lower（P<0.05）.Within two group,the INS,CP concentrations after OGTT were higher than basic level（P<0.05）,as well as GC concentration（P>0.05）.GLP-1 level was highest in 30 min after OGTT,then back to basic level within 2 hours,the difference at each time point was significant（P<0.05）.Correlation analysis showed that BMI was positively correlated with SBP,DBP,TG,FINS,FCP,AUC_ins,AUC_cp and HOMA-IR（r=0.386,0.274,0.35,0.214,0.336,0.222,0.234,0.209,0.288,P<0.05）,negatively correlated with HDL,ISI（r=-0.243,-0.288,P<0.05,P<0.01）.WC was positively correlated with SBP,DBP,TG,FCP,AUCCP,HOMA-IR（r=0.299,0.352,0.284,0.401,0.262,0.238 respectively,all P<0.05）,negatively correlated with HDL_C,ISI（r=-0.252,-0.234,all P<0.05）.WHR was positively correlated with SBP,DBP,TG,FCP（r=0.328,0.401,0.228,0.257 respectively,all P<0.05）.Stepwise regression analysis showed that:（1）Y_BMI=6.131+0.04X_SBP+0.146X_DBP+1.191 X_FCP,R²=34.5%;（2）Y_WC=56.57+3.423X_FCP+0.322 X_DBP,R²=22.8%;（3）Y_WHR=0.747+0.002 X_DBP,R²=14.9%.（all P =0.000）Conclusions:1 With the rising of BMI and WC,T2DM patients compensatorily increase insulin secretion capacity,indicated that obesity T2DM patients displayed more severe insulin resistance.And in evaluation of insulin resistance and sensitivity,BMI is more sensitive than WC.2 In obesity T2DM patients,GC levels after OGTT were inereased with the rising of INS,CP concentrations,suggested that the effect of insulin in suppressing GC secretion was weakened.Indicated that insulin resistance may also display in islet alpha cells.3 There was a trend that the plasma level of GLP-1was decreased with the rising of BMI and WC.