Incretin Hormones and Insulin Responses During OGTT in Newly Diagnosed T2DM Patients

Abstract

Several research groups have reported variable results about incretin effects of glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1(GLP-1) particularly, as well as cytokines balance in type 2 diabetes mellitus (T2DM). The present case-control prospective interventional study was conducted in 2014-2015 at Medical College for Women & Hospital, Dhaka, investigating responses of incretin hormones and insulin to oral glucose tolerance test (OGTT) in Bangladeshi subjects. Blood samples were collected from 36 OGTT positive adult T2DM patients (Pt) and 30 normal adults (NC) at '0' minute (fasting) and at 2 hours after OGTT. Routine laboratory investigations in blood were done and special parameters in serum, i.e. insulin, HGH, TSH, GIP and GLP-1 were analyzed using enzyme immunoassay kits. Pt had FBG and BG2Hr levels much higher than NC (p<0.001). In Pt, F-Insulin and Insulin2Hr were much lower than NC subjects (p<0.001), although Insulin2Hr level was higher than F-Insulin level in Pt. F-GIP (p=0.309) and F-GLP-1(p=0.984) levels were similar between Pt and NC. Interestingly, NC responded to OGTT by increasing GIP2Hr and GLP-1,2Hr levels about 3 times, whereas Pt responded by raising about 1.5 times only compared to F-GIP and F-GLP-1 (p<0.001). Reduced insulin levels, both fasting and postprandial, were possibly due to decreased responses of GIP and GLP-1 to glucose load in T2DM patients. Further studies with a larger sample size including cytokines are warranted.