274-OR: Beta-Cell Dysfunction Is Associated with Impaired Insulin-Mediated Suppression of Glucagon in Obese Hispanic Americans

Recent studies have demonstrated an increase in the glucagon:insulin ratio in lean versus obese subjects. We assessed insulin-mediated suppression of plasma glucagon levels in 260 obese Hispanic Americans (59 NGT, HbA1c= 5.1±0.1%, BMI= 32.6±0.7; 109 Prediabetes, HbA1c= 5.8±0.1%, BMI= 33.8±0.5; 92 T2D, HbA1c= 7.3±0.2%, BMI= 34±0.5) with varying glucose tolerance. Subjects participated in a 2-h OGTT with measurement of plasma glucose, insulin, glucagon concentrations. During the OGTT, we quantitated insulin-mediated suppression of plasma glucagon concentration, Matsuda Index of insulin sensitivity, and the insulin secretion/insulin sensitivity (disposition) index using plasma C-peptide concentration. There was no difference in fasting plasma glucagon level between obese subjects with normal glucose tolerance (NGT), prediabetes, and type 2 diabetes (T2D). However, there was a progressive decrease in fasting glucagon:insulin ratio from NGT to prediabetes to T2D (8.71±0.72 vs. 6.92±0.53 vs. 5.66±0.41, P<0.01). During OGTT at 60 min, glucagon:insulin ratio increased from NGT to T2D (0.93±0.09 vs. 0.89±0.07 vs. 2.33±0.20, P<0.001), and the suppression of plasma glucagon (compared to basal value) was markedly decreased (10.3±3.4% vs. 9.3±1.9% vs. 2.5±2.8%, P<0.05). At 120 min (OGTT), glucagon:insulin ratio was increased in T2D versus NGT (1.28±0.17 vs. 2.0±0.20, P<0.01). The glucagon:insulin ratio was closely correlated with whole body insulin sensitivity and β-cell function during the fasting state (Matsuda Index, r= 0.51, P<0.001; Disposition Index, r= 0.30, P<0.001) and with Disposition Index during the OGTT at 60 and 120 min (r= -0.41, P<0.001; r= -0.21, P<0.01), respectively. Collectively, these findings indicate that insulin-mediated suppression of glucagon secretion is impaired with increasing severity of glucose intolerance in obese Hispanic Americans and is closely associated with insulin resistance and β-cell dysfunction.