1646-P: The Effect of Glucagon-Like Peptide-1 Receptor Blockade and Acute Insulin Resistance on Islet Function and Glucose Metabolism in People without Diabetes

Intra-islet Glucagon-Like Peptide-1 (GLP-1) is increased by islet inflammation and diabetes. GLP-1 Receptor (GLP1R) blockade with exendin-9,39 impairs fasting islet function in people with and without type 2 diabetes (DM2). In addition, it decreases insulin secretion and glucagon suppression in response to hyperglycemia in people with DM2. We sought to examine if free fatty acid (FFA) elevation to induce acute insulin resistance in people without DM2 replicated the effects of GLP1R blockade seen in DM2. We studied 6 nondiabetic individuals (54 ± 4 years, 33 ± 1 kg/m2) on 4 occasions in random order. Glucose metabolism was measured after an overnight fast and during a hyperglycemic clamp (~9 mmol/l) using [3-3H] glucose. On two occasions Intralipid® and heparin were infused to raise FFA. Exendin-9,39 (300pmol/kg/min) was infused to block GLP1R in the presence or absence of FFA elevation, while on the other days saline was infused. In the absence of FFA elevation, exendin-9,39 infusion increased fasting glucose concentrations (5.0 ± 0.1 vs. 5.4 ± 0.1 mmol/l, saline vs. exendin-9,39 respectively, p = 0.01). This pattern was also observed when FFA were elevated (5.3 ± 0.1 vs. 5.7 ± 0.2 mmol/l, p = 0.02). Fasting insulin, C-peptide (without FFA: 0.9 ± 0.1 vs. 0.8 ± 0.1 nmol/l, p = 0.17; with FFA: 1.1 ± 0.1 vs. 1.0 ± 0.1 nmol/l, p = 0.08) and glucagon concentrations were unchanged, but inappropriate for the higher fasting glucose observed during exendin-9,39 infusion. Exendin-9,39 infusion did not alter islet hormone secretion during the clamp in the presence or absence of FFA elevation. The magnitude of changes induced by exendin-9,39 did not differ in the presence or absence of FFA elevation (p > 0.10). These experiments confirm the effects of GLP1R blockade on fasting α- and β-cell function in people without DM2. However, FFA elevation does not replicate the abnormalities of islet function observed in people with DM2 when exendin-9,39 is infused.