AIMS/HYPOTHESIS: We evaluated the insulinotropic properties of glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) in healthy individuals at risk of developing type 2 diabetes before and after glucocorticoid-induced insulin resistance.

METHODS: Nineteen healthy, glucose tolerant, first-degree relatives of type 2 diabetic patients underwent OGTT and 7 mmol/l and 15 mmol/l glucose clamps with concomitant infusions of GLP-1, GIP or NaCl and a final infusion of arginine for determination of maximum beta cell capacity before and after treatment with dexamethasone. In addition, first-phase insulin responses were determined at 7 mmol/l and 15 mmol/l and second-phase insulin responses at 7 mmol/l.

RESULTS: After dexamethasone treatment, all 19 participants had increased insulin resistance (HOMA-IR and insulin sensitivity index [M/I] values) and 2 h plasma glucose concentrations, while beta cell function indices generally increased according to the increased resistance. First-phase insulin responses induced by GLP-1 and GIP at 7 mmol/l and maximal beta cell secretory capacity did not differ before and after dexamethasone, while second-phase responses to 7 mmol/l and first-phase responses to 15 mmol/l glucose were reduced equally for both hormones.

CONCLUSIONS/INTERPRETATION: Glucocorticoid-induced insulin resistance in individuals at risk of type 2 diabetes leads to a reduced insulinotropic effect of the incretin hormones. This reduction was not associated with a decrease in the maximal beta cell secretory capacity, indicating that the reduced incretin effect in the developing dysglycaemia of the present experimental model is due to a specific early reduction of the insulinotropic effects of the incretin hormones.

TRIAL REGISTRATION: Clinicaltrials.gov NCT02235584.