Glucagon-like peptide-1 (GLP-1) is secreted from the L cell of the gut in response to oral nutrient delivery. To determine if endogenously released GLP-1 contributes to the incretin effect and postprandial glucose regulation, conscious dogs (n = 8) underwent an acclimation period (t = -60 to -20 min), followed by a basal sampling period (t = -20 to 0 min) and an experimental period (t = 0-320 min). At the beginning of the experimental period, t = 0 min, a peripheral infusion of either saline or GLP-1 receptor (GLP-1R) antagonist, exendin (9-39) (Ex-9, 500 pmol/kg/min), was started. At t = 30 min, animals consumed a liquid mixed meal, spiked with acetaminophen. All animals were studied twice (± Ex-9) in random fashion, and the experiments were separated by a 1-2-week washout period. Antagonism of the GLP-1R did not have an effect, as indicated by repeated-measures MANOVA analysis of the Δ AUC from t = 45-320 min of arterial plasma glucose, GLP-1, insulin, glucagon, and acetaminophen levels. Therefore, endogenous GLP-1 is not sufficient to alter postprandial glucose regulation in the dog.