Venous blood provides lower glucagon-like peptide-1 concentrations than arterialized blood in the postprandial but not the fasted state: Consequences of sampling methods

New Findings: What is the central question of this study? Glucagon-like peptide-1 (GLP-1) is an important obesity/diabetes target, with effects dependent on circulating GLP-1 concentrations. Peripheral tissues extract GLP-1; therefore, sampling venous versus arterialized blood might provide different GLP-1 concentrations. This study examined whether arterialization alters GLP-1 concentrations during fasting and feeding. What is the main finding and its importance? This study demonstrates that venous blood provides lower postprandial but not fasting GLP-1 concentrations versus arterialized blood. Therefore, when accurate assessment of postprandial peripheral availability of GLP-1 is required, blood sampling methods should be considered carefully, reported clearly, and arterialization is recommended. Abstract: Glucagon-like peptide-1 (GLP-1) displays concentration-dependent effects on metabolism, appetite and angiogenesis; therefore, accurate determination of circulating GLP-1 concentrations is important. In this study, we compared GLP-1 concentrations in venous versus arterialized blood in both fasted and fed conditions. Venous and arterialized blood samples were obtained simultaneously from 10 young, healthy men before and 30, 60 and 120 min after ingestion of 75 g glucose. Plasma GLP-1 concentrations increased in response to glucose ingestion (time effect, P < 0.01) and to a lesser extent in venous versus arterialized plasma (time × arterialization interaction, P < 0.01). Accordingly, the plasma incremental area under the curve was lower in venous versus arterialized plasma (974 ± 88 versus 1214 ± 115 pmol l (120 min)⁻¹, respectively, P = 0.049). In the postprandial state, there was a positive relationship between arterialized GLP-1 concentrations and the venous–arterialized difference in GLP-1 concentrations (r² = 0.51; P < 0.01). Both arterialized and venous peak GLP-1 concentrations showed positive relationships with peak arterialized insulin concentrations (both r² > 0.6, P < 0.01). Venous sampling results in lower concentrations of GLP-1 in the postprandial but not the fasted state compared with arterialized blood. This absolute difference is biologically meaningful and is magnified when GLP-1 availability is high. Therefore, sampling from arterialized blood may provide a better chance of detecting small differences in postprandial GLP-1 availability with interventions. If absolute GLP-1 concentrations are of interest, the blood sampling method should be considered carefully and reported clearly.