Analytical Procedures
Serum insulin concentrations were determined using a commercially available enzyme-linked immunosorbent assay (ELISA) with an assay sensitivity of 6 pmol/L (intra-assay, < 8.9%; Cat# 10-1113-01, RRID:AB_2877672; Mercodia AB, Sweden). Serum C-peptide concentrations were measured using an ELISA with an assay sensitivity of < 25 pmol/L (intra-assay, < 10%; Cat# 10-1136-01, RRID:AB_2750847; Mercodia AB, Sweden). Plasma glucagon concentrations were measured using a sandwich ELISA employing monoclonal antibodies against the C- and N- terminal regions of glucagon with a detection limit of 0.75 pmol/L (intra-assay, < 4.3%; inter-assay, 9.0%; Cat 10-1271-01, RRID:AB_2737304; Mercodia AB, Sweden). Plasma GIP concentrations (ie, [1-42] and [3-42]) were analyzed by ELISA with an assay sensitivity of 1 pmol/L (intra-assay, < 5.4%; inter-assay, 10%; Cat# EZHGIP-54K, RRID:AB_2801401; Merck Millipore, USA). Plasma GLP-1 (ie, [7-36] NH