2.8. GLP-1 secretion assay

At 8 and 20 h post-synchronization, cells were incubated for 2 h in 0.5% DMEM containing vehicle or the known secretagogue, 10⁻⁷ M GIP [7,8,39,40,44]. Peptides in the media and cells were isolated by reversed-phase adsorption using C18 Sep-Pak cartridges (Waters Associates, Milford, MA, USA), and GLP-1 levels were measured using a Total GLP-1 Radioimmunoassay kit (GLP-1T-36HK, Millipore, Etobicoke, ON, Canada). GLP-1 secretion was represented as the percent of GLP-1 in the media over the total GLP-1 content (media + cells).