We see no difference in potency between GLP-1 peptide, liraglutide (modified version GLP-1, which make it more stable in in vivo) and exenatide (a synthetic version of exendin-4). However, it has been shown that GLP-1 can cause the GLP-1R to recycle at faster rate in in vitro than liraglutide and exenatide (Mol. Cell. Endocrinol. 382: 938-949, 2014). Nevertheless, the difference in potency between these ligands is greater in vivo due to variation in their stability.
In our satiety studies (measuring glucose, insulin, and gut hormones), we assess levels of active ghrelin in plasma (assayed using an Epitope Diagnostic Elisa kit).
Refer to our paper: Stefoska-Needham, A., Beck, E.J., Johnson, S.K., Chu, J., Tapsell, L.C. (2015) Flaked sorghum biscuits increase post-prandial GLP-1 and GIP levels and extend subjective satiety in healthy subjects. Mol. Nutr. Food Res., 60, 1118–1128.