GCG and Impaired glucose tolerance: In addition, administration of GLP-1 receptor antagonist (RAn) during OGTT in healthy subjects primarily affected the glucose excursions only in the early postload phase, while GIP RAn led to impaired normalization of glycemic excursion during the whole postload period; further, coinfusion of GIP and GLP-1 RAn together led to overall impaired glucose tolerance and reduced β cell function, confirming the importance of the synergy between GIP and GLP-1 action in determining appropriate insulin response, at least in a physiological setting.