The graded glucose infusion protocol.

<p>The glucose infusion rate was increased in a step wise fashion every 40 minutes starting at time zero as shown in red. The primed-constant infusion of each peptide(s) was started at time zero and is shown in yellow. Note that GIP and Xen were each infused at the same rate when administered together. The primed-constant infusion of atropine (or saline) was initiated 30 minutes before the start of the graded glucose infusion as shown in blue. All infusions were terminated 240 minutes after the glucose infusion was initiated.