GIP: Glucose-dependent Insulinotropic Peptide

The small bowel makes a hormone called glucose-dependent insulinotropic peptide (GIP). It is released into the blood stream and goes to the pancreas. It works there with nutrients, especially glucose, in the digested food so that insulin is released in sufficient amounts from the pancreas. The insulin causes the nutrients from the food to be stored in the liver, fat and muscle until they are needed to provide energy. GIP also slows emptying of food from the stomach, which decreases the rate with which fats in food are broken down and stored. Once it is released into the blood, GIP is quickly broken down and becomes inactive. Individuals with type 2 diabetes do not make enough GIP and pharmacological doses of naturally occurring GIP do not increase insulin secretion in patients with type 2 diabetes. This study is testing a modified GIP (it had one amino acid difference from naturally occurring human GIP) that is not broken down as quickly in individuals with type 2 diabetes, to determine if it will improve insulin secretion, after eating, in patients with type 2 diabetes. The study will also compare its effects to that of naturally occurring, human GIP. Both human GIP and the modified GIP (GIP analog) are manufactured by peptide synthesis techniques (not extracted from human gut and not recombinant technology). A screening visit will be performed including blood work, EKG and physical exam. If eligible, patients would be scheduled for three infusion visits 2 months apart, where they will receive a normal saline infusion on the first visit and GIP or GIP analog on the remaining visits. The infusion visits will begin approximately 6:45 a.m. and patients will have frequent blood sampling through an intravenous line over a period of 7 hours. An additional intravenous line will be placed for the infusion of either the normal saline, GIP or GIP analog over a period of 3 hours. Patients will be given a breakfast meal consisting of 550 calories (one egg, piece of toast with margarine, corn flakes 2% milk and a banana). They will be given 2 Extra-Strength Tylenol to determine time frame that food is emptied from stomach by measuring Tylenol levels in the blood. At the end of each study visit, patients will be given lunch, intravenous lines will be discontinued and they will be discharged to home.