DPP4 Inhibition & Beta Cell Function

This study is being done to determine the role of a hormone, glucagon-like peptide 1 (GLP-1), on insulin secretion and to study how GLP-1 works in in diabetic individuals as compared to non-diabetic individuals, under fasting conditions. GLP-1 is a naturally occurring hormone made in the intestines. It is released into the circulating blood after eating and helps to control the blood glucose levels by increasing insulin secretion by cells in the pancreas. However, the exact method by which GLP-1 causes insulin secretion and how GLP-1 activity is changed in diabetic persons remain unclear. This research is being done to address these questions and better understand the function of GLP-1. In this research, the investigators will use a synthetic form of Exendin-9 to determine the effects of GLP-1 on insulin secretion in diabetic and non-diabetic persons. Exendin-9 acts as a blocker of GLP-1 action, allowing us to study the specific effects of the GLP-1 hormone. Exendin-9 is an investigational compound, which means it is still being tested in research studies and is not approved by the U.S. Food and Drug Administration (FDA). In this study, the investigators will also use the drug Sitagliptin, which is an FDA-approved drug for the treatment of type 2 diabetes mellitus. In this study, use of Sitagliptin is considered investigational since it is not being used for treatment of diabetes but is instead being used to understand how GLP-1 works and to better understand how medications like Sitagliptin work in patients with type 2 diabetes mellitus.