Impact of Exenatide on Cardiovascular Exercise Performance in Type 2 Diabetes

Subjects will come for a total of seven testing visits, including two screening visits, during which evaluations will take place. Visits are structured as follows: Visits 1, 2 and 3 will be completed over a four-week period. 1. After subjects review the study and give consent for study participation, a history and physical exam will be performed. In addition, the Low-level Physical Activity Recall (LoPAR) questionnaire, pulmonary function testing, and vital signs will be performed. 2. Subjects will be asked to fast prior to visit 2. Blood and urine samples will be collected for measurement of glycosylated hemoglobin(HbA1C), fasting glucose, fasting insulin, free fatty acids and microalbuminuria (these measures will be covariates in the analyses). A dietary survey will be administered for food preferences for the three day study diet administered prior to visits 3, 4, 6 and 7. Dual Energy X-ray Absorptiometry (DXA) and body composition tests will be done to ensure that groups are weight similar (using fat-free mass). Autonomic nervous system testing, a resting electrocardiogram (EKG) and familiarization bicycle test will be performed. 3. Subjects will receive a three day study diet prior to visit 3. A resting and exercise EKG will be performed on the day of the visit. Patients will have measures made of cardiac function and endothelial function on visit 3 as well using plethysmography and cardiac echo. The peak aerobic capacity (VO2max) test will be performed. Vital signs will be taken at rest. 4. Randomization: Subjects will receive a three day study diet prior to visit 4. During visit four, arterial stiffness/endothelial function will be non-invasively measured by the Sphygmocor system. Subjects will have three constant-load tests to measure oxygen (VO2) kinetics where oxygen saturation (StO2) will be measured during exercise. A resting and exercise EKG and vital signs will be performed during the visit. Subjects will be randomized to either taking exenatide or placebo and all must have been taking metformin (1-2 grams /d) for at least 3 months. Exenatide will be titrated starting at 5 mcg twice per day for two weeks then moving to 10 mcg twice per day as tolerated and the placebo dose will match this titration. During the treatment phase subjects will be given a log to keep track of their blood glucose each day. Study coordinators will contact each subject weekly to obtain these values which will be checked by the study doctors and shared with the subject's primary care physician if adjustments in other medications need to be made. 5. Week 4: Visit 5 will consist of a physical exam with a clinician as well as a blood draw and check of vital signs during exenatide treatment. 6. Week 12: After 3 months of exenatide or placebo administration, the procedures of Visit 3 will be repeated as Visit 6. Additional testing to be performed during visit 6 include a physical exam performed by a study physician, DXA scan and body composition tests to monitor any changes in body composition (fat-free mass), blood work for lab tests listed in Visit 2 and the LoPAR questionnaire. 7. Week 13: During visit 7, the testing performed during visit 4 will be repeated after 3 months of exenatide or placebo administration. Subjects will continue exenatide or placebo treatment while completing exit testing during Weeks 12 and 13.