The Role of Hepatic Denervation in the Dysregulation of Glucose Metabolism in Liver Transplant Recipients

In this study, investigators will study both diabetic and non-diabetic individuals who are otherwise healthy more than one year after receiving a liver transplant. They will participate in at least one of the following two parts of this study: The first involves functional magnetic resonance imaging (fMRI), and the second is using a day-long infusion study called a "pancreatic clamp." Functional magnetic resonance imaging (fMRI) is a technique for measuring and mapping brain activity that is noninvasive and safe. This technique relies on the fact that blood flow in the brain and the activity of brain cells are coupled. Investigators will observe the activity of metabolically-relevant areas of the brain by activating potassium channels with diazoxide at baseline and at 2-hour intervals vs when given placebo. In the pancreatic clamp study, glucose (a sugar) and insulin (a hormone produced in the pancreas that regulates the amount of sugar in the blood) are infused with an intravenous catheter. Blood samples are collected periodically throughout the procedure to measure blood sugar levels and the levels of several hormones that are found in the body which are related to glucose metabolism. The rates of endogenous glucose production (a measure of the body's production of sugar) will be measured as the main measurement of the study. All participants will be screened prior to study enrollment. For the fMRI studies, eligible participants will come on two separate occasions for day-long study visits (one day in which the brain will be imaged before and after receiving diazoxide (a potassium channel activator), and one day in which the brain will be imaged before and after placebo. For the pancreatic clamp studies, eligible participants will come on two separate occasions for day-long study visits (one study with diazoxide, and one study with placebo). All studies in participants with type 2 diabetes will include overnight admissions prior to the study day for gradual normalizing of blood glucose through the infusion of insulin. Participants without diabetes will not have to stay for an overnight admission. Study participants with type 2 diabetes will also be eligible for an additional study in which Nicotinic Acid will be infused overnight to lower free fatty acid (FFA) levels. It will be determined whether FFA lowering will impact the fMRI studies and clamp studies that will be performed the next day.