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

It is believed that important brain centers send signals through the vagus nerve to the liver to suppress the amount of glucose (sugar) that gets produced. People who have received liver transplants have had their vagus nerve cut during transplantation, and many of these individuals have diabetes at one year post-transplant. The goals of this study are: to see whether metabolic control centers in the brain can still be activated normally with the medication diazoxide in patients who have had a liver transplant, and to understand whether disrupting the vagus nerve would result in excess glucose being produced by the liver (ie. a potential mechanism for why these patients develop diabetes).

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.

Eligibility Criteria:
Inclusion Criteria:

* Liver Transplant at least one year ago
* Age: 21-70

Exclusion Criteria:

* BP \> 150/90 or \<90/60 on more than one occasion, unless there is a documented history of white coat hypertension by treating physician.
* Triglycerides \> 400 mg/dl and/or Total Cholesterol \>300 mg/dl
* Clinically significant liver dysfunction
* Clinically significant kidney dysfunction, GFR: \<60 mg/dL
* Anemia: HgB \<12.5 for men and \<11.0 for women
* Positive urine drug test. Occasional use of cannabis (once or twice per week) will not be a basis for exclusion.
* Urinalysis: Clinically significant abnormalities
* Clinically significant electrolyte abnormalities
* Smoking \>10 cig/day
* Alcohol: Men \>14 drinks/wk or \>4 drinks/day, Women \>7 drinks/wk or \>3 drinks/day
* History of active hepatitis infection, HIV/AIDS, chronic kidney disease (stage 3 or greater), active cancer, cardiovascular disease or other heart disease, systemic rheumatologic conditions, seizures, bleeding disorders, muscle disease
* Surgeries that involve removal of endocrine glands except for thyroidectomy (if euthyroid on thyroid hormone replacement - if such history T4 and TSH will be checked)
* Pregnant women
* Subject enrolled in another study less than one month prior to the anticipated start date in the proposed study, besides those done by our group
* Family history: family history of premature cardiac death
* Allergies to medication administered during study
* Uncontrolled psychiatric disorders
* Any condition which in the opinion of the PI makes the subject ill-suited for participation in the study