The Relationship Between Uric Acid and Inflammatory Markers

Background: \- Uric acid is a substance found in the blood that may contribute to certain chronic medical conditions and disorders, such as diabetes, insulin resistance, and high blood pressure. High uric acid concentrations have been associated with stroke and heart disease, as well as chronic heart failure. In particular, researchers are interested in determining the relationship between uric acid and inflammatory markers, or chemicals in the blood that can indicate inflammation and other problems with the body. Objectives: * To study the specific effects of changes in uric acid in the body. * To determine whether uric acid contributes to inflammation in the body. Eligibility: \- Healthy individuals between 50 and 75 years of age. Design: * This study will involve four visits: a screening visit, two study visits, and a followup visit. * At the screening visit, participants will have a physical examination, blood and urine tests, and an electrocardiogram. Participants will be divided into two groups based on the existing amount of uric acid in their blood. * Within 7 days of the screening visit, participants will have a full-day study visit with a magnetic resonance imaging scan, followed by a high-fat meal and further blood samples collected over the following 8 hours. * At least 2 days after the first study visit, participants will have the second study visit, which will require a 2-night stay at the National Institutes of Health. Participants will have a metabolism test, and will receive the following infusions based on the groups they were assigned to at the screening visit. * Group A (low uric acid) will receive either uric acid or a placebo. * Group B (moderate to high uric acid) will receive either Rasburicase (a drug that reduces the amount of uric acid in the blood) or a placebo. * After the infusions and related blood tests, participants will have a high-fat meal with further blood and urine samples. * Approximately 2 weeks after the second study v