A saline lock and/or intravenous line will be inserted at two different sites and a baseline blood and a separate sample for tissue banking (10 mL, optional) will be collected. After taking the baseline blood, 5 mL of iohexol(Omnipaque 300; 300 mg/mL of organic iodine) will be administered by a nurse at the Clinical and Translational Research Center (CTRC) over a period of approximately 15 seconds through an IV port, followed by a flush with approximately 10 mL of 0.9% normal saline solution. This intravenous line through which the iohexol was administered will then be removed. The syringe will be weighted to the nearest tenth gram on the same scale before and after injection. Blood samples for plasma clearance measurements will be obtained from the second IV line, which will remain in place throughout the course of the study visit. To maintain the patency of the IV access, normal saline will be administered at a rate of approximately 20-30 c.c. per hour from a 500 c.c. bag of normal saline.