 On the evening before this procedure, you will report to the GCRC at approximately 8:00 p.m. You will spend the night at the GCRC and will not be allowed to eat after 9:00 p.m. On the following morning, you will not be given breakfast. You will have an intravenous catheter placed into a vein in each arm, one for blood samples to be taken throughout the day, and one for the amino acid solution to be given. You will also be asked to breath one breath through a straw into a glass tube at different times, while the amino acid solution is being given. Before starting the amino acid solution, a blood sample about 7 teaspoons will be taken from a vein in one arm. Then the solution containing amino acids and nucleotides will be pumped slowly into your blood over the next 9-hour period. You will not be allowed to eat normal foods during this 9-hour period. However, you will be given a liquid nutritional formula to drink each hour during the day starting after the first blood sample is taken. Approximately 14 blood samples 9 mL, less than 2 teaspoons each and 8 breath samples will be taken from you while you receive the amino acid solution. In addition, at 6 times during the day you will be asked to lie quietly for 10 minutes while breathing into a special, clear hood that will measure your metabolic rate the rate at which your body uses energy. You will remain at the GCRC for the entire 9-hour period, although you will be able to do limited activities TV and reading. At the end of the 9-hour period, you will be able to go home and resume your activities. The following day you will resume eating meals prepared by the GCRC. While at the GCRC on days 3 and 4 after this procedure, you will be asked to give two more blood samples, one in the morning and one in the evening, and on day 5 you will be asked to give one blood sample in the morning 2 teaspoons each. 