Effectiveness of Prazosin on the Urinary Sodium Excretion Response to Mental Stress

High blood pressure, or hypertension, is a serious problem in the African-American (AA) population which affects nearly 7 of every 10 AAs in our area. Previously the investigators showed that a significant number of AAs held onto or retained salt during mental stress (sodium retainers). The investigators believe that the increased salt load and resulting blood pressure load contributes to the eventual development of hypertension in these individuals. The purpose of this study is to find out if this response is due to the direct stimulation of the kidney (the organ that controls salt levels in the body, by the brain). To do this, the investigators will determine if a drug that stops the connection between the brain and the kidney during mental stress will prevent sodium retention in sodium retainers. Prazosin is an alpha adrenergic receptor blocker that has been approved by the Food and Drug Administration (FDA). None of the subjects who participate in this study have high blood pressure. The subjects will not know which testing week is the drug week and which is the placebo week. Participants will test twice during this study, one of the weeks they will take Prazosin daily and the other week of testing they will take a placebo (sugar pill) daily in order to see if Prazosin changes how their body handles salt during stress. The participants will not be informed as to which of the testing weeks is the Prazosin week or the placebo week. This study will involve a screening visit, two first dose visits and two testing weeks over an approximate 5 week period (this include a one week "washout" period). Each testing week will have a 3 day salt-controlled diet prior to testing and an approximate 3-hour testing period on Day 4. The 3-hour testing period will include 10 minutes of a baseline rest, 45 minutes of mild stress (competitive video game), and 45 minutes of a recovery rest. A total of 4 blood and 4 urine samples will be collected during the 3-hour period. Each blood draw will consist of about 4 teaspoons for a total of 16 teaspoons. If the participants are female, a pregnancy test will be performed at the beginning of each testing visit (screening, first dose-1, test day-1, first dose-2 and test day-2) to confirm that they are not pregnant. Muscle sympathetic nerve activity will be measured during testing through the insertion of electrodes just below the knee on the outer part of the right leg. Additionally, an IV infusion will be administered for the phenylephrine challenge to insure total blockade of the sympathetic nervous system.