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.

Inclusion Criteria:

- of good general health

- not on any prescription medications

- between the ages of 18 and 50 years

- not pregnant

- African-American male or female

Exclusion Criteria:

- not African-American

- pregnant

- taking medications that will affect blood pressure

- not in good general health

- younger than 18 years of age or older than 50 years of age