This study investigates the role of salt and stress in blood pressure regulation. The interaction of these factors will be studied, and individuals who are more sensitive to a salt/stress interaction will be identified. Blacks and Whites, with and without mild essential hypertension will be studied with special attention paid to possible differences among the groups. Subjects will be characterized as to the amount of exposure to difficult life circumstances or stressors they face and their styles of anger expression. Patients will be hospitalized on the Clinical Research Center for two hospitalizations, a 4 day high salt stay (200 meq Na/d) and a 5 day low salt stay (10 meq Na/d). While they are hospitalized, ambulatory blood pressure monitors will be used to examine the effect of dietary salt on blood pressure level and reactivity to the hospital environment. Since dietary salt and exposure to stressors both affect the sympathetic nervous system, we plan to assess a number of indices of sympathetic nervous system activity, beginning with plasma catecholamines. However, since it is difficult to infer sympathetic activity from only this one measure, we will also study whole body norepinephrine release and clearance rate, and renal sympathetic nervous activity. The role of chromogranin, a substance recently found to be co-released with norepinephrine, will also be investigated. Infusions of sympathetic agonists will allow comparison of the reactivity to known amounts of alpha and beta agonists with the reactivity to behavioral stimuli. We also plan to study how the body handles sodium during stress by measuring urinary sodium output, renal blood flow, renin, and aldosterone. We will also examine atrial natriuretic factor, a hormone synthesized in the right atrial wall of the heart. This hormone has unusual characteristics which are apparently opposite those of norepinephrine in terms of sodium excretion and vasodilation.
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