This study examines the effect of angiotensin converting enzyme inhibition and dietary salt on physiological responses to behavioral stressors. It is difficult to tease apart the roles of the sympathetic nervous system, the renin-angiotensin system, and dietary salt. For instance, under low salt conditions, there is activation of both the sympathetic nervous system and the renin- angiotensin system. As a result, observing an increased pressor response to stressors in patients on high salt intake is not straightforward. A beginning way to understand this system is to block production of angiotensin II with an angiotensin covering enzyme inhibitor (captopril). Thirty hypertensive and 30 normotensive white men will be admitted for two 5-day hospitalizations on a Clinical Research Center while they consume a low salt diet (10 meq/d). These subjects will participate in a randomized crossover design employing either placebo on the initial hospitalization or captopril. Patients will be studied at rest, while they are exposed to behavioral stressors, and during infusions of norepinephrine. The following physiological variables will be monitored: blood pressure, heart rate, plasma and urinary catecholamines, renin, aldosterone, angiotensin II, atrial natriuretic factor, urinary sodium, and the slope of the dose response curve relating infused norepinephrine to blood pressure. The investigators will also have obtained data from another project on an additional 60 subjects, studied on the same reactivity protocol, but who are hospitalized on a high salt diet (200 meq/d). The reactivity of these subjects will be compared to that elicited by other subjects on a combination of salt depletion plus captopril. Thus the effects of salt intake will be studied while blocking the activation of the renin-angiotensin system on the low salt diet.
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