The Natriuretic Peptide System in African-Americans.
Condition: Healthy; Prehypertension
MeSH terms: Prehypertension
Study type: Interventional

Summary: 
      This study aims to assess the natriuretic peptide response to dietary salt loading in
      African-American individuals compared with white individuals.
    

Detailed description: 
      High blood pressure, or hypertension, is a major cause of heart disease, heart failure, and
      stroke. Natriuretic peptides are cardiac derived hormones that may protect against
      hypertension. The classical actions of the natriuretic peptides include natriuresis,
      vasodilation, and inhibition of the renin-angiotensin-aldosterone system (RAAS), which
      support a key role for these hormones in blood pressure regulation.

      Race based differences exist in the risk and severity of hypertension and cardiovascular
      disease, with African-American individuals typically being at greater risk compared with
      white individuals. Nearly half of African-American adults have hypertension, compared with
      one-third of whites. Additionally, salt-sensitivity denotes the impaired ability to handle a
      salt load with resulting increases in blood pressure. It is estimated that 75% of
      hypertensive African-Americans exhibit salt-sensitivity, compared with 35% of hypertensive
      whites. Why this predilection towards salt-sensitivity exists, particularly among
      African-American individuals, is not well understood. Thus, establishing the origins of salt
      retention in African Americans has biologic, preventative, and therapeutic importance, and
      may provide insight regarding racial differences in cardiovascular risk.

      The natriuretic peptide system is the principal counter-regulatory mechanism to salt
      retention. However, little is known regarding racial differences in the natriuretic peptide
      system. Recently, it was discovered that African-Americans have lower natriuretic peptide
      levels compared with whites, raising the possibility that African-Americans individuals can
      have a relative "natriuretic peptide deficiency" with reduced natriuretic peptide responses
      to salt loading. However, the prior studies were based on epidemiologic data with individuals
      on random salt backgrounds. This highlights the need for more detailed physiologic studies,
      under controlled salt conditions and with standardized assessment of the natriuretic peptide
      and RAAS and tissue sodium stores.

      The aim of this study is to assess the natriuretic peptide response to dietary salt loading
      in African-American individuals compared with white individuals. This study will test the
      primary hypothesis that compared with whites, African-American individuals have blunted
      natriuretic peptide responses to dietary salt loading.

      Secondary hypotheses include:

        1. Compared with white individuals, African-American individuals have higher baseline
           tissue sodium content, and

        2. Compared with white individuals, African-American individuals have impaired "target
           organ" responses to salt loading, as manifested by higher blood pressure and increased
           frequency of salt-sensitive hypertension, decreased urinary sodium excretion, less
           suppression of plasma renin and serum aldosterone, and lack of increase in left
           ventricular early diastolic relaxation velocities.
    

Intervention name(s): Low-Salt Diet; High-Salt Diet
Intervention type(s): Dietary Supplement; Dietary Supplement
Intervention description(s): The low-salt diet (7 days) will consist of meals, snacks, and sodium free water provided by the study staff.; The high-salt diet (7 days) consists of each subject's usual diet, supplemented each day with 2 bouillon broth packets, which will be provided to the subject by the study staff.
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Single (Outcomes Assessor)
Primary purpose: Health Services Research