Race, Natriuretic Peptides and Physiological Perturbations

The purpose of the study is to understand the origins of differential response to beta-blockers in African-Americans and may provide insight regarding racial differences in cardiovascular risk.

The heart is an endocrine organ. The natriuretic peptides are hormones produced in the heart and are secreted in response to increased wall stress in atria and ventricles. The principal circulating NPs are Atrial Natriuretic Peptide (ANP) and B-type Natriuretic Peptide (BNP). The endocrine actions of NPs are natriuresis and dilatation of peripheral arteries. The NPs concentrations are elevated in heart failure (HF) and hypertension (HTN) due to volume and pressure overload. Therefore, NPs are used as diagnostic and prognostic markers in heart failure. However, NPs role in healthy individuals is not known. Previous studies have shown that reduced NP levels are associated with a greater risk of HTN. Moreover, African-Americans have lower resting NP levels than Caucasians. We hypothesize that relative NP deficiency in African American compared to Caucasian has the potential to contribute to increase risk of all-cause mortality, HTN, HF and its sequelae. Evidence from multiple clinical trials has positioned beta-blockers as a standard heart failure therapy. Beta-blocker therapy leads to increased NP levels and suppression of Renin-aldosterone-angiotensin system (RAAS) system. Suppression of renin levels by beta-blockers has been shown as a potential mechanism of benefit in HF. However, study shows that beta-blockers are less effective in African-Americans compared to Caucasians in HF treatment. So, the investigators have proposed a pilot study to look for race-based differences in the NP and RAAS response to metoprolol in healthy individuals. Additionally, exercise has been reported to increase NP levels. ANP increases more than BNP with exercise. But there is no data of NP changes in African-American with exercise. So the investigators have proposed a sub-study of race-based difference in ANP and BNP response to exercise. 40 African-American and 40 Caucasians normotensive or pre-hypertensive (healthy) individuals will be enrolled.