The Diurnal Rhythm in Natriuretic Peptide Levels

The purpose of the study to assess the diurnal rhythm in natriuretic peptide levels and its temporal relationship with nocturnal blood pressure in obese and African-American individuals as compared with lean and white individuals.

Obese and African-American individuals are at greater risk for cardiovascular morbidity and mortality than lean and white individuals. One of the key reasons for this health disparity is a higher risk of hypertension among obese and African-American individuals. The reasons for why these disparities develop are not well understood.

Natriuretic peptides are hormones produced by the heart and have a wide range of favorable cardiovascular effects such as natriuresis (sodium excretion), vasodilation, and direct inhibition of the renin-angiotensin-aldosterone system. Human studies showed the existence of 24-hour (diurnal) variations in the circulating natriuretic peptide levels.

Prior work from the investigators and others demonstrated that individuals with genetically-determined lower circulating natriuretic peptides levels have higher blood pressure and greater risk of hypertension. Further, the investigators have shown that obesity and African-American race are associated with lower natriuretic peptide levels, suggesting that relatively low natriuretic peptide levels may be a biologic determinant contributing to health disparities.

Obese and African-American individuals have a greater prevalence of nocturnal hypertension \[nighttime blood pressure \>120/80 mmHg\], which is an independent risk factor for cardiovascular events. The underlying reasons for 24-hour variations in blood pressure are unknown.

The investigators hypothesize that loss of the natural 24-hour rhythm of natriuretic peptide levels plays a role in the development of nocturnal hypertension in obese and African-American individuals. The aims of this study are:

1. to examine whether there is a presence of a 24-hour rhythm in natriuretic peptide levels among normotensive obese and African-American individuals and whether there is a difference in the rhythmicity of natriuretic peptide levels between obese and lean as well as in African-Americans and whites;
2. to examine whether there is an existence of a relationship between 24-hour variability of natriuretic peptide levels and 24-hour patterns of blood pressure and whether this relationship of rhythmicity of natriuretic peptide levels and nocturnal blood pressure differed in obese and lean individuals and by race.

Eligibility Criteria:
Inclusion Criteria:

* Age 18 to 40 years
* Blood pressure less than 140/90
* Body Mass Index between 18.5 to 25 kg/m2 (lean) or 30 to 45 kg/m2 (obese)
* Self identified African-American or white individuals
* Willingness to comply with the study diet
* Provide informed consent

Exclusion Criteria:

* History of hypertension
* History of cardiovascular, renal, or liver disease
* Diabetes or use of glucose-lowering medications
* Use of vasoactive or diuretic medications
* Atrial fibrillation
* Anemia (Hematocrit \<41%)
* Abnormal serum sodium or potassium
* Abnormal liver function tests (\>3x upper limit of normal)
* Current smokers
* Regular users of non-steroid anti-inflammatory medications