the diurnal rhythm in natriuretic peptide levels

Conditions: Natriuretic Peptides; Obesity; Nocturnal Blood Pressure

Summary: 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

Keywords: diurnal rhythm race