ABSTRACT
To investigate the effects of physiological increases in plasma brain natriuretic peptide concentration in humans, we studied six healthy volunteers who received incremental infusions (0.25 pmol/kg per minute in the first hour and 0.50 pmol/kg per minute in the second) of synthetic human brain natriuretic peptide-32 in a placebo-controlled, crossover study. Peptide plasma levels were 1.69 +/- 0.39 pmol/L at baseline and rose 1.5- and 3-fold with the lower and higher doses, respectively. These values were within the normal range and also comparable to those reported in patients with mild essential hypertension. The urinary excretion rate of cGMP also increased during brain natriuretic peptide infusion, indicating stimulation of natriuretic peptide receptors. Peptide administration induced a significant 1.7-fold increase in urinary sodium excretion without affecting renal plasma flow (para-aminohippurate clearance), glomerular filtration rate (creatinine clearance), and urine flow rate. Fractional proximal sodium reabsorption (lithium clearance method) was unchanged, and fractional distal sodium reabsorption significantly decreased. Brain natriuretic peptide caused no changes in arterial pressure, heart rate, hematocrit, and serum proteins, but it exerted an inhibitory effect on the renin-aldosterone axis, as indicated by the significant 50% or more decrease of plasma renin activity and urinary excretion rate of aldosterone. These results suggest that brain natriuretic peptide may be involved in the overall regulation of body fluid and cardiovascular homeostasis in humans, mainly through its natriuretic and endocrine effects.
