Differential effects of atrial natriuretic peptide infusion at physiological doses in different postures in humans

To evaluate potential physiological actions of atrial natriuretic peptide (ANP) in humans, normal male volunteers were studied in the supine and head-up tilt positions both in the absence and presence of an ANP infusion at a rate which increased plasma ANP levels to ranges observed during physiological stimuli such as volume expansion. Infusion of ANP in the supine position provoked a significant natriuresis and diuresis and suppressed aldosterone secretion. Head-up tilt alone caused expected decreases in urine flow rate and the absolute and fractional excretion rates of sodium and increases in plasma renin activity and aldosterone levels. The combination of head-up tilt and ANP infusion resulted in a less marked decrease in urine flow rate and sodium excretion and a similar increase in plasma renin activity. However, there was a significant decrease in plasma aldosterone levels. These data support a physiologic action of ANP on renal and adrenal function.