A possible physiological role of atrial natriuretic peptide in body fluid volume regulation

To study whether or not atrial natriuretic peptide (ANP) is physiologically involved in body fluid volume regulation, we examined the relationship between plasma ANP level and renal function during NaCl loading and ANP infusion. In study I, six normotensives (NTs) and seven hypertensives (HTs) were placed on 7-day low (3 g/day) and then 7-day high NaCl diets (20 g/day). The plasma ANP level increased by 60% (p less than 0.01) on the high NaCl diet. Although the plasma ANP level was higher in HTs than in NTs, the changes in plasma ANP due to NaCl loading were similar between the two groups. Furthermore, increases in urinary Na excretion due to ANP infusion at 25 ng/kg/min were greater for the high NaCl diet than for the low NaCl diet (p less than 0.02). In study II, graded doses of ANP were infusion into 16 other HTs and Nts on an 8 g/day NaCl diet. ANP infusion at 2.5 ng/kg/min increased the plasma levels of ANP by 80% (p less than 0.001). Such increments were associated with an increase in urinary Na excretion by 25% (p less than 0.02) in both HTs and NTs. This rise in plasma ANP was comparable to that induced by high NaCl intake. Thus, a slight increase in plasma ANP induced by dietary Na loading seems to augment renal Na excretion, suggesting that ANP may play a physiological role in body fluid volume regulation.