Effect of a chronic infusion of atrial natriuretic peptide on sodium balance in normotensive and two-kidney, one-clip hypertensive rats

We have previously found that chronic infusion of atrial natriuretic peptide (ANP) decreased mean arterial pressure (MAP) by 16% in two-kidney, one-clip (2K-1C) hypertensive rats, and we hypothesized that natriuresis might be modified through the pressure-natriuresis mechanism. We therefore decided to evaluate sodium balance in 2K-1C rats infused with ANP (0.5 micrograms/h for 4 days). The ANP infusion to the 2K-1C rats induced a significant decrease in MAP from 171 +/- 3 to a minimum value of 147 +/- 6 mm Hg after 2 days of treatment (p less than 0.001). Sodium excretion fell from 2,536 +/- 60 to 2,047 +/- 86 (p less than 0.001) and 2,211 +/- 96 mu Eq/24 h (p less than 0.05) by days 1 and 2 of ANP administration. Furthermore, fractional excretion of sodium intake decreased from 99.1 +/- 1.5 to 81.1 +/- 2.9 (p less than 0.001), 84.1 +/- 2.6 (p less than 0.05) and 85.9 +/- 5.15% (p less than 0.05) by days 1, 2 and 3 of ANP infusion, respectively, returning to basal values thereafter. The administration of vehicle (0.9% NaCl) did not induce any significant change in 2K-1C hypertensive rats. The infusion of either vehicle or the same dose of ANP to normotensive rats (0.5 micrograms/h, for 4 days) did not modify sodium balance throughout the experiment. These results strongly suggest that the ANP-induced decrease in MAP might be responsible for the transitory sodium retention observed in 2K-1C hypertensive rats during the administration of the peptide.