Atrial natriuretic peptide and pressure natriuresis: interactions with the renin-angiotensin system

The aim of this study was to quantitate the effects of increases in atrial natriuretic peptide (ANP), within the pathophysiological range, on the acute pressure natriuresis mechanism and the role of the renin-angiotensin system (RAS) in modulating these effects. Renal hemodynamics and electrolyte excretion were measured in anesthetized dogs while renal perfusion pressure (RPP) was controlled at three levels (120-122, 100, and 75 mmHg) with and without intrarenal infusion of ANP at 5 ng.kg-1.min-1. Sodium excretion was significantly higher during ANP infusion at RPP of 122 +/- 3 mmHg, averaging 55.8 +/- 13.7 during control and 113.3 +/- 23.3 mueq/min during ANP infusion. AT RPP of 101 +/- 1 mmHg, sodium excretion was 51.8 +/- 17.4 during control and 93.0 +/- 17.6 mueq/min during ANP infusion, but at RPP of 75 +/- 0 mmHg there was no difference in sodium excretion between control and ANP infusion. In a second set of dogs, angiotensin II (ANG II) formation was blocked with captopril (20 micrograms.kg-1.min-1), circulating (5 ng.kg-1.min-1), and the above protocol was repeated. When the RAS was fixed, the renal responses to ANP infusion were abolished, even at the higher pressure levels. These data indicate that ANP increases the slope of pressure natriuresis; at higher levels of RPP, ANP potentiates pressure natriuresis but not at lower pressures. In addition, part of this effect may be due to suppression of the RAS, because the ANP-induced shift in the pressure natriuresis relationship was abolished when circulating ANG II was maintained constant.