1. This study was designed to quantify the role of angiotensin II in determining the chronic relationships between arterial pressure, renal haemodynamics and sodium excretion.
2. In six control dogs sodium balance was achieved during chronic increases in sodium intake from 5 to 495 mmol/day with small increases in arterial pressure (7mmHg), moderate increases in glomerular filtration rate (19%) and decreases in filtration fraction. Similar increases in sodium intake in dogs whose circulating levels of angiotensin II were fixed, due to a constant intravenous infusion of 4.85 pmol of angiotensin II min−1 kg−1, caused large increases in arterial pressure (42%), glomerular filtration rate (31%), filtration fraction and calculated renal sodium reabsorption above control. In six dogs whose angiotensin II formation was blocked by SQ 14 225, sodium balance at intakes of 5–80 mmol/day occurred at reduced arterial pressure, glomerular filtration rate, filtration fraction and sodium reabsorption although plasma aldosterone concentration was not substantially different from that in control dogs. At sodium intakes above 240 mmol/day arterial pressure was not altered by SQ 14 225.
3. These data indicate that during chronic variations in sodium intake angiotensin II plays a major role, independently of changes in plasma aldosterone concentration, in allowing sodium balance without large fluctuations in glomerular filtration rate or arterial pressure. The mechanism whereby angiotensin II conserves sodium chronically is through increased sodium reabsorption, since steady-state sodium reabsorption was increased by angiotensin II and decreased by SQ 14 225.