Is aldosteronism important in the maintenance of arterial blood pressure and electrolyte balance during sodium depletion?

SUMMARY To evaluate quantitatively the importance of aldosteronism in the maintenance of sodium balance and arterial blood pressure during sodium depletion, dogs were subjected to 2 weeks of dietary sodium restriction first while intact and, subsequently, after adrenalectomy, while continuously infused with basal ("sodium-replete") amounts of aldosterone and cortisol. Mean arterial pressure (MAP) was recorded continuously. During the control period (sodium intake = 50 mEq/day), the values for all measured variables in the adrenalectomized dogs were similar to those observed when the dogs were intact. When the dogs were intact and sodium intake was severely restricted, sodium balance Was achieved with a 10- and 14-fold increase in plasma renin activity (PRA) and plasma aldosterone concentration, respectively; MAP did not change. During sodium restriction in the adrenalectomized state, plasma aldosterone concentration was unchanged; this was associated with relatively small disturbances in sodium and water balance but more prominent perturbations in potassium balance. Establishment of sodium balance in the adrenalectomized dogs was associated with a 50% greater increase in PRA than in the intact state and a small fall in MAP (only 8 mm Hg). Changes in renal function were similar in both groups of dogs during sodium depletion — GFR was unchanged and effective renal plasma flow (ERPF) fell 7%-9%. The data from the 2-week period of sodium restriction indicate that the maintenance of sodium balance and arterial pressure during sodium depletion is not critically dependent upon enhanced aldosterone secretion.