Competitive effects of hypokalemia and volume depletion on plasma renin activity, aldosterone and catecholamine concentrations in hemodialysis patients

The effects of isokalemic and hypokalemic ultrafiltration dialysis on plasma renin activity (PRA), aldosterone (ALDO) and plasma catecholamine (CA) concentrations were investigated in eight patients with end-stage renal failure. Plasma sodium concentration was kept constant during each hemodialysis, but plasma potassium decreased (4.8 to 3.4 mEq/liter, P < 0.001) only in the hypokalemic dialysis group. The falls in mean body weight (-1.77 vs. -1.66 kg) and mean blood pressure (125 to 109 vs. 126 to 108 mm Hg) were similar in the isokalemic and hypokalemic dialysis patient groups. PRA increased during dialysis both in the isokalemic (4.55 to 8.85 ng/ml/hr, P < 0.02) and hypokalemic (2.18 to 3.19 ng/ml/hr, P < 0.01) groups. These changes in body wt, blood pressure, and PRA were not significantly different in the isokalemic and hypokalemic dialyses. There were, however, important differences between the isokalemic and hypokalemic groups. While the mean ALDO increased (105 to 198 pg/ml, P <0.05) during the isokalemic dialyses, ALDO actually fell significantly during the hypokalemic dialyses (120 to 36.8 pg/ml, P < 0.005). Prior to dialysis, CA's were increased significantly above normal values in both dialysis groups. With dialysis, CA's did not change significantly in the isokalemic group and actually fell in the hypokalemic group (1.27 to .93 ng/ml, P < 0.02). In spite of decreased body wt and blood pressure in both groups, heart rate increased only during the isokalemic dialysis. These results demonstrate a dominant effect of a fall in plasma potassium concentration to suppress ALDO, despite a concomitant fall in blood pressure and body wt and a rise in PRA. The elevated CA concentrations in these patients may possibly interact with sodium balance and contribute to the hypertension in these patients. The fall in CA's and absence of tachycardia during hypokalemic dialysis raises the possibility that a fall in plasma potassium concentration may cause or unmask autonomic insufficiency in these chronic renal failure patients who are predisposed to this disorder.