In 19 patients with chronic renal failure and still preserved residual diuresis the inulin clearance (Cin) and renal potassium excretion were assessed before and 12 hours after haemodialysis (HD), combined with conventional ultrafiltration. The mean value of Cin after HD declined significantly (p less than 0.001). As a result of HD a significant decline of the plasma potassium concentration occurred (p less than 0.005) and of the urinary excretion (p less than 0.01). The mean value of the fractional potassium excretion (FEK) did not change significantly as a result of HD. The reduced urinary K excretion after HD correlated significantly (p less than 0.05) with the decline of Cin. The findings suggest that the decline of the urinary potassium excretion after HD is above all due to a decline of the glomerular filtration rate. The tubular potassium secretion does not change significantly under these conditions. These findings support indirectly the idea that the increased tubular potassium secretion in residual nephrons in patients with chronic renal failure is not conditioned by retention of low-molecular dialysable substances.

Keywords: Female; Humans; Kidney Failure, Chronic /therapy/; Male; Middle Aged; Nephrons /metabolism/; Potassium /urine/; Renal Dialysis