Potassium excretion in renal failure in the rat: the role of distal tubule flow and aldosterone.

1. This study examines the contribution of an increased distal tubule flow and of aldosterone to the handling of a potassium load in conscious rats with renal failure induced by subtotal nephrectomy or by gentamicin on a control of high K+ diet. 2. Glomerular filtration rate was reduced by subtotal nephrectomy to 40% and by gentamicin treatment to 60% of control. Subtotal nephrectomy induced significant hypertrophy of glomeruli and proximal and distal tubules, but gentamicin did not. Both experimental groups had a normal iothalamate space and plasma potassium after a 20 h fast. 3. Two hours after an acute KCl load rats with renal failure excreted less potassium than control rats. There was also a lesser natriuretic effect of KCl in the renal failure groups. 4. A high K+ diet, given for 5-7 days, increased excretion of an acute KCl load in control rats and rats with renal failure. 5. (UNaV + UKV) was used as an estimate of distal tubule flow. Potassium excretion, related to distal tubule flow, was similar in the renal failure and control rats when on the same diet. This is consistent with potassium excretion being strongly, but not necessarily solely, dependent on distal flow. 6. Adrenalectomy reduced, and aldosterone restored, potassium excretion in the renal failure and control groups. This suggests a role for aldosterone in excretion of an acute potassium load with this degree of renal failure.