A comparison between the natriuretic response to potassium in lithium- and amiloride-treated rats

The effect of an increase of the potassium content of the food on the natriuretic and diuretic effects of lithium and amiloride was examined in Wistar rats pretreated with the respective drugs for a period of three weeks. Lithium (60 mmol/kg) or amiloride (200 mg/kg) was added to the food and the animals had access to water and a 0.46 M NaCl solution. An increase of the potassium content of the food resulted in a potassium dose-dependent increase of the natriuretic effect in both lithium-treated and amiloride-treated rats. The effect was temporary in lithium-treated rats but persistent in amiloride-treated rats. Lithium treatment resulted in a 10-fold increase of the water intake compared to control rats and amiloride-treated rats. An increase of the potassium intake reduced the water intake in the lithium-treated animals and modestly increased the water intake in amiloride-treated rats. The results show that the exaggerated natriuretic effect produced by administration of potassium to rats treated with lithium is not a specific phenomenon. It is suggested that a lowered ability of the kidneys to secrete potassium may be responsible for the exaggerated natriuretic response to potassium in amiloride- and lithium-treated rats.