Effect of dietary sodium content on renal handling of lithium. Experiments in conscious diabetes insipidus rats.

Previous studies have shown that the clearance of lithium (CLi) is a quantitative measure of the delivery of tubular fluid to Henle's loop in rats given food with an ordinary or high sodium content but not in rats given food with a low sodium content, because under these circumstances lithium is also reabsorbed to some extent in the distal nephron segment. The present study examines CLi, CNa and urine flow in diabetes insipidus rats at various dietary sodium contents. The results showed that CLi was 120 microliter/min/100 g b.w. when no distal reabsorption took place at a dietary sodium content of 300 mmol/kg. At a dietary sodium content of 5 mmol/kg the calculated distal lithium reabsorption reduced CLi by 55 microliter/min/100 g b.w.; at 25 mmol/kg distal reabsorption was reduced to half this value; at 50 mmol/kg distal reabsorption was slight and barely significant, and at 75-300 mmol/kg there was no distal reabsorption of lithium. It is concluded that CLi can be used as a quantitative measure of the delivery of tubular fluid to the loop of Henle at dietary sodium contents higher than 50-75 mmol/kg in the rat.