Effect of low dietary sodium and potassium on lithium clearance in rats

The influence of dietary sodium and potassium intake on lithium clearance (CLi) was examined in conscious Wistar rats without surgical stress. CLi was not influenced by variations in the dietary content of Na and K in the range of 50-600 mmol/kg, but decreased at values of 25 mmol/kg and was lowered by about 50% at a value of 5 mmol/kg of either ion. The lowering of CLi produced by a reduction in one of the ions was independent of variations in the dietary content of the other. The reductions in CLi were additive, CLi being reduced to almost zero in rats given a diet low in both Na and K. The reductions in the fractional excretion of lithium produced by either a low Na or a low K diet were both fully reversible after administration of amiloride, which suggests that they were due to reabsorption of Li in the distal nephron segments. It is concluded that a low Na diet and a low K diet both lead to distal tubular reabsorption of Li and that the effect is additive. If CLi is to be used as an index of proximal tubular fluid output, the dietary contents of Na and K should both be at least 50 mmol/kg in unanesthetized Wistar rats without surgical stress.