Evidence for an intestinal lithium excretion in rats

Renal, biliary, and faecal lithium excretion as well as intracellular lithium concentrations in different segments of the intestine were measured simultaneously in anaesthetized adult rats following sham operation, after ligation of the hilus of one or both kidneys, and after bilateral ligation of the renal hilus and additional bile duct ligation. Lithium was administered intravenously (300 mumol/100 g b.wt.) and thereafter lithium, sodium and potassium were measured up to 3 h in the different biological materials. The results give evidence that only one fifth of the lithium determined in faeces reached the small intestine via bile. Dependent on the type of restricted elimination, an increased lithium content was measured in faeces, which was distinctly higher in the colon than in the two small intestine segments. In contrast, no changes in biliary lithium excretion were observed. A slower decrease in the time course of serum lithium concentrations demonstrated that the loss of the other elimination routes cannot be compensated completely by the enhanced faecal lithium output. But lithium concentrations were found to be lower in serum than in the intestinal tissue segments and were highest in the segmental samples of faeces. On this basis an active transcellular transport step for lithium must be supposed beside the possibility of a paracellular transfer across the intestine. The lithium-induced changes of the sodium and potassium concentrations observed in the intestinal tissue and in the faeces support this interpretation.