On the capacity of the rat intestine to excrete lithium ions at therapeutic and toxic plasma lithium concentrations.

Lithium (Li) excretion into the intestinal lumen was quantitated in rats in situ by use of a pendular perfusion technique. Male Sprague-Dawley rats were injected daily (7-10 days) i.p. with 1, 3, and 6 mmol LiCl per kg body weight (n = 9-12). Jejunal as well as ileal and colonic segments were perfused with isotonic saline containing 3H-PEG-4000. Perfusate samples were taken after 0, 5, 10, 20, and 60 min. At the highest dose toxic symptoms were observed. At 6 mmol Li per kg the plasma Li concentrations were higher than those linearly extrapolated from the lower-dose groups, which may be due to inappropriate renal excretion. The Li concentration in the perfusate increased linearly over time and was not significantly different between jejunal and colonic segments. The same ratio between the Li concentration in the plasma and in the luminal perfusate was observed in all groups. Intestinal Li excretion is not impaired by high plasma concentrations. The intestinal capacity to excrete Li is considerable: 45 cm of jejunum is able to excrete the intire plasma Li content in 30-40 min, when Li is not resupplemented from intracellular stores. The renal clearance of lithium (Li) decreases when toxic Li plasma concentrations are reached. Therefore, if it were possible to trap Li in the intestinal lumen, this excretion route might be of therapeutic interest in cases of Li intoxication with impaired renal Li-excretion.