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 ra ts in situ by use of a pendular perfusion technique. Male Sprague-Dawl ey rats were injected daily (7-10 days) i.p. with 1, 3, and 6 mmol LiC l per kg body weight (n = 9-12). Jejunal as well as ileal and colonic segments were perfused with isotonic saline containing H-3-PEG-4000. P erfusate samples were taken after 0, 5, 10, 20, and 60 min. At the hig hest dose toxic symptoms were observed. At 6 mmol Li per kg the plasma Li concentrations were higher than those linearly extrapolated from t he lower-dose groups, which may be due to inappropriate renal excretio n. The Li concentration in the perfusate increased linearly over time and was not significantly different between jejunal and colonic segmen ts. The same ratio between the Li concentration in the plasma and in t he luminal perfusate was observed in all groups. Intestinal Li excreti on is not impaired by high plasma concentrations. The intestinal capac ity 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 resupplemen ted from intracellular stores. The renal clearance of lithium (Li) dec reases when toxic Li plasma concentrations are reached. Therefore, if it were possible to trap Li in the intestinal lumen, this excretion ro ute might be of therapeutic interest in cases of Li intoxication with impaired renal Li-excretion.