Excretion of lithium by kidney, bile and faeces in rats of different ages

In 5-, 15- and 105-day-old rats the renal, biliary and faecal excretion of lithium was measured after administration of 150 mumol Li+/100 g b.wt. daily for two days and a load of 300 mumol Li+/100 g b.wt. intraperitoneally on the third day. The balance between the doses administered and elimination characterizes quantitative age-dependent differences concerning the two important excretion routes of lithium (kidney, faeces). Up to 72 hr after the 3rd lithium administration, in 5-day-old rats 50% of the total dose is excreted by kidney and approximately 40% in faeces. In 15- and 105-day-old rats, the renal elimination rate is distinctly higher: 80 or 90% of the lithium supply is excreted with urine and 15 or 10% with faeces, respectively. In both age groups only one fifth of the lithium eliminated with faeces is secreted via the bile. It is supposed that the major quantity of lithium secretion into faeces occurs through the intestinal mucosa. The results are in good accordance with findings of the age-dependent kinetics of lithium.