Effect of the size of an oral dose of aluminium on the relative importance of biliary v. urinary aluminium excretion in conscious rats.

We compared biliary and urinary aluminium (Al) excretion following ingestion of dietary or gavage dosing of low to moderate pharmacological doses of aluminium. Bile was collected from 26 conscious, male Sprague Dawley rats following administration of a single gavage dose of 0, 0.25, 0.5 or 1 mmol Al/kg body weight in 1 ml 16% citrate solution (equivalent to 0-650 mg Al to a 70-kg human). Urine was collected from 20 additional rats following similar dosing. Biliary Al secretion rates were highest in the first hour after dosing. Cumulatively, rats given 0.5 or 1 mmol Al/kg body weight excreted significantly more Al in bile than rats dosed with 0.25 mmol Al/kg body weight, which excreted more Al bile than control rats. Urinary Al excretion was many-fold higher than biliary Al excretion by rats dosed with Al but was less than biliary Al excretion by control rats exposed to dietary Al only. These results suggest that the liver was capable of secreting small amounts of absorbed dietary Al into bile but that the kidneys became the primary excretory organs for Al when the liver's secretory capacity was surpassed after ingestion of pharmacological doses of Al.