Biliary excretion of cadmium by rats: effects of zinc, cadmium, and selenium pretreatments.

The significance of bile as an excretory route for cadmium (Cd) was studied in anesthetized, bile-duct-cannulated Sprague-Dawley rats during a 6-hr collection period. Observations were made on bile flow rates, the concentrations of Cd in bile following dietary and parenteral Cd exposure, and the influences of zinc (Zn), selenium (Se), and Cd pretreatments upon the biliary excretion of subsequently administered Cd. The bile flow rates ranged between 1.96 and 2.89 mg/g rat-hr (22 +/- 3 ppb Cd) for normal rats and between 2.68 and 4.09 mg/g rat-hr (58 +/- 6 ppb Cd) for rats fed 100 ppm Cd. Less than 0.1% of the Cd administered subcutaneously at rates ranging from 0.25 to 40 mg/kg rat could be accounted for in bile collected during the 5-hr period following the parenteral Cd injections. Subcutaneous administration of 8 mg Zn/kg rat or 0.5 mg Cd/kg rat on days 1 and 6, respectively, before the postcannulation administration of 1 mg Cd/kg rat caused a significant reduction in the biliary excretion of Cd during the bile collection period. Administering 2 mg Se/kg rat 3 days prior to the postcannulation administration of 1 mg Cd/kg rat caused a significant increase in the biliary excretion of Cd during the bile collection period. The biochemical bases for these observations are believed associated with the type of metal-binding protein induced by the respective pretreatments.