The Effect of Cadmium Pretreatment On the Disposition and Excretion of Methylmercury and Trace Elements (Zinc, Copper) in Rats

Abstract

Cadmium chloride (Cd) was injected s.c. into male rats at a dose rate of 3mgCd/kg 3 times a week for 4 weeks. The animals were maintained for administration of methylmercury (203 Hg) chloride at a dose of 3 mg CH3 Hg/kg given p. o. 3 times a week for 2 weeks, followed by 3 weeks of recovery period. Animals were sacrificed 24 h after the final dose of MeHg, or 5 weeks after cessation of Cd administration. Cd-pretreat ment significantly decreased total Hg concentration in the kidney and RBC and almost completely inhibited demethylation of MeHg in the kidney (from 32% to 3% of inorganic Hg). Cd-pretreatment did not affect urinary excretion of total Hg, but significantly increased daily excretion of total Hg infeces. MeHg given alone significantly increased renal but not hepatic copper levels and decreased copper in the plasma and brain. In Cd-pretreated rats, both renal and hepatic copper con centration were in the normal ranges. Zinc levels in Cd-pretreated rats significantly increased in the kidney, liver and brain but decreased in plasma (compared to control and MeHg-alone treated animals). From these results it can be concluded that Cd-pretreatment may decrease MeHg toxicity by increasing the fecal mercury excretion and by inhibiting the formation of inorganic mercury in the kidney, which is a more potent renal toxin than MeHg.