Further study of effects of chelating agents on excretion of inorganic mercury in rats

The effects of three chelating agents, N-benzyl-D-glucamine dithiocarbamate (BGD), 2,3-dimercaptopropanol (BAL) and D-penicillamine (D-PEN), on the excretion of mercury in rats exposed to mercuric chloride (HgCl2), the chemical forms of mercury compounds excreted in the bile and urine and the intestinal reabsorption of mercury compounds in the bile were studied. Rats were injected intraperitoneally with 203HgCl2 (300 micrograms Hg and 74 kBq of 203Hg/kg) and 24 h later, they were injected intraperitoneally with a chelating agent (a quarter of an LD50). The injection of the chelating agents significantly enhanced the biliary and urinary excretions of mercury. The enhancing effect of BGD on the excretions of mercury was almost the same as that of BAL and much larger than that of D-PEN. The major chemical form of mercury in the bile and urine of rats injected with BGD after HgCl2 treatment was Hg-BGD compounds. The chemical form of mercury in the bile and urine of rats injected with BAL after HgCl2 treatment was mainly Hg-GSH compound. The mercury after HgCl2 and D-PEN treatment was excreted mainly via the urine in the form of Hg-D-PEN compound. The intestinal reabsorption of mercury from the bile of rats injected with BGD or D-PEN was only 0.18% or 0.38% of the dose, respectively. The intestinal reabsorption of mercury from the bile of rats injected with BAL was 27.38% of the dose. It was suggested that the Hg-GSH compound excreted in the bile after HgCl2 and BAL treatment is partly degraded to Hg-cysteine (Cys) by the intestinal membranous enzymes and that the ligand of Hg-Cys is replaced by BAL in the bile, resulting in the effective reabsorption of Hg-BAL compound from the intestine.