Effect of Chelating Agent Administration on the Removal of Monomeric and Polymeric Thorium

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Abstract
Monomeric and polymeric thorium are compared with respect to distribution and ease of removal after intravenous injection into rats. In addition, the comparative efficiency of 2 chelating agents, diethylenetriaminepentaacetic acid (DTPA) and ethylenediaminetetraacetic acid (EDTA) for removal of monomeric thorium are evaluated. Sixty per cent of the injected dose of monomeric thorium is deposited in the skeleton and only 8% in the soft tissues. Treatment with DTPA given intraperitoneally at 370 mg/kg on the 2nd, 5th, 6th and 7th days after the thorium injection, reduced the skeletal content to 43% of the injected dose, whereas EDTA, under these conditions, was ineffective. When thorium was injected in the polymeric form, the primary site of depostion was the liver, which received 77% of the injected dose; in this case, the skeleton received only 6.5%. DTPA treatment at 330 mg/kg had no effect on this retention, but when massive, near-toxic levels were used, it reduced the liver content appreciably. Excretion patterns reflect these differences.