The fate of intravenously administered coproporphyrin III in normal and lead-treated rabbits

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Abstract
Expts. were performed to discover why coproporphyrin III appears in the urine, but not in the feces, in Pb poisoning. At least half the urinary coproporphyrin in Pb-treated rabbits is formed from a precursor after the urine is passed. Coproporphyrin HI was obtained from the urine of Pb-treated rabbits, crystallized as its methyl ester, hydrolyzed and injd. in 100 ug. doses intraven. into conscious and anesthetized normal and Pb-treated rabbits. No additional urinary excretion of coproporphyrin III was found. In anesthetized rabbits the mean rate of excretion of coproporphyrin in the bile was 1.3 + 0.6 (S.E. ug./hr. for normal rabbits and 1.7 [plus or minus]1.1 (S. E.) [mu]g./hr. for Pb-treated rabbits. When 100 [mu]g. coproporphyrin were injd. intraven., this rose to 18-36 [mu]g./hr., and 35-75% of the dose was accounted for in the 4 hrs. after injn. No difference was apparent between the biliary excretion of the normal and that of Pb-treated rabbits. It is suggested that the coproporphyrin found in the urine in Pb-treated rabbits is excreted entirely as a precursor, and that the metabolic disorder produced by Pb is an overproduction or failure of utilization of a precursor of coproporphyrin and not of coproporphyrin itself. The administered coproporphyrin had no effect on the behavior, blood pressure or water diuresis of either normal or Pb-treated rabbits.