Excretion of Urinary Coproporphyrin in Lead Poisoning. Part 1 and 2

In lead poisoning there are, in addition to other changes, disturbances in the metabolism of the pyrrole derivatives of blood pigments, and one of these is a high level of urinary coproporphyrin. The object of this paper was to find in what form coproporphyrin is eliminated in the urine. Saillet found as early as 1896 that coproporphyrin was partly eliminated in the urine in the form of a non-fluorescent precursor, but this problem has been studied in more detail only in recent years. Watson, de Mello, Schwartz, Hawkinson, and Bossenmaier (1951) found in fresh urine of healthy subjects that the precursor formed more than half of the total value of the coproporphyrin. Weatherall (1952) found in the fresh urine of rabbits, poisoned with lead, as much as 83% of the precursor, with an average value of 49%. In both these papers the extraction method of determination was used, in which, during the extraction, the precursor is transformed to coproporphyrin. Eriksen (1951a) used adsorption on calcium phosphate for the determination of preformed coproporphyrin and found as much as two-thirds of the precursor in the urine of subjects with lead poisoning. He did not work, however, with sufficiently fresh urine. No experimental proof has so far been given of the presence of preformed coproporphyrin in the urine of healthy subjects or in lead poisoning. On the contrary, it was found that injected coproporphyrin was eliminated by the liver (Weatherall, 1952; Goldberg, 1955; Hoffbauer, Watson, and Schwartz, 1953), not by the kidneys. We are of the opinion that the coproporphyrin found in the urine had passed through the kidneys in the form of the precursor. The precursor of coproporphyrin has not been isolated. It appears that it is a four-pyrrole compound which is very readily oxidized to coproporphyrin (Watson et al., 1951), and we have investigated experimentally the theory that in lead poisoning only the precursor of coproporphyrin and not preformed coproporphyrin is present in fresh urine. In the determination of coproporphyrin in the urine immediate measurement, or the exclusion of light even for very short periods, is imperative.

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