Studies on Abnormality of Porphyrin Metabolism Induced by Lead

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The increased excretion of urinary delta-aminolevulinic acid (ALA) is one of the most specific indices for evaluating the lead-induced porphyrin metabolic disorders.In the present study, we found the significant difference in urinary ALA concentration between ddY and C57BL/6 mice strains. To deduce a possible mechanism for this difference, we measured the activities of both ALA synthase (ALAS) and ALA dehydratase (ALAD) which are regulating the concentration of ALA in the body. The activity of hepatic ALAS in ddY Mice was similar to that in C57BL/6 mice. On the other hand, a significant difference in hepatic ALAD activity was found in these mice strains.From these results, we speculated that if the relative levels of ALAS and ALAD activities in the bone marrows of mice are similar to those of ALAS and ALAD activity in the liver, the significant difference in the urinary excretion of ALA between ddY mice and C57BL/6 mice may result from the activity level of ALAD rather than ALAS.When such mice was exposed to lead in drinking water (500 ppm as Pb) for 14 days, the rate of elevated excretion of urinary ALA might be expected to differ in the two groups of mice. The data, however, has demonstrated that rate of increasing excretion of urinary ALA (7.9-times control) in lead-exposed ddY mice is almost the same as (7.6-times control) in lead-exposed C57BL/6 mice.