抄録
An experimental study on rabbits was carried out to make clear the relationship between lead doses and changes in porphyrin metabolism. Four levels of lead doses (0.10, 0.25, 0.50, 1.00 mg/kg) were chosen, and lead was injected intravenously into rabbits on alternate days (3 times/week) for several months repeatedly. Urinary δ-aminolevulinic acid (ALA-U), porphobilinogen (PBG-U) and coproporphyrin (CP-U), δ-aminolevulinic acid dehydratase (ALA-D) activity in peripheral red blood cells, and free erythrocyte protoporphyrin (FEP) were determined during the experimental perlod. The changes of these parameter values during the period of lead administration and after its cessation were discussed in this paper in regard to the administered lead doses. ALA-D activity dropped rapidly after the injection of lead (Fig. 2). In the rabbits treated with 0.1 mg/kg dose, ALA-D activity was maintained at about 20% of the initial level during the period of lead injection. In the groups treated with the large doses of lead, ALA-D was inhibited almost completely at the end of the first week of lead injection, and a further drop was no more observed by the subsequent lead administration. Increase of ALA-U and CP-U were observed in the large dose groups during the period of lead administration, but no overt dose-response relationship was demonstrated after the cessation of lead injection (Figs. 3 and 4). FEP levels in rabbits were elevated in proportion to the increase in lead doses (Fig. 1). The levels of FEP reached to 100 μg/dl·pcv after 2-2.5 mg/kg of lead administration in total, but in the group of 0.1 mg/kg dose of lead the FEP kept the constant level (100±10 μg/dl·pcv) during a long-term period after 50th day of the experiment. A dose-response relationship between FEP and injected lead was clearly observed even in the period after the cessation of lead injection as well as in the administration period. A close positive correlation was found between logarithms of the blood lead level (Pb-B) and log FEP (γ=0.84) in this experiment (Fig. 6). These results indicate that FEP is one of the useful and adequate indicators for detecting or evaluating sub-clinical lead poisoning.
