摘要：Erythrocyte δ-aminolevulinic acid dehydratase (ALAD) activity has not been used as a parameter of occupational lead exposure at high concentrations because it is too sensitive to lead. However, as high concentrations of occupational lead exposure are less frequently found due to envionmental improvement and other measures, the importance of measuring ALAD activity should be reevaluated. This study was thus performed to clarify the relationship between exposure to lead and lead content in the blood, the ALAD activity and the activity ratio, by comparing these parameters between lead workers and non-lead workers (controls). Animal experiments were also carried out to check blood lead content, ALAD activity and activity ratio at the beginning, during, and after lead administration. The following results were obtained. For the human subjects, the mean blood lead content of the controls was 4.13μg/100ml, the mean ALAD activity was 38.4μmolALA/min⋅1RBC, and the mean activity ratio was 1. The correlation coefficient r between blood lead content and ALAD activity was -0.13, that bet ween blood lead, content and activity ratio -0.27. The mean blood lead content, ALAD activity and activity ratio of lead workers were 58.1μg/100ml, 11.9μmolALA/min⋅1RBC and 4, respectively. Between blood lead content and ALAD activity or activity ratio, r was -0.83 or 0.86, respectively. The validity (sensitivity+specificity) of ALAD for each cut-off level of blood lead of 20, 50 and 60μg/100ml was calculated to be 1.60 (0.94+0.66), 1.78 (0.91+0.87) and 1.72 (0.89+0.83) at each cut off level of ALAD of 95% upper limit of non exposed group, 75% decreasing value of non exposed group and 80% decreasing value of non exposed group. The validity of ALAD activity ratio was calculated to be 1.89 (0.89+1), 1.63 (0.76+0.87) and 1.50 (0.89+0.61) in the same way as ALAD activity. In rats, ALAD activity, activity ratio and blood lead content (in descending order of magnitude) changed even on day 1 of lead administration. During the administration period, ALAD activity remained low; the activity ratio rose on days 1 and 2 but remained unchanged thereafter; the blood lead content increased dose-dependently. In rats receiving 1% lead, ALAD activity began to rise on day 1 of observation following administration and recovered to the control level on day 2 of observation; in 5%-lead-treated rats, ALAD activity was still low on day 1 of observation but sharply jumped to higher levels than controls on days 2 and 4, reaching the control value 2 weeks later. The activity ratio and blood lead content promptly decreased after the end of administration and did not return to the control level during the observation period. These data suggest that ALAD activity and activity ratio can serve as reliable parameters of lead exposure because both accurately reflect the blood lead content.
