The activity of delta-aminolevulinate dehydratase (ALAD) of erythrocytes, the lead (Pb-B) and cadmium (Cd-B) concentration in whole blood, the content of reduced glutathion (GSH) in erythrocytes, and the regeneration rate of GSH by intact erythrocytes were measured during an epidemiological survey of 84 men employed in a Belgian cadmium and lead producing plant. A control group of 26 persons (students and laboratory staff) was also examined. The logarithm of the ALAD activity is highly inversely correlated with log Pb-B (r = -0.760) but no correlation was found with log Cd-B. There exists a significant negative correlation between GSH and log Pb-B (r = -0.423) but not between GSH AND LOG Cd-B. The apparently good relationship between log ALAD and GSH disappeared completely by holding log Pb-B constant, but log ALAD remained highly inversely correlated with log Pb-B when standardized for GSH concentration (r = -0.748). In vivo investigation of the GSH regeneration rate of intact erythrocytes demonstrated clearly that the overall activity of the glutathione oxidation-reduction pathways is not impaired in Pb and Cd-exposed workers with significantly increased Pb-B and Cd-B, since their initial GSH regeneration rate (first 15 minutes) was identical with that of the control group. Results of similar in vitro experiments in which control whole blood was incubated before-hand with Pb2+ or Cd2+, or both, reinforce this conclusion. Since increased Cd-B and Pb-B do not influence the glutathione reductase system of erythrocytes, and since endogenous erythrocyte GSH is not correlated with Cd-B, the moderate decrease in endogenous erythrocyte Gsh found in Pb-exposed workers might result from a Pb-induced impairment for the erythrocyte mechanism for glutathione synthesis.

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