Influence of dietary factors on blood and tissue lead concentrations and lead toxicity

Abstract

The effect of dietary protein and amino acids (methionine or cystine) on blood and tissue lead concentrations and lead toxicity was investigated in 5-week-old rats receiving lead acetate (1 mg of Pb/ml) in their drinking water for 5 weeks. The criteria for lead toxicity were decreased growth rate and food utilization, increased urinary aminolevulinic acid excretion (ALA), and the production of lead-induced anemia, measured by a decrease in hemoglobin, hematocrit, and red cell count. Rats fed a low-protein diet (8% casein + 1% alanine) had severe signs of lead toxicity and high (369 μg/100 ml) blood lead concentrations. Substitution of methionine or cystine for alanine decreased lead toxicity, and blood lead decreased without a corresponding lowering of tissue lead concentration. Rats receiving a normal protein diet (27% casein) showed appreciable signs of lead toxicity as judged by ALA excretion and lead-induced anemia. Blood lead concentrations were only one-sixth of the values obtained on the low-protein diet, but there was no corresponding decrease in kidney and liver lead and there was even an increase in bone lead concentration. On the various diets, blood lead often did not reflect tissue lead concentrations, the extent of lead toxicity, or lead exposure. If the lack of correlation between blood lead, tissue lead concentrations, lead toxicity, and lead exposure observed in rats occurs also in humans, then blood lead would not be adequate as the sole criterion in screening human populations for lead exposure.