Postabsorptive effect of increased dietary zinc on toxicity and removal of tissue lead in rats.

Weanling male albino rats were fed a diet containing 12 ppm zinc and 200 ppm lead for 3 weeks. At the end of this time a representative number of samples were collected to determine tissue zinc and lead, inhibition of the lead-sensitive liver enzyme delta-aminolevulinic acid dehydratase (ALAD), and urinary delta-aminolevulinic acid (ALA). Dietary lead exposure was terminated, and the remaining rats were fed diets containing either 12 or 200 ppm zinc. Analyses were repeated at 5-day intervals over a 15-day period after lead exposure. As expected, inhibition of liver ALAD, excretion of urinary ALA and soft tissue lead content rapidly decreased after lead was removed from the diet approaching control levels by day 15. Although high dietary zinc increased the zinc content of plasma, liver and tibia, there was little or no therapeutic effect on recovery of liver ALAD, urinary ALA excretion or on the removal of lead from liver, kidney or tibia. Removal of red blood cell lead, however, was greater for rats fed the high zinc diet. Results of this study indicate that the postabsorptive interaction between zinc and lead is considerably less important than the previously reported intestinal interaction.