Antagonistic effects of zinc on inhibition of b-aminolevulinic acid dehydratase by lead

Pb2+ blocked the entrance of 65Zn into the red blood cells when PbAc2 was added in vitro to human whole blood, but when PbAc2 was given ip 25 mg/kg to mice pretreated with ip 65ZnC12 1.11 MBq/kg, the amount of 65Zn retention in the whole blood. liver, kidneys. and brain were increased. The addition of PbC12 3.75 vmol/L to human whole blood in vitro caused a significant decrease in ALAD activity. When PbAc2 3.75 vmol/L and ZnAc2 (0.1-0.5 vmol/L) were added to human whole blood in vitro the inhibitory effect of ALAD activity was reduced by PbAc2. Suckling rats were exposed to PbAc2 tbrough the milk of their dams which were given PbAc2 625 ppm in deionized drinking water for 21 d after birth. and were ip ZnAc2 5 mg/kg in 0.1 ml saline every 3 d. The whole blood and hepatic ALAD activity of ZnAc2-treated suckling rats did not change as compared with the controls. These observations suggest that Pb2+ may influepce the redistribution of Zn2+ in some organs and that Zn2+ may play a role in the prevention of the damage of heme biosynthesis by Pb2+.