Effects of lead and/or zinc exposure during the second stage of rapid postnatal brain growth on delta-aminolevulinate dehydratase and negative geotaxis of suckling rats

Lead has been shown to produce cognitive and motor deficits in young rats t hat could be mediated, at least in part, by inhibition of the zinc-containi ng heme biosynthetic enzyme delta -aminolevulinate dehydratase (ALA-D). In the present study we investigated the effects of lead and/ or zinc treatmen t during the second stage of rapid postnatal brain development on brain, ki dney and blood ALA-D specific activity, as well as the negative geotaxis be havior of rats. Eight-day-old Wistar rats were injected intraperitoneally w ith saline, lead acetate (8 mg/kg) and/or zinc chloride (2 mg/kg) daily for five consecutive days. Twenty four hours after treatment, ALA-D activity w as determined in the absence and presence of DL-dithiothreitol (DTT). The n egative geotaxis behavior was assessed in 9- to 13-day-old rats. Treatment with lead and/or zinc did not affect body, brain or kidney weights or brain -or kidney-to-body weight ratios of the animals. In spite of the absence of effect of any treatment on ALA-D specific activity in brain, kidney and bl ood, the reactivation index with DTT was higher in the groups treated with lead or lead + zinc than in the control group, in brain, kidney and blood ( mean +/- SEM; brain: 33.33 +/- 4.34, 38.90 +/- 8.24, 13.67 +/- 3.41; kidney : 33.50 +/- 2.97, 37.60 +/- 2.67, 15.80 +/- 2.66; blood: 63.95 +/- 3.73, 56 .43 +/- 5.93, 31.07 +/- 4.61, respectively, N = 9-11). The negative geotaxi s response behavior was not affected by lead and/or zinc treatment. The res ults indicate that lead and/or zinc treatment during the second stage of ra pid postnatal brain growth affected ALA-D, but zinc was not sufficient to p rotect the enzyme from the effects of lead in brain, kidney and blood.