Effects of lead exposure on skeletal development in rats

The effects of lead on growth in female rats and on growth and skeletal development in their offspring were investigated. No alteration in growth rate, compared to the growth rate in pair-fed controls, was observed in 48 weanling females continuously exposed to 250 or 1000 ppm lead in drinking water and fed a replete diet. After 49 days of exposure, all rats (24 pair-fed controls, 12 exposed to 250 ppm lead, and 12 exposed to 1000 ppm lead) were mated with control males. At parturition, six lactating dams each from the 250 and 1000 ppm lead groups were removed from lead exposure and given control drinking water, and six lactating dams each from the control group were given either 250 or 1000 ppm lead in drinking water. Exposure conditions for the remaining dams in the control, 250, and 1000 ppm groups were not changed. Maternal blood lead in the continuously lead-exposed groups was higher at the end of lactation than prior to mating. Lead exposure prior to parturition caused greater maternal tibial lead accumulation than lead exposure after parturition. In contrast, lead exposure prior to parturition had a lesser impact on offspring tibial lead accumulation than lead exposure after parturition. Decreases in tibial calcium and phosphorus were observed in dams exposed continuously to 250 or 1000 ppm lead; however, there was no apparent effect of lead on maternal growth-plate morphology or on growth-plate width. Offspring body weight was depressed relative to controls during suckling (Day 11) and after weaning (Day 24) in high-dose and continuously lead-exposed groups. Continuous lead exposure caused a greater decrease in offspring body weight than lead exposure only prior to or after parturition. Decreased tail length growth suggested possible effects of lead on tail vertebral bone growth. While tibial calcium and phosphorus levels were not changed in the weanlings, increased weanling growth-plate width, with disruption of chondrocyte organization, and wider metaphyseal trabeculae were observed. Although the mechanisms of these effects are not known, the results suggest that local lead-related effects on growth-plate chondrogenesis and metaphyseal mineralization may be involved.