Retention of lead acetate in weanling and adult rats

The relative toxicity of lead acetate provided at uniform dosages (mg/kg body weight/week) in drinking water or by a single weekly po administration was studied in weanling and adult Sprague-Dawley rats. Free erythrocyte protoporphyrins, urinary δ-aminolevulinic acid, and lead levels in blood, brain, kidney, and femur were measured. Effects of age and schedule of administration were evaluated by calculating the percentage of ingested lead retained in brain, kidney, and femur. No effects of age on levels of lead in blood or in brain tissue were observed within the same dosage schedule group when dosing was equivalent on the basis of body weight. Weanling rats had lower levels of lead in kidney and higher levels in femur than did equivalently dosed adult rats. Concentrations of lead in blood, kidney, and femur were significantly higher in weanling rats exposed to lead daily in drinking water than in weanling animals receiving an equivalent dose of lead once per week. Brain lead levels were significantly higher in adult rats receiving lead in drinking water than in intermittently exposed adult animals. Weanling rats retained significantly higher fractions of ingested lead in brain tissue and in femur than did equivalently dosed adult rats under both schedules of lead administration. Under conditions of intermittent exposure to equivalent doses of lead, adult rats retained a higher percentage of lead in kidney tissue than did weanling animals. Lead retention in kidney tissue of weanling rats was significantly higher when lead was provided daily than when equivalent doses were administered at weekly intervals.