Retention of lead in growing rats with varying dietary lead supplements.

144 female rats with a beginning weight of 35 +/- 3 g were fed for 23 days a half-synthetic diet with a lead content that varied over 18 concentrations (0.025 to 600 mg/kg). Absolute lead retention was calculated as total body concentration of lead in animals at the end of the experiment minus the average lead concentration in carcasses of reference animals that had been sacrificed at the beginning of the experiment. The relative retention was calculated with regard to lead intake. Absolute lead retention increased in association with a lead supply of 0.225 mg per kg diet, but decreased thereafter. Not until a lead concentration of 5 mg per kg diet was reached did lead retention rise again. Relative lead retention decreased exponentially with an increasing lead supply and finally approached a constant value. Live mass development and feed intake were not affected by an increase in lead supply. Altogether, these results demonstrate that lead metabolism is homeostatically regulated.