Lead exposure during advanced age: alterations in kinetics and biochemical effects

The transition from maturity to advanced age is accompanied by a multitude of degenerative processes, several of which could be hypothesized to enhance the vulnerability of animals to the toxic effects of lead (Pb). That premise was examined in this study which evaluated kinetic and biochemical responses of young (21 day old), adult (8 months), and old rats (16 months) exposed to 0, 2, or 10 mg Pb acetate/kg/day for a period of 9.5 months. Results indicated an enhanced vulnerability to Pb in older rats which may be due both to increased Pb exposure as a result of elevated soft tissue target organ levels and to a greater sensitivity to the biochemical effects of Pb. Differences in the tissue distribution of Pb with age included lower bone levels, but increased concentrations in brain, liver, and kidney. These effects did not appear to reflect enhanced Pb uptake from the GI tract with age since differences in blood Pb levels over the course of exposure were not remarkable. Instead, they may be due to changes in bone physiology with age, combined with altered patterns of urinary Pb excretion over time. Biochemical effects of Pb, as manifested by elevation of erythrocyte zinc protoporphyrin and urinary delta-aminolevulinic acid excretion occurred earlier in the course of exposure (3 months) in older rats than in young rats (9.5 months of exposure). Grossly enlarged spleens were noted only in old rats exposed to Pb. These findings raise questions and concerns about the contributions of a lifetime of lead exposure to the deteriorating health conditions associated with old age.