The coupling between the degenerative processes of aging and toxicant exposure has received little experimental attention. This experiment compared the tissue lead (Pb) distribution of adult and old rats exposed to 50 ppm Pb acetate in drinking water for 11 months and fed a semipurified diet. Blood Pb and zinc protoporphyrin (ZPP) determinations were carried out after 6 months of exposure; after 11 months of exposure blood lead and tissue Pb levels were determined. Several age-related differences between adult and old rats were noted: old rats exposed to Pb exhibited lower brain weights than old controls, a difference not noted between adult-control and adult-Pb rats. Pb-induced elevations of ZPP were confined to old-Pb rats while adult-Pb rats showed no increase relative to adult-controls. Blood lead values of adult-Pb and old-Pb rats showed differential trends over the course of exposure: adult values declined, while those of old rats tended to increase further. Brain lead concentrations, and to a marginally significant extent, liver Pb levels, rose higher in old-Pb rats than in adult-Pb rats, while bone Pb levels were significantly less than those of adult-Pb rats. The current findings confirm the assertion that tissue Pb distribution patterns may be markedly altered when Pb exposure occurs during the later stages of the life cycle.
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