The pathogenesis of lead encephalopathy

Summary The toxic effects of inorganic lead feedings on the immature brain were studied in the rat pup. Beginning when litters were two weeks old, PbCO₃ was fed to nursing mothers and then to pups directly after weaning. Results in lead-fed pups were compared to age-matched controls and to lead-fed young adult males (60 days old). Anaemia and growth failure developed in both pups and adults. In the second week, more than half the pups developed an encephalopathy, with haemorrhage and oedema predominately in the cerebellum and lead-containing densities in the cerebellar molecular layer. The latter were confirmed by X-ray microanalysis. No lead-fed adults showed signs of an encephalopathy.Cerebellar mitochondria from lead-fed pups, studied polarographically, showed a very early loss of respiratory control and a subsequent inhibition of phosphorylation-coupled respiration with NAD-linked substrates but not with succinate. Compared to the pup cerebellum, these changes were much less marked in immature cerebral mitochondria and were not found in adult cerebral or cerebellar mitochondria.Cerebral and cerebellar homogenates from immature and mature lead-fed animals showed large increases in lead content measured by atomic absorption spectrophotometry. Immature cerebellar mitochondrial lead contents were increased to the same extent as in the homogenates. Mitochondria from immature cerebrum and from both regions in the mature brain showed less immediate and smaller increases in lead content.In conclusion, altered mitochondrial respiration occurs early in regional and age-dependent association with lead encephalopathy in the rat pup. The development of lead encephalopathy also is associated with increased mitochondrial lead concentrations.