SELECTIVE EFFECT OF CHRONIC LEAD INGESTION ON TYROSINE HYDROXYLASE ACTIVITY IN BRAIN REGIONS OF RATS

Abstract

Alterations of tyrosine hydroxylase activity in various regions of brain from rats postnatally exposed to lead were tested. Three groups of animals were prepared; (1) Rats exposed to lead at a low dose (0.05 % lead acetate, PbAc) ; (2) Rats exposed to lead at a high dose (0.2 % PbAc) ; (3) Age-matched normal control rats. At 2, 4, 6, and 8 weeks of age, weight of brain and body, and concentrations of lead in whole brain of animals in each group were measured. Activities of tyrosine hydlroxylase and Na⁺-K⁺ ATPase were also measured at the same ages in 4 brain regions of each animal. Body weight gain was decreased after 6 weeks of age in rats exposed to lead at a high dose. Concentrations of lead in whole brain were increased from 0.37 to 0.83 (ng/mg wet tissue) in these animals. Exposure of rats to lead generally increased tyrosine hydroxylase activity and decreased Na⁺-K⁺ ATPase activity. However, changes of tyrosine hydroxylase activity were detected without concomitant changes of Na⁺-K⁺ ATPase activity in pons-medulla at 2 weeks of age and telencephalon at 6 weeks of age in rats exposed to lead at a low dose, and in midbrain at 4 and 6 weeks of age in rats exposed to lead at a high dose. These data imply that catecholaminergic nervous system in the brain regions described above could be selectively affected by lead.