Influence of thyroid hormone on norepinephrine metabolism in rat brain during maturation.

The effect of thyroid hormone on norepinephrine (NE) metabolism was investigated in various regions of the developing rat brain. Neonatal hypothyroidism, induced by daily propylthiouracil injection starting at birth, caused an increase in NE levels in the brain stem and hypothalamus. The turnover of brain NE, as indicated by its rate of depletion following alpha-methyl-p-tyrosine administration, was decreased in the hypothalamus of 30-day-old hypothyroid rats but was unchanged in the brain stem and basal ganglia. The activities of monoamine oxidase (MAO) and catechol-o-methyl transferase (COMT) were decreased in certain brain regions of hypothyroid rats. The data suggest that thyroid hormone may influence the ontogenic patterns of NE metabolism in the brain.