Influence of thyroid hormone deficiency on the citrate synthase activity in rat brain regions during early postnatal development.

The developmental pattern of citrate synthase activity has been studied in the liver and several brain areas of hypothyroid rats during the 4 first weeks of life. While citrate synthase activity in the liver showed a rise during the 2 first weeks of life, different patterns of enzyme activity were found in the brain regions of euthyroid animals. Citrate synthase activity increased in the cerebellum, decreased in the cerebral cortex and did not change significantly in the brain stem during the period studied. In the liver and brain areas, too, a decrease in citrate synthase activity was observed during hypothyroidism. From the 2nd week of birth, the citrate synthase activity in the brain but not in the liver was found to have recovered. The newly elevated citrate synthase activity coincided with a slight increase in thyroid hormone serum levels.