Tissue-Specific Regulation of Malic Enzyme by Thyroid Hormone in the Neonatal Rat

Abstract Two recent studies have claimed that thyroid hormone administration accelerates malic enzyme gene expression in the neonatal brain (1,2) in contrast to the well-documented lack of effect of triiodothyronine on malic enzyme gene expression in the adult brain (3,4). Since these observations conflict with earlier observations in our laboratory (3), we reinvestigated the effect of thyroid hormone status on the ontogeny of malic enzyme gene expression in the neonatal rat. Neither hypothyroidism nor hyperthyroidism influenced the ontogenesis of malic enzyme gene expression or malic enzyme activity in neonatal brain whereas the patterns of gene expression and enzyme activity in liver were markedly affected. Our results suggest that tissue-specific factors in brain block thyroid hormone-induced gene expression by thyroid hormone.