BIOSYNTHESIS AND COMPOSITION OF BRAIN GALACTOLIPIDS IN NORMAL AND HYPOTHYROID RATS

Abstract— Newborn rats were rendered hypothyroid by methimazole treatment. Incorporation of [1-¹⁴C]galactose both in vivo and in vitro into brain cerebrosides of hypothyroid rats was significantly lower than in normals. Biosynthesis of sulphatides was affected by hypothyroidism to a smaller extent than cerebrosides. Assay of cerebroside biosynthesis from [1-¹⁴C]galactose or UDP-[1-¹⁴C]galactose by brain preparations revealed that incorporation of the sugar in both cases is affected to the same extent by methimazole treatment, suggesting that the phenomenon is not due to impairment of the nucleotide biosynthesis. A radioactive galactolipid tentatively characterized as glycerogalactolipid was synthesized in vitro and its biosynthesis was reduced to a large extent in the brain preparations from hypothyroid rats. The fatty acid composition of cerebrosides and sulphatides from the brains of hypothyroid rats was found to be different from that of normal rats. The percentage of normal C₂₄ fatty acids was significantly decreased in the methimazole-treated rats. Brain sphingomyelin fatty acids did not differ between normal and hypothyroid rats.