DEVELOPMENT OF LIPOGENESIS IN RAT BRAIN CORTEX: THE DIFFERENTIAL INCORPORATION OF GLUCOSE AND ACETATE INTO BRAIN LIPIDS IN VITRO

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Abstract
—The oxidation to CO2 and the incorporation of [U‐14C]glucose and [U‐14C]acetate into lipids by cortex slices from rat brain during the postnatal period were investigated. The oxidation of [U‐14C]glucose was low in 2‐day‐old rat brain, and increased by about two‐fold during the 2nd and 3rd postnatal weeks. The oxidation of [U‐14C]acetate was increased markedly in the second postnatal week, but decreased to rates observed in 2‐day‐old rat brain at the time of weaning. Both labeled substrates were readily incorporated into non‐saponifiable lipids and fatty acids by brain slices from 2‐day‐old rat. Their rates of incorporation and the days on which maximum rates occurred were different, however, maximum incorporation of [U‐14C]glucose and [U‐14]acetate into lipid fractions being observed on about the 7th and 12th postanatal days, respectively. The metabolic compartmentation in the utilization of these substrates for lipogenesis is suggested. The activities of glucose‐6‐phosphate dehydrogenase, cytosolic NADP‐malate dehydrogenase, cytosolic NADP‐isocitrate dehydrogenase, ATP‐citrate lyase and acetyl CoA carboxylase were measured in rat brain during the postnatal period. All enzymes followed somewhat different courses of development; the activity of acetyl CoA carboxylase was, however, the lowest among other key enzymes in the biosynthetic pathway, and its developmental pattern paralleled closely the fatty acid synthesis from [U‐14C]glucose. It is suggested that acetyl CoA carboxylase is a rate‐limiting step in the synthesis de novo of fatty acids in developing rat brain.