A COMPARATIVE STUDY OF THE METABOLISM OF DE NOVO SYNTHESIZED FATTY ACIDS FROM ACETATE AND GLUCOSE, AND EXOGENOUS FATTY ACIDS, IN SLICES OF RABBIT CEREBRAL CORTEX DURING DEVELOPMENT

— Slices of rabbit cerebral cortex, from the foetal stage to the adult have been used to compare lipid synthesis from fatty acids synthesized de novo from [U‐ 14 C]glucose and [1‐ 14 C]acetate, with lipid synthesis from exogenous albumin‐bound [1‐ 14 C]palmitate. Incorporation into cellular lipid has been determined in terms of DNA, protein, wet wt. of tissue and wet weight of whole brain. On a wet wt. basis, maximum incorporation of glucose carbon into lipid occurred in the foetal brain while lipid synthesis from acetate and palmitate was maximum at 4–14 days after birth. Glucose and acetate were incorporated into a diversity of lipids (with increasing amounts of phosphatidylcholine synthesized during maturation), while palmitate was incorporated into the free fatty acid and triglyceride fractions. A greater proportion of acetate was incorporated into fatty acids of chain‐length longer than C16 compared with the incorporation of palmitate. However, on a molar basis de novo synthesized and exogenous palmitate were elongated, desaturated and incorporated into phospholipids at a similar rate, while exogenous palmitate was incorporated to a greater extent than de nova synthesized fatty acid into the triglyceride fraction. This difference in metabolism may be due to the different size of the non‐esterified fatty acid pool in the two situations. At the period of their most active formation, the very long‐chain fatty acids may be synthesized from a pool of the C18 series of fatty acids (saturated and monoenoic) not in equilibrium with the bulk of C 18 acids in cerebral lipids. This could be a pool of acyl groups derived from ethanolamine phospholipids.