Metabolism in vitro of palmitic acid and linoleic acid in the heart and diaphragm of essential fatty acid-deficient rats

Rats kept for 75–90 days on an essential fatty acid-deficient diet, showed a marked fall in linoleic acid content and a rise in the trienoic acid/tetreanoic acid ratio in heart as well as in diaphragm. Electron microscopic study of myocardium showed enlarged mitochondria with marked disorganization of cristae and swelling. Neutral lipid and phospholipid content of heart and diaphragm was not different from that of controls, supplemented with 4% soya-bean oil. Rat hearts were perfused and hemidiaphragms were incubated with a medium containing [1-¹⁴C]palmitic or [1-¹⁴C]linoleic acid. During 20 min of perfusion both fatty acids were oxidized to CO₂ to a similar extent. The fatty acid composition of the medium affected the mode and rate of incorporation of individual fatty acids in heart as well as diaphragm. In the presence of an equipmolar mixture of palmitic and linoleic acid, more linoleic acid was incorporated into phospholipids and more palmitic into neutral lipids, than when each fatty acid was the only substrate. In the essential fatty acid-deficient rats the specific activity of the phospholipids synthesized with [1-¹⁴C linoleic acid in heart as well as in diaphragm was higher than in controls. An increased turnover of certain fatty acids in phospholipids in the essential fatty acid-deficient rats is indicated and the mechanism discussed.