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Resistance of Lung Fatty Acid Synthesis to Inhibition by Dietary Fat in the Meal-Fed Rat^1,2,

Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN 55108

One-half of the palmitate utilized by the lung for production of the surfactant phospholipid, dipalmitoyl phosphatidylcholine, originates from de novo palmitate synthesis in the lung. In this report the lung was examined for the influence of dietary fat on the lung de novo fatty acid synthesis pathway. Lung lipogenesis was reduced by fasting and accelerated by carbohydrate refeeding or insulin injection. However, in general lung fatty acid synthesis was unaffected by dietary fat. Supplementing one meal (high glucose diet) with as much as 36% additional fat kilocalories did not suppress lung fatty acid synthesis. An inhibition of fatty acid synthesis resulted from a fat supplement of +60 and +120% of meal kilocalories, but this inhibition was likely due to an attenuated rate of glucose absorption. Ingestion of a high carbohydrate diet supplemented with 10, 17, or 30% added kilocalories as safflower oil or palmitate had no effect on lipogenesis after 10 days. On the other hand, liver fatty acid synthesis and acetyl-CoA carboxylase were selectively suppressed by safflower oil, whereas dietary palmitate was ineffective as an inhibitor of lipogenesis. These data clearly demonstrate that the well-characterized preferential suppression of liver lipogenesis by dietary polyunsaturated fats does not extend to lung tissue, and, more importantly, the inhibition of liver lipogenesis is not secondary to an essential fatty acid deficiency. The marked resistance of lung fatty acid synthesis to inhibition by dietary fat might be a biological protective mechanism to ensure adequate palmitate for dipalmitoyl phosphatidylcholine synthesis.

KEY WORDS: • lung • lipogenesis • dietary fat

¹ This investigation was supported by Grant HL-27875 from the National Institutes of Health, U.S. Public Health Service.

² University of Minnesota Agricultural Experiment Station Journal article No. 13,227.

Manuscript received 22 August 1983.