DIETARY SOYBEAN OIL CHANGES LIPOLYTIC RATE AND COMPOSITION OF FATTY-ACIDS IN PLASMA-MEMBRANES OF OVINE ADIPOCYTES

A study was conducted to determine which fatty acids in plasma membranes of adipose tissue from ruminants are changed when the diet is supplemented with unsaturated fatty acids and to determine the effect of the fat supplement on adipocyte metabolism. Ten sheep were randomly assigned to two isonitrogenous diets containing either no added fat (control) or 5 g soybean oil/100 g diet. Perirenal fat was removed at slaughter, adipocytes isolated by collagenase digestion, and plasma membranes prepared by centrifugation on a Percoll gradient. Feeding soybean oil to the sheep increased (P < 0.05) linoleic acid [18:2(n-6)] concentration in subcutaneous fat and isolated adipocytes, suggesting partial escape of dietary unsaturated fatty acids from ruminal biohydrogenation. Soybean oil consumption also decreased (P < 0.05) concentrations of myristic acid, arachidonic acid [20:4(n-6)] and anteiso 17:0 in plasma membranes, but increased (P < 0.05) trans 18:1. Lipogenesis was not affected by diet, but lipolysis tended to be greater (P = 0.07) in sheep fed the soybean oil-containing diet than in those fed the control diet. In ruminants, fatty acids of ruminal origin, namely trans intermediates of biohydrogenation or branched-chain fatty acids of microbial lipid, may account for as much change in the composition of plasma membranes and in cellular metabolism as do the small quantities of unsaturated fatty acids in the diet that escape biohydrogenation.