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 membran es of adipose tissue from ruminants are changed when the diet is suppl emented with unsaturated fatty acids and to determine the effect of th e fat supplement on adipocyte metabolism. Ten sheep were randomly assi gned to two isonitrogenous diets containing either no added fat (contr ol) or 5 g soybean oil/100 g diet. Perirenal fat was removed at slaugh ter, adipocytes isolated by collagenase digestion, and plasma membrane s prepared by centrifugation on a Percoll gradient. Feeding soybean oi l to the sheep increased (P < 0.05) linoleic acid [18:2(n-6)] concentr ation in subcutaneous fat and isolated adipocytes, suggesting partial escape of dietary unsaturated fatty acids from ruminal biohydrogenatio n. Soybean oil consumption also decreased (P < 0.05) concentrations of myristic acid, arachidonic acid [20:4(n-6)] and anteiso 17:0 in plasm a 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 she ep fed the soybean oil-containing diet than in those fed the control d iet. In ruminants, fatty acids of ruminal origin, namely trans interme diates of biohydrogenation or branched-chain fatty acids of microbial lipid, may account for as much change in the composition of plasma mem branes and in cellular metabolism as do the small quantities of unsatu rated fatty acids in the diet that escape biohydrogenation.