DIETARY (N-3) AND (N-6) POLYUNSATURATED FATTY-ACIDS RAPIDLY MODIFY FATTY-ACID COMPOSITION AND INSULIN EFFECTS IN RAT ADIPOCYTES

The influence of dietary (n-3) compared with (n-6) polyunsatured fatty acids (PUFA) on the lipid composition and metabolism of adipocytes wa s evaluated in rats over a period of 1 week. Isocaloric diets comprise d 16.3 9/100 g protein, 53.8 g/100 g carbohydrate and 21.4 g/100 g lip ids, the latter containing either (n-3) PUFA (32.4 mol/100 mol) or (n- 6) PUFA (37.8 mol/100 mol) but having identical contents of saturated, monounsaturated and total unsaturated fatty acids and identical polyu nsaturated to saturated fatty acid ratios and double bond indexes. Des pite comparable food intake, significantly smaller body weight increme nts and adipocyte size were observed in rats of the (n-3) diet group a fter feeding for 1 wk. Rats fed the (n-3) diet also had significantly lower concentrations of serum triglycerides, cholesterol and insulin c ompared with those fed the (n-6) diet, although levels of serum glucos e and free fatty acids did not differ in the two dietary groups. In th e (n-6) diet group, the (n-6) and (n-3) PUFA contents of plasma trigly cerides, free fatty acids and phospholipids were 30-60% higher and 60- 80% lower, respectively, than in the (n-3) diet group, whereas adipocy te plasma membrane phospholipids showed a significantly higher unsatur ated to saturated fatty acid ratio and greater fluidity, Glycerol rele ase in response to noradrenaline was significantly higher in the adipo cytes of rats fed the (n-3) diet, whereas the antilipolytic effect of insulin generally did not differ in the two groups. Finally, insulin s timulated the transport of glucose and its incorporation into fatty ac ids to a lesser extent in adipocytes of (n-3) diet fed rats compared w ith (n-6) diet fed rats. This reduction in the metabolic effects of in sulin in rats fed a (n-3) diet for 1 wk could be related to smaller nu mbers and a lower binding capacity of the insulin receptors on adipocy tes and/or to a lesser degree of phosphorylation of the 95 kDa beta su bunit of the receptor. In conclusion, dietary intake for 1 wk of (n-3) rather than (n-6) PUFA is sufficient to induce significant difference s in the lipid composition and metabolic responses to insulin of rat a dipocytes.