The dosage effect of oleic acid in food. Is this acid conditionally essential?

In order to determine exactly the effect of the presence and concentration of dietary oleic acid on the fatty acid composition of different organs, tr iglycerides were synthesized using chemical and enzymological methods. Comm ercial vegetable oils cannot be used, since they always contain oleic acid. The triglycerides were formed from either oleic acid, alpha-linolenic acid , or linoleic acid. The dose-effect was determined using an experimental pr otocol with 7 groups of rats who received a diet in which the oleic acid le vel varied from 0 to 6,000mg per 100g diet, but the other ingredients were identical (in particular the essential fatty acids, linoleic and alpha-lino lenic acid). Rats were fed the diets from two weeks before mating and their pups were sacrificed aged either 21 or 60 days. When the level of oleic ac id in the diet was increased the main modifications observed in 21-day-old deficient animals were as follows. - For 18:1(n-9), in liver, muscle, heart, kidney, and testis, plateau was r eached at about 4g oleic acid per 100g diet. Below this level, the higher t he dose the greater the response. In brain, myelin, and nerve endings (but not sciatic nerve) the oleic acid level remained optimal and constant whate ver the level of oleic acid in the diet. - For 16:1(n-7), the concentration decreased in liver and muscle when dieta ry oleic acid was increased from 0 to 3g/100g. At higher oleic acid levels the concentration plateaued. A similar profile was observed in heart, kidne y, and testis, but was less marked. Brain structures were not changed;in sc iatic nerve the level of 16:1(n-7) decreased with increasing dietary oleic acid and plateaued at 3g oleic acid per 100g of diet. - The concentration of 18:1(n-7) decreased in kidney, muscle, and testis at up to 3-4g/100g dietary oleic acid and then stabilized. Levels in the nerv ous system samples (including sciatic nerve) did not change when dietary ol eic acid was increased. - Some minor modifications were noted for the other fatty acids: decrease i n palmitic acid, in particular in liver and muscle, but no changes in stear ic acid. The sum of (n-6) fatty acids was constant except in heart, kidney, and sciatic nerve (but in these, 22:5(n-6) remained unchanged). There were no changes in fatty acids of the (n-3) series. In animals sacrificed at 14 days, when dietary oleic acid increased, the le vels of 18:1(n-9) in stomach contents also increased. The increase was regu lar and did not reach a plateau. In parallel with this increase, 16:1(n-7) decreased and plateaued at 3g oleic acid per 100g diet, whereas 18:1(n-7) r emained stable, 16:0 decreased markedly, and 18:0 was unchanged. In 60-day- old animals, results were generally similar to those in 21-day-old animals, but with some differences, in particular a slight decrease in oleic acid c oncentration in the liver and kidney at the highest dietary oleic acid leve l.