Effect of dietary fatty acids on delta 5 desaturase activity and biosynthesis of arachidonic acid in rat liver microsomes.

The effect of different fatty acids supplemented to a fat-free diet on the activity of delta 5 desaturase was studied. Fat-free diet produces a reduction in the conversion of eicosa-8,11,14-trienoic acid to arachidonic acid. The addition of the cis-omega 6 acids, linoleic, gamma-linolenic or arachidonic to the diet produces an increase of eicosatrienoic acid desaturation, shifting delta 5 desaturase activity towards the controls on a balanced diet. This reactivation is apparently produced by induction of enzyme biosynthesis since linoleate effect was suppressed by simultaneous cycloheximide injection. On the contrary, no changes in delta 5 desaturation activity were found when the diet was supplemented with palmitic or 9-trans,12-trans-linoleic acid. The changes on the activity of delta 5 desaturase were compared with the fatty acid composition of plasma and liver microsomes.