Biosynthesis of polyunsaturated fatty acids of (n-6) and (n-3) series in isolated adrenocortical cells of rats. Effect of ACTH.

Both the capacity of isolated adrenocortical cells to incorporate and transform [1-14C]linoleic and [1-14C]alpha-linolenic acids and the effect of ACTH on the biosynthesis of polyunsaturated fatty acids from [1-14C]alpha-linolenic acid were investigated. The cells were able to incorporate both labeled precursor acids and convert them into higher homologs. This transformation increases along the incubation time tested. When linoleic acid was the precursor, the biosynthesis of higher homologs was carried out following the desaturating-elongating route. Both pathways, the desaturating-elongating and the elongating, were detected when the substrate was alpha-linolenic acid. The results proved the existence of delta 6, delta 5 and delta 4-desaturases in this type of cells. Isolated adrenocortical cells obtained from rats treated with ACTH showed an increase in the amount of [1-14C]alpha-18:3 that remained in the cells without metabolization and, consequently, a decrease in the last product formed (20:5 n-3) was evident compared to the controls. Simultaneously, the desaturation-elongation products decreased significantly. Similar results were obtained when cells isolated from untreated rats were incubated for 3 h in the presence of ACTH. In this case, the values obtained returned to normal levels 6 h after incubation. These results were mimicked by dibutyryl-cyclic AMP. It can be concluded that the effect of ACTH on the biosynthesis of polyunsaturated fatty acids from alpha-linolenic acid was mediated through an enhancement of the intracellular levels of cAMP.