Metabolism of arachidonate in rat testis: characterization of 26-30 carbon polyenoic acids.

Fatty acid methyl esters of long-chain polyenoic fatty acids (LCPA) from rat testis injected with [1-14C] arachidonate were analyzed and separated by reversed-phase high performance liquid chromatography (RP-HPLC). Earlier, all previously identified LCPA were prepared in high purity along with 4 previously unidentified fatty acids, which were further characterized by capillary gas chromatography (GC), catalytic hydrogenation and alkaline isomerization. Unidentified fatty acids proved to be 26:4, 26:5, 28:5 and 30:5. All of these LCPA incorporated 14C from arachidonate (20:4) to specific activities that were comparable to that of 20:4 and previously identified metabolites of 20:4 and much greater than specific activities of 18:1n-9 or 22:6n-3. LCPA were analyzed on a capillary GC system capable of resolving known cis-trans and positional isomers of the n-3, n-6, n-7 and n-9 families of unsaturated fatty acids. Log plots of isothermal retention times and normal plots of temperature programmed retention times were linear (r = 0.999) in carbon number when values for known and previously unidentified LCPA of 4 or 5 double bonds, respectively, were coplotted. Thus, the newly identified fatty acids belong to the n-6 family of fatty acids synthesized from arachidonic acid.