The metabolism of linoleic and arachidonic acids in rat testis

Abstract

Abstract Linoleic and arachidonic acids, labeled with 14 C and injected intratesticularly, were used to study with time the interconversion of polyunsaturated fatty acids in rat testis and their incorporation into the major lipid classes. With both substrates 14 C activity was readily incorporated into longer chain, more highly unsaturated fatty acids. After the injection of 1‐ 14 C‐linoleic acid the major portion of the 14 C was found in palmitic, linoleic, 8,11,14‐eicosatrienoic, 5,8,11,14‐eicosatetraenoic, 7,10,13,16‐docosatetraenoic and 4,7,10,13,16‐docosapentaenoic acids. Hydrogenation of the total fatty acids isolated from rat testes after intratesticular injection of 1‐ 14 C‐linoleate revealed that the polyenoic acids hydrogenating to lignoceric acid (previously characterized as 9,12,15,18‐tetracosatetraenoate and 6,9,12,15,18‐tetracosapentaenoate) had a relatively high specific activity. After the injection of 1‐ 14 C‐arachidonate significant 14 C activity was found in palmitate, 7,10,13,16‐docosatetraenoate, 4,7,10,13,16‐docosapentaenoate, 9,12,15,18‐tetracosatetraenoate and 6,9,12,15,18‐tetracosapentaenoate. The biosynthesis of the ω 6 polyunsaturated fatty acids in rat testis is discussed in relation to these data. Investigation of the distribution of label in the complex lipid fractions demonstrated the majority of the 14 C activity to be present in phosphatides and triglycerides after injection of either of these 14 C substrates with only small quantities being present as nonesterified acids. At the time periods studied the polyenoic acids of triglycerides had a higher specific activity than the corresponding acids of phosphatides with the exception of linoleate.