The metabolism of linoleic and arachidonic acids in rat testis

Linoleic and arachidonic acids, labeled with¹⁴C 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 substrates¹⁴C activity was readily incorporated into longer chain, more highly unsaturated fatty acids. After the injection of 1-¹⁴C-linoleic acid the major portion of the¹⁴C 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 1-¹⁴C-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 1-¹⁴C-arachidonate significant¹⁴C 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 ω⁶ 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 the¹⁴C activity to be present in phosphatides and triglycerides after injection of either of these¹⁴C 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. Presented in part at the Meeting of the American Institute of Nutrition, Atlantic City, April 1968 and at the AOCS Meeting in New York, April 1969. These data were taken from a thesis submitted by R. B. Bridges in partial fulfillment of the requirements for the Ph.D. degree, Vanderbilt University.