Metabolism of very long chain polyunsaturated fatty acids in isolated rat germ cells

Which cell type is responsible for the high levels of very long chain polyu nsaturated fatty acids in testis and whether this fatty acid pattern is a r esult of a local synthesis are not presently known. In this study, fatty ac id conversion from 20:4n-6 to 22:5n-6 and from 20:5n-3 to 22:6n-3 was inves tigated in isolated rat germ cells incubated with [1-C-14]-labeled fatty ac ids. The germ cells elongated the fatty acids from 20- to 22-carbon atoms a nd from 22- to 24-carbon atoms but had a low Delta6 desaturation activity. Thus, little [C-14]22:5n-6 and [C-14]22:6n-3 were synthesized. When Sertoli cells were incubated with [1-C-14]20:5n-3 for 24 h, an active fatty acid e longation and desaturation were observed. In vivo germ cells normally have a higher content of 22:5n-6 or 22:6n-3 than Sertoli cells. An eventual tran sport of essential fatty acids from Sertoli cells to germ cells was thus st udied. Different co-culture systems were used in which germ cells were on o ne side of a filter and Sertoli cells on the opposite side. When isolated p achytene spermatocytes or round spermatids were added to the opposite side of a semipermeable filter, approximately 1 nmol [C-14]- 22:6n-3 crossed the filter. Little of this was esterified in the germ cells. Similarly, in usi ng [1-C-14]20:4n-6 in identical experiments, very little [C-14]22:5n-6 was esterified in germ cells on the opposite side of the filter. Although the v ery active synthesis of 22:5n-6 and 22:6n-3 observed in Sertoli cells sugge sts a transport of these compounds to germ cells, this was not experimental ly determined.