A COMPARATIVE-STUDY OF THE METABOLISM OF N-9, N-6 AND N-3 FATTY-ACIDSIN TESTICULAR CELLS FROM IMMATURE RAT

Dietary 18 and 20-carbon fatty acids of the n-6 and the n-3 families a re metabolized to 22:5,n-6 and 22:6,n-3 by a sequence of specific desa turases and chain elongation vie 24-carbon intermediates. This pathway is regulated so that more 22:6,n-3 than 22:5,n-6 is found in the tiss ues. Rat testis is an exception since 22:5,n-6 is present in large pro portions in this organ. Therefore rat testis appears to be interesting for studies of the detailed synthesis of 22:5,n-6 compared with that of 22:6,n-3. By using fresh preparations of rat testicular cells from 19-day-old rats enriched in Sertoli cells, we compared the metabolism of 1-C-14-labelled n-3, n-6 and n-9 fatty acids. The testicular cells actively synthesized 22:6,n-3 and 22:5,12-6, but not 22:4,n-9 from the 18 and 20-carbon precursors. Of 200 mol C-14-labelled C-18 and C-20 f atty acids added initially, approximately 20-40 mol were found as 24-c arbon intermediates after 24 h of incubation. This indicates that the balanced capacity of elongation, desaturation and chain shortening fav ours the accumulation of 24-carbon intermediates in these cells. One e xception was [1-C-14]20:3,n-9 which was efficiently elongated to 22:3, n-9 but not to C,, fatty acids. Our data suggests that the poor elonga tion of n-9 fatty acids from C-22- to C-24 may be an important hindran ce in the synthesis of 22:4,n-9. The efficient synthesis of 22:5,n-6 m ay also partly explain why this is the major 22-carbon fatty acid in r at testis. (C) 1998 Elsevier Science B.V. All rights reserved.