The pathway from arachidonic to docosapentaenoic acid (20:4n-6 to 22:5n-6) and from eicosapentaenoic to docosahexaenoic acid (20:5n-3 to 22:6n-3) studied in testicular cells from immature rats.
The concentration-dependent metabolism of 1-(14)C-labelled precursors of 22:5n-6 and 22:6n-3 was compared in rat testis cells. The amounts of [(14)C]22- and 24-carbon metabolites were measured by HPLC. The conversion of [1-(14)C]20:5n-3 to [3-(14)C]22:6n-3 was more efficient than that of [1-(14)C]20:4n-6 to [3-(14)C]22:5n-6. At low substrate concentration (4 microM) it was 3.4 times more efficient, reduced to 2.3 times at high substrate concentration (40 microM). The conversion of [1-(14)C]22:5n-3 to [1-(14)C]22:6n-3 was 1.7 times more efficient than that of [1-(14)C]22:4n-6 to [1-(14)C]22:5n-6 using a low, but almost equally efficient using a high substrate concentration. When unlabelled 20:5n-3 was added to a cell suspension incubated with [1-(14)C]20:4n-6 or unlabelled 22:5n-3 to a cell suspension incubated with [1-(14)C]22:4n-6, the unlabelled n-3 fatty acids strongly inhibited the conversion of [1-(14)C]20:4n-6 or [1-(14)C]22:4n-6 to [(14)C]22:5n-6. In the reciprocal experiment, unlabelled 20:4n-6 and 22:4n-6 only weakly inhibited the conversion of [1-(14)C]20:5n-3 and [1-(14)C]22:5n-3 to [(14)C]22:6n-3. The results indicate that if both n-6 and n-3 fatty acids are present, the n-3 fatty acids are preferred over the n-6 fatty acids in the elongation from 20- to 22- and from 22- to 24-carbon atom fatty acids. In vivo the demand for 22-carbon fatty acids for spermatogenesis in the rat may exceed the supply of n-3 precursors and thus facilitate the formation of 22:5n-6 from the more abundant n-6 precursors.
Retterstøl
K
K
Institute of Clinical Biochemistry, National Hospital, University of Oslo, N-0027, Oslo, Norway. kjetil.retterstol@rh.uio.no
Haugen
T B
TB
Christophersen
B O
BO
D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism*; D002250:Carbon Radioisotopes; D002478:Cells, Cultured; D004281:Docosahexaenoic Acids / Q000378:metabolism*; D015118:Eicosapentaenoic Acid / Q000378:metabolism*; D004951:Esterification; D044943:Fatty Acid Desaturases / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000378:metabolism*; D008297:Male; D010084:Oxidation-Reduction; D020675:Peroxisomes / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012708:Sertoli Cells / Q000378:metabolism; D013091:Spermatogenesis; D013737:Testis / Q000254:growth & development / Q000378:metabolism*
D002250:Carbon Radioisotopes; D005231:Fatty Acids, Unsaturated; D004281:Docosahexaenoic Acids; D016718:Arachidonic Acid; D015118:Eicosapentaenoic Acid; D044943:Fatty Acid Desaturases; C026219:docosapentaenoic acid