IN-VITRO METABOLISM OF C-14 POLYUNSATURATED FATTY-ACIDS IN MIDGUT GLAND AND OVARY CELLS FROM PENAEUS-KERATHURUS FORSKAL AT THE BEGINNING OFSEXUAL-MATURATION

The incorporation and metabolism via the desaturase/elongase pathway o f [1-C-14]18:2(n-6) linoleic acid (LA), [1-C-14]18:3(n-3) linolenic ac id (LNA), [1-C-14]20:4(n-6) arachidonic acid (AA) and [1-C-14]20: 5(n- 3) eicosapentaenoic acid (EPA) were studied in midgut gland and ovary cell suspensions from wild-caught adult females of Penaeus kerathurus Forskal at the beginning of sexual maturation. The incorporation and r ecovery of radioactivity in total lipids of midgut gland cells was gre ater for [1-C-14]LA and [1-C-14]LNA than for [1-C-14]AA or [1-C-14]EPA , indicating a preferential retention of C-18-polyunsaturated fatty ac ids (PUFAs) in this organ. The recovery of radioactivity from all PUFA decreased Juring the time course. The incorporation of [1-C-14]PUFAs into total polar lipids in mid,out gland cells increased during the ti me course (from 33.4% to 65.2%) with a concomitant decrease into total neutral lipids. These changes were due to significantly increased inc orporation into phosphatidylcholine (PC), phosphatidylethanolamine (PE ) and phosphatidylinositol (PI), with significantly decreased incorpor ation into triacylglycerol (TAG). [1-C-14]AA and [1-C-14]EPA were pref erentially incorporated into PI, and [1-C-14]EPA was more important in phospholipid synthesis in midgut gland cells than [1-C-14]-labeled LA , LNA or AA. The incorporation and recovery of radioactivity in local lipids from ovary cells was significantly lower than in midgut gland c ells bur significantly increased during the time course with all the [ 1-C-14]PUFAs. The distribution of radioactivity from [1-C-14]AA and [1 -C-14]EPA in ovary cells showed preferential retention into polar lipi d classes compared with [1-C-14]LA or [1-C-14]LNA, and the general pat tern was of net synthesis of PC at the expense of PE, free fatty acid and TAG. The results indicated that midgut gland and ovary cells have only a limited ability to convert C-18-PUFA to C-20- and C-22-highly u nsaturated fatty acid. The recovery of radioactivity in 22:6(n-3) was similar to 10-fold greater with [1-C-14]EPA than with [1-(1)4(C)]LNA a s precursor. Substantial amounts of radioactivity were recovery in 24: 5(n-6), 24:5(n-3) and 24:6(n-3), particularly in cells incubated with [1-C-14]EPA, indicating that the conversion of EPA to DHA in both orga ns may occur by a pathway using Delta(6)-desaturase activity rather th an by a Delta(4)-desaturation.