DISTRIBUTION AND METABOLISM OF ARACHIDONIC AND DOCOSAHEXAENOIC ACIDS IN RAT PINEAL CELLS - EFFECT OF NOREPINEPHRINE

The time-course incorporation of 10 mu M [C-14]arachidonic (AA) and do cosahexaenoic (DHA) acids into glycerolipids was studied in rat pineal cells. The incorporation of both labeled fatty acids into total lipid s was approximately equal, but their distribution profiles among the v arious cell lipids showed marked differences. The esterification of [C -14]DHA in the neutral lipids, triacylglycerols (TAG) and cholesterol esters (CE), was 2-fold higher than that of [C-14]AA whereas the oppos ite could be observed in total phospholipids (PL). The order of incorp oration into PL was phosphatidylcholine (PC) > phosphatidylinositol (P I) = phosphatidylethanolamine (PE) for [C-14]AA and PC = PE for [C-14] DHA, the incorporation of both fatty acids being not detected in phosp hatidylserine (PS) and that of DHA not in PI. When using 0.5 mu M [H-3 ] fatty acids, the respective distribution patterns resembled that of fatty acids at 10 mu M, except for a lower proportion in TAG. The stim ulation of H-3-labeled cells by 100 mu M norepinephrine induced a 170% increase of basal release of [H-3]AA into the medium, while [H-3]DHA was virtually not released. However, the analysis of cell labeling rev ealed that both [H-3] fatty acid levels were decreased in PL and incre ased in TAG. These findings suggest different involvement for AA and D HA in the pineal function. The preferential incorporation of DHA in TA G suggests that TAG might play an important role in the pineal enrichm ent with DHA. The absence of DHA release after NE stimulation, which h owever cannot be ascertained, may raise the question of the role of DH A in NE transduction.