ELSEVIER Biochimica et Biophysica Acta 1254 (1995) 147-154 BB Biochi~ic~a et Biophysica Acta Distribution and metabolism of arachidonic and docosahexaenoic acids in rat pineal cells. Effect of norepinephrine Isabelle Delton, Abdallah Gharib *, Patrick Moli~re, Michel Lagarde, Nicole Sarda INSERM U352, B.406, 20 Av. A. Einstein, Chimie Biologique INSA-L YON, 69621 Villeurbanne, France Received 18 March 1994; revised 26 May 1994 Abstract The time-course incorporation of 10 /xM [14C]arachidonic (AA) and docosahexaenoic (DHA) acids into glycerolipids was studied in rat pineal cells. The incorporation of both labeled fatty acids into total lipids was approximately equal, but their distribution profiles among the various cell lipids showed marked differences. The esterification of [laC]DHA in the neutral lipids, triacylglycerols (TAG) and cholesterol esters (CE), was 2-fold higher than that of [14C]AA whereas the opposite could be observed in total phospholipids (PL). The order of incorporation into PL was phosphatidylcholine (PC) > phosphatidylinositol (PI) = phosphatidylethanolamine (PE) for [IaC]AA and PC = PE for [laC]DHA, the incorporation of both fatty acids being not detected in phosphatidylserine (PS) and that of DHA not in PI. When using 0.5 /xM [3H] fatty acids, the respective distribution patterns resembled that of fatty acids at 10 /xM, except for a lower proportion in TAG. The stimulation of 3H-labeled cells by 100 /xM norepinephrine induced a 170% increase of basal release of [3H]AA into the medium, while [3H]DHA was virtually not released. However, the analysis of cell labeling revealed that both [3HI fatty acid levels were decreased in PL and increased in TAG. These findings suggest different involvement for AA and DHA in the pineal function. The preferential incorporation of DHA in TAG suggests that TAG might play an important role in the pineal enrichment with DHA. The absence of DHA release after NE stimulation, which however cannot be ascertained, may raise the question of the role of DHA in NE transduction. Keywords: Arachidonic acid; Docosahexaenoic acid; Norepinephrine stimulation; (Rat pineal gland) I. Introduction Together with arachidonic acid (AA), docosahexaenoic acid (DHA) is a major polyunsaturated fatty acid (PUFA) of the n - 3 family that is specifically found in the pineal gland [1] and some particular tissues such as retina [2] and neural tissues [3]. Both fatty acids represent about 25% of total lipids recovered from the rat pineal gland with a little predominance of AA [1]. Several studies have provided evidence for the role of AA in the pineal function, especially when regulated by norepinephrine (NE), which is known to involve an all fl Abbreviations: AA, arachidonic acid; CE, cholesterol ester; DAG, diacylglycerol; DHA, docosahexaenoic acid; NE, norepinephrine; PC, phosphatidylcholine; PE, phosphatidylethanolamine; PI, phosphatidyl- inositol; PL, phospholipid; PS, phosphatidylserine; TAG, triacylglycerol. * Corresponding author. Fax: +33 72 43 85 24. 0005-2760/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0005-2760(94)00177-4 adrenergic synergy to increase cyclic AMP and cyclic GMP [4], and consequently the pineal hormone melatonin [5]. These include the findings that stimulation of a t- adrenergic receptors with specific al-agonists or treatment with al-mimetic agents induce the release of AA [6]. The AA released is the major precursor of biologically active eicosanoids produced via the cyclooxygenase and lipoxy- genase pathways [7]. The physiological role of AA metabolites in the pineal gland has not been clearly estab- lished, although prostaglandins E 2, Fz,~ [8,9], 12- and 15-hydroperoxyeicosatetraenoic acids [10], and more re- cently hepoxilin A 3 [11] have been implicated. The role of DHA in the pineal gland function has received much less attention. However, by using a n- 3 fatty acid-deficient diet, which indeed affected the level of DHA in phospholipids, we have recently revealed a signif- icant alteration of the pineal gland activity [12]. This fatty acid, esterified at the sn-2 position of glycerolipids as AA, has been reported to be a potent inhibitor of AA metabolism