LIPID-COMPOSITION OF THE PINEAL ORGAN FROM RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

The lipid composition of the pineal organ from the rainbow trout (Onco rhynchus mykiss) was determined to establish whether the involvement o f this organ in the control of circadian rhythms is reflected by speci fic adaptations of lipid composition. Lipid comprised 4.9% of the tiss ue wet weight and triacylglycerols were the major Lipid class present (47% of total lipid). Phosphatidylcholine (PC) Was the principal polar lipid, and smaller proportions of other phospholipids and cholesterol were also present. Plasmalogens contributed 11% of the ethanolamine g lycerophospholipids (EGP). No cerebrosides were detected. The fatty ac id composition of triacylglycerols was generally similar to that of to tal lipids in which saturated, monounsaturated and polyunsaturated fat ty acids (PLEA) were present in almost equal proportions. Each of the polar lipid classes had a specific fatty acid composition. With the ex ception of phosphatidylinositol (PI), in which 20:4n-6 comprised 27.4% of the total fatty acids, 22:6n-3 was the principal PUFA in all Lipid classes. The proportion of 20:5n-3 never exceeded 6.0% of the fatty a cids in any lipid class. The predominant molecular species of PC were 16:0/22:6n-3 and 16:0/18:1, which accounted for 33.2 and 28.5%, respec tively, of the total molecular species of this phospholipid. Phosphati dylethanolamine (PE) contained the highest level of di-22:6n-3 (13.0%) of any phospholipid. There was also 4.9% of this molecular species in phosphatidylserine (PS) and 4.1% in PC. In PE, the species 16:0/22:6, 18:1/22:6 and 18:0/22:6 totalled 45.1%, while in PS 18:0/22:6 account ed for 43.9% of the total molecular species. The most abundant molecul ar species of PI was 18:0/20:4n-6 (37.8%). The lipid composition of th e pineal organ of trout, and particularly the molecular species compos ition of PI, is more similar to the composition of the retina than tha t of the brain.