Eicosanoid generating capacities of different tissues from the rainbow trout,Oncorhynchus mykiss

The eicosanoid generating potential of the brain, gills, skin, ovary, muscle, eye, liver, spleen, heart, and alimentary canal in the rainbow trout,Oncorhynchus mykiss, was examined. All the organs/tissues examined synthesized the 12‐lipoxygenase products, 12‐hydroxyeicosatetraenoic acid (12‐HETE), and 12‐hydroxyeicosapentaenoic acid (12‐HEPE), implying the widespread nature of this enzyme in trout. Both prostaglandin E and LTC were also found in variable amounts in the organs, with the greatest amount of PGE found in the gill. Leukotriene (LT) B4 and LTB5 were found in supernatants from calcium ionophore‐challenged brain, skin, ovary, liver, spleen, and heart, but the lipoxins A4 and A5 were only present in brain, ovary, and spleen in relatively small amounts. As lipoxins have previously been shown to be synthesized by macrophages in rainbow trout [Pettittet al., J. Biol. Chem. 266, 8720–8726 (1991)], and related cells (microglial cells) are found in the brain of mammals, the localization of macrophage‐like cells in trout brain was investigated immunocytochemically. Monoclonal antibodies specific for trout leucocytes failed to identifity any microglial‐like cells in sections of the brain, although microvessels containing immuno‐positive reaction products were observed. A number of distinct lipoxygenase products were found in supernatants of ionophore‐challenged gill, including 14‐hydroxydocosahexaenoic acid, 12‐HETE, and 12‐HEPE, and a large number of dihydroxy fatty acid derivatives with conjugated triene chromophores. One of these products was tentatively identified as 8(R),15(S)‐dihydroxyeicosatetraenoic acid, a dual 12‐ and 15‐lipoxygenase product, but apparently no LTB4 was generated by this tissue.