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 exam ined synthesized the 12-lipoxygenase products, 12-hydroxyeicosatetraen oic acid (12-HETE), and 12-hydroxyeicosapentaenoic acid (12-HEPE), imp lying the widespread nature of this enzyme in trout. Both prostaglandi n E and LTC were also found in variable amounts in the organs, with th e greatest amount of PGE found in the gill. Leukotriene (LT) B-4 and L TB(5) were found in supernatants from calcium ionophore-challenged bra in, skin, ovary, liver, spleen, and heart, but the lipoxins A(4) and A (5) were only present in brain, ovary, and spleen in relatively small amounts. As lipoxins have previously been shown to be synthesized by m acrophages in rainbow trout [Pettitt et al., J. Biol. Chem. 266, 8720- 8726 (1991)], and related cells (microglial cells) are found in the br ain of mammals, the localization of macrophage-like cells in trout bra in was investigated immunocytochemically. Monoclonal antibodies specif ic for trout leucocytes failed to identify any microglial-like cells i n sections of the brain, although microvessels containing immune-posit ive reaction products were observed. A number of distinct lipoxygenase products were found in supernatants of ionophore-challenged gill, inc luding 14-hydroxydocosahexaenoic acid, 12-HETE, and 12-HEPE, and a lar ge number of dihydroxy fatty acid derivatives with conjugated triene c hromophores. One of these products was tentatively identified as 8(R), 15(S)-dihydroxyeicosatetraenoic acid, a dual 12- and 15-lipoxygenase product, but apparently no LTB(4) was generated by this tissue.