The effects of the polyunsaturated fatty acids (PUFAs)--eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and arachidonic acid (AA)--on in vitro steroid production by full-grown prematurational ovarian follicles from goldfish and rainbow trout were investigated. EPA and DHA inhibited gonadotropin-stimulated testosterone production in a dose-related manner, but AA was inhibitory only at the highest dose tested (400 microM). AA alone stimulated testosterone production by increasing cAMP production, but the effects of other PUFAs alone were marginal. The inhibitory actions by PUFAs were not restricted to long-chain PUFAs, as linoleic and linolenic acids had similar actions in the goldfish. The inhibitory action of EPA on testosterone production was reversible upon removal of the PUFA from medium. Testosterone production stimulated by the addition of the cAMP analogues, dibutyryl cAMP, and 8-bromo cAMP, was attenuated by PUFAs, suggesting that they act at a site distal to cAMP formation. A post-cAMP site regulating cholesterol availability may be involved as testosterone production induced by addition of 25OH-cholesterol was not affected by the PUFAs in either fish species. Together, these findings underscore the importance of lipids in ovarian physiology and suggest that PUFAs may participate in the regulation of ovarian steroidogenesis in teleost fish.

No abstract

To establish if there are sex-specific differences in the utilization of specific fatty acids in salmon during migration, we monitored plasma nonesterified fatty acids (NEFA) in male and female early-run Stuart sockeye salmon, Oncorhynchus nerka, during their spawning migration in the Fraser River. Total plasma NEFA concentrations declined in both males and females to 60 and 40% of their respective initial levels. Palmitic (C 16:0), oleic (C 18:1), docosahexaenoic (C 22:6n3), and eicosapentaenoic (C 20:5n3) acids consistently represented between 66 and 77% of the total plasma NEFAs throughout the migration. These fatty acids are probably utilized as a source of energy to sustain swimming during the migration. A difference in monoene levels between sexes suggest that females utilized monoenes, particularly oleic acid, for yolk production. Fatty acid concentrations of the n6) series remained constant in both sexes; however, a sudden increase of C 20 polyunsaturate proportions of both the n3 and n6 series was observed at the time of gonadal maturation in both sexes. While plasma NEFAs are important as energy sources for migrating sockeye salmon, there is also a selective utilization of plasma NEFAs for gonadal development and reproduction that is reflected in altered NEFA profiles of male and female fish, respectively. Résumé : Nous avons surveillé la concentration plasmatique d'acides gras non estérifiés (AGNE) chez des saumons rouges, Oncorhynchus nerka, femelles et mâles qui passent dans la rivière Fraser au début de la remonte vers la Stuart pour déterminer si l'utilisation de ces acides gras diffère selon le sexe chez le saumon en migration. Nous avons constaté, tant chez les mâles que chez les femelles, une diminution de la concentration plasmatique des AGNE totaux, les valeurs ayant baissé à 60 et 40% de ce qu'elles étaient initialement. L'acide palmitique (C 16:0), l'acide oléique (C 18:1), l'acide docosahexanoïque (C 22:6n3) et l'acide eicosapentanoïque (C 20:5n3) ont représenté 66 et 77% des AGNE plasmatiques totaux durant toute la migration. Il est probable que ces acides gras fournissent l'énergie nécessaire à la nage soutenue durant la migration. Nous avons observé une différence entre les concentrations de monoènes des deux sexes, ce qui pourrait signifier que les femelles utilisent des monoènes, et plus particulìèrement l'acide oléique, pour la production du vitellus. Les concentrations d'acides gras de la série n6 sont restées constantes chez les deux sexes; toutefois, une brusque augmentation des proportions de polyinsaturés en C 20 des séries n3 et n6 est apparue chez les deux sexes au moment de la maturation des gonades. Les AGNE plasmatiques sont d'importantes sources d'énergie pour le saumon rouge en migration, mais certains sont aussi utilisés pour le développement gonadique et la reproduction, utilisation sélective que traduisent les changements du profil des AGNE observés chez mâles et chez les femelles. [Traduit par la Rédaction]

Plasma total lipids were significantly higher in 17 -oestradiol (E 2 )-treated immature rainbow trout Oncorhynchus mykiss at week 4 after implantation, due to increases in polar and neutral lipids. The lipid classes responding were phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine, sterols and sterol esters, in a proportion that approximately reflected the increase in plasma vitellogenin (VtG) levels as measured by a non-competitive enzyme-linked immunosorbent assay (ELISA). Plasma non-esterified fatty acids and triacylglycerol were not affected by E 2 treatment. Plasma growth hormone GH levels were increased, and plasma somatostatin-14 (SRIF) levels decreased in E 2 -treated fish, responses which could be secondary to elevated plasma lipid (VtG) content, although a direct E 2 action on somatotroph function is possible. Plasma T 4 concentrations were not affected by E 2 treatment, but plasma T 3 concentrations were significantly lower than in controls 1 week after implantation when plasma E 2 concentrations were the highest; this is in support of the hypothesis that E 2 has a suppressive action on T 3 production. 2001 The Fisheries Society of the British Isles