Adrenocorticotrophic hormone-stimulated cortisol release by the head kidney inter-renal tissue from sea bream (Sparus aurata) fed with linseed oil and soyabean oil.

The mode of action of highly unsaturated fatty acids (HUFA) in regulating gilthead sea bream (Sparus aurata) head kidney (HK) cortisol production was studied through in vitro trials using a dynamic superfusion system. Fish were previously fed with different diets containing several inclusion levels of linseed oil (LO) or soyabean oil (SO) for 26 weeks. Five diets were tested; anchovy oil was the only lipid source for the control diet (fish oil, FO) and two different substitution levels (70 and 100 %) were tested using either LO or SO (70LO, 70SO, 100LO and 100SO). Fatty acid compositions of the HK reflected the dietary input, thus EPA, DHA, arachidonic acid and n-3 HUFA were significantly (P < 0·05) reduced in fish fed vegetable oils compared with fish fed the FO diet. Feeding 70 or 100 % LO increased significantly (P < 0·05) cortisol release in HK after stimulation with adrenocorticotrophic hormone (ACTH), while feeding SO had no effect on this response. Cortisol stimulation factor (SF) was increased in fish fed the 70LO and 100LO diets compared with fish fed the control diet. Moreover, eicosanoid inhibition by incubating the HK tissue with indomethacin (INDO) as a cyclo-oxygenase (COX) inhibitor, or nordihydroguaiaretic acid (NDGA) as a lipoxygenase (LOX) inhibitor, significantly reduced (P < 0·05) the cortisol release after ACTH stimulation in the 70LO and 100LO diets. Cortisol SF was reduced in the FO, 70LO and 100LO diets when incubating the HK with INDO or NDGA, while it was increased in the 70SO diet. The present results indicate that changing the fatty acid profile of gilthead sea bream HK by including LO and/or SO in the fish diet affected the in vitro cortisol release, and this effect is partly mediated by COX and/or LOX metabolites.