The effect of sublethal endrin exposure on rainbow trout, Salmo gairdneri Richardson. II. The effect of altering serum cortisol concentrations on the immune response

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Abstract
The effect of altering serum cortisol concentrations on the immune response was elucidated in endrin‐ and non‐endrin‐exposed rainbow trout, Salmo gairdneri. Fish were immunized with 10 μg of Yersinia ruckeri O‐antigen following 30 days of treatment. The migration inhibition factor assay (MIF), plaque‐forming cell assay (PFC) and serum agglutination titres (SAG) were performed 2, 14 and 30 days post‐antigen inoculation. Endrin exposure was continued subsequent to antigen inoculation. Control fish were fed 20 and 35 mg kg−1 body weight day−1 of cortisol and metyrapone, respectively. Endrin‐exposed fish received 35 mg kg−1 body weight day−1 of metyrapone in their diet. Control fish receiving cortisol had significantly reduced MIF, PFC and SAG responses. The MIF response was completely restored in endrin‐exposed fish receiving dietary metyrapone. The PFC response and SAG titres were partially restored, 61 and 69% respectively, in endrin‐exposed fish receiving metyrapone. The results indicate that elevated serum cortisol concentration obtained in endrin‐exposed fish has a central role in repression of the immune response.