THE EFFECT OF CORTISOL ADMINISTRATION ON BLOOD-PLASMA IMMUNOGLOBULIN-M (IGM) CONCENTRATIONS IN MASU SALMON (ONCORHYNCHUS-MASOU)

Immunoglobulin M (IgM) is known as a main factor in the humoral immune system of teleosts. In the present study, the effect of cortisol on p lasma IgM concentrations was investigated using a specific antibody to IgM in masu salmon (Oncorhynchus masou). Cortisol was orally administ ered each day for 2 weeks at a dose of 1 mg g-1 in the diet, and for t he following week the fish were fed a non-treated diet. Blood plasma s amples were collected at 0, 1, 2 and 3 weeks after the initiation of t reatment. Oral administration of cortisol elevated plasma cortisol con centrations to about 40 ng/ml for 2 weeks after administration and sli ghtly reduced plasma IgM concentration; the suppression was statistica lly significant one week after the period of hormone administration. H owever, treatment with cortisol did not affect plasma concentrations o f total protein or alpha1-protein, one of the major serum proteins, du ring the experimental period. These results indicate that cortisol spe cifically suppresses plasma IgM concentrations.