THE ROLE OF CORTISOL IN AMINO-ACID MOBILIZATION AND METABOLISM FOLLOWING EXHAUSTIVE EXERCISE IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS WALBAUM)

The role of cortisol in the mobilization and metabolism of amino acids following exhaustive exercise in rainbow trout (Oncorhynchus mykiss) was investigated. Plasma cortisol levels were elevated for 4h followin g exercise and 6, of a total of 22 amino acids, showed significant res ponses. In white muscle, alanine and glutamine were elevated immediate ly after exercise through to 4h, whereas glutamate, and the branched-c hain amino acids (BCAA), isoleucine, leucine and valine, all decreased over this time. In plasma all of these amino acids increased from 2-4 h post-exercise, while in liver, alanine and glutamine increased, glut amate did not change and the BCAAs declined over this time. Blockade o f the post-exercise elevation in plasma cortisol with either metyrapon e (cortisol synthesis inhibitor) or dexamethasone (cortisol release bl ocker) prevented the changes in tissue amino acid levels. This study d emonstrates that cortisol can act rapidly (within minutes to hows) to alter amino acid metabolism in fish. A model is presented to explain t he action of cortisol on amino acid metabolism.