Adrenocortical Response to Stress and ACTH in Pacific Salmon (Oncorhynchus tshawytscha) and Steelhead Trout (Salmo gairdnerii) at Successive Stages in the Sexual Cycle

Abstract

With the purpose of acquiring information concerning the functional activity of the adrenocortical tissue of the Pacific salmon (O. tshawytscha) during various stages of its migration from the sea to the spawning grounds, ACTH administration, the stress of holding in a confined space and repeated bleeding were employed to determine the response of the adrenocortical tissue as reflected in the changing concentration of 17-hydroxycorticosteroids (17-OHCS) in the blood plasma. The stress of holding sea salmon in a tank on board ship, without other disturbance, resulted after 1 hr. in a progressive rise in plasma 17-OHCS to as much as a 4-fold increase by the end of 24[long dash]48 hr. This change was accompanied by hyperplasia of the adrenocortical tissue. At the beginning of the salmon''s river migration, both holding alone plus bleeding and ACTH injection produced a marked increase in plasma 17-OHCS, but not quite as great as that shown by salmon taken in the sea. Thereafter, as the salmon continued their migration and maturation of the gonads, their adrenocortical reactivity diminished progressively until, by the time of spawning, little response to ACTH or stress could be elicited. At this terminal period in the salmon''s life cycle the levels of 17-OHCS in the plasma remained high. Except at the beginning of their fluvial migration, females, both maturing and spawning, exhibited higher plasma concentrations of 17-OHCS than did male salmon. Spawning steelhead trout showed a higher rise in plasma corticosteroid levels than did spawning salmon following ACTH injection.