EVIDENCE THAT CORTISOL MAY PROTECT AGAINST THE IMMEDIATE EFFECTS OF STRESS ON CIRCULATING LEUKOCYTES IN THE TROUT

Rainbow trout stressed by an intraperitonal injection of saline displa yed reduced phagocytic activity of their spleen and head-kidney macrop hages within 3 hr. Phagocytic activity was similarly depressed by inje cting noradrenalin, but was maintained in fish injected with the adren ergic blocking agent phentolamine, suggesting that endogenous catechol amines are involved in this stress response. Since stress may increase the number of circulating granulocytes, it is proposed that noradrena lin, released during stress, causes the liberation of active macrophag es from the lymphocytic tissue, the remaining macrophages therefore sh owing a lowered phagocytic index. Cortisol injection, like phentolamin e, prevented the depressive effect of stress on the phagocytic index b ut did not antagonize the depressive effect of exogenous noradrenalin. It is suggested that the stress-induced release of endogenous catecho lamines may be prevented by cortisol. Injection stress caused a declin e in the number of circulating lymphocytes/thrombocytes, indicating th eir retrafficking into some other tissue. This was opposed by cortisol and by high doses of noradrenalin. It is proposed that cortisol or no radrenalin may oppose, directly or indirectly, the expression of adhes ion molecules which are normally induced after stress. (C) 1996 Academ ic Press, Inc.