Direct evidence of acute stress-induced facilitation of ACTH response to subsequent stress in rats

To determine the role of glucocorticoids in the appearance of the facilitat ory effect of stress on the ACTH response to a subsequent stress, sham-oper ated (Sham) rats and rats adrenalectomized (ADX) and supplemented with 50 m g/l corticosterone (B) in the drinking saline (ADX + B) were subjected to 1 min of immobilization stress (Imo) four consecutive times with an interstr essor interval of 90 min. Sham rats showed a similar pattern of ACTH respon se to the first and fourth exposures to Imo. ADX + B rats showed an exacerb ated ACTH response to the fourth Imo, despite higher prestress levels than those observed before the first Imo. In another experiment, no facilitatory effect of previous stress on ACTH response was found in ADX rats, but supp lementation with B in the drinking saline for 1 wk resulted in facilitation of the ACTH response. We conclude that repeated exposure to a short-time s tress induces a facilitatory effect on the ACTH response that is uncovered by eliminating stress-induced glucocorticoid release but needs B doses resu lting in approximately basal circulating glucocorticoid levels to be induce d or expressed.