We report on dynamic changes in plasma corticosteroid-binding globulin (CBG) binding and basal hypothalamic-pituitary-adrenal (HPA) activity following acute stress in adult rats. Plasma CBG binding was significantly reduced at 24 and 48 h following a single 60 min period of restraint. Basal levels of plasma ACTH and total corticosterone (B) during the light phase of the cycle were elevated at 24 h following restraint. These effects occurred only when animals were stressed in the light phase of the cycle; animals exposed to restraint stress during the dark phase of the cycle showed no change in plasma CBG binding or in basal HPA activity. Pituitary intracellular transcortin, which is derived from circulating CBG, was also decreased by restraint stress. The decrease in CBG binding was also associated with a significant increase in resting-state free B levels. Together, these effects produced a substantially (i.e. approximately 10-fold) increased 'basal' glucocorticoid signal 24 h following acute stress. These data suggest that the increase in the circulating glucocorticoid signal associated with acute stress endures well beyond the period of increased total B levels.

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