DYNAMIC VARIATIONS IN PLASMA CORTICOSTEROID-BINDING GLOBULIN AND BASAL HPA ACTIVITY FOLLOWING ACUTE STRESS IN ADULT-RATS

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 signific antly reduced at 24 and 48 h following a single 60 min period of restr aint. 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 dar k phase of the cycle showed no change in plasma CBG binding or in basa l HPA activity. Pituitary intracellular transcortin, which is derived from circulating CBG, was also decreased by restaint stress. The decre ase in CBG binding was also associated with a significant increase in resting-state free B levels. Together, these effects produced a substa ntially (i.e. similar to 10-fold) increased 'basal' glucocorticoid sig nal 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.