A LONG-TERM INCREASE IN BASAL LEVELS OF CORTICOSTERONE AND A DECREASEIN CORTICOSTEROID-BINDING GLOBULIN AFTER ACUTE STRESSOR EXPOSURE

Adrenal glucocorticoids play an important role in mediating many of th e behavioral and physiological effects of exposure to stressors. Focus has been primarily on the acute stress-induced rise in glucocorticoid s [corticosterone (CORT) in the rat]. There are reports, however, that exposure to chronic stressors can produce an increase in basal CORT a nd a decrease in corticotropin-binding globulin (CBG). These changes o ccur subsequent to the stress-induced rise in CORT. The following expe riments examined whether exposure to an acute stressor (100 5-sec ines capable tail shocks; IS) could also produce long term changes in basal CORT and CBG. We report that a single session of IS results in an inc rease in basal total serum CORT that persists 48-96 h after IS termina tion. The increase is present only at the diurnal trough (morning). CB G levels are also decreased for 24-48 h. The decrease is present at bo th the diurnal peak (evening) as well as the trough (morning). These c hanges result in an increase in the percent and amount of biologically active CORT (unbound or free). Thus, glucocorticoid-sensitive targets are exposed to high levels of free CORT for several days after IS ter mination. The long term increase in free CORT reported here may play a n important role in mediating some of the effects produced by IS as we ll as those produced by other acute stressors.