Circadian corticosterone rhythm and stress response in rats with adrenal autotransplants

A significant circadian variation in plasma corticosterone concentrations as determined by sequential sampling was observed in rats with adrenals autotransplanted (ADT) to the inguinal region as well as in sham-operated controls when studied 3 wk after surgery. Phase shifting of plasma corticosterone concentrations was observed in a second ADT group placed in reverse photoperiod (D12:L12, lights on 1900) for 2 wk. Intravenous injections of ACTH in dexamethasone-suppressed animals resulted in significant increments in plasma corticosterone concentrations in sham-operated but not in ADT animals. ADT and sham groups both showed elevated plasma corticosterone concentrations after ether or 30-min immobilization stress, although greater responses were present in the sham group. It appears that direct innervation of the adrenal is unnecessary for the maintenance of circadian plasma corticosterone concentrations or certain stress responses.