Effect of dexamethasone on pituitary-adrenocortical response to acute irradiation stress in rats.

After the irradiation with a lethal dose of 387 mC kg-1 (1500 R) an increase of plasma and adrenal corticosterone concentration was found in male rats (about 250 g body weight) during first 24 h as compared to sham-irradiated animals, the maximum increase being observed at 60 min after irradiation. A second period of corticosterone increase was found at 48 and 72 h. At the same time the adrenal weight increased and severe lesions of gastrointestinal tract were found. In a second experiment dexamethasone (50 mg kg-1) was injected 3 h before irradiation and this prevented the increase of plasma and adrenal corticosterone level at 60 min after irradiation. It was suggested that the degradation of corticosterone might be slowed down during the first period after irradiation, while at the same time the feed-back regulatory mechanism of ACTH release from the pituitary apparently remained intact. The second period of corticosterone increase was apparently due to severe gastrointestinal lesions.