Previous chronic ACTH administration does not protect against the effects of acute or chronic stress in male rats.

The effect of previous chronic ACTH administration on the physiological response to acute and chronic immobilization stress was studied in adult male rats. Chronic ACTH administration slightly reduced food intake and drastically inhibited body weight gain. Serum corticosterone levels were similar in saline- and ACTH-treated rats twenty hours after the last administration. However, the corticosterone response to 1 hr immobilization was greatly reduced by previous ACTH administration. When the exposure to the stressor was prolonged up to 18 hours, the corticosterone response was similar in saline, and ACTH-treated rats. While body weight loss caused by starvation and acute stress was lower in ACTH-treated rats, stomach ulceration was greater in the latter animals. Although ACTH-treated rats showed higher body weight gain than saline-treated animals during chronic immobilization, this was probably due to catch-up growth as food intake inhibition caused by the stressor was similar in the two groups. Pituitary-adrenal adaptation to the repeated stressor was the same in saline- and ACTH-treated rats. Therefore, the effects of previous ACTH treated on the physiological response to either acute or chronic stress appear to be mixed, depending on the variable studied.