THE EFFECT OF ACUTE AND CHRONIC ACTH ADMINISTRATION ON PITUITARY-ADRENAL RESPONSE TO ACUTE IMMOBILIZATION STRESS - RELATIONSHIP TO CHANGES IN CORTICOSTEROID-BINDING GLOBULIN

The effect of single and chronic ACTH administration on serum levels o f the corticosteroid-binding globulin (CBG) and pituitary-adrenal (PA) responsiveness to acute immobilization (IMO) stress was studied in ad ult Sprague-Dawley rats. Single ACTH administration significantly redu ced CBG levels but did not alter PA response to acute IMO. Chronic ACT H administration caused a greater fall in CBG than single ACTH adminis tration and blunted PA response to IMO. The effect of chronic ACTH adm inistration on CGB levels recovered 2 days after the last administrati on, but the ACTH response to IMO was normal only by day 7 after the la st ACTH injection. The present data indicate that ACTH administration to rats reduced CBG levels and impaired PA response to acute stress, b ut impaired PA responsiveness cannot be solely attributed to changes i n CBG.