Inhibition of pituitary beta-endorphin by ACTH and glucocorticoids

beta-Endorphin and ACTH are secreted concomitantly in baseline conditions and in response to physiological and pharmacological stimuli. However, few and contradictory data are available on their feedback inhibition mechanisms. To investigate this aspect, the effects of exogenous ACTH1-24 and glucocorticoids on endogenous ACTH1-39 and beta-endorphin were tested in 18 patients with Addison's disease. Two main experimental protocols were employed: (1) 7 patients were given ACTH1-24 50 micrograms as an intravenous bolus followed by a 50-micrograms infusion in 90 min. Blood samples for beta-endorphin, ACTH and cortisol were obtained at 0, 15, 30, 45, 60, 90, 120 min. Six other patients were given oCRH 100 micrograms i.v. plus ACTH1-24, as described above. (2) In 5 other patients, hydrocortisone 37.5 mg was administered i.v. in 90 min. Blood samples for beta-endorphin, ACTH and cortisol were drawn at 0, 15, 30, 45, 60, 90, 120 min. One week later, the same patients were given oCRH 100 micrograms i.v. and hydrocortisone 37.5 mg, as described above. ACTH1-24 administration caused a significant (p less than 0.01) decrease in endogenous ACTH but not in beta-endorphin. oCRH injection significantly stimulated both ACTH and beta-endorphin. The response of both ACTH and beta-endorphin was inhibited by exogenous ACTH1-24. There was a potent inhibition by hydrocortisone on both basal and stimulated beta-endorphin, confirming that the feedback mechanism of glucocorticoids concomitantly inhibits ACTH and beta-endorphin. On the other hand, only CRH-stimulated but not basal secretion of beta-endorphin seems affected by ACTH ultrashort feedback, suggesting an intrapituitary regulation.