Effect of ACTH, β-endorphin, morphine and naloxone on the release of cortisol by isolated adrenal glands

Abstract The release of cortisol (determined by RIA) from isolated slices of adrenal glands of guinea pigs is stimulated by ACTH, by β-endorphin, and by morphine in a concentration-dependent way; naloxone gives a small stimulation which is not related to its concentration. Naloxone inhibits the effect of ACTH (1.11×10 −11 M) in a competitive manner with an IC 50 of about 3.10 −9 M. Also morphine and β-endorphin inhibit the effect of ACTH, but not in competitive manner. Naloxone (10 −9 – 10 −7 M) gives a concentration-related inhibition of the increase of cortisol release produced by morphine (10 −8 M) and by β-endorphin (1.44×10 −10 M). These data suggest a similarity in the conformation of ACTH, β-endorphin, morphine and naloxone towards the binding sites of ACTH of the guinea pig adrenal glands.