[ 3H] corticosterone binding activity of adrenal incubation media in response to in vivo and in vitro ACTH stimulation

The influence of in vivo or in vitro administration of ACTH upon in vitro adrenal corticosterone production as well as [ 3H] corticosterone binding activity of incubation media have been examined. ACTH, regardless of the route of administration, significantly elevated corticosterone during an initial incubation period. During initial incubation periods ACTH also elevated [ 3H] corticosterone binding activity of the incubation media. Ensuing incubations were characterized by either a marked decline in binding activity ( in vivo ACTH administration) or a marked decline with an attendant negative correlation between binding activity and ACTH level. Corticosteroidogenic response to ACTH remained intact during ensuing incubations. The data suggest the existence of an ACTH-sensitive intraglandular corticosterone binding ligand(s), the activity or concentration of which is dramatically altered by incubation protocol and time of sacrifice.