title: Corticotropin receptors, cyclic AMP and steroidogenesis.
abstract: The detection and characterization of the physiologically relevant receptors for corticotropin (ACTH) in rat adrenocortical cells is described. By the use of a radioligand with full biological potency and high specific radioactivity (1800 +/- 75 Ci/mmol), a single class of receptors with an apparent Kd of 1.41 +/- 0.21 nM was detected and the number of sites was estimated to be 3840 +/- 1045 per cell. The binding curve was superimposable on the concentration-response curve for cAMP but dissociated from that for steroidogenesis. These data are best explained by the receptor-reserve model in which occupancy of a small fraction of the receptors is sufficient for inducing maximal steroidogenesis.
mesh_terms: D000302:Adrenal Cortex / Q000378:metabolism*; D000324:Adrenocorticotropic Hormone / Q000031:analogs & derivatives; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D000242:Cyclic AMP / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008954:Models, Biological; D011494:Protein Kinases / Q000378:metabolism; D011869:Radioligand Assay; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism*; D018043:Receptors, Corticotropin; D013256:Steroids / Q000096:biosynthesis*
chemical_list: D011956:Receptors, Cell Surface; D018043:Receptors, Corticotropin; D013256:Steroids; D000324:Adrenocorticotropic Hormone; D000242:Cyclic AMP; D011494:Protein Kinases