title: Studies of corticotropin receptors on rat adipocytes.
abstract: Synthetic [125I]-Tyr23, Phe2, Nle4-adrenocorticotropin (ACTH)-(1-38) [( 125I]-ACTH analog) with full biological potency and near theoretical specific radioactivity (1800 +/- 75 Ci/mmol) was used to investigate ACTH receptors on isolated rat adipocytes derived from 42-day-old rats. Binding to adipocytes was studied in the presence of 1% bovine serum albumin (BSA) as well as 4% BSA. The interaction of the [125I]-ACTH analog with adipocytes was highly specific, rapid, saturable, and reversible. Scatchard analysis of the binding data obtained in medium containing 1% BSA revealed a single class of binding sites with an apparent KD = 170 +/- 11.9 pM. Competition experiments with unlabeled ACTH also yielded a comparable value for the apparent KD (143 +/- 16.5 pM). The number of receptors per adipocyte was quite low (521-841/cell). The stimulation of lipolysis by ACTH was closely correlated with the binding, the apparent Km being 145-177 pM. At a concentration of 4% BSA in the incubation medium, the binding curve was shifted significantly to the right (apparent KD = 446 +/- 77 pM) and the binding capacity was also significantly enhanced (1663 +/- 208/cell) without any change in the apparent Km for glycerol release (187 +/- 7.1 pM).
mesh_terms: D000273:Adipose Tissue / Q000187:drug effects / Q000378:metabolism*; D000324:Adrenocorticotropic Hormone / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D007700:Kinetics; D008066:Lipolysis / Q000187:drug effects; D008297:Male; D010446:Peptide Fragments / Q000378:metabolism / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000378:metabolism*; D018043:Receptors, Corticotropin
chemical_list: C027550:ACTH (1-38); D010446:Peptide Fragments; D011956:Receptors, Cell Surface; D018043:Receptors, Corticotropin; D000324:Adrenocorticotropic Hormone