title: 3H-cyproterone acetate: binding characteristics to human uterine progestagen receptors.
abstract: The availability of tritium labeled cyproterone acetate (CPA) facilitated the systematic investigation of the binding characteristics of this compound for human uterine progesterone receptors (PgR). The binding parameters of 3H-CPA are compared to those of 3H-R5020 and 3H-progesterone. The rate constants of association (k1M-1sec-1) to PgR were 7.8 X 10(3) for 3H-R5020, 4.5 X 10(4) for 3H-progesterone and 4.0 X 10(4) for 3H-CPA. The rate constants of dissociation (k-1, sec-1) were 3.6 X 10(-5) for 3H-R5020, 21.3 X 10(-5) for 3H-progesterone and 17.8 X 10(-5) for 3H-CPA. The Kd-values (M), as obtained by titration analysis and subsequent Scatchard plot analysis were 1.2 X 10(-9) for 3H-R5020, 6.0 X 10(-9) for 3H-progesterone and 5.2 X 10(-9) for 3H-CPA. On sucrose density gradient analysis binding in the 3.5, 5 and 8 S area could be observed using 3H-R5020. For 3H-progesterone and 3H-CPA binding was exclusively found in the 5 S area. The specificity of the steroid binding site of PgR is identical for 3H-R5020 and 3H-CPA. The order of potency of binding for various competitors decreases identically for both radioactive ligands: R5020 less than progesterone less than R1881 less than CPA less than dihydrotestosterone less than dexamethasone less than cyproterone less than 15 beta-OH-cyproterone. CPA resembles progesterone very closely in its binding characteristics to human uterine PgR.
authors.forename: H J
authors.initials: HJ
authors.lastname: Grill
authors.forename: B
authors.initials: B
authors.lastname: Manz
authors.forename: W
authors.initials: W
authors.lastname: Elger
authors.forename: K
authors.initials: K
authors.lastname: Pollow
mesh_terms: D001667:Binding, Competitive; D002499:Centrifugation, Density Gradient; D003534:Cyproterone / Q000031:analogs & derivatives* / Q000378:metabolism; D017373:Cyproterone Acetate; D005260:Female; D006801:Humans; D007700:Kinetics; D011374:Progesterone / Q000378:metabolism; D011397:Promegestone / Q000378:metabolism; D011980:Receptors, Progesterone / Q000378:metabolism*; D013223:Statistics as Topic; D014316:Tritium; D014599:Uterus / Q000378:metabolism*
chemical_list: D011980:Receptors, Progesterone; D014316:Tritium; D011374:Progesterone; D017373:Cyproterone Acetate; D011397:Promegestone; D003534:Cyproterone