OUABAIN RECEPTOR BINDING OF HYDROXYPROGESTERONE DERIVATIVES

Abstract

1 A specific and sensitive radioreceptor assay has been devised which is based on high affinity, saturable binding of 9 nm [³H]-ouabain to the total particulate fraction isolated from dog heart. Ouabain and other cardiac glycosides, including the aglycones, were about equipotent in their ability to displace [³H]-ouabain from its receptor, the IC₅₀s ranging from 10 to 30 nm. 2 The only other substances found to compete significantly in the assay were derivatives of hydroxy-progesterone having a 17α-acetate substituent: chlormadinone acetate, megestrol acetate, cyproterone acetate and medroxyprogesterone acetate, with IC₅₀s of 2, 7.4, 9 and 21 μm, respectively. Prednisolone-3,20-bisguanyl-hydrazone, reported to have inotropic activity, gave an IC₅₀ of 6.4 μm. Cyproterone-17α-OH was less active (IC₅₀ 90 μm) than cyproterone-17α-acetate. 3 A large number of peptide and protein hormones, steroid hormones and their metabolites, amines, and drugs were inactive.