RADIOIMMUNOASSAY FOR SERUM LEVELS OF AN ANTIANDROGEN TSAA-291 (OXENDOLONE) IN RATS

A simple radioimmunoassay method was established to determine serum levels of a steroidal anti-androgen, TSAA-291 (Oxendolone, 16β-ethyl-17β-hydroxy-4-estren-3-one) utilizing ether-extract of serum. Using an antiserum raised against TSAA-291-3-oxime-BSA conjugate in a rabbit, a standard curve was obtained in the assay range from 30 Pg to 12 ng/tube. Intra- and inter-assay coefficients of variation were calculated to be 11 and 21%, respectively. Recovery rate of unlabeled TSAA -291 was 84%. Cross-reaction with endogenous steroids was less than 0.2%. TSAA-291 estimates were compared with those determined after further purification on a Celite column, or with those assayed with a gas-liquid chromatograph. The difference between these estimates was less than 16 and 25%, respectively, suggesting little contribution of the metabolites of TSAA-291 to the estimates by the radioimmunoassay. After successive treatments of male rats with TSAA-291 in an aqueous suspension in daily doses of 5, 15 and 50 mg/kg body weight for two weeks, Serum TSAA-291 levels were determined by the radio immunoassay and calculated to be 22.7, 76.9 and 194.9 ng/ml, respectively.