Radioimmunoassay technique for detecting urinary excretion products after administration of synthetic anabolic steroids to the horse.

1. Cross-bred and thoroughbred geldings were injected with veterinary doses of various synthetic anabolic steroids. Urines collected sequentially from treated animals were analysed, following solvent extraction, by radioimmunoassay using 19-[3H]nortestosterone and an antibody raised against a 19-nortestosterone immunogen. 2. Urinary excretion of 19-nortestosterone and/or its cross-reacting metabolites was detectable for various times after administration of different nortestosterone esters, as follows: phenylpropionate (400 mg), greater than 14 days; cyclohexylpropionate (100 mg), greather than 10 days; laurate (200 mg) greater than 50 days. After administration of the parent steroid (150 mg) cross-reacting compounds were detectable in urine for ca. 3 days. 3. Urinary excretion of esters of other anabolic steroids cross-reacting with the 19-nortestosterone antibody (e.g. 1-dehydrotestosterone and trienbolone) could also be followed by analysing solvent extracts of urines by the radioimmunoassay. Cross-reacting compounds in urine after administration of 1-dehydrotestosterone undecylenate (250 mg) and trienbolone acetate (75 mg) could be detected for greater than 35 days and greather than 5 days, respectively.