A radioimmunoassay for 11-oxotestosterone: its application in the measurement of levels in blood serum of rainbow trout (S. Gairdneri).

17beta-Hydroxyandrost-4-ene-3,11-dione was linked via its 3-(O-carboxymethyl) oxime to bovine serum albumin to give a conjugate which was used to generate antiserum in rabbits. The antiserum, at an overall dilution of 1 in 16,000, together with [1,2-3H] 17beta-hydroxyandrost-4-ene-3,11-dione synthesized from [1,2-3H] cortisone have been used to develop a radioimmunoassay for the parent steroid. The assay incorporates a purification step in which serum or plasma extracts are chromatographed on silica gel layers bound to plastic or aluminum sheets and the steroid containing zones cut out and eluted directly with assay buffer. The cross-reactivities of several steroids with the antiserum and the specificity, sensitivity, accuracy and precision of the assay are described. Blood sera from immature male rainbow trout contain ca 0.2-0.4 mature, serum levels rise sharply to reach values of 2 to greater than 9 microng/100 ml of 17beta-hydroxyandrost-4-ene-3,11 dione. As male fish mature, serum levels rise sharply to reach values of 2 to greater than 9 microng/100 ml. Levels in immature females rarely exceeded the assay sensitivity but serum from three ripe females showed low but detectable levels (ca 0.2 microng/100 ml) of steroid. The assay has found application in sexing live fish for experimental purposes.