[Radioimmunologic assay of steroids. Comparison of 3H- and 125I-ligands].

Characteristic properties of radioimmunoassay (RIA) of steroids with 3H- and 124I-ligands as a label were studied using two anabolic steroids methandrostenolone and 19-nortestosterone. Antisera towards 124I-steroids were used at higher dilutions as their specific activity was distinctly more than in the antisera to 3H-substances. However, 125I-steroid must be in a stereochemical correspondence with the antiserum otherwise antibodies do not bind the label. The antisera towards 3H-steroids were obtained after coupling of a carrier at any position of the steroid molecule. Standard curves for 3H-steroids were very steep; this pattern of the curves enabled to increase the accuracy of calculations. Sensitivity of RIA with 3H-label was also higher as compared with 125I-steroids in the experiments where unlabelled steroids inhibited the label binding with antibodies by 50%. Distinct differences were not observed in RIA specificity for methandrostenolone and 19-nortestosterone.