Radioimmunoassay of Rabbit Growth Hormone

Preparation of rabbit growth hormone which is suitable for trace labeling is described. The molecular weight of rabbit growth hormone as determined by polyacrylamide-gel electrophoresis i s 18,000. The assay uses purified rabbit growth hormone labeled with radioiodine-125. An enzymatic procedure which utilizes 4 µg of lactoperoxidase and 0.88 mM hydrogen peroxide was adapted for the iodination. The antiserum was prepared in rhesus monkeys and used in the assay in a final dilution of 1:100,000. The reference standard had a potency of 0.60 IU/mg by the body weight gain bioassay. Separation of antibody-bound growth hormone from free growth hormone was achieved with goat anti-monkey gamma globulin. The affinity constant of the antigen-antibody reaction of the assay equaled 109 L/M and the average standard deviation of duplicate aliquots within a single assay over the range of 2 to 50 ng was 1.9 ng (4%). Interassay variability over the same range for unknowns measured in two different assays was 2.8 ng (6%). P...