Production of specific antisera for radioimmunoassay of human luteinizing hormone (LH) in the presence of human chorionic gonadotropin (hCG).

A specific radioimmunoassay for LH, which measures plasma LH in the presence of human chorionic gonadotropin (hCG) is described. Rabbits were immunized with highly purified native LH. One of the antisera with a difference in its reactivity against LH and hCG was further purified by affinity chromatography on a column with hCG coupled to Sepharose 4B. The adsorbed antiserum and 125I-LH was used in a double antibody assay. The LH standard (MRC 68/40) efficiently inhibited the binding of 125I-LH, and the standard curve showed a sensitivity of 0.5 ng/ml in the sample. hCG up to 10 000 ng/ml did not inhibit the binding of 125I-LH. The plasma level of LH in pregnant women in the first trimester was low (1.3 +/- 0.1 ng/ml). When LH was measured in fertile or menopausal women with or without stimulation with LH/FSH releasing hormone (LH-RH)X the results agreed to those found with our conventional LH-assay based on antiserum against hCG.