Application of a radioligand receptor assay for determination of luteinizing hormone in human serum.

A sensitive, specific and economic radioligand receptor assay is described for measurement of LH in human serum (RRA-LH). By means of ethanol fractionation of (NH4)2SO4-precipitation serum can be prepared for LH-quantitation and tested in the RRA-LH without interference of a non-specific inhibiting substance present in untreated serum from various human sources. Treatment of serum with 8% ethanol separates non-specific inhibiting substances from LH, the latter remaining in the supernatant at this ethanol concentration. The criteria of specificity are examined. The results of experiments designed to produce evidence for or against specificity suggest specificity of the RRA-LH. Recoveries, as estimated by administration of [125I]hLH and unlabelled hLH to untreated serum samples are shown to be between 80 and 95% for the thanol fractionation procedure and between 65 and 75% for the (NH4)2SO4-precipitation method. The ethanol fractionation procedure is preferred for routine serum-LH determination because of its simplicity, speed and higher recoveries. Ethanol-treated sera from post-menopausal women show, on average, higher RRA-LH concentrations than ethanol-treated sera from young women. RRA-LH values are consistently higher than LH-values found by radioimmunoassay (RIA-LH). The LH-concentrations in sera from two menstrual cycles and from two LH-releasing hormone tests are measured by RRA-LH and RIA-LH. Similarities and discrepancies of the LH-profiles found by the two assay systems are described.