Development and validation of a radioligand receptor assay for measurement of luteinizing hormone in human serum.

Studies of circulating LH physiology and pathophysiology are dependent upon measurements of immuno- and bioactivity, both of which have methodologic limitations. We have developed and validated a RRA which allows direct measurement of receptor-bindable LH in human serum. Using a cultured Leydig tumor cell line (MA-10) known to express the CG/LH receptor as the receptor source and polyacrylamide-gel electrophoresis purified hCG as the radioligand, we have established an assay system with the requisite sensitivity (0.04 ng/tube) to measure circulating LH, without significant alteration in total specific binding upon addition of up to 150 microL gonadotropin-free serum when compared to no serum. Standard curves of hLH diluted in gonadotropin-free serum were not statistically different in slope or ED50 from buffer curves. Dilutions of human serum from postmenopausal women and men with Klinefelter's syndrome containing LH measured in the assay were parallel to the standard curve. Further validation of the RRA included measurement of LH by RRA and RIA in daily serum samples from normal women across the menstrual cycle (n = 6) where there was excellent correlation (P less than 0.001) between RRA and RIA measurements with the exception of the mid-cycle surge where the RRA/RIA ratio fell to 0.5. This LH RRA will be useful in further studies of the physiology and biochemistry of LH in human serum.