The expression of the urinary forms of human luteinizing hormone beta fragment in various populations as assessed by a specific immunoradiometric assay.

Human gonadotrophins undergo metabolic transformations which result in the presence of several smaller, structurally and immunologically related forms of gonadotrophins in the urine. For luteinizing hormone (LH), a beta core fragment (LHbcf) has been isolated from the pituitary and characterized. The corresponding urinary fragment is inferred from mass spectral and immunochemical analysis of chromatographically separated urinary forms. Physicochemical characteristics, primarily mass spectral and chromatographic, indicate that the pituitary and urinary forms of LHbcf have a different structure, probably in the carbohydrate moieties. This communication characterizes the expression of LHbcf in the urine of both reproductive and post-reproductive age women and in men, employing assays highly specific for the pituitary form of the fragment. It was found that LHbcf is the predominant LH associated molecular form in the urine during peri-ovulatory period, peaking 1‐3 days later than intact LH and reaching a concentration of ~600 fmol/mg creatinine, 7-fold higher than either LH or LH free beta subunit. Corresponding concentrations of human chorionic gonadotrophin (HCG) bcf were ,1% that of LHbcf. LHbcf cross-reaction with some LH or LHb monoclonal antibodies may well interfere with the accurate estimation of the day of the LH surge when urinary tests are utilized.