PHYSIOLOGICAL ESTRADIOL ADMINISTRATION DOES NOT CHANGE THE BIOLOGICALTO IMMUNOLOGICAL RATIO OF LH IN SERUM FROM POSTMENOPAUSAL WOMEN

OBJECTIVE We investigated the effect of chronic physiological concentr ations of oestradiol on the bioactivity (B) and immunoactivity (I) of LH in serum using radioimmunoassay (RIA) and a sensitive immunoradiome tric (IRMA) assay. DESIGN Twelve post-menopausal, hysterectomized wome n received a 50-mg subcutaneous E2 implant, in the absence of progesto gen treatment. Pretreatment serum samples were obtained on two occasio ns for measurement of E2 and FSH by radioimmunoassay and for measureme nt of LH by bioassay (BIO), immunoradiometric assay and radioimmunoass ay. Further serum samples were obtained monthly for 6 months for assay as above. RESULTS The serum E2 level (basal levels <70 pmol/l) rose f ollowing implant (P < 0.01) peaking at 1 month (mean 454, range 356-58 0 pmol/l) and remaining within premenopausal physiological levels for 6 months. There were falls in FSH, LH-RIA, LH-IRMA and LH-BIO (P < 0.0 01). There was no change in the B:I ratio for B:I-RIA or B:I-IRMA for LH which were 18 and 3.3, respectively pretreatment and 1.7 and 2.9 af ter 1 month's treatment. CONCLUSION The treatment of post-menopausal w omen with 50-mg E2 subcutaneous implants produces physiological premen opausal E2 levels for at least 6 months. There is no change in the B:I ratio of LH using either the RIA or IRMA during chronic E2 treatment.