Discrepancies Between Radioimmunoassays and Bioassay for Rat FSH: Evidence that Androgen Treatment and Withdrawal Can Alter Biossay—Immunoassay Ratios1

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Abstract
An antiserum generated against partially purified rat pituitary FSH was used to develop a radioimmunoassay (RIA). This RIA was tested in parallel with the two other RIA systems for rat FSH which are currently available. Testing included use of a group of rat pituitary and serum samples in which widely varied ratios of FSH, LH and TSH bioactivities had been produced by appropriate pretreatments of the donors. Minor quantitative disagreements were found among the three RIA systems but marked differences were found between the RIA systems and FSH bioassay. These differences were most evident as changes in the index of discrimination (bioassay/immunoassay ratio) following orchidectomy and/or androgen treatment. Although such treatments alter FSH:LH ratios and these antisera do appear to cross—react with LH (and also with rat serum proteins) the major discrepancies between bio— and immunoassay do not appear attributable to LH cross—reaction since the “FSH” immunoreactivity of purified rat LH (NIAMD rat LH—I–1) is too low to account for them. The data thus suggest that androgen treatment and withdrawal may alter the molecular form of FSH in the rat. (Endocrinology92: 1065, 1973)

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