A Heterologous Radioimmunoassay for Follicle-Stimulating Hormone: Application to Measurement of FSH in the Ovine Estrous Cycle and in Several Other Species Including Man1

A heterologous radioimmunoassay system, using an antiserum to human FSH in combination with radioiodinated ovine FSH was highly specific for FSH for a number of species, and was used to measure plasma FSH levels in sheep, rat and man in a range of physiological states. Within-assay coefficient of variation (CV) was <10% over the range 35–500 ng FSH/ml and between-assay CV was 15%. Sensitivity was 1.3 ng NIH-FSH-S6 per tube and mean recovery of FSH added to plasma was 98%. Specificity was demonstrated by the finding of parallel inhibition curves between serial dilutions of plasma from an oophorectomised ewe and standard ovine FSH, and by the failure of ovine LH, GH, prolactin and albumin, human LH, TSH, hCG, bovine LH and GnRH to show significant inhibition. Ewes were bled at 2-hr intervals for 4 days over various stages of the estrous cycle and the samples assayed for FSH and LH. Sharp peaks of FSH, ranging from 80–150 ng/ml NIH-FSH-S6 were detected at estrus, coinciding with the preovulatory LH peak. For...