Development of a Radioligand Receptor Assay for Measuring Follitropin in Serum: Application to Premature Ovarian Failure

We have developed a radioligand receptor assay (RRA) with sufficient sensitivity and specificity for quantifying follitropin (FSH) in unextracted serum samples. Standard curves prepared by adding pituitary FSH to either buffer or gonadotropin-free serum were parallel and statistically indistinguishable in this assay, whereas gonadotropin-free serum alone had no activity. Cross-reactivity with related pituitary hormones was negligible. Pituitary FSH was calibrated with commonly used reference prepara-tions so that RRA results could be compared with AlA results for identical standards. The patterns in daily blood samples in six normal menstrual cycles were similar by both methods. The mean RIA:RIA ratio in both the follic-ular and luteal phases was between 0.6 and 0.7, and at mid-cycle decreased to 0.48, suggesting an alteration o