Development of a radioimmunoassay for human seminal plasma inhibin.

Research on the characterization and purification of inhibin and on the determination of its physiological role has been greatly hampered by lack of sensitive and precise methods for detecting and determining inhibin. This paper presents a sensitive and specific radioimmunoassay (RIA) for the inhibin in human seminal plasma; the assay developed has also been used to detect serum inhibin levels in developing male and female rats. The method includes alcohol precipitation ether extraction column chromatography on Sephadex G-100 zone electrophoresis on a Pevikon block and separation on a DEAE-cellulose column. The tested purified hormones (LH FSH and prolactin) from different species did not show any cross-reaction in this RIA. The tested hormones (testosterone dihydrotestosterone estradiol-17B and progesterone) did not interfere with the assay. The antiserum exhibited an affinity constant (Ka) of 2.379 x 10 ; assay sensitivity was 10-15 ng/tube and intra- and inter-assay coefficients of variation were 5.7% (n=6) and 15% (n=10) respectively. When added to the serum of a castrated man recovery for inhibin was 95-110%. Inhibin levels in different biological fluids and tissues were determined using this RIA. Normo-spermic semen exhibited substantially higher inhibin levels compared to oligospermic semen. A significant amount of inhibin was detected in the human prostate. A cross-reaction in the RIA was observed in monkey semen rat serum and bovine ovine and porcine follicular fluids; ram testicular inhibin and bull semen did not cross react. RIA for human seminal plasma inhibin may be used to monitor the purification of inhibin to measure inhibin in other fluids and tissues and to study the physiological role of inhibin.