No abstract

A number of immunoassay methods have been developed recently to detect specifically the bioactive alpha-beta A subunit inhibin dimer (inhibin A) in human plasma. However, the specificity of these assays in terms of their ability to detect the range of inhibin forms found in plasma and their relationship to bioactivity have not been investigated. Inhibin was fractionated from human follicular fluid (hFF) and serum/plasma from women stimulated with gonadotropins (IVF serum), and from postmenopausal and male plasma, using a combined immunoaffinity/preparative SDS-PAGE procedure. The molecular weight profile of inhibin was established by inhibin in vitro bioassay, three alpha-beta A subunit specific immunoassays, and three alpha subunit-directed immunoassays that detect the alpha subunit as well as inhibin A and B forms. In hFF inhibin forms of 33, 36, 55 and 66K were detected by in vitro bioassay and by most immunoassays except for 33 k inhibin, which was nondetectable by one alpha-beta A ELISA. The alpha subunit-directed assays also detected activity in the 29-31K region, in some assays in considerably high levels. In IVF serum in vitro bioactivity and immunoactivities were detected between 27 and 100K with the alpha-beta A assays failing to detect all bioactive forms. Alpha subunit-directed assays gave similar immunoactive profiles. Neither in vitro bioassay nor alpha-beta A assays detected activity in post-menopausal plasma or male plasma, while alpha subunit-directed assays showed peaks predominantly at 36 k, although at low levels. It is concluded that dimeric inhibin A specific assays detected bioactive inhibin forms in hFF and to a lesser extent in IVF serum. Alpha subunit-directed assays correlated poorly with in vitro bioassay in hFF because of the high alpha subunit levels in this sample. The higher correlation between these assays in IVF serum suggested that there was little free alpha subunit. The 36K form in male plasma may be free alpha subunit or inhibin B.

Five patients with advanced ovarian granulosa cell malignancies resistant to cytotoxic chemotherapy were treated with monthly subcutaneous injections of long-acting gonadotropin releasing hormone (GnRH) agonist analog. One partial response and one stabilization of the disease were observed. In three patients, the tumor continued to progress. Treatment response was monitored with serum inhibin assay. Four patients had high serum inhibin concentrations at the beginning of GnRH analog treatment, while one patient had an inhibin-negative tumor. In three of four patients, serum inhibin remained relatively constant, or decreased during the first 3 months of therapy. It subsequently increased, in parallel with clinical deterioration. Further clinical trials with GnRH analogs are warranted in this malignancy in which serum inhibin appeared to be a clinically valuable tumor marker.

Inhibin (and its alpha-subunit) may be of particular value as a marker for follicular development in in-vitro fertilization (IVF) in comparison with the classic follicle stimulating hormone (FSH)-dependent marker oestradiol in patients following pituitary desensitization and treatment with recombinant FSH (rFSH). This preparation lacks luteinizing hormone (LH), which is essential for thecal cell androgen secretion and thus oestradiol production. Our study has assessed oestradiol and immunoreactive inhibin-like secretion following ovarian stimulation with rFSH or a purified urinary FSH preparation (Metrodin) (uFSH). A randomized, assessor-blind study was initiated using patients receiving a single treatment cycle of IVF (using fresh embryos) following pituitary desensitization with intranasal buserelin (500 microg daily) and the i.m. injection of either rFSH (n = 38) or uFSH (n = 17). Ovarian ultrasound examinations were performed and bloods (10 ml) collected prior to FSH treatment and every 1-2 days until ovulation induction with human chorionic gonadotrophin. LH and FSH concentrations were measured by an immunoradiometric assay, and inhibin-like immunoreactivity by a radioimmunoassay and an enzyme-linked immunosorbent assay, both with alpha-subunit specificity. Oestradiol concentration was measured with a coated tube radioimmunoassay. Following desensitization, basal LH, FSH and oestradiol concentrations were measured, as was that of immunoreactive inhibin. Following treatment with either rFSH or uFSH, LH concentrations remained low while FSH concentrations rose to a plateau of 5.6-6.7 IU/l in both groups. In contrast, the concentration of oestradiol was higher (P < 0.05) with rFSH than with uFSH in the last four days of treatment, a pattern that was repeated for inhibin-like immunoreactivity. The change in oestradiol and inhibin concentrations during treatment was approximately 2-fold higher with rFSH. The total number of follicles obtained with rFSH was similar to that with uFSH. However, the number of follicles with a diameter of >/= 15 mm was higher the rFSH group, and there was a concomitant increase in the number of oocytes recovered. Oestradiol concentration and inhibin-like immunoreactivity (determined by either method) were associated with total follicle number and number of follicles >/= 15 mm in diameter, as well as with each other (P < 0.001). When ovarian hormone output was normalized per follicle produced, oestradiol output was higher for rFSH than for uFSH P = 0.04). Inhibin output was clearly higher using rFSH than uFSH. There were seven pregnancies (one miscarriage) with rFSH and two with uFSH. Despite similar concentrations od FSH in patients, rFSH (Puregon) appears to be more potent in vitro in terms of follicular number, ovarian hormone secretion (both concentration and output/follicle) and oocyte recovery. In both groups, LH concentrations of approximately 1.3 IU/l were sufficient to support oestradiol secretion similar to that normally found in IVF programmes using human menopausal gonadotr...