BIOASSAYS OF GONADOTROPINS BASED ON CLONED RECEPTORS

Because of the microheterogeneities of gonadotropins, immunoreactive m easurements of gonadotropins do not necessarily reflect their bioactiv ity. Follicle-stimulating hormone (FSH) bioassays have relied on measu rement of aromatase activity in primary cultures of immature rat Serto li cells or rat granulosa cells (GAB assay). Luteinizing hormone (LH) bioassays have relied on measurement of androgen production in primary cultures of rat interstitial testicular cells (RICT) or mouse Leydig cells. Those bioassays are cumbersome because they rely on primary cul ture and on indirect, measurement of estradiol or testosterone by RIAs . The cloning of the cDNAs of FSH and LH receptors has allowed the est ablishment of cell lines expressing human receptors. The cotransfectio n of the recombinant gonadotropin receptor with a cAMP reporter gene a llows a nonisotopic measurement of gonadotropin bioactivity. Furthermo re, patient serum can be tested directly without prior extraction. We and other groups have developed a CHO cell line expressing the human F SH receptor and a luciferase reporter gene (CHO-FSHR). The CHO-FSHR as say is specific for FSH and free of serum interference up to a final c oncentration of 20%. The clinical sensitivity is 3 IU/l, the interCV 1 6%, the intraCV 8%. Studies were performed in normal women (n = 11) du ring the menstrual cycle using the CHO-FSHR cells. The ratio of bioact ive to immunoactive FSH (B/I) equals 1.1 +/- 0.04 across the follicula r and early luteal phase. During the mid to late luteal phase the mean B/I rises significantly to 1.65 +/- 0.07 (P < 0.001). Gonadotropin bi oassays based on cloned receptors have been used to search for immunog lobulins, directed against the FSH or the LH receptors in premature ov arian failure patients. No blocking antibodies were found among the 38 women studied. A recent study of FSH bioactivity in patients with FSH secreting pituitary adenomas shows increased values of the B/I ratio. In summary, cell lines expressing the LH and the FSH human receptors are now available. Those homologous systems enable clinicians to study potential forms of mutated FSH or antibodies directed against gonadot ropin receptors. Furthermore, bioassays based on cloned receptors are interesting tools to test anti-LH or anti-FSH molecules mainly in cont raceptive research. Copyright (C) 1996 Elsevier Science Ireland Ltd.