title: Dimeric inhibin A and B production are differentially regulated by hormones and local factors in rat granulosa cells.
abstract: In the present study, we have examined the role of hormones and growth factors in regulating dimeric inhibin production in immature rat granulosa cells. Purified granulosa cells from estrogen-primed immature rats were cultured under defined conditions. Inhibins A and B in the culture media were measured using a two-site enzyme-linked immunosorbent assay specific for each dimer. Under basal conditions, granulosa cells produced 14-fold more inhibin A than inhibin B (inhibin A, 2.0; inhibin B, 0.14 ng/ml, measured against human standards; average A/B apparent ratio, 14). Addition of increasing doses of FSH elicited dose-dependent increases in both inhibins, the effects being more pronounced on inhibin A than on inhibin B (9.4- and 4.1-fold increases, respectively; average A/B ratio, 34). Estradiol, when added alone, stimulated inhibin A production 3- to 6-fold, whereas minor changes were observed in inhibin B production. Insulin-like growth factor-I produced a similar stimulation of both inhibins (3-fold stimulation over control). This growth factor, however, induced a marked dissociation in the sensitivity of inhibins A and B to FSH stimulation, with maximal stimulation of inhibin B observed at comparatively lower concentrations of the gonadotropin. Transforming growth factor-beta (TGF-beta, 5 ng/ml) had a more marked stimulatory effect on inhibin B than on inhibin A production (7- to 14-fold vs. 2- to 5-fold for inhibin B and A, respectively). A more pronounced differential stimulation of inhibin B was also exerted by another member of the TGF-beta superfamily, activin A (A/B ratio, 0.66). This preferential stimulation of inhibin B by TGF-beta and activin A was amplified in the presence of FSH. Coculture of rat granulosa cells with freshly isolated bovine oocytes was also associated with a marked stimulation of inhibin B production (100-fold increase) and a comparatively lower stimulation of inhibin A (10-fold increase; A/B ratio, 1). The discrepancy between the proportion of inhibin dimers in serum (A/B ratio, 0.13) and those produced by untreated granulosa cells may suggest that intraovarian factors, such as TGF-beta, activin A, or oocyte-derived factor(s), are responsible for the shift of the ratio toward the predominance of inhibin B.
authors.affiliation: Instituto de Biología Experimental, CONICET and Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina.
authors.forename: G M
authors.initials: GM
authors.lastname: Lanuza
authors.forename: N P
authors.initials: NP
authors.lastname: Groome
authors.forename: J L
authors.initials: JL
authors.lastname: Barañao
authors.forename: S
authors.initials: S
authors.lastname: Campo
mesh_terms: D000818:Animals; D002417:Cattle; D018920:Coculture Techniques; D019281:Dimerization; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology; D006107:Granulosa Cells / Q000378:metabolism*; D006801:Humans; D007265:Inhibins / Q000096:biosynthesis* / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D009865:Oocytes / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D016212:Transforming Growth Factor beta / Q000494:pharmacology
chemical_list: D016212:Transforming Growth Factor beta; D004958:Estradiol; D007265:Inhibins; D007334:Insulin-Like Growth Factor I; D005640:Follicle Stimulating Hormone