title: Inhibin-B secretion and FSH isoform distribution may play an integral part of follicular selection in the natural menstrual cycle.
abstract: The aim of the present paper is to expand the concept on how follicular selection takes place in the follicular phase of the natural menstrual cycle. It is suggested that inhibin-B exerts a more intimate role in this process than previously understood. Inhibin-B shows a peak in the circulation around cycle day 7, simultaneous with selection of the dominant follicle, whereas levels of estradiol and inhibin-A only start to increase a few days later suggesting that inhibin-B is mainly responsible for downregulating pituitary FSH release. New data now demonstrate that the circulatory peak of inhibin-B is reflected by peak production of inhibin-B, in contrast to inhibin-A, in the selected follicle with a diameter of 10-12 mm, where concentrations are one thousand times higher than in the circulation. This high inhibin-B concentration also exerts paracrine effects, stimulating theca cell androgen production in concert with LH. New data now suggest that in the corresponding granulosa cells androgens upregulate FSH receptor (FSHR) and LH receptor (LHR) mRNA expression, which in turn stimulate CYP19a mRNA expression providing the follicles which most effectively undertake these processes with the best chance of becoming selected. Inhibin-B production is stimulated by FSH and it appears that the acidic isoforms of FSH induce inhibin-B secretion most efficiently thereby, for the first time, placing the changing FSH isoform profile during the follicular phase in a physiological context. Collectively, it appears that inhibin-B is an integral part of follicular selection in the normal menstrual cycle, exerting both endocrine and paracrine effects and facilitating continued growth of the selected follicle.
authors.affiliation: Laboratory of Reproductive Biology, Section 5712, The Juliane Marie Centre for Women, Children and Reproduction, Copenhagen University Hospital and Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 9, Rigshospitalet, DK-2100 Copenhagen, Denmark yding@rh.dk.
authors.forename: C
authors.initials: C
authors.lastname: Yding Andersen
mesh_terms: D000728:Androgens / Q000096:biosynthesis / Q000378:metabolism; D001141:Aromatase / Q000235:genetics / Q000378:metabolism; D004958:Estradiol / Q000096:biosynthesis / Q000378:metabolism; D005260:Female; D005640:Follicle Stimulating Hormone / Q000235:genetics* / Q000378:metabolism; D005498:Follicular Phase / Q000235:genetics* / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D006107:Granulosa Cells / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D007265:Inhibins / Q000235:genetics* / Q000378:metabolism; D007986:Luteinizing Hormone / Q000235:genetics / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011962:Receptors, FSH / Q000235:genetics / Q000378:metabolism; D011974:Receptors, LH / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D013799:Theca Cells / Q000166:cytology / Q000378:metabolism*
chemical_list: D000728:Androgens; D020033:Protein Isoforms; D011962:Receptors, FSH; D011974:Receptors, LH; C422362:inhibin A; C422364:inhibin B; D004958:Estradiol; D007265:Inhibins; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D001141:Aromatase; C561410:CYP19A1 protein, human
keywords: FSH isoform distribution; androgen synthesis; follicular phase; follicular selection; inhibin-A; inhibin-B; paracrine action