Ovarian Endocrine Activity: Role of Follistatin, Activin and Inhibin

CAMPO, STELLA; LORETI, NAZARETH; ANDREONE, LUZ

Reproductive Endocrinology: a Molecular Approach

Springer Science and Business Media

Lugar: Norwell, MA, USA; Año: 2009; p. 249 - 256

Inhibin, activin and follistatin are proteins involved in the control of Follicle-Stimulating Hormone (FSH) secretion. The development of specific and sensitive assays for the different molecular forms of these peptides permitted the elucidation of their sources, the hormonal regulation of their production and the possible clinical application of their serum levels in the assessment of gonadal function at different stages of development. Activins and follistatins exert their action as paracrine or autocrine growth factors through local production at many sites. Inhibin A, B and the inhibin á-subunit are produced by the ovarian follicle, released into the circulation and exert their action on the pituitary FSH secretion. FSH and several local factors regulate inhibin production by granulosa cells. A predominant production of inhibin B is sustained by TGF-â, activin A and oocyte derived factors in a low oestrogenic follicular tone. FSH and estradiol stimulate both dimeric inhibins production, but this effect is more pronounced on inhibin A. Inhibin A and B are absent in serum in girls at birth but their levels increase concomitantly during the two weeks of life. This unique profile characterizes the posnatal period in girls and reflects the presence of granulosa cells in an advanced stage of maturation and differentiation. Inhibin B is the only dimeric form of inhibin produced in the ovary during infancy and childhood and its levels increases concomitantly with those of FSH during pubertal development. Inhibin A is detectable again in circulation before the clinical onset of puberty. Once the ovarian cyclic activity is established, changes in serum inhibin profile may be a reflection of the change in the concentration of intrafollicular regulators and FSH stimulation. Inhibin B is the only dimer present in the follicular phase and reflects the presence of follicles at early stages of development. Inhibin A appears in circulation in the pre-ovulatory period and reaches its maximal levels in the luteal phase reflecting the endocrine activity of pre-ovulatory follicles and the corpus luteum. At present, dimeric inhibins are considered reliable markers to assess ovarian endocrine activity from birth to adulthood. Inhibin B is a widely used parameter to evaluate ovarian reserve concomitantly with FSH and AntiMullerian Hormone (AMH) in infertile women.