Synthesis and Function of Protein Hormones in Ovary
المؤلف:
Marcello Ciaccio
المصدر:
Clinical and Laboratory Medicine Textbook 2021
الجزء والصفحة:
p370-371
2025-10-13
78
In addition to steroid hormones, the ovary synthesizes pep tides with regulatory action on ovarian function. Inhibins A and B, Anti-Müllerian Hormone (AMH), and activins belong to this class.
Inhibins were first isolated in the late 1980s from the follicular fluid as peptides capable of inhibiting pituitary FSH secretion. Two isoforms were identified, inhibin A and B, belonging to the TGF-β superfamily. Inhibins regulate ovarian function locally, through paracrine mechanisms, or by inhibiting pituitary FSH release. Inhibins act as antagonists of activins, constituting a structural homolog. The active form of the inhibins is a heterodimer consisting of an exclusive α subunit and a β subunit, shared with the activins, of which there are two isoforms, A and B. The combination of these subunits gives rise to inhibin A (α/βA) and inhibin B (α/βB). Given the structural homology with activins, inhibins bind to the pituitary receptor and, through the betaglycans, considere co-receptors, on the cell surface, inhibit the access of activins to the receptor, blocking the intracellular signal transduction pathway.
Inhibin B is mainly produced by the granulosa cells of mature follicles, while inhibin A is expressed by granulosa and theca cells. Circulating levels of the two molecules vary physiologically as a function of the ovarian cycle: inhibin B increases in response to FSH, increasing in the follicular and ovulatory phases, while inhibin A peaks in the lutein phase. Activins act oppositely to inhibins by stimulating the pituitary release of FSH and inducing the action of FSH- dependent aromatase.
AMH is a glycoprotein also belonging to the TGF-β superfamily. Its function has long been known in relation to its ability to direct sexual differentiation during the early stages of embryonic development. AMH is synthesized primarily by antral follicles. It has been proposed that AMH acts by inhibiting follicle sensitivity to FSH and may play a role in the process of dominant follicle selection. In the early stages of follicle development, AMH synthesis is high, inhibiting the recruitment of non-dominant follicles by paracrine mechanisms. As soon as the antral follicle increases in size, AMH synthesis rapidly decreases, making the follicle susceptible to the action of FSH and ensuring its subsequent development.
Given their biological actions, Inhibin B and AMH have now been considered
الاكثر قراءة في الغدة التناسلية
اخر الاخبار
اخبار العتبة العباسية المقدسة
