Question

Identify the correct statement on ‘inhibin’
A. Inhibits the secretion of LH,FSH and prolactin.
B. Is produced by granulosa cells in the ovary and inhibits the secretion of FSH.
C. Is produced by granulosa cells in the ovary and inhibits the secretion of LH.
D. Is produced by nurse cells in testes and inhibits the secretion of LH.

Answer 1

It is a 32-kD dimeric glycoprotein hormone involved in pituitary-gonadal feedback system regulation. An alpha-subunit connected to one of two
β-subunits is inhibin secreted in the ovary.

Complete Answer:
- Activin and inhibin are two closely related protein complexes whose biological effects are almost exactly opposite. Activin, discovered in 1986, increases the biosynthesis and secretion of FSH and participates in controlling the menstrual cycle.
- Activin plays many other functions, including roles in cell proliferation , differentiation, apoptosis, metabolism, homeostasis, immune response, repair of wounds, and endocrine function. Inhibin, by comparison, downregulates FSH synthesis and prevents the secretion of FSH.
- As early as 1916, the existence of inhibin was assumed; however, it was not shown to exist until the work of Neena Schwartz and Cornelia Channing in the mid-1970s, after which both proteins were molecularly characterised 10 years later.
- Activin is a dimer formed by two beta subunits which are identical or very similar. Inhibin is also a dimer in which a beta subunit similar or equivalent to the beta subunit in activin is the first part.
- However, unlike activin, a more distantly-related alpha subunit is the second portion of the inhibin dimer. The TGF-β protein superfamily contains activin, inhibin and many other structurally-related proteins such as anti-Müllerian hormone, bone morphogenetic protein and growth differentiation factor.

So the answer is option B.

Note: In females, the gonads, the pituitary gland, the placenta, the corpus luteum and other organs produce inhibin. FSH facilitates inhibin secretion from the granulosa cells of the ovarian follicles in the ovaries. The inhibin, in fact, suppresses FSH. At the early-to mid-follicular period, inhibin B hits a peak and a second peak at ovulation. In the mid-luteal phase, Inhibin A reaches its peak. GnRH reduces inhibin secretion, and insulin-like growth factor-1 (IGF-1) increases it. It is secreted in males from the Sertoli cells found within the testes in the seminiferous tubules. Inhibin production is stimulated by androgens; this protein may also help to regulate spermatogenesis locally.