Inibinas

Inibinas, or inhibins, are dimeric glycoproteins that belong to the transforming growth factor-beta (TGF-β) superfamily. They function to regulate the secretion of follicle-stimulating hormone (FSH) from the anterior pituitary. The molecules consist of an alpha subunit (INHA) paired with a beta subunit: inhibin A (alpha + beta A; INHBA) and inhibin B (alpha + beta B; INHBB).

Inibinas are primarily produced by gonadal tissues. In females, granulosa cells generate inhibins, with inhibin A predominating in the mid to late follicular phase and during pregnancy, while inhibin B is more prominent in the early to mid-follicular phase. In males, Sertoli cells secrete inhibin B as a marker of Sertoli cell function and spermatogenesis. The placenta also contributes inhibin A during pregnancy.

Functionally, inhibins counteract activins to suppress FSH production, helping regulate the hypothalamic–pituitary–gonadal axis. They act through specific receptors in the pituitary and influence the transcription and secretion of FSH. The different beta subunits give rise to distinct circulating forms with complementary patterns across the reproductive cycle and life stages.

Clinically, inhibin measurements are used to assess gonadal function and ovarian reserve. Low inhibin B correlates with diminished ovarian reserve, while altered levels of inhibin A or B can aid in diagnosing gonadal tumors such as granulosa cell tumors or monitoring pregnancy (inhibin A as part of prenatal screening in certain contexts). Inibinas are thus important biomarkers in reproductive physiology and clinical endocrinology.