Inhibin BEdit
Inhibin B is a hormone of the inhibin/activin family within the transforming growth factor beta (TGF-β) superfamily. It functions as a negative regulator of follicle-stimulating hormone (FSH) secretion and thus helps coordinate gametogenesis with overall endocrine control. Inhibin B is a heterodimer composed of a common alpha subunit (INHA) paired with a beta B subunit (INHBB), produced in a tissue-specific manner by cells in the gonads. In women, the principal source is the granulosa cells of small growing follicles, while in men it is the Sertoli cells of the testis. Alongside activin and follistatin, Inhibin B participates in a finely tuned network that governs the hypothalamic-pituitary-gonadal axis. granulosa cells Sertoli cells INHA INHBB FSH Transforming growth factor beta activin follistatin hypothalamic-pituitary-gonadal axis
Inhibin B's role as a biomarker and its clinical relevance differ between females and males, reflecting distinct patterns of gonadal development and aging. In females, Inhibin B levels track the数 number of small, growing follicles and thus provide information about ovarian reserve. Levels rise with puberty, reach a peak in early adulthood, and then decline with advancing age, becoming markedly low as menopause approaches. In males, Inhibin B reflects Sertoli cell activity and spermatogenesis, correlating with sperm production and overall testicular function. Clinically, Inhibin B is used, often in combination with other markers, to evaluate fertility, assess ovarian aging, and monitor gonadal health over time. ovarian reserve antral follicle count anti-Müllerian hormone AMH menopause spermatogenesis male infertility hypogonadism Sertoli cell granulosa cell
Biological role and regulation
Inhibin B is part of a hormone system that includes activin, inhibin, and follistatin. The alpha and beta subunits assemble to form the active inhibin B dimer, which is then secreted by its gonadal source into the bloodstream. Inhibin B primarily feeds back to the anterior pituitary to suppress FSH synthesis and release, thereby modulating follicle maturation and spermatogenesis in a gender- and life-stage–dependent manner. The balance between inhibin and activin signaling—shaped by follistatin's neutralizing action on activin—helps stabilize gonadotropin output and reproductive function. activin follistatin FSH anterior pituitary granulosa cell Sertoli cell ##
Regulation and clinical measurement
FSH stimulates the production of Inhibin B in target gonadal cells, while rising levels of Inhibin B feedback to dampen further FSH secretion. This feedback loop is most evident in the regulation of folliculogenesis in females and the maintenance of spermatogenesis in males. In practice, Inhibin B concentrations are influenced by age, sex, reproductive phase, and various physiological or environmental factors (for example, pregnancy, smoking, body composition, and certain medications). Clinically, Inhibin B is measured using immunoassay methods, including enzyme-linked immunosorbent assays (ELISA) and other immunoassay platforms; there is ongoing standardization work due to assay variability and differences among laboratories. Correct interpretation often requires context from other markers such as anti-Müllerian hormone (AMH), antral follicle count (AFC), and clinical history. immunoassay ELISA radioimmunoassay AMH antral follicle count ovarian reserve granulosa cell granulosa cell Sertoli cell
Clinical significance and controversies
In women, Inhibin B serves as a surrogate marker of ovarian reserve, offering information about the pool of recruitable follicles. It complements other indicators like AMH and AFC, especially when evaluating fertility potential, diagnosing diminished ovarian reserve, or guiding decisions around assisted reproduction. However, debate persists about the standalone predictive value of Inhibin B for IVF outcomes and pregnancy success; some guidelines favor AMH and AFC as more robust or easier-to-standardize measures, and the utility of Inhibin B may be best realized when interpreted alongside a panel of markers rather than in isolation. The issue of assay standardization complicates cross-study comparisons and clinical decision-making, reinforcing calls for harmonized reference ranges and assay-specific interpretation. in vitro fertilization IVF ovarian reserve AMH antral follicle count clinical guidelines
From a policy and public-discussion standpoint, there are broader debates about how fertility testing should be utilized in healthcare systems and private practice. Proponents argue that biomarker panels, including Inhibin B, empower patients with information to plan families and pursue appropriate treatment options efficiently. Critics sometimes frame broad biomarker screening as an overreach or as reinforcing social or political agendas around reproduction; however, the core scientific claim—that Inhibin B reflects specific aspects of gonadal function—remains grounded in reproducible biology. Supporters emphasize the importance of evidence-based medicine and patient-centered care, while acknowledging the limits of any single biomarker and the need for careful interpretation in the context of each patient. The discussion is typically framed around practical outcomes, cost-effectiveness, and the responsible deployment of diagnostic tools rather than ideological debates. health policy cost-effectiveness clinical practice guideline hypogonadism male infertility granulosa cell Sertoli cell