activin
noun
ac·ti·vin
| \ ˈak-ti-ˌvin, ak-ˈti-vən
\
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Medical Definition of activin
: a glycoprotein hormone produced especially in the pituitary gland and gonads that stimulates the secretion of follicle-stimulating hormone, induces the formation of mesoderm during embryological development, and modulates the proliferation and differentiation of red-blood-cell precursors during hematopoiesis — compare inhibin