Definition - What does Activin mean?

Activin is a hormone critical to both male and female reproductive systems and is produced in the gonads, pituitary gland, placenta, and other organs. As the name implies, activin predominantly stimulates (or activates) the formation and secretion of follicle-stimulating hormone (FSH) from the pituitary gland. In addition, activin plays a significant role in the menstrual cycle. Activin can also indirectly trigger the release of another hormone, known as gonadotropin-releasing hormone (GnRH) that subsequently stimulates the release of FSH.

Given its pronounced effects in both the male and female reproductive systems, loss of activin or an interference in activin activity can lead to infertility; for instance by stopping the development of ovarian follicle in females.

FertilitySmarts explains Activin

In women, the activin-induced release of FSH stimulates the growth of immature ovarian follicles in the early phase of menstrual cycle. A closely related protein called inhibin works in close proximity but in opposition to activin via inhibiting FSH secretion. FSH levels then plummet so that only the most matured follicle will proceed to ovulation.

Activin-induced FSH also stimulates the formation of luteinizing hormone (LH), which is also released by the pituitary. In females, an acute rise of LH prompts ovulation and the development of the corpus luteum. This structure becomes a center for the formation of progesterone to support implantation. In males, LH accelerates the production of testosterone. Hence, activin also augments the development of sperm in males both directly and indirectly.

Other effects of activin-induced FSH include conversion of androgens into estrogens in the ovaries.

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