- Follicle-stimulating hormone (FSH) is a key glycoprotein hormone secreted by the anterior pituitary gland and is essential for the normal function of the reproductive systems in both males and females.
- Along with luteinizing hormone (LH), FSH is classified as a gonadotropin—a group of hormones that regulate the activity of the gonads (ovaries and testes). Its secretion is controlled by gonadotropin-releasing hormone (GnRH) from the hypothalamus, and its activity is a central part of the hypothalamic-pituitary-gonadal (HPG) axis.
- In females, FSH is instrumental in regulating the menstrual cycle and ovarian follicle development. During the follicular phase of the menstrual cycle, FSH stimulates the growth and maturation of ovarian follicles—small sacs within the ovary that contain developing eggs. It acts primarily on the granulosa cells of the follicles, promoting cell proliferation and the production of estradiol, a potent form of estrogen. Rising levels of estrogen help prepare the endometrium for potential implantation and, through feedback mechanisms, regulate the secretion of both FSH and LH. As one follicle becomes dominant, FSH levels begin to decline, and the LH surge triggered by elevated estrogen levels ultimately leads to ovulation.
- In males, FSH plays a critical role in spermatogenesis, the production of sperm. It acts on the Sertoli cells of the seminiferous tubules in the testes, stimulating them to support the development and maturation of sperm cells. FSH also promotes the production of androgen-binding protein (ABP), which helps maintain high concentrations of testosterone in the testes, a requirement for efficient sperm production. FSH and LH work synergistically in males, with LH stimulating Leydig cells to produce testosterone, which in turn enhances the action of FSH on the Sertoli cells.
- FSH secretion is regulated through complex feedback loops involving the sex hormones estrogen, testosterone, and inhibin. In females, inhibin B, secreted by granulosa cells of developing follicles, provides negative feedback to the pituitary to suppress FSH release. In males, inhibin B, secreted by Sertoli cells, performs a similar function. These feedback mechanisms ensure the appropriate timing and levels of FSH necessary for reproductive health.
- Clinically, FSH levels are measured to assess fertility, gonadal function, and pituitary health. Elevated FSH levels in women may indicate primary ovarian insufficiency or menopause, whereas low levels can be associated with hypothalamic or pituitary dysfunction. In men, high FSH may reflect testicular failure, while low levels can be seen in hypogonadotropic hypogonadism. FSH testing is also used in the evaluation of delayed puberty, amenorrhea, and infertility in both sexes.
- In reproductive medicine, exogenous FSH is commonly used in assisted reproductive technologies (ART) such as in vitro fertilization (IVF) to stimulate controlled ovarian hyperstimulation, enabling the development of multiple follicles for egg retrieval. Recombinant FSH preparations have replaced earlier urine-derived products, offering greater purity and consistency.
