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Gonadotropins are a group of glycoprotein hormones secreted primarily by the anterior pituitary gland and, in some cases, by other tissues such as the placenta. They play a vital role in regulating the functions of the gonads, which include the testes in males and the ovaries in females. These hormones act by stimulating the growth, development, and functional activity of reproductive organs and by controlling the production of gametes (sperm in males and ova in females) and reproductive hormones such as testosterone, estrogen, and progesterone.

The term “gonadotropin” generally refers to two main pituitary hormones—luteinizing hormone (LH) and follicle-stimulating hormone (FSH)—and, in pregnancy, to the placental hormone human chorionic gonadotropin (hCG). All these hormones share a similar structural nature as glycoproteins, consisting of two subunits: alpha and beta. The alpha subunit is common among them, whereas the beta subunit is unique for each hormone and determines its specific biological function.

The secretion of gonadotropins is under the control of gonadotropin-releasing hormone (GnRH) from the hypothalamus, which stimulates the anterior pituitary to release LH and FSH in a pulsatile manner. Their release is further regulated by feedback mechanisms involving sex steroids (estrogen, progesterone, testosterone) and inhibin.

Gonadotropins are essential not only for the initiation and regulation of puberty and fertility but also for maintaining normal reproductive health throughout life. In clinical medicine, both natural and synthetic forms of gonadotropins are widely used for the treatment of infertility, hormonal imbalances, and certain reproductive disorders in both men and women.

Functions of Gonadotropins

Gonadotropins are hormones secreted by the anterior pituitary gland, mainly luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These hormones are critical in controlling the reproductive system in both males and females. Their functions are centered around regulating the development and function of the gonads—ovaries in females and testes in males.

In females, FSH stimulates the growth and maturation of ovarian follicles. It acts on the granulosa cells of the follicles, promoting the production of estrogen, which is essential for the development of female secondary sexual characteristics and preparation of the uterus for pregnancy. LH triggers ovulation, the process by which a mature egg is released from the ovary. After ovulation, LH supports the formation and maintenance of the corpus luteum, which produces progesterone necessary to sustain the early stages of pregnancy. Together, FSH and LH regulate the menstrual cycle by controlling estrogen and progesterone levels.

In males, FSH acts on the Sertoli cells within the seminiferous tubules of the testes to stimulate spermatogenesis, the production and maturation of sperm cells. LH targets the Leydig cells of the testes, stimulating them to produce testosterone. Testosterone is essential for the development of male secondary sexual characteristics such as facial hair, deepening of the voice, and muscle growth, as well as for maintaining libido and normal sperm production.

Regulation of Gonadotropins

The regulation of gonadotropins—Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH)—is a complex process controlled primarily by the hypothalamus, the pituitary gland, and feedback from the gonads (ovaries and testes). This regulatory system ensures proper reproductive function by maintaining hormonal balance and coordinating the production of sex hormones and gametes.

The process begins in the hypothalamus, which secretes Gonadotropin-Releasing Hormone (GnRH) in a pulsatile manner. GnRH travels through the blood vessels to the anterior pituitary gland, where it stimulates the release of LH and FSH. The frequency and amplitude of GnRH pulses are crucial because they determine the relative amounts of LH and FSH secreted.

Once released, LH and FSH act on the gonads. In females, FSH promotes follicle development and estrogen production, while LH triggers ovulation and corpus luteum formation, leading to progesterone secretion. In males, LH stimulates testosterone production from Leydig cells, and FSH supports spermatogenesis via Sertoli cells.

The levels of sex steroids produced by the gonads—estrogen, progesterone, and testosterone—exert feedback control on the hypothalamus and pituitary gland. This feedback can be either negative or positive. Negative feedback occurs when rising levels of sex steroids inhibit GnRH, LH, and FSH secretion to prevent overstimulation. For example, high testosterone in males reduces GnRH and gonadotropin release to maintain hormone balance.

In females, the feedback regulation is more dynamic and varies during the menstrual cycle. During most of the cycle, estrogen exerts negative feedback. However, just before ovulation, a sustained high level of estrogen switches to positive feedback, causing a surge in GnRH and LH secretion. This LH surge induces ovulation. After ovulation, progesterone produced by the corpus luteum again applies negative feedback to regulate gonadotropin secretion.

Other factors such as inhibin, a hormone produced by the gonads, also play a role in regulating FSH. Inhibin selectively inhibits FSH secretion without significantly affecting LH. Additionally, various internal and external influences such as stress, nutrition, and health status can impact the regulation of gonadotropins.