Gonadotropin-releasing hormone (GnRH), a crucial neurohormone synthesized by neurons in the hypothalamus, stands as a key regulator of reproductive function in all mammals. As a releasing hormone, GnRH is responsible for the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary gland. These gonadotropins control gametogenesis and steroidogenesis, underscoring GnRH's pivotal role in sexual development and reproduction.
Key Functions and Regulatory Mechanisms:
- Gonadotropin Release: GnRH stimulates the synthesis and secretion of FSH and LH by activating its receptor, GnRHR, on gonadotrope cells in the anterior pituitary.
- Pulsatile Secretion: GnRH secretion is pulsatile and essential for proper reproductive function. The frequency and amplitude of these pulses dictate the synthesis and secretion of LH and FSH. Low-frequency pulses favor FSH release, while high-frequency pulses stimulate LH release.
- Neurohormonal Control: As a neurohormone, GnRH production is regulated by various afferent neurons and neurotransmitters, including norepinephrine, GABA, glutamate, and kisspeptin. Estrogen also regulates GnRH release.
Research Applications and Clinical Significance:
- Reproductive Disorders: Dysregulation of GnRH activity is implicated in various reproductive disorders, including hypothalamic-pituitary disease and polycystic ovary syndrome (PCOS).
- Fertility Treatment: Understanding GnRH's role in stimulating LH and FSH production is crucial for developing fertility treatments.
- Developmental Biology: GnRH activity is elevated during fetal life and minipuberty, contributing to the development of sexual organs.