A trophicpeptide responsible for the release of follicle stimulating hormone and luteinizing hormone from the anterior pituitary, synthesized and released from the hypothalamus. Regulation of the reproductive system is a process that requires the action of hormones from the pituitary gland, the adrenal cortex, and the gonads. During puberty, in both males and females, the hypothalamus produces gonadotropin-releasing hormone (GnRH).

Gonadotropin Releasing Hormone (GnRH) (Pic. 1) is mainly made in the preoptic area of the hypothalamus from where it travels to the pituitary gland where it stimulates the synthesis and secretion of the gonadotropins, follicle-stimulating hormone, and luteinizing hormone.

Control of FSH (Follicle-stimulating hormone) and LH (Luteinizing hormone):

These hormones regulate the gonads (testes in males and ovaries in females); they are called gonadotropins. In both males and females, FSH stimulates gamete production and LH stimulates production of hormones by the gonads.

These processes are controlled by the size and frequency of GnRH pulses, as well as by feedback from androgens and estrogens. Low-frequency GnRH pulses are required for FSH release, whereas high-frequency GnRH pulses stimulate LH pulses in a one to one manner.

There are differences in GnRH secretion between females and males. In males, GnRH is secreted in pulses at a constant frequency; however, in females, the frequency of the pulses varies during the menstrual cycle, and there is a large surge of GnRH just before ovulation. Adult reference ranges are in males: 4.0 - 8.0 pg/mL and in females: 2.0 - 10.0 pg/mL (Pic. 2).

GnRH activity

GnRH activity is very low during childhood, and is activated at puberty or adolescence. During the reproductive years, pulse activity is critical for successful reproductive function as controlled by feedback loops. However, once a pregnancy is established, GnRH activity is not required. Pulsatile activity can be disrupted by hypothalamic-pituitary disease, either dysfunction (i.e., hypothalamic suppression) or organic lesions (trauma, tumor). Elevated prolactin levels decrease GnRH activity. In contrast, hyperinsulinemia increases pulse activity leading to disorderly LH and FSH activity, as seen in polycystic ovary syndrome (PCOS). GnRH formation is congenitally absent in Kallmann syndrome.

Other organs

GnRH is found in organs outside of the hypothalamus and pituitary, and its role in other life processes is poorly understood. For instance, there is likely to be a role for GnRH in the placenta and in the gonads. GnRH and GnRH receptors are also found in cancers of the breast, ovary, prostate, and endometrium.

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Hormonal regulation of the Male reproductive system ―sourced from Lumen licensed under CC BY 4.0
GNRH1 structure ―by BorisTM licensed under CC0 1.0
Gonadotropin-releasing hormone ―by Petráková, created for licensed under CC BY-SA 4.0
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