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Gonadotropin-releasing hormone, a neurohormone also knownas luteinizing hormone-releasing hormone, is a peptide consisting of 10 amino acids and is produced in the arcuate nuclei of the hypothalamus. This hormone stimulates the synthesis and secretion of the two pituitary gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), by the anterior pituitary gland.
The effects of gonadotropin-releasing hormone on the secretion of luteinizing hormone and follicle-stimulating hormone are not exactly parallel, and the variations are probably due to other modulating factors such as the serum concentrations of sex steroids.
Characteristic of all releasing hormones and most striking in the case of gonadotropin-releasing hormone is the phenomenon of pulsatile secretion. Normally, gonadotropin-releasing hormone is released in pulses at intervals of about 90 to 120 minutes. In order to increase serum gonadotropin concentrations in patients with gonadotropin-releasing hormone deficiency, gonadotropin-releasing hormone must be administered in pulses.
In contrast, constant administration of gonadotropin-releasing hormone suppresses gonadotropin secretion, which has therapeutic benefits in certain patients, such as children with precocious puberty and men with prostate cancer.
The neurons that secrete gonadotropin-releasing hormone have connections to an area of the brain known as the limbic system, which is heavily involved in the control of emotions and sexual activity. In rats that are deprived of their pituitary gland and ovaries but are given physiological amounts of estrogen, injection of gonadotropin-releasing hormone results in changes in posture characteristic of the receptive female stance for sexual intercourse.
Hypogonadism, in which the functional activity of the gonads is decreased and sexual development is inhibited, can be caused by a congenital deficiency of gonadotropin-releasing hormone. Patients with this type of hypogonadism typically respond to pulsatile treatment with gonadotropin-releasing hormone.
Many of these patients also have deficiencies of other hypothalamic-releasing hormones. A subset of patients with hypogonadism have isolated gonadotropin-releasing hormone deficiency and loss of the sense of smell (anosmia).
This disorder is calledKallmann syndromeand is usually caused by a mutation in a gene that directs the formation of the olfactory (sense of smell) system and the formation of parts of the hypothalamus. Abnormalities in the pulsatile secretion of gonadotropin-releasing hormone result insubnormal fertility and abnormal or absent menstruation.
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