Gonadotrophin-releasing hormone

Gonadotrophin-releasing hormone is released from the hypothalamus in the brain. It controls the production of luteinising hormone and follicle stimulating hormone from the pituitary gland.

Alternative names for gonadotrophin-releasing hormone

GnRH; gonadotropin-releasing hormone; luliberin; luteinising-hormone-releasing hormone; LHRH; luteinizing-hormone-releasing hormone

What is gonadotrophin-releasing hormone?

Gonadotrophin-releasing hormone is produced and secreted by specialised nerve cells in the hypothalamus of the brain. It is released into tiny blood vessels that carry this hormone from the brain to the pituitary gland, where it stimulates the production of two more hormones – follicle stimulating hormone and luteinising hormone. These hormones are released into the general circulation and act on the testes and ovaries to initiate and maintain their reproductive functions. Follicle stimulating hormone and luteinising hormone control the levels of hormones produced by the testes and ovaries (such as testosterone, oestradiol and progesterone), and are important in controlling the production of sperm in men and the maturation and release of an egg during each menstrual cycle in women.

How is gonadotrophin-releasing hormone controlled?

During childhood, the levels of gonadotrophin-releasing hormone are extremely low, but as puberty approaches there is an increase in gonadotrophin-releasing hormone, which triggers the onset of sexual maturation.

When the ovaries and testes are fully functional, the production of gonadotrophin-releasing hormone, luteinising hormone and follicle stimulating hormone are controlled by the levels of testosterone (in men) and oestrogen (e.g. oestradiol) and progesterone (in women). If the levels of these hormones rise, the production of gonadotrophin-releasing hormone decreases and vice versa.

There is one exception to this rule; in women, at the midpoint of their menstrual cycle, oestradiol (produced by the follicle in the ovary that contains the dominant egg) reaches a critical high point. This stimulates a large increase in gonadotrophin-releasing hormone secretion and, consequently, a surge of luteinising hormone, which stimulates the release of a mature egg. This process is called ovulation.

In women, at the end of a menstrual cycle, the circulating level of progesterone drops and the production of gonadotrophin-releasing hormone increases gradually again.

What happens if I have too much gonadotrophin-releasing hormone?

It is not known what the effects are of having too much gonadotrophin-releasing hormone. Extremely rarely, pituitary adenomas (tumours) can develop, which increase production of gonadotrophins (Luteinising hormone and follicle stimulating hormone) leading to overproduction of testosterone or oestrogen.

What happens if I have too little gonadotrophin-releasing hormone?

A deficiency of gonadotrophin-releasing hormone in childhood could lead to a delay or absence of puberty of an individual. An example is a rare genetic syndrome known as Kallmann’s syndrome, which is caused by loss of the development of gonadotrophin-releasing hormone-producing nerve cells, with a consequent loss of pubertal development and sexual maturation. It is more common in men than women and leads to loss of development of the testes or ovaries and infertility. Some patients of Kallmann’s syndrome may also develop loss of sense of smell.

Any trauma or damage to the hypothalamus can also cause a loss of gonadotrophin-releasing hormone secretion, which will stop the normal production of follicle stimulating hormone and luteinising hormone, causing loss of menstrual cycles (amenorrhoea) in women, loss of sperm production in men, and loss of production of hormones from the testes and ovaries.

For diagnosis, blood tests are first taken to determine the circulating level of gonadotrophin-releasing hormone in the patients. Blood tests may be followed by magnetic resonance imaging/ultrasound scan of internal organs and a bone density scan. Once the diagnosis is established, patients are treated with sex hormone replacement therapy.