Luteinising hormone

Luteinising hormone is produced by the pituitary gland and is one of the main hormones that control the reproductive system.

Alternative names for luteinising hormone

Interstitial cell stimulating hormone; luteinizing hormone; lutropin; LH

What is luteinising hormone?

Luteinising hormone, like follicle stimulating hormone, is a gonadotrophic hormone produced and released by cells in the anterior pituitary gland. It is crucial in regulating the function of the testes in men and ovaries in women.

In men, luteinising hormone stimulates Leydig cells in the testes to produce testosterone, which acts locally to support sperm production. Testosterone also exerts effects all around the body to generate male characteristics such as increased muscle mass, enlargement of the larynx to generate a deep voice, and the growth of facial and body hair.

In women, luteinising hormone carries out different roles in the two halves of the menstrual cycle. In weeks one to two of the cycle, luteinising hormone is required to stimulate the ovarian follicles in the ovary to produce the female sex hormone, oestradiol. Around day 14 of the cycle, a surge in luteinising hormone levels causes the ovarian follicle to rupture and release a mature oocyte (egg) from the ovary, a process called ovulation. For the remainder of the cycle (weeks three to four), the remnants of the ovarian follicle form a corpus luteum. Luteinising hormone stimulates the corpus luteum to produce progesterone, which is required to support the early stages of pregnancy, if fertilisation occurs.

How is luteinising hormone controlled?

The secretion of luteinising hormone from the anterior pituitary gland is regulated through a system called the hypothalamic-pituitary-gonadal axis. Within the hypothalamus, kisspeptin stimulates the release of Gonadotrophin-releasing hormone, which binds to receptors in the anterior pituitary gland. This stimulates both the synthesis and release of luteinising hormone (and follicle stimulating hormone). The released luteinising hormone is carried in the bloodstream where it binds to receptors in the testes and ovaries to regulate their hormone secretions and the production of sperm or eggs, respectively.

The release of hormones from the gonads can suppress the secretion of kisspeptin and gonadotrophin-releasing hormone, resulting in reduced secretion of luteinising hormone from the anterior pituitary gland. When levels of hormones from the gonads fall, the reverse happens, and kisspeptin, gonadotrophin-releasing hormone and hence luteinising hormone levels rise. This is known as negative feedback.

In men, testosterone exerts this negative feedback and in women oestrogen and progesterone exert the same effect except at the midpoint in the menstrual cycle. At this point, high oestrogen secretions from the ovary stimulate a surge of luteinising hormone from the pituitary gland, which triggers ovulation.

The fine tuning of luteinising hormone release is vital to maintaining fertility. Because of this, compounds designed to mimic the actions of gonadotrophin-releasing hormone, luteinising hormone and follicle stimulating hormone are used to stimulate gonadal function in assisted conception techniques such as in vitro fertilisation (IVF). Measuring the levels of luteinising hormone present in urine can be used to predict the timing of the luteinising hormone surge in women, and hence ovulation. This is one of the methods employed in ovulation prediction kits used by couples wishing to conceive.

What happens if I have too much luteinising hormone?

Too much luteinising hormone can be an indication of infertility. Since the secretion of luteinising hormone is tightly controlled by the hypothalamic-pituitary-gonadal axis, high levels of luteinising hormone in the bloodstream can indicate decreased sex steroid production from the testes or ovaries (for example, as in premature ovarian failure).

Polycystic ovary syndrome is a common condition in women associated with high levels of luteinising hormone and reduced fertility. In this condition, an imbalance between luteinising hormone and follicle stimulating hormone can stimulate inappropriate production of testosterone.

Genetic conditions, such as Klinefelter’s syndrome and Turner syndrome, can also result in high luteinising hormone levels. Klinefelter’s syndrome is a male-only disorder and results from carrying an extra X chromosome (so that men have XXY, rather than XY chromosomes). As a result of this, the testes are small and do not secrete adequate levels of testosterone to support sperm production. Turner syndrome is a female-only disorder caused by a partial or full deletion of an X chromosome (so that women have XO, rather than XX). In affected patients, ovarian function is impaired and therefore luteinising hormone production increases to try to stimulate ovarian function.

What happens if I have too little luteinising hormone?

Too little luteinising hormone will also result in infertility in both men and women, as a critical level of luteinising hormone is required to support testicular or ovarian function.

In men, an example of a condition where low levels of luteinising hormone are found is Kallmann’s syndrome, which is associated with a deficiency in gonadotrophin-releasing hormone secretion from the hypothalamus.

In women, a lack of luteinising hormone means that ovulation does not occur and menstrual periods may not occur regularly. An example of a condition which can be caused by too little luteinising hormone is hypothalamic amenorrhoea.