Index
It is produced by the pituitary gland and is one of the main hormones that control the reproductive system.
Luteinizing hormone (LH), like follicle stimulating hormone, is a gonadotrophic hormone produced and released by cells of the anterior pituitary gland .
Function
It is crucial for regulating the function of the testicles in men and the ovaries in women.
In men
In men, luteinizing hormone stimulates the Leydig cells in the testes to produce testosterone, which acts locally to support sperm production.
Testosterone also exerts effects throughout the body to generate masculine characteristics such as increased muscle mass, enlarged larynx to generate a deep voice, and growth of facial and body hair.
In the women
In women, luteinizing hormone plays different roles in the two halves of the menstrual cycle. In week one or two of the cycle, luteinizing hormone is required to stimulate the ovarian follicles in the ovary and produce the female sex hormone, estradiol.
Around day 14 of the cycle, an increase in luteinizing hormone levels causes the ovarian follicle to tear and release a mature oocyte (ovum) from the ovary, a process called ovulation. During the remainder of the cycle (weeks three to four), the remnants of the ovarian follicle form a corpus luteum.
Luteinizing hormone stimulates the corpus luteum to produce progesterone, which is required to support the early stages of pregnancy, if fertilization occurs.
Alternative names for luteinizing hormone
Interstitial Cell Stimulating Hormone; luteinizing hormone; lutropin; LH.
How is luteinizing hormone controlled?
Luteinizing hormone secretion from the anterior pituitary gland is regulated through a system called the hypothalamic-pituitary-gonadal axis.
Gonadotropin-releasing hormone is released from the hypothalamus and binds to receptors in the anterior pituitary gland to stimulate both the synthesis and release of luteinizing hormone (and follicle-stimulating hormone).
The luteinizing hormone released is transported into the bloodstream where it binds to receptors in the testes and ovaries to regulate their hormonal secretions and the production of sperm or eggs.
The release of hormones from the gonads can suppress the secretion of gonadotropin-releasing hormone and, in turn, luteinizing hormone from the anterior pituitary gland.
When gonad hormone levels drop, the reverse occurs and gonadotropin-releasing hormone and therefore luteinizing hormone increase. This is known as negative feedback.
In men, testosterone exerts this negative feedback, and in women estrogen and progesterone exert the same effect, except at the midpoint of the menstrual cycle.
At this point, the ovary’s high estrogen secretions stimulate an increase in luteinizing hormone from the pituitary gland, which triggers ovulation. Fine-tuning the release of luteinizing hormone is vital to maintaining fertility.
Because of this, compounds designed to mimic the actions of gonadotropin-releasing hormone, luteinizing hormone, and follicle-stimulating hormone are used to stimulate gonadal function in assisted conception techniques, such as in vitro fertilization (IVF).
Measurement of the levels of luteinizing hormone present in the urine can be used to predict the timing of the increase in luteinizing hormone in women and thus ovulation.
This is one of the methods used in ovulation prediction kits used by couples who want to conceive.
What if I have too much luteinizing hormone?
Too much luteinizing hormone can be an indication of infertility.
Since luteinizing hormone secretion is tightly controlled by the hypothalamic-pituitary-gonadal axis, elevated levels of luteinizing hormone in the bloodstream may indicate decreased production of sex steroids in the testes or ovaries (for example, in premature ovarian failure).
Polycystic ovary syndrome is a common condition in women associated with high levels of luteinizing hormone and reduced fertility. In this condition, an imbalance between luteinizing hormone and follicle-stimulating hormone can stimulate inadequate testosterone production.
Genetic conditions, such as Klinefelter syndrome and Turner syndrome, can also cause high levels of luteinizing hormone.
Klinefelter syndrome is an exclusively male disorder and is the result of carrying an extra X chromosome (so males 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 an exclusively female disorder caused by a partial or total deletion of an X chromosome (so women have XO, instead of XX).
In affected patients, ovarian function is impaired and therefore luteinizing hormone production increases to try to stimulate ovarian function.
What if I have too little luteinizing hormone?
Too little luteinizing hormone will also cause infertility in men and women, as a critical level of luteinizing hormone is required to support testicular or ovarian function.
In men, an example of a condition with low levels of luteinizing hormone is Kallmann syndrome, which is associated with a deficiency in gonadotropin-releasing hormone secretion from the hypothalamus.
In women, a lack of luteinizing hormone means that ovulation does not occur and menstrual periods may not occur regularly. An example of a condition that can be caused by too little luteinizing hormone is amenorrhea .
