Understanding the function of luteinizing hormone (LH) and its role in reproduction will explain why an LH test is sometimes performed in cases of infertility. LH is gonadotropin. Gonadotropins are hormones that stimulate the reproductive process. LH is also known as lutropin. Production of LH begins in the anterior region of the pituitary gland. It is necessary for the proper functioning of the reproductive system of both males and females.
Female LH Function
In females, mature ovarian follicles send a signal to the hypothalamus, indicating that there are higher levels of estradiol in the follicles. An elevated level of LH is then released from the pituitary gland, in what is known as a preovulatory surge. This surge will continue for 24 to 48 hours.
The follicles receive the LH and begin to form corpora lutea, which secrete progesterone and prepare the endometrium for possible pregnancy. The LH sent out in the preovulatory surge continues to function for approximately two weeks.
In females, the LH levels fluctuate throughout the reproductive cycle; however, some medical conditions are associated with persistently high or low levels of LH. It should be noted that LH levels tend to remain elevated in post-menopausal women. Several conditions can affect LH levels.
High levels of LH in women of reproductive age may be an indicator of premature menopause.
Polycystic Ovarian Syndrome (PCOS)
LH levels may be higher in some women who suffer from PCOS.
Kallmann syndrome is a malfunction of the hypothalamic system, which inhibits the production of LH. It can be congenital or acquired. It is characterized by the inability to smell (asnomia.)
Eating Disorders and Hypothalamic Suppression
Women suffering from anorexia nervosa or bulimia are susceptible to low LH levels. Severe weight loss and long-term strenuous exercise places stress on the reproductive system. This stress results in the suppression of GnRH, which in turn inhibits the release of LH.
Hyperprolactinemia occurs when there is a malfunction within the pituitary gland, which causes a decrease in LH production. Medical conditions and some medications can contribute to this condition.
Female Athlete Triad
Female athlete triad occurs in women who participate in sports requiring lean body mass and low weight. This condition can lead to amenorrhea (lack of menses) and osteoporosis, and can be fatal.
Male LH Function
In males, estrogen in the gonads (testes) signals the hypothalamic system and LH is released through a series of pulses. The released LH bonds to Leydig cells and stimulates the release of testosterone. Granulosa cells further convert the testosterone into estrogen. This is called interstitial cell-stimulating hormone (ICSH), which is necessary for spermatogenesis (sperm cell development.) Conditions that affect male LH levels are similar to those that affect women.
Kallmann syndrome also affects males. It may be congenital or it may be caused by stress, infection or injury.
As men age, the Leydig cells decrease; therefore, LH bonds to fewer cells.
Obesity in males has been linked to low LH levels.
Secondary Male Hypogonadism
Secondary male hypogonadism occurs when there is a malfunction in the hypothalamic system or pituitary gland. Production and release of LH may be absent or decreased.
As in women, LH levels in males may be affected by stress, eating disorders and medical conditions.