Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are calledgonadotropins because stimulate the gonads – in males, the testes, and in females, the ovaries. They are not necessary for life, but are essential for reproduction. These two hormones are secreted from cells in the anterior pituitary called gonadotrophs. Most gonadotrophs secrete only LH or FSH, but some appear to secrete both hormones.
As describef for thyroid-simulating hormone, LH and FSH are large glycoproteins composed of alpha and beta subunits. The alpha subunit is identical in all three of these anterior pituitary hormones, while the beta subunit is unique and endows each hormone with the ability to bind its own receptor.
Follicle-Stimulating Hormone
As its name implies, FSH stimulates the maturation of ovarian follicles. Administration of FSH to humans and animals induces “superovulation”, or development of more than the usual number of mature follicles and hence, an increased number of mature gametes.FSH is also critical for sperm production. It supports the function of Sertoli cells, which in turn support many aspects of sperm cell maturation.
Gonadotropins: Luteinizing and Follicle Stimulating Hormones
What is Luteinizing Hormone (LH)?
LH is an acronym which stands for Luteinising Hormone. Hormones are chemicals in your body that are made in one place and are used in another. As the name suggests, LH is responsible for luteinising the mature follicle in your ovaries after ovulation. It is one of the two gonadotropins (so called because it stimulates the gonads), the other being its partner, FSH, which stands for follicle stimulating hormone. LH and FSH are secreted by the pituitary gland, a small pea-shaped gland below the base of your brain. LH is necessary for fertility. In women, LH helps regulate ovulation. In men, LH helps the testes to make and secrete testosterone.
LH levels vary during the menstrual cycle, and peak prior to ovulation. In fact, it is the surge of LH production ( called the LH surge) which induces ovulation in a normal woman. It is this LH surge which is measured by the home ovulation test kits ( OPKs, ovulation prediction kits) which check for LH levels in the urine.
In both sexes, LH stimulates secretion of sex steroids from the gonads. In the testes, LH binds to receptors on Leydig cells, stimulating synthesis and secretion of testosterone. Theca cells in the ovary respond to LH stimulation by secretion of testosterone, which is converted into estrogen by adjacent granulosa cells.
What is the Luteinizing Hormone Test?
The LH test is a simple blood test . It is typically measured on Day 3, along with the FSH testand the estradiol test.
What do the Results Mean?
On Day 3, normal LH values are between 3 and 10 mIU/mL. LH levels can also be artificially raised by ovulation inducing drugs such as clomiphene citrate ( clomid).
Low levels of LH ( less than 2 mIU/ml) are found in a condition called hypogonadotropic hypogonadism. Women on birth control pills as well as pregnant women also have low levels of FSH.
LH levels are usually interpreted in conjunction with the FSH levels. Normally, the ratio is 1, which means the FSH level and LH level are approximately the same. In patients with polycystic ovarian disease ( PCOD) , this ratio is reversed; and patients with PCOD typically have a high LH level and a normal FSH level. This is called a reversal of the FSH:LH ratio; and in patients with PCOD it is 2 or more.
Disease States
Diminished secretion of LH or FSH can result in failure of gonadal function (hypogonadism). This condition is typically manifest in males as failure in production of normal numbers of sperm. In females, cessation of reproductive cycles is commonly observed.
Elevated blood levels of gonadotropins usually reflect lack of steroid negative feedback. Removal of the gonads from either males or females, as is commonly done to animals, leads to persistent elevation in LH and FSH. In humans, excessive secretion of FSH and/or LH most commonly the result of gonadal failure or pituitary tumors. In general, elevated levels of gonadotropins per se have no biological effect.
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