Luteinizing hormone

Luteinizing Hormone (LH) is a hormone secreted by the anterior pituitary gland that plays a key role in the reproductive system of both males and females. In females, it triggers ovulation and stimulates the corpus luteum to produce progesterone; in males, it stimulates Leydig cells in the testes to produce testosterone.

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Luteinizing hormone levels during the menstrual cycle

Biochemistry and Physiology of Luteinizing Hormone

Luteinizing hormone is a glycoprotein hormone, composed of two subunits (alpha and beta) that are non-covalently associated. The alpha subunit is common to other pituitary hormones including follicle-stimulating hormone (FSH), thyroid-stimulating hormone (TSH), and human chorionic gonadotropin (hCG). The beta subunit of LH, however, is unique to the hormone, conferring its biological specificity.

In females, the surge of LH in the middle of the menstrual cycle triggers ovulation and the development of the corpus luteum, which secretes progesterone to prepare the endometrium for potential implantation of a fertilized egg.

In males, LH stimulates the Leydig cells in the testes to produce testosterone, which supports spermatogenesis and contributes to the male secondary sexual characteristics.

Measurement and Clinical Significance

The levels of luteinizing hormone can be measured in blood or urine and are useful for diagnosing various reproductive disorders. Elevated LH levels can indicate primary ovarian failure, polycystic ovary syndrome, or testicular failure, whereas low LH levels may suggest hypothalamic or pituitary disorders.LH testing is also used in fertility treatments to determine the optimal timing for procedures like intrauterine insemination (IUI) or in vitro fertilization (IVF). Additionally, LH urine tests are commonly used in over-the-counter ovulation predictor kits to identify the time of ovulation for couples trying to conceive.

Disorders Associated with Luteinizing Hormone

As mentioned earlier, abnormal levels of LH can be associated with several reproductive and endocrine disorders.

Polycystic Ovary Syndrome (PCOS): Women with PCOS often have higher than normal levels of LH, contributing to the abnormal production and development of eggs in the ovaries. Kallmann Syndrome: This is a condition characterized by delayed or absent puberty and a poor sense of smell, resulting from low levels of LH and FSH due to problems with the hypothalamus. Luteinized Unruptured Follicle (LUF) Syndrome: Despite a normal LH surge, the follicle fails to release the egg, leading to infertility. Hypogonadism: Both men and women may experience low sex hormone levels (testosterone in men, estrogen in women) due to low LH levels.

See Also

• Follicle-stimulating hormone
• Hypothalamic–pituitary–gonadal axis
• Ovulation
• Testosterone

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