- Luteinizing hormone (LH) is a critical glycoprotein hormone secreted by the anterior pituitary gland and plays an essential role in regulating the reproductive system in both males and females.
- LH works in concert with follicle-stimulating hormone (FSH) and is under the regulatory control of gonadotropin-releasing hormone (GnRH), which is released in a pulsatile manner by the hypothalamus. These hormones are central to the hypothalamic-pituitary-gonadal (HPG) axis, which governs the development, function, and regulation of the gonads—ovaries in females and testes in males.
- In females, LH is primarily involved in the menstrual cycle and ovulation. During the first half of the cycle, known as the follicular phase, LH stimulates the theca cells in the ovaries to produce androgens, which are then converted into estrogens by granulosa cells under the influence of FSH. As estrogen levels rise and reach a threshold, they trigger a positive feedback loop on the hypothalamus and pituitary, leading to a dramatic surge in LH—commonly referred to as the LH surge. This surge is the key signal that induces ovulation, the process by which a mature egg is released from the dominant ovarian follicle. Following ovulation, LH also supports the transformation of the ruptured follicle into the corpus luteum, which secretes progesterone and helps maintain the uterine lining in preparation for possible implantation of a fertilized egg.
- In males, LH acts on the Leydig cells in the testes, stimulating them to produce testosterone, the primary male sex hormone. Testosterone is essential for spermatogenesis, the development of male secondary sexual characteristics, libido, and overall reproductive function. Unlike the cyclic nature of LH in females, LH secretion in males is more stable but still pulsatile and regulated by GnRH and testosterone through negative feedback mechanisms.
- The levels of LH vary with age and physiological state. In children, LH levels are low but rise at the onset of puberty, triggering sexual maturation. In postmenopausal women, LH levels are significantly elevated due to decreased ovarian feedback and lower estrogen levels. LH is also a key marker used in clinical and laboratory evaluations of infertility, menstrual disorders, pituitary function, and gonadal failure. In women, an ovulation predictor kit detects the LH surge in urine as an indicator of impending ovulation. Abnormally high levels of LH may suggest polycystic ovary syndrome (PCOS), primary ovarian insufficiency, or Klinefelter syndrome in males, while low levels may indicate hypogonadotropic hypogonadism, pituitary dysfunction, or hypothalamic disorders.
- Therapeutically, recombinant LH or LH analogs are sometimes used in assisted reproductive technologies (ART) to stimulate ovulation. Likewise, medications that affect the LH pathway, such as GnRH agonists or antagonists, are employed in treatments for hormone-sensitive conditions like endometriosis, prostate cancer, and precocious puberty.
