Luteinizing hormone: Description
Luteinizing hormone, lutropin, interstitial cell-stimulating hormone (LH) is a glycoprotein secreted by the anterior part of the pituitary gland (known as the adenohypophysis) which initiates and maintains the second phase of the menstrual cycle.
Gonadotropins are produced by the gonadotropic cells of the anterior part of the pituitary gland. LH is a glycoprotein composed of α and β subunits with a molecular weight of 32 kDa. α subunits made of 92 amino acids are similar for all the gonadotropins, whereas β subunits represent the specific characteristics of LH.
Role of Luteinizing hormone in the body
LH works synergically with the follicule-stimulating hormone (FSH) to regulate the menstrual cycle, promote ovulation and regulates the secretion of androgens and progesterone. LH is necessary for the occurrence and maintenance of the secretory phase of the menstrual cycle which starts after the ovulation. Lutropin is responsible for the corpus luteum formation and secretion of progesterone. Due to the decreased levels of estrogens the concentration of LH reaches its peak (the LH surge) in the mid-cycle (at least 12 hours prior before the ovulation) causing the rupture of the Graafian follicule and the ovum is released (the process called ovulation).
After the oocyte is released, the increased levels of LH control the luteinization – the development of the corpus luteum, which produces progesterone and estradiol in response to the pulsatile LH secretion and, thus, the second phase of the menstrual cycle is maintained and the endometrium (the inner lining of the uterus) prepares for the possible implantation of the zygote and future pregnancy.
In males the hormone stimulates the development and functioning of the Leydig cells in the testes which produce testosterone necessary for spermatogenesis.
Physiological effects of luteinizing hormone
- Activation of LH receptors in the theca cells to stimulate the androgen and estrogen production;
- Luteinization of the granulosa cells, which are left after the ovulation in order to secrete progesterone. Formation and maintenance of corpus luteum;
- Stimulation of the synthesis of prostaglandins;
- Stimulation of the ovulation – rupture of the mature follicle and release of the mature oocyte;
Concentrations of the LH in the blood are low during childhood and in postmenopausal period in women.
- Adult: 0.7-7.4 mIU/mL
- Prepubertal: 0-4.0 mIU/mL
- Pubertal: 0.3-31.0 mIU/mL
- Follicular: 0.8-10.5 mIU/dL
- Mid-cycle: 18.4-61.2 mIU/mL
- Luteal: 0.8-10.5 mIU/mL
- Postmenopausal: 8.2-40.8 mIU/mL
Indications for Luteinizing hormone testing
- Evaluate male and female infertility;
- To evaluate the hormonal therapy;
- To evaluate the endocrine problems related to puberty disorders;
- Prediction of ovulation and planning pregnancy;
High Luteinizing hormone levels
- Klinefelter syndrome;
- Turner syndrome (ovarian dysgenesis);
- Ovarian failure, or premature menopause;
- Precocious puberty;
- Polycystic ovarian syndrome (Stein-Levinthal syndrome);
- Swyer syndrome;
Some medications including anticonvulsants, naloxone and spironolactone are associated with the increased concentration of luteinizing hormone in the blood.
Low LH levels
- Kallmann syndrome;
- Pasqualini syndrome;
- Isolated idiopathic hypogonadotropic hypogonadism (GnRH deficiency);
- Stress-related hypogonadotropic hypogonadism (eg, strenuous exercise, anorexia nervosa, bulimia, excessive exercising and exhausting dieting);
- Mass lesions of the pituitary gland (eg, pituitary adenomas, cysts, metastatic disease);
- Hypothalamic/pituitary surgery, hypophysectomy or radiation;
- Pituitary apoplexy;
- Head trauma;
- Primary hypothyroidism;
- Testicular failure;
The administration of digoxin, estrogen compounds, oral contraceptives, phenothiazines, progesterone, stanozlol, and testosterone may decrease the concentration of LH.
Combined preparations for parenteral administration containing both LH and FSH as well as recombinant LH are available.