luteinizing hormone (LH) /lo̅o̅″tē·inī′zing/ [L, luteus, yellow; Gk, izein, to cause, hormein, to begin activity] , a glycoprotein hormone produced by the anterior pituitary gland. It stimulates the secretion of sex hormones by the ovary and the testes and is involved in the maturation of spermatozoa and ova. In men, it induces the secretion of testosterone by the interstitial cells of the testes. Testosterone, together with follicle-stimulating hormone (FSH), induces the maturation of seminiferous tubules and stimulates them to produce sperm. In females, LH, working together with FSH, stimulates the growing follicle in the ovary to secrete estrogen. High concentrations of estrogen stimulate the release of a surge of LH, which stimulates ovulation. LH then induces the development of the ruptured follicle into the corpus luteum, which continues to secrete estrogen and progesterone. The normal LH concentration in the plasma of men is less than 11 mIU/mL. In premenopausal women it is less than 25 mIU/mL; at midcycle peak it is greater than three times the baseline concentration; in postmenopausal women it is more than 25 mIU/mL. See also interstitial cell-stimulating hormone, menstrual cycle.
