Human Luteinizing Hormone (hLH) belongs to a subset of glycoprotein hormones, called gonadotropins, that regulate gonadal function. Secreted by the anterior pituitary gland, hLH stimulates testosterone secretion from Leydig cells in men, and stimulates the ovarian theca to produce several androgen precursors of estradiol, then promotes the formation of the corpus luteum and the subsequent production of progesterone in women.

Immunoassays for hLH serum levels, along with those for follicle stimulating hormone (hFSH), are useful in the evaluation of disorders of reproduction and puberty, such as hypogonadism, ovulation timing, and infertility. In addition, hLH and hFSH serum levels are monitored in ovulation induction and in the clinical administration of gonadotropins.

hLH can be dissociated to yield two dissimilar subunits, α-LH and β-LH. Taken separately, these hormonal subunits exhibit very little of the biological activity associated with whole molecule hLH. The α-subunit (approximate molecular weight of 13,500 Daltons) is virtually identical to the α-subunits of the related pituitary hormones, hFSH and thyroid stimulating hormone (hTSH), and that of chorionic gonadotropin (hCG), a placental hormone. The biological activity of hLH is dependent on the distinct make-up of the β-subunit (approximate molecular weight of 14,500 Daltons), which differs in amino acid sequence from the β-subunits of hFSH, hTSH, and hCG.

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