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Luteinizing hormone (LH) is a hormone synthesized and secreted by gonadotropes in the anterior lobe of the pituitary gland. In concert with the other pituitary gonadotropin follicle stimulating hormone (FSH) it is necessary for proper reproductive function. more...

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In the female, an acute rise of LH – the LH surge – triggers ovulation. In the male, where LH had also been called Interstitial Cell Stimulating Hormone (ICSH), it stimulates Leydig cell production of testosterone.

Structure

LH is a glycoprotein. Each monomeric unit is a protein molecule with a sugar attached to it; two of these make the full, functional protein. Its structure is similar to the other glycoproteins, FSH, TSH, and hCG. The protein dimer contains 2 polypeptide units, labeled alpha and beta subunits that are connected by two disulfide bridges. The alpha subunits of LH, FSH, TSH, and hCG are identical, and contain 92 amino acids. The beta subunits vary. LH has a beta subunit of 121 amino acids (LHB) that confers its specific biologic action and is responsible for interaction with the LH receptor. This beta subunit contains the same amino acids in sequence as the beta sub unit of hCG and both stimulate the same receptor, however, the hCG beta subunit contains an additional 24 amino acids, and both hormones differ in the composition of their sugar moieties. The different composition of these oligosaccharides affects bioactivity and speed of degradation. The biologic half-life of LH is 20 minutes, shorter than that of FSH (3-4 hours) or hCG (24 hours).

Genes

The gene for the alpha subunit is located on chromosome 6q12.21. The luteinizing hormone beta-subunit gene is localized in the LHB/CGB gene cluster on chromosome 19q13.32. In contrast to the alpha gene activity, beta LH subunit gene activity is restricted to the pituitary gonadotropic cells. It is regulated by the gonadotropin releasing hormone from the hypothalamus. Inhibin, activin, and sex hormones do not affect genetic activity for the beta subunit production of LH.

Activity

In both males and females, LH is essential for reproduction. In females, at the time of menstruation, FSH initiates follicular growth, specifically affecting granulosa cells. With the rise in estrogens, also LH receptors are expressed on the maturing follicle that produces an increasing amount of estradiol. Eventually at the time of the maturation of the follicle, the estrogen rise leads via the hypothalamic interface to the “positive feed-back” effect, a release of LH over a 24-48 hour. This LH surge triggers ovulation hereby not only releasing the egg, but also initiating the conversion of the residual follicle into a corpus luteum that, in turn, produces progesterone to prepare the endometrium for a possible implantation. LH is necessary to maintain luteal function for the first two weeks. In case of a pregnancy luteal function will be further maintained by the action of hCG from the newly established pregnancy. LH supports thecal cells in the ovary that provide androgens and hormonal precursors for estradiol production.

Read more at Wikipedia.org