Clinical Significance

Human Luteinizing Hormone (hLH, Lutropin) is made up of two non-identical, non-covalently associated glycoprotein subunits, denoted alpha and beta. It has been reported that the 28,500 dalton molecular weight hLH contains two N-linked carbohydrate chains on the alpha subunit and one asparagine-linked oligosaccharide on the beta subunit. The alpha subunit is similar in structure for the glycoproteins hLH, hCG, hFSH, and hTSH. It is the differences in the beta subunit of these glycoproteins which contributes to immunological and physiological specificity.

In the female, hLH stimulates the final maturation of the follicle, follicular rupture, and ovulation. Human LH is secreted by the gonadotropin releasing hormone (GnRH) from the medial basal hypothalamus. Both hLH and hFSH are secreted in a pulsatile nature; however, this is less noticeable for hFSH perhaps due to the longer half-life in circulation. In a normal menstrual cycle negative feedback by estradiol suppresses hLH secretion in the follicular phase. As the follicle develops (in response to hFSH estradiol production increases which triggers an increase in GnRH and an increased sensitivity of the pituitary to GnRH. A GnRH surge results in the preovulatory (mid-cycle) surge of hLH and ovulation. Following this surge, hLH is suppressed during the luteal phase due to negative feedback from progersterone and estradiol.

Variation in cycle lengths are observed in nomally menstruating females due to variations in the length of the follicular phase. In the menopausal female, hLH levels are elevated in response to decreased production of ovarian estrogens and progesterones, which eliminates the negative feedback mechanism on the pituitary gland. As a result, ovulation and mentrual cycles decrease and eventually cease.

In the mael, hLH is often reffered to as interstitial cell-stimulating hormone and influences the production of testosterone by the Leydig cells of the testes.

_{Source: Access LH IFU #33510, 12/15/16}