Background information on the luteinizing hormone
Since its discovery, the luteinizing hormone (LH), has been vital in the study and understanding of the human reproductive system. Pivotal to various biological processes, deficiencies or excesses in the LH often point towards several underpinning diseases, making it an area of interest in medical research.
The LH protein, composed of two subunits - alpha and beta, differs in structure according to sex. The beta-subunit is specific for LH and responsible for its biological activity. While the alpha-subunit is shared with other glycoprotein hormones, the beta subunit is unique. When it comes to the gene locus, the LH beta subunit gene (LHB) is situated on chromosome 19q13.32. Its protein structure comprises 121 amino acids, with a predicted molecular mass of about 14 kDa.
Luteinizing Hormone Function
Primarily, the luteinizing hormone stimulates the gonads - testes in males and ovaries in females. In men, it influences the Leydig cells to produce testosterone. On the other hand, in women, LH is responsible for the maturation and release of the egg during ovulation and stimulates the production of estrogen and progesterone.
LH-Related Signaling Pathways
LH functions via the activation of the luteinizing hormone receptor, a G protein-coupled receptor. This interaction triggers multiple intracellular signaling pathways. Essential among these are Gs protein/cAMP/protein kinase A pathway resulting in steroidogenesis, and Gq/11 protein/phospholipase C pathway leading to ovulation.
Role of LH in Diseases
The harmony of the reproductive hormones is a crucial factor in the proper functioning of the reproductive system. Malfunction in the LH production can lead to a myriad of diseases. Men can undergo hypogonadism - diminished functional activities of the gonads. In women, polycystic ovary syndrome and amenorrhea - loss of menstruation, can occur due to an excess or insufficient release of LH.
Medically, the LH level is a valuable diagnostic index. It helps identify the cause of infertility and monitor the effectiveness of infertility treatments. Low LH levels can signify pituitary disorders, while high LH levels are indicators of Polycystic Ovary Syndrome (PCOS) or menopause. Additionally, LH is also used in assisted reproductive technologies to stimulate ovulation.
Drug Candidates Related to LH
Several drugs act on the LH levels. For instance, in women with anovulation, human menopausal gonadotropins, containing both FSH and LH, are applied to stimulate the ovaries. Gonadotropin-releasing hormone agonists and antagonists are also used in assisted reproductive technologies to control LH surge.
Moreover, LH can also be modulated to prevent unwanted pregnancy. Hormonal contraceptives, both mixed formulations and progestin-only methods, function by either preventing the normal surge in LH that leads to ovulation or by altering the natural hormonal milieu to create a pseudopregnancy state.
