Luteinising Hormone, abbreviated as LH, is a key reproductive hormone that promotes the functioning of the gonads i.e. the primary reproductive organs - testes in men and ovaries in women. Also known as interstitial cell stimulating hormone, luteinising hormone is produced by specialized cells called gonadotropic cells in the pituitary gland – a pea-sized gland situated at the base of the brain. Along with the follicle stimulating hormone (FSH), also synthesized by the pituitary gland, luteinising hormone plays a crucial role in supporting optimal fertility and reproduction processes in both men and women.

Also Read: Follicle-Stimulating Hormone (FSH): Structure, Crucial Functions And Adverse Effects

The production and release of luteinising hormone is controlled by a system known as the hypothalamic-pituitary-gonadal axis. A hormone called gonadotropin-releasing hormone is released from the hypothalamus segment of the brain and affixes onto cell receptors in the anterior pituitary gland, which in turn prompts the synthesis and release of luteinising hormone. LH then travels across the bloodstream and attaches onto its target cells in the testes in men and ovaries in women, to facilitate optimal sexual and reproductive activities.

Luteinising Hormone And Its Structure:

The key role of the pituitary gland in the regulation of reproductive and sexual characteristics in men and women, by the synthesis of two hormones, was established by two individuals - the renowned German scientist Zondek and the well-known German gynaecologist Ascheim. In 1929 – 1930, through extensive research, they proved that both follicle-stimulating hormone and luteinising hormone influenced the cellular and tissue activities of the endometrium and vaginal epithelium in women.

However, the luteinising hormone was first successfully isolated only in the following year in 1931, by three reputed American researchers – Fevold, Hisaw and Leonard. They separated the two protein hormones – FSH and LH – from hog anterior lobes and discovered that FSH kindled ovarian follicular development and sexual maturity in immature rats, while LH stimulated the activated follicles by FSH to luteinize i.e. develop into the corpus luteum, for further reproductive and sexual functions.

Luteinising hormone is a heterodimeric glycoprotein. It is composed of two polypeptide chains – one alpha subunit with 92 amino acids and one beta subunit with 120 amino acids. The beta subunit provides the ability for LH to become biologically active and exert its influence on the reproductive organs – ovaries in women and testes in men. The molecular weight of luteinising hormone is approximately 30 – 33 kDa (kilo Daltons, with Dalton being a central unit of atomic mass).

Functions Of Luteinising Hormone:

The luteinising hormone carries out numerous pivotal operations in the body, encompassing:

• Activates specific sexual components known as Leydig cells in men to produce testosterone – the central reproductive hormone in males, which sustains healthy sperm production and development of sexual characteristics in males including facial hair, deep voice
• Acts on the ovarian follicles and theca cells in women, to secrete estrogen during menstrual cycles and if fertilization has occurred, ensures the synthesis of progesterone to foster healthy pregnancy – estrogen and progesterone being the chief reproductive hormones in females

Also Read: Estrogen: Structure, Crucial Functions And Adverse Effects

Adverse Effects Of Hormonal Imbalance In Luteinising Hormone:

Low Levels:

Luteinising hormone is involved in regulating reproductive functions in males and females and hence low levels of this pituitary gonadotropic hormone results in infertility.

A disorder termed as Kallmann’s syndrome develops in men, wherein insufficient amounts of gonadotropin-releasing hormone are secreted in the hypothalamus region of the brain. This leads to lesser than normal levels of luteinising hormone being produced and prompts complications of infertility and poor sexual performance in men.

Low levels of luteinising hormone in women signifies problems with ovulation and menstruation, giving rise to gynaecological issues of irregular periods, amenorrhea and hormonal imbalance.

High Levels:

High amounts of luteinising hormone being released into the bloodstream also triggers infertility in men and women, since it causes decreased production of sexual hormones of testosterone in men and estrogen, progesterone in women.

In women, vast volumes of LH being secreted triggers PCOS – Polycystic Ovarian Syndrome, which is characterized by hormonal imbalance, irregular menstrual cycles and reduced fertility. A genetic disorder called Turner Syndrome that entails deletion of the X chromosome – X and Y being the sex chromosomes in humans is a known cause of high levels of LH in the system.

Men also face health anomalies of infertility and lack of sexual stimulation due to higher than normal levels of LH in blood. Moreover, a genetic defect called Klinefelter Syndrome wherein an extra copy of the sex chromosome - X chromosome is present in men is a major factor that triggers high levels of LH in males.