Luteinizing hormone (LH)

Structure and regulation

Biochemically, LH is a heterodimer made of a common alpha subunit shared with other pituitary glycoproteins and a hormone-specific beta subunit that confers biological activity. It is produced by gonadotrophs in the anterior pituitary and released in pulses. Circulating levels are regulated by gonadal steroids (estrogens, progesterone, testosterone) and inhibins that provide negative and, at midcycle in females, positive feedback to generate an LH surge.

Physiological roles

In females, a rapid rise in LH triggers ovulation and supports the formation and function of the corpus luteum, which secretes progesterone to prepare the uterus for possible pregnancy; see progesterone. In males, LH acts on Leydig (interstitial) cells to stimulate synthesis of testosterone, a role historically referred to as interstitial cell–stimulating hormone (ICSH); see testosterone. LH and follicle-stimulating hormone (FSH) act together to control gametogenesis and steroidogenesis.

Clinical relevance and uses

Measurement of LH is widely used in fertility assessment, diagnosis of pituitary or gonadal disorders, and evaluation of puberty timing. Home ovulation predictor kits detect the midcycle LH surge to estimate the fertile window. In assisted reproduction, preparations that mimic or replace LH activity—sometimes using human chorionic gonadotropin because of its similar receptor action—are employed to induce ovulation or support luteal function.

Disorders and distinctions

• Low LH secretion can contribute to hypogonadism and impaired sexual development.
• Elevated LH with altered FSH balance may appear in conditions such as polycystic ovary syndrome or certain gonadal failures.
• Human chorionic gonadotropin (hCG) is structurally related to LH and activates the same receptor but is produced by the placenta, an important distinction in pregnancy testing and clinical therapy.

Historical names for LH include lutropin and lutrophin; understanding its central role in reproductive endocrinology helps explain many diagnostic tests and therapeutic strategies in both male and female reproductive medicine. For further background, consult general endocrine references or fertility resources via the provided links.