LUTEINISING HORMONE (LH): Key Regulator of Ovulation
Luteinising hormone (LH) is a central hormone in reproductive physiology, responsible for triggering ovulation, supporting corpus luteum function and regulating sex steroid production. Secreted by the anterior pituitary in response to pulsatile GnRH, LH works in precise coordination with FSH to ensure orderly follicular development, ovulation and preparation of the endometrium for possible pregnancy. In females, LH’s most dramatic action is the mid-cycle LH surge, a rapid and substantial rise in secretion that induces ovulation. In males, LH stimulates Leydig cells to produce testosterone, the essential androgen supporting spermatogenesis and secondary sexual characteristics. LH therefore plays a essential role in fertility in all sexes.
What You Need to Know
Luteinising hormone is a gonadotrophin produced by the anterior pituitary in response to pulsatile gonadotropin-releasing hormone from the hypothalamus. Its secretion pattern is dynamic and tightly linked to circulating sex steroid levels. During the early follicular phase, LH levels remain relatively low, rising gradually as estrogen increases. Once estrogen reaches a sustained high concentration, feedback switches from inhibitory to stimulatory, triggering the mid-cycle LH surge that defines ovulation.
The LH surge is the critical event that converts follicular growth into ovulation. It induces final oocyte maturation, rupture of the dominant follicle, and luteinisation of granulosa cells. Following ovulation, LH supports formation and maintenance of the corpus luteum, enabling continued progesterone and estrogen production during the luteal phase. This hormonal environment stabilises the endometrium and prepares it for possible implantation.
LH has several essential physiological actions across reproductive systems:
Ovulation induction, through triggering follicular rupture and oocyte release
Luteal support, maintaining corpus luteum function and progesterone secretion
Steroidogenesis, stimulating estrogen production in females and testosterone synthesis in males
Reproductive axis regulation, responding to and shaping feedback from sex steroids
In males, LH binds to receptors on Leydig cells in the testes, stimulating testosterone production. High intratesticular testosterone concentrations are required to sustain spermatogenesis, while circulating testosterone supports libido, muscle mass, bone density, erythropoiesis, and secondary sexual characteristics. In this context, LH acts as the primary hormonal driver of androgen production rather than gamete development directly.
Across sexes, LH secretion is tightly regulated by negative feedback from sex steroids. Estrogen and progesterone modulate LH release in females, while testosterone provides dominant feedback in males. This feedback ensures hormonal stability while still allowing rapid, high-amplitude LH secretion when physiologically required, particularly during ovulation.
Beyond the Basics
The LH Surge and Ovulation Physiology
The mid-cycle LH surge represents a rare example of sustained positive hormonal feedback in human physiology. Rather than suppressing pituitary output, prolonged high estradiol levels from the dominant follicle alter hypothalamic and pituitary sensitivity, triggering a rapid and high-amplitude increase in LH secretion. This surge is brief but decisive, converting a hormonally primed follicle into one capable of ovulation.
Within the dominant follicle, LH initiates a tightly coordinated cascade of events. The oocyte resumes meiosis and progresses to metaphase II, while enzymatic and inflammatory mediators weaken the follicular wall. Prostaglandin production and protease activity increase, and the cumulus cells surrounding the oocyte expand, facilitating release. Together, these processes culminate in follicular rupture and expulsion of the oocyte into the peritoneal cavity, where it is quickly captured by the fimbriae of the uterine tube. Ovulation typically occurs within 24 to 36 hours of the onset of the LH surge.
Corpus Luteum Support and Luteal Phase Regulation
Following ovulation, LH drives luteinisation, transforming granulosa and theca cells into luteal cells specialised for steroid hormone production. The corpus luteum becomes a temporary endocrine gland, secreting large amounts of progesterone and smaller quantities of estrogen. This hormonal output stabilises the endometrium, suppresses uterine contractility, and prepares the uterus for possible implantation.
LH maintains corpus luteum function for approximately 14 days in a non-pregnant cycle. If fertilisation occurs, human chorionic gonadotropin released by the early embryo binds to LH receptors and preserves luteal function, allowing progesterone production to continue until placental steroidogenesis is sufficient. In the absence of pregnancy, declining LH support leads to luteal regression, falling progesterone levels, and menstruation.
LH in Male Physiology
In males, LH plays a continuous rather than cyclical role. It binds to receptors on Leydig cells within the testicular interstitium, stimulating testosterone synthesis from cholesterol. High intratesticular testosterone concentrations are essential for spermatogenesis and act locally within the seminiferous tubules alongside FSH-mediated Sertoli cell support.
Although LH secretion in males remains pulsatile, it is relatively stable compared with the dramatic surges seen in females. Testosterone provides negative feedback at both the hypothalamic and pituitary levels, while inhibin B from Sertoli cells selectively regulates FSH. This coordinated feedback maintains stable androgen levels and consistent sperm production over time.
Receptor Action and Intracellular Signalling
LH exerts its effects through G protein–coupled LH receptors expressed on theca and luteal cells in females and Leydig cells in males. Receptor activation stimulates cyclic AMP production and downstream protein kinase pathways that regulate steroidogenic enzyme activity. The responsiveness of these receptors changes across the menstrual cycle, reaching peak sensitivity during the pre-ovulatory period and declining as luteal tissue regresses.
These receptor-level adaptations explain the ovary’s dramatic response to the LH surge and its subsequent insensitivity once luteal involution begins. Understanding LH receptor signalling is essential for interpreting ovulatory disorders, luteal phase dysfunction, and the clinical use of LH or hCG in fertility treatment.
Clinical Connections
Normal fertility depends on tightly regulated LH secretion, and disruption of its timing or amplitude has clear clinical consequences. In females, abnormal LH patterns interfere with ovulation rather than follicular growth alone. Excessive LH stimulation can promote androgen production and arrest follicular development, while insufficient LH fails to trigger ovulation and luteal formation. These patterns often present as irregular or absent menstrual cycles rather than isolated hormonal abnormalities.
Several common reproductive conditions are closely linked to altered LH dynamics:
Polycystic ovary syndrome, where elevated LH relative to FSH contributes to excess androgen production and chronic anovulation
Hypothalamic amenorrhoea or pituitary dysfunction, associated with low LH secretion and failure of ovulation
Anovulatory infertility, where follicles develop but the LH surge does not occur or is inadequate
Use of ovulation predictor kits, which rely on urinary detection of the LH surge to estimate the fertile window
In males, LH abnormalities primarily affect androgen production rather than sperm transport or maturation directly. Low LH results in reduced Leydig cell stimulation, leading to decreased testosterone, impaired spermatogenesis, reduced libido, and features of hypogonadism. In contrast, elevated LH in the presence of low testosterone indicates primary testicular failure, reflecting loss of negative feedback rather than excessive pituitary drive.
LH physiology is also deliberately manipulated in clinical practice. LH analogues and recombinant gonadotrophins are used in fertility treatments to induce ovulation, support follicular maturation, or control cycle timing. Human chorionic gonadotropin is commonly used as a functional LH substitute because it binds the same receptor and reliably triggers ovulation and luteinisation. Understanding LH regulation allows clinicians to interpret fertility investigations accurately and apply hormone-based therapies with precision rather than relying on hormone levels in isolation.
Concept Check
What hormonal conditions trigger the LH surge, and why is this considered a positive-feedback mechanism?
How does the LH surge induce the final maturation and release of the oocyte?
What roles does LH play in maintaining the corpus luteum during the luteal phase?
How does LH contribute to testosterone production in males?
What clinical scenarios might present with elevated LH but low sex steroid levels?