Luitenising Hormone (LH)

Human luteinising hormone (LH, lutropin) is a glycoprotein secreted by the gonadotroph cells of the pituitary gland in response to the secretion of gonadotropin-releasing hormone (LHRH, GnRH) by the medial basal hypothalamus.

Ovarian steroids, mainly oestrogens, modulate the secretion of LH and FSH, which in turn regulate the menstrual cycle in women.

In women, LH stimulates the final maturation of the follicle, the rupture of the follicle and ovulation.
In a normal menstrual cycle, negative feedback from estradiol suppresses LH secretion during the follicular phase.

As the follicle develops (in response to FSH), estradiol production increases, triggering an increase in GnRH and increased sensitivity of the pituitary gland to GnRH. A surge in GnRH leads to a pre-ovulatory (mid-cycle) surge in LH and ovulation.

After this surge, LH is dampened during the luteal phase by negative feedback from progesterone and oestradiol.

In men, LH is often referred to as the interstitial cell-stimulating hormone and influences the production of testosterone by the Leydig cells in the testes.
Determining LH concentration is an essential part of predicting ovulation, assessing infertility and diagnosing pituitary and gonadal disorders.

Increasing concentrations of LH precede ovulation and in cases where the optimal fertile period must be defined for the timing of sexual intercourse or artificial insemination, daily LH concentrations are decisive in predicting ovulation.

At menopause, or following oophorectomy in women, oestrogen concentrations fall to low levels. The drop in oestrogen levels leads to a loss of negative feedback on gonadotropin release. The result is an increase in LH and FSH concentrations.