Nafarelin

Like GnRH, initial or intermittent administration of nafarelin stimulates release of the gonadotropins luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary gland, which in turn transiently increases production of estradiol in females and testosterone in both sexes. However, with continuous daily administration, nafarelin continuously occupies the GnRH receptor, leading to a reversible down-regulation of the GnRH receptors in the pituitary gland and desensitization of the pituitary gonadotropes. This causes a significant and sustained decline in the production of LH and FSH. A decline in gonadotropin production and release causes a dramatic reversible decrease in synthesis of estradiol, progesterone, and testosterone by the ovaries or testes. Like normal endometrium, endometriotic implants contain estrogen receptors. Estrogen stimulates the growth of endometrium. Use of nafarelin induces anovulation and amenorrhea and decreases serum concentrations of estradiol to the postmenopausal range, which induces atrophy of endometriotic implants. However, nafarelin does not abolish the underlying pathophysiology of endometriosis. In children with central precocious puberty receiving nafarelin, serum LH, testosterone, and estradiol concentrations return to prepubertal levels. This results in the supression of secondary sexual characteristics and decrased rate of linear growth and skeletal maturation. Following disconinuation of nafarelin, the effects of the drug is reversed, meaning FSH and LH concentrations usually return to pretreatment levels.