Video
Source: Secreted from lactotrophs of the anterior pituitary gland.
Function: The primary physiological action of prolactin is the preparation of the breasts for milk production, or lactation, in the postpartum period. Prolactin also suppresses gonadotropin-releasing hormone (GnRH) production from the hypothalamus, which results in inhibition of ovulation in females, leading to amenorrhea, and inhibition of spermatogenesis in males, leading to decreased libido and infertility.
Regulation: Prolactin secretion from the anterior pituitary is tonically inhibited by dopamine from the hypothalamus. Prolactin, in turn, inhibits its own secretion by increasing dopamine synthesis and secretion from the hypothalamus. Thyrotropin-releasing hormone (TRH) increases prolactin secretion, particularly in primary or secondary hypothyroidism. Dopamine agonists, like bromocriptine, inhibit prolactin secretion and can be used in the treatment of prolactinoma. Dopamine antagonists, such as most antipsychotics, and estrogens, like oral contraceptives and during pregnancy, stimulate prolactin secretion.
Osmosis.
Notes.
Pituitary tumors usually originate from one of the five main cell types of the anterior pituitary gland. About 60% of these tumors are prolactin-secreting adenomas, the most common type being a prolactinoma, or lactotroph adenoma.
Prolactin is a peptide hormone produced by lactotrophs in the pituitary gland. Its primary physiological role is to prepare breasts for milk production or lactation after childbirth.
Prolactinomas cause inappropriate milk production in non-postpartum females (galactorrhea). Prolactin also inhibits the production of gonadotropin-releasing hormone (GnRH) from the hypothalamus, which can lead to decreased libido, amenorrhea, and infertility.
The diagnosis of prolactinomas in males is usually delayed for several reasons. Men with these tumors do not experience galactorrhea or amenorrhea, and they are often hesitant to report erectile dysfunction. As a result, prolactinomas in men are generally larger at the time of presentation than in women.
Pituitary tumors can grow beyond the sella turcica, compressing and eroding nearby structures. If the tumor grows upwards, it can erode the optic chiasm; sideways, it can invade the cavernous sinus; downwards, it can grow into the sphenoid sinus. An expanding pituitary tumor can compress normal pituitary cells, causing hypopituitarism.
The characteristic bitemporal hemianopsia is caused by compression of the optic chiasm due to suprasellar extension of pituitary tumors. The tumor can also increase intracranial pressure, leading to headaches.
Postmenopausal women with prolactinomas are already experiencing amenorrhea and infertility. Thus, they mainly present with headaches and visual field no defects.