A 31-year-old woman is referred by her Ob-Gyn for elevated prolactin. She initially presented with a three-month history of amenorrhea, a negative home pregnancy test, and 100% compliance with condom use. She denies hirsutism and acne but admits to thin milky nipple discharge upon squeezing (but not spontaneous).
Two weeks ago, her Ob-Gyn ordered labs; results were negative for serum beta human chorionic gonadotropin and within normal ranges for thyroid-stimulating hormone (TSH), luteinizing hormone, follicle-stimulating hormone, estradiol, free and total testosterone, dehydroepiandrosterone sulfate (DHEAs), complete chemistry panel, and complete blood count. Her serum prolactin level was 110 ng/mL (normal, 3 to 27 ng/mL).
Q: How is prolactin physiologically regulated?
The primary role of prolactin, which is produced by lactotroph cells in the anterior pituitary gland, is to stimulate lactation and breast development. Prolactin is regulated by dopamine (also known as prolactin inhibitory hormone), which is secreted from the hypothalamus via an inhibitory pathway unique to the hypothalamus-pituitary hormone system. Dopamine essentially suppresses prolactin.
Other hormones can have a stimulatory effect on the anterior pituitary gland and thus increase prolactin levels. Estrogen can induce lactotroph hyperplasia and elevated prolactin; however, this is only clinically relevant in the context of estrogen surge during pregnancy. (Estrogen therapy, such as oral contraception or hormone replacement therapy, on the other hand, is targeted to “normal” estrogen levels.) Thyrotropin-releasing hormone (TRH) from the hypothalamus also stimulates the anterior pituitary gland, so patients with inadequately treated or untreated primary hypothyroidism will have mildly elevated prolactin.
Neurogenic stimuli of the chest wall, through nipple suckling or varicella zoster infection (shingles), can also increase prolactin secretion. And since prolactin is eliminated by the liver (75%) and the kidney (25%), significant liver disease and/or renal insufficiency can raise prolactin levels, due to decreased clearance.
What are the possible etiologies for elevated prolactin? See answer on the next page...