Hyperprolactinemia

Prolactin is secreted by lactotrophs in the anterior pituitary. Unlike most anterior-pituitary hormones, its baseline secretion is held down continuously by hypothalamic dopamine acting at D2 receptors. Dopamine functions as a brake: reduce dopamine delivery, and prolactin rises. This explains the main pathological patterns. A D2-antagonist drug blocks the brake at the lactotroph; a sellar mass can compress the pituitary stalk and interrupt dopamine delivery; hypothalamic disease can impair dopamine production; and a prolactinoma secretes prolactin autonomously. Important physiological or systemic contributors include pregnancy, lactation, chest-wall stimulation or injury, primary hypothyroidism, renal failure, and hepatic cirrhosis. Medication review should specifically include risperidone and paliperidone, metoclopramide, domperidone, verapamil, opioids, and estrogens. Domperidone belongs on the medication checklist in Canadian practice. Drug-induced elevations are usually below about 100 ng/mL, numerically equivalent to 100 µg/L, although the concentration alone never replaces the clinical assessment. Excess prolactin suppresses hypothalamic GnRH pulsatility. The resulting hypogonadism may cause oligo- or amenorrhea, galactorrhea, infertility, vaginal dryness, or reduced libido in patients with ovaries, and reduced libido, erectile dysfunction, infertility, or gynecomastia in patients with testes. Prolonged hypogonadism...