Prolactin

Where it comes from

Made in

Lactotroph cells of the anterior pituitary; also the uterine lining, breast, immune cells and brain

Sent out by

Unusually, the hypothalamus holds it back (dopamine) rather than driving it; suckling, oestrogen, TRH, stress, sleep and orgasm release it

Acts on

• Breast (milk synthesis)
• Hypothalamus (GnRH suppression)
• Ovary and testis
• Immune cells
• Brain (parental behaviour)

What it does

• Makes milk once the breast is prepared by oestrogen and progesterone
• Suppresses ovulation during breastfeeding, nature’s contraceptive
• Over 300 actions in vertebrates, from osmoregulation in fish to parental care

In medicine

• Measured for prolactinoma, the commonest pituitary tumour, and for the high prolactin that antipsychotics and other dopamine blockers cause, which stops periods and causes milk and bone loss ¹
• Cabergoline and bromocriptine, dopamine agonists, shrink prolactinomas and lower prolactin ¹
• Macroprolactin, an inert antibody-bound form, is a common cause of a falsely high reading ¹

Beyond the body’s own use

• No prolactin product exists; the medicines in this area either lower it through dopamine or raise it as an unwanted effect ¹
• Domperidone, which raises prolactin, is used off-label to increase milk supply. In 90 mothers of very preterm infants, 78 per cent reached a 50 per cent rise in milk volume against 58 per cent on placebo, though the absolute gain was small ²
• Domperidone is not approved in the United States, and European regulators reviewed it in 2014 over QT prolongation and sudden cardiac death and then cut its dose, duration and indications ³
• Prolactin is studied in autoimmune disease, where it drives immune activity, and no trial of blocking it has reported