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The History of Prolactin

American zoologist Oscar Riddle first identified and named prolactin in 1928 while studying pigeons, discovering that a specific pituitary gland extract stimulated the birds to produce a nutrient-rich "crop milk" used to feed their young, and he named the newly identified hormone "prolactin" directly for this genuinely important milk-promoting function he had observed and carefully documented. For decades afterward, scientists mistakenly believed growth hormone and prolactin were actually the very same molecule performing two different jobs in the body, a misconception finally and decisively corrected in 1970 when Canadian endocrinologist Henry Friesen successfully isolated and characterized human prolactin as a genuinely distinct hormone in its own right. Friesen's landmark discovery opened the door to reliable human prolactin testing, finally allowing doctors to accurately diagnose prolactin-related disorders that had previously been genuinely impossible to properly identify or effectively treat.

What Prolactin Actually Is

Prolactin is a hormone produced directly by the anterior pituitary gland, best known specifically for stimulating breast milk production during and after pregnancy, though it also plays several other, considerably less widely recognized roles throughout the body in both women and men alike. Prolactin levels naturally rise dramatically during pregnancy and breastfeeding, and elevated levels during this time normally suppress ovulation, a natural, well-documented biological mechanism that historically helped space out successive pregnancies in breastfeeding mothers throughout human history. Outside of pregnancy, abnormally elevated prolactin can suppress reproductive hormones in both sexes, causing irregular periods or reduced fertility in women and low testosterone or erectile dysfunction in men, a pattern often traced directly back to a benign pituitary tumor called a prolactinoma affecting hormone regulation.

How Prolactin Is Measured

Prolactin is measured from a standard blood sample using automated chemiluminescent immunoassay platforms, in which antibodies bind specifically to prolactin molecules, generating a measurable light signal directly proportional to the hormone concentration present in that particular sample tested. Because prolactin naturally rises with stress, exercise, and even recent breast stimulation, doctors generally recommend a calm, fasting morning blood draw to avoid falsely elevated results that don't genuinely reflect a patient's true baseline hormone level. When results come back unexpectedly high, laboratories can also test for a phenomenon called macroprolactinemia, in which a harmless, larger form of prolactin falsely inflates the measured result without ever actually causing any real, clinically meaningful symptoms in the patient.

Scientists Behind the Science

Oscar Riddle's foundational 1928 pigeon research gave modern science its very first named hormone specifically associated with milk production, establishing the essential biological concept decades before anyone could properly isolate or study the equivalent human hormone directly. Henry Friesen's transformative 1970 isolation of human prolactin then decisively corrected a long-standing scientific misconception and finally gave physicians a genuine, reliable way to accurately measure and study this hormone in actual human patients. Together, spanning more than four decades of steady scientific progress, their combined contributions transformed prolactin from an obscure avian curiosity into a clinically essential hormone now routinely tested in fertility clinics and endocrinology practices worldwide today.