The Discovery of Prolactin
| Category | Research |
|---|---|
| Also known as | prolactin history, lactogenic hormone, LTH |
| Last updated | 2026-04-14 |
| Reading time | 3 min read |
| Tags | historyprolactinpituitarylactationdopamine |
Overview
Prolactin is a 199-amino-acid peptide hormone secreted by lactotroph cells of the anterior pituitary. It was identified as a distinct lactation-stimulating pituitary factor in the late 1920s and 1930s, primarily through the work of Oscar Riddle, Robert W. Bates, and Simon Dykshorn at the Carnegie Institution in Cold Spring Harbor. Their 1933 paper, which named the hormone "prolactin," demonstrated that extracts of anterior pituitary contained a principle distinct from growth hormone that could induce crop-milk production in pigeons and mammary development in mammals.
Over subsequent decades, prolactin was purified and shown to have structural similarities with growth hormone and placental lactogen, forming a family of related hormones. Its regulation proved unique among anterior pituitary hormones: it is predominantly under tonic inhibition by hypothalamic dopamine, released through the median eminence into the hypophyseal portal system. This inhibitory regulation, rather than a dominant releasing hormone, sets prolactin apart.
Today, more than three hundred biological actions of prolactin have been described across reproduction, immunity, behavior, osmoregulation, and metabolism. Clinically, prolactin-secreting pituitary adenomas (prolactinomas) are the most common functional pituitary tumors, and dopamine agonists remain the first-line medical therapy.
Key People
- Oscar Riddle (1877ā1968): Carnegie Institution biologist who led the Cold Spring Harbor studies.
- Robert W. Bates and Simon Dykshorn: Riddle's collaborators on the 1933 paper naming prolactin.
- Henry Friesen: Canadian endocrinologist who purified human prolactin in the 1970s, confirming it as distinct from growth hormone.
- Paul MacLeod, Kenneth McGinley and Andrzej Bartke: Contributors to prolactin physiology and regulation studies.
Timeline
- 1928: Stricker and Grueter demonstrate a lactogenic factor in pituitary extracts.
- 1933: Riddle, Bates, and Dykshorn coin "prolactin" and publish the pigeon crop-sac bioassay.
- 1940sā1950s: Prolactin activity is distinguished from growth hormone in non-human species.
- 1971: Friesen and Hwang purify human prolactin as a distinct hormone.
- 1972: Radioimmunoassay for prolactin is developed.
- 1980s: Dopamine agonists (bromocriptine, cabergoline) become first-line therapy for prolactinomas.
- 1990s: Prolactin receptor is cloned.
Background
For decades, a major scientific controversy concerned whether human prolactin existed at all as a distinct hormone or whether growth hormone performed both lactogenic and somatic growth functions in humans. The issue was not fully resolved until Friesen's 1971 purification of human prolactin, driven by sensitive bioassays and immunological methods. The availability of human prolactin enabled the subsequent radioimmunoassay, which transformed endocrine diagnostics.
The hypothalamic regulation of prolactin is unusual. Where most anterior pituitary hormones are predominantly controlled by stimulatory hypothalamic peptides, prolactin is dominantly inhibited by dopamine. Stimulators such as thyrotropin releasing hormone can also increase prolactin, contributing to the hyperprolactinemia sometimes seen in hypothyroidism. Prolactin surges accompany suckling, emotional stress, and estrogen exposure.
Modern Relevance
Dopamine agonists, especially cabergoline, are the mainstay of medical therapy for prolactinomas, often producing tumor shrinkage as well as hormone normalization. Understanding the dopamine-prolactin axis is also crucial for managing the hyperprolactinemia commonly associated with antipsychotic medications, which block dopamine D2 receptors.
Prolactin's broader biology is still being unpacked. Research on prolactin's roles in immune regulation, maternal behavior, osmoregulation in freshwater fish, and bone remodeling continues to expand the physiological reach of the hormone. The ancient evolutionary origins of prolactin ā it is conserved across vertebrates with diverse functions ā make it a model for studying how a single peptide can acquire new roles over evolutionary time.
Related Compounds
Related entries
- History of Growth Hormone Researchā An overview of the discovery, purification, and recombinant production of growth hormone over the twentieth century.
- The Discovery of Somatostatinā Somatostatin, the hypothalamic peptide that inhibits growth hormone release, was identified in 1973 by Brazeau and Guillemin.
- The Discovery of Vasopressinā Vasopressin, the antidiuretic hormone of the posterior pituitary, was identified through late 19th- and early 20th-century research on pituitary extracts.