The discovery of human prolactin: a very personal account

Abstract

Although prolactin was discovered in the early 1930's in sheep, cows, birds etc., no human form had been because it was thought to be identical to human growth hormone (HGH). In fact, prior to 1970, most endocrinologists doubted human prolactin even existed. Prolactin-like effects could be demonstrated from a homogenate of human pituitary but attempting to purify it identified only growth hormone. Independent histological studies had identified prolactin-secreting "pregnancy cells" fuelling the conviction that prolactin was a distinct and separate pituitary hormone. A search was begun for prolactin through protein synthesis studies using pituitaries from pregnant and postpartum monkeys. Proteins obtained in a radioactive peak were similar to, but not identical with, growth hormone by molecular weight and electrophoretic mobility. The hypothesis that the unknown protein peak represented synthesis of prolactin rather than growth hormone proved correct. Evidence was then obtained confirming that in the human pituitary prolactin and growth hormone synthesis could be distinguished using antibodies to human growth hormone or to sheep prolactin. Human prolactin purified from pituitary glands using immunological tools capable of distinguishing between the two hormones provided ultimate proof of a separate and distinct human prolactin, a hormone which has its major impact today in endocrinology and reproductive medicine. This discovery represented an exciting and truly international collaborative effort.