Prolactin

Publisher Summary In the late 1920s and early 1930s, it was found that pituitary extracts could induce milk secretion. Riddle and coworkers found that this substance, which they named prolactin (PRL), could be differentiated from the known growth- and gonad-stimulating substances. In these experiments, they showed that PRL stimulated milk production by guinea pig mammary glands and a milk-like substance from the crop sacs of pigeons and doves, giving rise to the pigeon crop sac bioassay for PRL. Over the ensuing years, PRL was characterized, sequenced and specific radioimmunoassays (RIAs) developed for PRL from a number of species. Because of the high lactogenic activity of even very highly purified preparations of human growth hormone (GH), however, it was impossible to separate human PRL from GH using the relatively crude pigeon crop assay. Finally, in 1970, Frantz and Kleinberg developed a sensitive in vitro bioassay which involved staining milk produced by cultured, lactating mouse mammary tissue in response to PRL that was capable of measuring PRL levels as low as 5 ng/ml. In this assay, they added excess antibody to GH to neutralize any potential lactogenic effects it had and, for the first time, were able to demonstrate measurable PRL levels in women with puerperal and nonpuerperal galactorrhea, but not in most normal men and women. Shortly thereafter, an RIA for human RL was developed which could finally measure PRL levels in the sera of normal individuals, permitting the eventual sequencing of human PRL and determination of its cDNA sequence.