Modulation of prolactin release by a 25 kD peptide of human seminal plasma

Prolactin-regulating factor (PRF) of molecular size of 25 kD has been isolated from human seminal plasma. This 25 kD factor inhibits circulating PRL levels in intact adult male rats to the extent of about 48% at dose level of 10 micrograms. Furthermore, in vitro incubation of pituitary demonstrated that PRF inhibits the release of PRL in the medium. PRF also interferes with the binding of I125 PRL to its receptors in liver, prostate, and spermatozoa. However, I125 PRF itself does not bind to these receptors. PRF seems to modulate PRL release as well as its binding to receptors. A sensitive, specific RIA was developed for PRF. Using the RIA, levels of PRF in seminal plasma were measured. PRF levels were low in vasectomized subjects as compared with controls. A negative correlation was noted with seminal plasma PRF levels and sperm count.