Abstract
A possible physiological role of prolactin (PRL) in human milk was studied. The concentrations of milk PRL were 36.5±5.8ng/ml on the first day after delivery and increased rapidly on the second day. Higher levels continued up to the fifth day. The levels of milk PRL showed no significant correlation with milk yield. Milk PRL was capable of binding to its receptors, suggesting its biological activities. In conclusion, human milk contains significant amounts of immunoreactive PRL. Milk PRL appears to be biologically potent, which raises the possibility that it may have certain physiological significance for the newborn.
