The Initiation of Human Lactation and Prolactin Response to Suckling

Abstract

In order to assess the role of prolactin (PRL) in the initiation oflactation in the early postpartum period, serum levels of PRL in 18 nursing mothers were determined by homologous RIA, near term, immediately after delivery, and before and after a morning nursing on the 2nd, 4th and 6th postpartum day. The mothers were divided into 3 groups (good, moderate and poor lactation) according to the amount of milk produced during the first 5 postpartum days. Basal levels of PRL gradually declined in all groups and were not significantly different between the 3 groups. However, significant post-nursing increases in PRL levels (P < 0.05) were observed 4 days (168%) and 6 days (236%) after delivery in the good lactation group, and on the 6th postpartum day (172%) in the moderate lactation group. But no post-nursing increases were found in the poor lactation group. In order to clarify the cause of different responses of PRL to nursing stimulus, 26 nursing mothers volunteered to have a 20 min breast pump stimulation on the 5th postpartum day, and serum PRL levels were determined before and after the stimulation. Significant increases in PRL levels following uniform breast stimulation (P < 0.05) were observed in all 3 groups and these were not different between groups. These data suggest that the initiation of milk secretion in the human seems to be closely related to the increase in PRL levels induced by an adequate baby's suckling.