Relationship between Maternal Parity, Basal Prolactin Levels and Neonatal Breast Milk Intake

Abstract

Basal serum levels of prolactin (PRL) in 21 nursing mothers were measured by radioimmunoassay on the 2nd, 3rd and 4th days of the puerperium. The quantity of breast milk suckled during the 4th day of life was also evaluated by calculating the difference in the baby’s weight before and after each feeding. During the first postpartum days, mean basal levels of PRL did not change. However these levels were noted to be significantly lower in the multiparas (p < 0.05) than in the primiparas. In addition, the milk intake in neonates of multiparous mothers was significantly greater (p < 0.05) than that in neonates of primiparous mothers. The authors’ hypothesis, based on the results of animal experimentation described in the literature, is that initiation of breast-feeding is facilitated in multiparas by the increased number of occupied PRL receptors in the mammary glands reflected by the lowered serum levels of the hormone.

Early lactation performance in primiparous and multiparous women in relation to different maternity home practices. A randomised trial in St. Petersburg

“…An analogous finding is that the prolactin surge to suckling is blunted in rats having previous experience of lactation [30]. Studies in humans actually indicate a similar increased sensitivity of prolactin receptors in multiparous when compared to primiparous women [31]. …”

Maternal concentrations of perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) and duration of breastfeeding

“…Hormonal concentrations differ between multiparous and primiparous women. It has been shown that serum levels of prolactin were lower among multi-than primiparas (36). They also have different lactation performance, such as early suckling, numbers of feedings, milk intake in neonates and use of formula (37).…”

Reproductive Experience Alters Prolactin Receptor Expression in Mammary and Hepatic Tissues in Female Rats1

“…Related studies in rats have reported that parity results in increased estrogen receptor expression in the mammary gland with increased expression of both ESR1 (previously ER alpha) and ESR2 (previously ER beta) detected in multiparous dams [17]. In humans, milk intake in neonates of multiparous mothers is greater than that in neonates of primiparous mothers [24]. Moreover, body weight gains of the neonates of multiparous mothers are higher, presumably reflecting some combination of greater PRLR occupation and activity during the first few days of life and/or enhanced milk letdown and altered nursing patterns.…”

“…The physiological significance of these changes is not clearly understood. However, given the higher level of PRL-stimulated milk production associated with a second lactation [1,24], it is possible that these changes in mammary Prlr expression and receptor protein may participate in the elevations in lactogenesis in multiparous animals. It is possible that the changes in receptor isoform protein ratios found in this study may underlie a shift in sensitivity of the mammary glands with the PRLRS acting as a dominant negative.…”