The relationship between suckling-induced prolactin response and lactogenesis

Evolutionary biological perspectives on current social issues of breastfeeding and weaning

Breastfeeding and weaning are actively studied from evolutionary, medical, and social research perspectives because of their close association with infant mortality, lifetime health, and human population dynamics. Each discipline benefits from an interdisciplinary exchange of knowledge regarding the bases, processes, and consequences of these phenomena. However, current social issues related to breastfeeding and weaning have received little attention from an evolutionary biology perspective. We address this gap by reviewing current social issues related to human breastfeeding and weaning in an evolutionary framework. This approach helps build a conceptual framework with the goal of better understanding ultimate causes of or influences on these current social issues. The six social issues reviewed here fall into three categories: the spatiotemporal constraints of breastfeeding, abuse of breast milk as valuable material, and mismatch in breastfeeding practices. Some of these issues have an evolutionary basis. We analyze the structure of these social issues and discuss their possible solutions in terms of extension of the trade-off theory in evolutionary biology. Our discussion on the current social issues in breastfeeding and weaning highlights the effectiveness of an approach rooted in evolutionary theory and biological anthropology.

Lactation alters the relationship between liver lipid synthesis and hepatic fat stores in the postpartum period

In mothers who are nursing their infants, increased clearance of plasma metabolites into the mammary gland may reduce ectopic lipid in the liver. No study to date has investigated the role of lactation on liver lipid synthesis in humans, and we hypothesized that lactation would modify fatty acid and glucose handling to support liver metabolism in a manner synchronized with the demands of milk production. Lactating (n = 18) and formula-feeding women (n = 10) underwent metabolic testing at 6-week postpartum to determine whether lactation modified intrahepatic triacylglycerols (IHTGs), measured by proton magnetic resonance spectroscopy. Subjects ingested oral deuterated water to measure fractional de novo lipogenesis (DNL) in VLDL-TG during fasting and during an isotope-labeled clamp at an insulin infusion rate of 10 mU/m²/min. Compared with formula-feeding women, we found that lactating women exhibited lower plasma VLDL-TG concentrations, similar IHTG content and similar contribution of DNL to total VLDL-TG production. These findings suggest that lactation lowers plasma VLDL-TG concentrations for reasons that are unrelated to IHTG and DNL. Surprisingly, we determined that the rate of appearance of nonesterified fatty acids was not related to IHTG in either group, and the expected positive association between DNL and IHTG was only significant in formula-feeding women. Further, in lactating women only, the higher the prolactin concentration, the lower the IHTG, while greater DNL strongly associated with elevations in VLDL-TG. In conclusion, we suggest that future studies should investigate the role of lactation and prolactin in liver lipid secretion and metabolism.

Impact of Nipple Shield Use on Milk Transfer and Maternal Nipple Pain

Background: Nipple pain is a common cause of early cessation of breastfeeding. A nipple shield (shield) is often used to improve breastfeeding comfort. There are concerns that shield use may limit milk transfer. The aims of this study were to determine whether shield use reduces milk transfer and maternal nipple pain. Methods: A within-subject study of two groups of breastfeeding dyads (infants <6 months) was conducted; Control Group (CG): no breastfeeding difficulties; Pain Group (PG) shield used for nipple pain. There were two monitored sessions where shield use was randomized. Test weights and pain questionnaires were completed, and percentage of available milk removed (PAMR) was calculated. Results: Twenty-five PG (6 ± 4 postnatal weeks) and 34 CG (9 ± 6 postnatal weeks) had similar 24-hour milk production (PG: 676 ± 239 mL, CG: 775 ± 162 mL, p = 0.083). PG mean milk transfer volume and PAMR did not differ with shield use (no shield: 46 mL, 59%; shield: 40 mL, 53%, volume p = 0.38, PAMR p = 0.64). CG mean volume and PAMR were reduced with shield use (no shield: 65 mL, 64%; shield: 31 mL, 33%, volume p < 0.001, PAMR p < 0.001). PG pain scores were similar with and without shield use (Visual Analog Scale p = 0.44, McGill p = 0.97). Conclusions: Shield use did not impact either milk production or milk transfer in breastfeeding women experiencing nipple pain.

Lactation Versus Formula Feeding: Insulin, Glucose, and Fatty Acid Metabolism During the Postpartum Period

Milk production may involve a transient development of insulin resistance in nonmammary tissues to support redistribution of maternal macronutrients to match the requirements of the lactating mammary gland. In the current study, adipose and liver metabolic responses were measured in the fasting state and during a two-step (10 and 20 mU/m²/min) hyperinsulinemic-euglycemic clamp with stable isotopes, in 6-week postpartum women who were lactating (n = 12) or formula-feeding (n = 6) their infants and who were closely matched for baseline characteristics (e.g., parity, body composition, and intrahepatic lipid). When controlling for the low insulin concentrations of both groups, the lactating women exhibited a fasting rate of endogenous glucose production (EGP) that was 2.6-fold greater and a lipolysis rate that was 2.3-fold greater than the formula-feeding group. During the clamp, the groups exhibited similar suppression rates of EGP and lipolysis. In the lactating women only, higher prolactin concentrations were associated with greater suppression rates of lipolysis and lower intrahepatic lipid and plasma triacylglycerol concentrations. These data suggest that whole-body alterations in glucose transport may be organ specific and facilitate nutrient partitioning during lactation. Recapitulating a shift toward noninsulin-mediated glucose uptake could be an early postpartum strategy to enhance lactation success in women at risk for delayed onset of milk production.

Which breast pump for which mother: an evidence-based approach to individualizing breast pump technology

The majority of new mothers in the United States use breast pumps in the first 4 months postbirth in order to achieve their personal human milk feeding goals. Although these mothers seek guidance from health-care professionals with respect to the type and use of breast pumps, there are few evidence-based guidelines to guide this professional advice. This paper reviews the evidence to facilitate professional individualization of breast pump recommendations using three categories of literature: the infant as the gold standard to which the pump is compared; the degree of maternal breast pump dependency (for example, the extent to which the breast pump replaces the infant for milk removal and mammary gland stimulation); and the stage of lactation for which the pump replaces the infant. This review can also serve to inform public and private payers with respect to individualizing breast pump type to mother-infant dyad characteristics.

Recombinant human prolactin for the treatment of lactation insufficiency

CONTEXT

Lactation insufficiency has many aetiologies including complete or relative prolactin deficiency. Exogenous prolactin may increase breast milk volume in this subset. We hypothesized that recombinant human prolactin (r-hPRL) would increase milk volume in mothers with prolactin deficiency and mothers of preterm infants with lactation insufficiency.

DESIGN

Study 1: R-hPRL was administered in an open-label trial to mothers with prolactin deficiency. Study 2: R-hPRL was administered in a randomized, double-blind, placebo-controlled trial to mothers with lactation insufficiency that developed while pumping breast milk for their preterm infants.

PATIENTS

Study 1: Mothers with prolactin deficiency (n = 5). Study 2: Mothers of premature infants exclusively pumping breast milk (n = 11).

DESIGN

Study 1: R-hPRL (60 μg/kg) was administered subcutaneously every 12 h for 28 days. Study 2: Mothers of preterm infants were randomized to receive r-hPRL (60 μg/kg), placebo or r-hPRL alternating with placebo every 12 h for 7 days.

MEASUREMENTS

Change in milk volume.

RESULTS

Study 1: Peak prolactin (27·9 ± 17·3 to 194·6 ± 19·5 μg/l; P < 0·003) and milk volume (3·4 ± 1·6 to 66·1 ± 8·3 ml/day; P < 0·001) increased with r-hPRL administration. Study 2: Peak prolactin increased in mothers treated with r-hPRL every 12 h (n = 3; 79·3 ± 55·4 to 271·3 ± 36·7 μg/l; P < 0·05) and daily (101·4 ± 61·5 vs 178·9 ± 45·9 μg/l; P < 0·04), but milk volume increased only in the group treated with r-hPRL every 12 h (53·5 ± 48·5 to 235·0 ± 135·7 ml/day; P < 0·02).

CONCLUSION

Twice daily r-hPRL increases milk volume in mothers with prolactin deficiency and in preterm mothers with lactation insufficiency.

Prolactin regulates ZNT2 expression through the JAK2/STAT5 signaling pathway in mammary cells

The zinc transporter ZnT2 (SLC30A2) plays an important role in zinc secretion into milk during lactation. The physiological process of mammary gland secretion is regulated through complex integration of multiple lactogenic hormones. Prolactin plays a primary role in this regulation through the activation of various signaling cascades including Jak2/STAT5, mitogen-activated protein kinase (MAPK), p38, and phosphatidylinositol 3-kinase (PI3K). The precise mechanisms that regulate the transfer of specific nutrients such as zinc into milk are not well understood. Herein we report that prolactin increased ZnT2 abundance transcriptionally in cultured mammary epithelial (HC11) cells. To delineate the responsible mechanisms, we first determined that prolactin-mediated ZnT2 induction was inhibited by pretreatment with the Jak2 inhibitor AG490 but not by the MAPK inhibitor PD-98059. Using a luciferase reporter assay, we demonstrated that ZnT2 promoter activity was increased by prolactin treatment, which was subsequently abolished by expression of a dominant-negative STAT5 construct, implicating the Jak2/STAT5 signaling pathway in the transcriptional regulation of ZnT2. Two putative consensus STAT5 binding sequences in the ZnT2 promoter were identified (GAS1:-674 to -665 and GAS2:-377 to -368). Mutagenesis of the proximal GAS2 element resulted in complete abrogation of PRL-induced ZnT2 promoter activity. The promoter incorporating the distal GAS1 mutation was only able to respond to very high PRL concentrations. Results from both the mutagenesis and gel shift assays indicated that a cooperative relationship exists between GAS1 and GAS2 for PRL-induced activation; however, the proximal GAS2 plays a more critical role in STAT5-mediated signal transduction compared with the GAS1 element. Finally, chromosome immunoprecipition assay further confirmed that prolactin activates STAT5 binding to the ZnT2 promoter in vivo. Taken together, these results illustrate that prolactin regulates the transcription of ZnT2 through activation of the Jak2/STAT5 signaling pathway to assist in providing optimal zinc for secretion into milk during lactation.

Association of Serum Prolactin and Oxytocin With Milk Production in Mothers of Preterm and Term Infants

The present study was designed to compare milk production and hormone responses (prolactin [PRL], oxytocin [OT]) and to determine associations of hormone levels with milk production in mothers of preterm (PT) and term (TM) infants during the first 6 weeks postpartum. Mothers of PT infants ( n = 95) were all pump dependent; mothers of TM infants ( n = 98) were all feeding their infant at breast. Mothers of nonnursing PT infants produced less milk over time compared to mothers of TM infants. A higher proportion of PT mothers had lower basal PRL levels compared with TM mothers. PRL and frequency of breast stimulation combined positively influenced milk production in PT mothers. OT levels were higher in PT versus TM mothers, but OT was not related to milk production. Further study is warranted regarding interventions to enhance milk production, particularly in pump-dependent mothers of PT infants.

Biphasic effects of moderate drinking on prolactin during lactation

BACKGROUND

Contrary to the popular lore that encourages women to drink alcohol as an aid to lactation, we previously showed that alcohol consumption disrupted lactational performance and the hormonal milieu of the lactating mother in the short term.

METHODS

Thirteen lactating women participated in a 4-session, double-blind, 2 x 2 within-subject study to test several hypotheses related to the effects of alcohol on prolactin (PRL) responses and milk yield over time. The two within-subject factors were beverage condition (control or 0.4 g/kg dose of alcohol) and pumping condition (pumping occurred at fixed intervals once or twice during the 5.3-hour session). Plasma PRL, blood alcohol concentrations (BAC), and milk yield were measured.

RESULTS

Alcohol consumption increased basal PRL levels (p < 0.0001) and modified the PRL response to pumping (p < 0.0001) but the directionality of the response depended on when pumping occurred along the BAC curve. Pumping enhanced PRL response when it occurred during the ascending BAC limb but blunted the response when it occurred during the descending limb, providing evidence that the effects were transient and of a biphasic nature. The slower the alcohol was metabolized, the greater the relative PRL response to breast pumping (p < 0.05). The dynamics of the PRL response between pumping sessions was also altered if women drank. If women pumped within the hour after drinking alcohol, the PRL response during the next pumping some 1.5 hours later, was delayed by a few minutes. Milk yield was significantly lower after drinking alcohol but such deficits were not significantly related to PRL or the speed at which alcohol was eliminated.

CONCLUSIONS

Effects of alcohol on suckling-induced PRL were biphasic in nature, but could not explain the deficits in lactational performance. Such findings provide further evidence that the dynamic changes in neuroendocrine state are integrally involved in alcohol's effects over time and underscore the complexity of lactation.

A critical review of pharmaceutical galactagogues

Use of plant and drug products to enhance lactation is widespread, and numerous papers have been published in the medical literature claiming efficacy for various products. This paper will review and evaluate the published literature on the most widely used pharmaceuticals that are used as galactagogues. Breastfeeding physiology is reviewed with the aim of creating a framework for understanding galactagogue pharmacology. Published articles were selected and evaluated using the principles of evidence-based medicine, and were also evaluated using the principles of good lactation management. Only three studies on oxytocin and seven studies on dopamine antagonists were found to be useful. Oxytocin is probably not useful as a galactagogue, except possibly in rare circumstances of tetraplegic mothers. Dopamine antagonists appear not to enhance milk supply if mothers are given good lactation support and employ these practices. The safety of the dopamine antagonists has not been adequately evaluated, so their use should be avoided unless other measures have failed.

Short-term prolactin administration causes expressible galactorrhea but does not affect bone turnover: pilot data for a new lactation agent

Background

Medications used to augment lactation increase prolactin secretion but can have intolerable side effects. We examined the biological activity of recombinant human prolactin (r-hPRL) as preliminary data for its use to augment lactation.

Methods

Healthy, non-postpartum women (n = 21) with regular menstrual cycles underwent a seven day randomized, double-blind, placebo-controlled trial of r-hPRL. Expressible galactorrhea, markers of bone turnover, calcium homeostasis and gonadal function were measured and side effects recorded.

Results

Prolactin levels increased during r-hPRL administration (20.0 ± 2.8 to 231.7 ± 48.9 μg/L at 6 hours; p < 0.05). Five of nine participants who received r-hPRL developed expressible galactorrhea (p < 0.001). Urinary deoxypyridinoline decreased and bone specific alkaline phosphatase increased in r-hPRL and placebo groups. Menstrual cycle lengths were not altered and side effects were similar between r-hPRL and placebo groups.

Conclusion

In summary, r-hPRL can cause expressible galactorrhea. Seven days of r-hPRL administration does not adversely affect bone turnover or menstrual cyclicity. Thus, r-hPRL may be a viable option for short-term lactation augmentation.

Trial registration

Clinical Trials.gov NCT00438490

Prolactin responses to infant cues in men and women: effects of parental experience and recent infant contact

We used a longitudinal design to test whether parental experience differentially affects the development of prolactin responses to infant cues in men and women. Couples provided two blood samples at three tests, one test just before their babies were born, and two tests during the early postnatal period (n=21). Nine couples repeated the tests near the birth of their second babies. In the 30 min between the two samples, couples listened to recorded infant cries at the prenatal test and held their baby (fathers) or a doll (mothers) at the postnatal tests. Blood samples were analyzed for prolactin concentrations. Prolactin values were then related to sex and parity differences as well as to questionnaire data concerning emotional responses to infant cries and previous infant contact. We found that (1) prior to the birth of both the first and second babies, women's prolactin concentrations increased after exposure to infant stimuli, whereas men's prolactin concentrations decreased; postnatal sex differences varied with parity; (2) women's prolactin reactivity did not change significantly with parental experience; (3) the same men's prolactin concentrations decreased after holding their first newborns but increased after holding their second newborns; this change was not gradual or permanent; (4) men reporting concern after hearing recorded infant cries showed a different postnatal pattern of prolactin change after holding their babies than men not reporting concern; and (5) men who had little contact with their babies just prior to testing had a more positive prolactin response than men who had recently held their babies for longer periods. Although parental experience appears to affect men's prolactin responses, differences in reactivity were also related to patterns of recent infant contact and individual differences in responses to infant cues.

Human breast areolae as scent organs: morphological data and possible involvement in maternal-neonatal coadaptation

In humans, areolar skin glands (AG) enlarge during pregnancy and lactation. Their role in mother-infant interactions may pertain to protective, mechanical, and communicative functions. It was questioned here whether more profuse AG could be related to more optimal adaptation to breastfeeding. A morphological study of the areolae was undertaken between birth and day 3 to assess the number, secretory status, and spatial distribution of AG. These data were related to infants' weight variation, mothers' perception of their infant's behavior at breast, and time between delivery and onset of lactation. AG were seen in virtually all women but with great interindividual variations; their areolar distribution was nonrandom, and about 1/5 of the women had AG giving off a secretion. The AG number was positively related with neonatal weight gain between birth and day 3, and with the mother's perception of infant's latching speed and sucking activity. AG numbers were also positively related with the onset of lactation in first-time mothers. In conclusion, the maternal endowment in AG may contribute to the infants' breastfeeding performance, early growth, and the mother's lactation onset.

Acute alcohol consumption disrupts the hormonal milieu of lactating women

Despite the lack of scientific evidence to support the claim that alcohol is a galactagogue, lactating women have been advised to drink alcohol as an aid to lactation for centuries. To test the hypothesis that alcohol consumption affects the hormonal response in lactating women, we conducted a within-subjects design study in which 17 women consumed a 0.4 g/kg dose of alcohol in orange juice during one test session and an equal volume of orange juice during the other. Changes in plasma prolactin, oxytocin, and cortisol levels during and after breast stimulation, lactational performance, and mood states were compared under the two experimental conditions. Oxytocin levels significantly decreased, whereas prolactin levels and measures of sedation, dysphoria, and drunkenness significantly increased, during the immediate hours after alcohol consumption. Changes in oxytocin were related to measures of lactational performance such as milk yield and ejection latencies, whereas changes in prolactin were related to self-reported measures of drunkenness. Although alcohol consumption resulted in significantly higher cortisol when compared with the control condition, cortisol levels were not significantly correlated with any of the indices of lactational performance or self-reported drug effects. Moreover, cortisol levels steadily decreased on the control day, indicating that the procedures were not stressful to the subjects. In conclusion, recommending alcohol as an aid to lactation may be counterproductive. In the short term, mothers may be more relaxed, but the hormonal milieu underlying lactational performance is disrupted, and, in turn, the infant's milk supply is diminished.

Endocrinology of lactation

The endocrine control of lactation is one of the most complex physiologic mechanisms of human parturition. Mammogenesis, lactogenesis, galactopoiesis, and galactokinesis are all essential to assure proper lactation. Prolactin is the key hormone of lactation and seems to be the single most important galactopoietic hormone. Oxytocin, serotonin, opioids, histamine, substance P, and arginine-leucine modulate prolactin release by means of an autocrine/paracrine mechanism, whereas estrogen and progesterone hormones can act at the hypothalamic and adenohypophysial levels. Human placental lactogen and growth factors play an essential role to assure successful lactation during pregnancy. Oxytocin is the most powerful galactokinetic hormone.

Prepregnant overweight and obesity diminish the prolactin response to suckling in the first week postpartum

OBJECTIVE

The population subgroups with the highest proportion of overweight and obese women often are characterized by the lowest rates of initiation and shortest durations of breastfeeding. We previously documented that these 2 population-level trends may be related. In a population of white women who lived in a rural area, we observed that prepregnant overweight and obesity were associated with failure to initiate and also to sustain lactation. The means by which being overweight or obese negatively affect lactational performance is unknown and likely to be multifactorial in origin, including the simple mechanical difficulties of latching on and proper positioning of the infant. In addition, we have shown that prepregnant body mass index (BMI) is negatively associated with the timing of lactogenesis II, the onset of copious milk secretion. Although the effects of obesity on the prolactin response to infant suckling have never been studied, we postulated that maternal obesity could compromise this important response. We proposed that this might occur because obesity alters the 24-hour spontaneous release of prolactin and also because prolactin secretion is blunted in response to various stimuli among obese subjects. The fall in progesterone concentration that occurs immediately postpartum is the trigger for the onset of copious milk secretion, but maintenance of prolactin and cortisol concentrations is necessary for this trigger to be effective. Adipose tissue concentrates progesterone. We proposed that this additional source of progesterone would lead to consistently higher progesterone concentrations among obese compared with normal-weight women. This, in turn, would lead to a delay in reaching the appropriate concentration to trigger the onset of lactogenesis II. We tested the hypotheses that a reduced prolactin response to suckling and higher-than-normal progesterone concentration in the first week after delivery might be among the means by which maternal overweight could compromise early lactation.

METHODS

We enrolled 40 mothers of term infants from the same population that we studied previously. We measured serum prolactin and progesterone concentrations by radioimmunoassay before and 30 minutes after the beginning of a suckling episode at 48 hours and 7 days after delivery. We used path analysis to develop a parsimonious multivariate prediction of the prolactin response to suckling at 48 hours and 7 days postpartum.

RESULTS

As expected, prolactin values decreased from 48 hours to 7 days postpartum. Women who were overweight or obese (using the Institute of Medicine's cutoff for women of a BMI >26 kg/m2) before conception had a lower prolactin response to suckling than normal-weight women at 48 hours but not at day 7. In multivariate analyses, overweight/obesity, primiparity, and birth weight were negatively associated with the prolactin response to suckling at 48 hours. After adjustment for confounding by time since delivery and the duration of the nursing episode, only overweight/obesity remained a significant negative predictor of prolactin response to suckling at day 7. Concentrations of progesterone decreased dramatically from 48 hours to 7 days postpartum but did not differ between normal-weight and overweight/obese women at either time. In addition, the decreases in progesterone concentrations from 48 hours to 7 days postpartum did not differ between the prepregnant BMI groups.

CONCLUSION

The unique and important finding from this study is that overweight/obese women had a lower prolactin response to suckling. This would be expected to compromise the ability of overweight/obese women to produce milk and, over time, could lead to premature cessation of lactation. These findings are important because, during our observation period (just before and after lactogenesis II, the time of onset of copious milk secretion), the prolactin response to suckling is more important for milk production than it is later in lactation. We have previously shown that a high proportion of the overweight and obese women in women in this population who give up on breastfeeding do so at this time. This finding thus provides evidence of a biological basis for this association, and additional study of it is likely to be informative. We postulated that there would be consistently higher progesterone concentrations in the early postpartum period among obese compared with normal-weight women because adipose tissue is an extraplacental source of this hormone. This hypothesis was not supported in this study because there were no significant differences between normal-weight and overweight/obese women in progesterone concentrations at either 48 hours or 7 days postpartum. The values that we observed at these times were similar to those reported by others in the early postpartum period. The findings from this study add plausibility to our observation that initiation, not just duration of breastfeeding, is negatively affected by maternal overweight/obesity. Although women should begin pregnancy at a healthy weight and gain reasonably during gestation, not all will. Pediatricians can help overweight/obese women to succeed at breastfeeding by targeting them for contact with a lactation consultant before discharge from the hospital to be sure that they have received optimal advice on breastfeeding techniques. In addition, early contact with the mother after discharge--by calling her at home to offer her support and counseling for breastfeeding, by scheduling the first pediatric visit earlier than for other patients, or by enlisting the assistance of public health nurses for a home visit if this is possible--would help overweight/obese women to continue to breastfeed. Being overweight or obese is negatively associated with the prolactin response to suckling in the first week postpartum and, thus, may contribute to early lactation failure.

Intention to use the female condom following a mass-marketing campaign in Lusaka, Zambia

OBJECTIVES

This report examines intention to use the female condom among men and women in Lusaka, Zambia, who were exposed to mass-marketing of the female condom.

METHODS

The study used data from a representative sample of consumers at outlets that sell or distribute the female condom and the male condom.

RESULTS

In spite of a high level of awareness of the female condom, use of this method in the last year was considerably lower than use of the male condom. Intention to use the female condom in the future was highest among respondents who had used only the female condom in the last year.

CONCLUSIONS

The female condom is likely to be most important for persons who are unable or unwilling to use the male condom.

Maternal smoking and the risk of early weaning: a meta-analysis

OBJECTIVES

This study reviewed evidence on the effect of maternal smoking on early weaning.

METHODS

The following databases and journals were searched: Medline, Scientific Citation Index, Pediatrics, Journal of Pediatrics, New England Journal of Medicine, and Lancet. Analysis was restricted to studies in which infants who had never been breastfed were excluded or the prevalence of breastfeeding initiation was more than 90%.

RESULTS

In smoking vs nonsmoking mothers, the random effects odds ratio for weaning before 3 months was 1.93 (95% confidence interval [CI] = 1.55, 2.40). An adjusted odds ratio of 1.50 (95% CI = 1.34, 1.68) was shown in studies that had lost-to-follow-up rates below 15% and included adequate adjustment for confounding.

CONCLUSIONS

Maternal smoking increases the risk of early weaning.

Anatomy and physiology of lactation

Milk secretion is a robust process that proceeds normally in at least 85% of women postpartum. Anecdotal evidence suggests that, with assistance in the techniques of breastfeeding, at least 97% of women can successfully breastfeed their infants. The causes of lack of success in breastfeeding are not well understood because, at least in Western societies, when infants fail to thrive on the breast, formula substitution is easy. Although this article is not the place to discuss possible pathologic mechanisms, breastfeeding failure usually occurs at approximately the first week postpartum, and a much better understanding of the mechanisms by which milk secretion is initiated during this period may help researchers to understand why some women have severe problems with lactation. The general understanding of the mechanisms of milk secretion is fairly good, but the regulatory mechanisms at the cellular and molecular levels have not been given adequate attention and are ripe for future investigation. Other areas that require attention are the behavior correlates of breastfeeding and the transfer of drugs and toxins into milk. The latter may have a long-term impact on infant health and should receive increased attention.

Serum prolactin in breastfeeding: state of the science

Prolactin is one of two major hormones involved in lactation. While the role of infant suckling and oxytocin in the lactation process are well understood, the role of prolactin is less clear. A variety of factors related to prolactin have been investigated, and these are used as an organizing framework for this article. Factors include pregnancy, lactation, nursing frequency, prior lactation experience, milk production, and pharmacologic agents. The literature, while substantial in amount, presents inconsistencies. Implications for practice are discussed.

Compression stimuli increase the efficacy of breast pump function

OBJECTIVE

The dynamics of milk ejection and also prolactin concentration in the blood during milk expression by means of a breast pump were studied in 82 lactating women.

STUDY DESIGN

The design of the breast pump used in this study is new. It is based on the correlation with the amplitude, duration and frequency of vacuum and compression stimuli formed by the baby's mouth apparatus during the suckling process.

RESULTS

It was found that during continuous co-action of the vacuum and compression stimuli at a frequency of 1 cycle per second, the rate of milk ejection from the breast changed periodically. The highest rates of milk ejection coincided with the greatest rises in intramammary pressure. When the compression stimulus was turned off, leaving only the vacuum, the period of the first rise in pressure increased 1.5-2 fold, with a 1.5-2 fold reduction in the milk ejection rate as compared with the normal function of the breast pump. The basal prolactin level on day 3 and 5 post delivery in women who used a breast pump was not significantly different from that of puerperal women who only breast-fed their babies. Prolactin concentration in the blood of puerperal women did not change within the 5-6 min of expression and stimulation with the breast pump. The prolactin level began to increase by the 10th minute, whereas by the 25th minute it exceeded the initial concentration 1.3-1.5-fold.

CONCLUSION

It is suggested that by introducing a tactile component to the mechanism of the breast pump, milk secretion is enhanced, as well as stimulating the breast milk flow. This directly improves the dynamics of breast milk expression.

On the quantification of suckling intensity in primates

The inhibitory effect that suckling has on the reproductive function of primate mothers varies as a function of the intensity with which they are suckled. Here we present an easily computed index of one parameter of suckling intensity, namely the temporal patterning of suckling bouts. High intensity suckling is characterized by frequent nursing bouts demarcated by short interbout intervals. Therefore, our suckling index is based on the brevity of observed interbout intervals, more specifically the proportion of such intervals that fail to exceed a criterion length. The index is an appropriate means of making interspecific comparisons of the development of infant suckling and is well suited for application to field data that include interbout intervals that were not observed in their entirety. To demonstrate its utility, we apply the index to field data collected on the suckling behavior of free-ranging rhesus monkey (Macaca mulatta) infants in India. In this context, we demonstrate that, in rhesus, between-infant differences in suckling intensity manifest themselves early in the postpartum period and contribute to between-female differences in the timing of first mating postpartum.

The effect of sequential and simultaneous breast pumping on milk volume and prolactin levels: a pilot study

Mothers who must express milk for a prolonged period frequently report that milk volumes decrease. The purpose of this pilot study was to assess the feasibility of having a sample of lactating mothers of preterm infants follow a specific breast pumping protocol, express milk mechanically for six weeks, and have a subsample consent to venipuncture. This pilot study compared the effects of pumping breasts sequentially or simultaneously on milk volume and prolactin levels in mothers of preterm infants. Nine lactating mothers were randomly assigned to a sequential single or simultaneous double electric breast pumping system. Prolactin levels were examined in four mothers on days 21 and 42 postpartum. The sequential single and simultaneous double groups had mean baseline prolactin levels of 50.8 ng/ml and 40.6 ng/ml, respectively on day 21, and 26.6 ng/ml and 34.5 ng/ml, respectively, on day 42 postpartum. At 9 and 12 weeks postpartum mothers were queried about their lactational status. The results suggested that milk yield may be maintained or increased with frequent use of the simultaneous double pumping system. Further study is needed to confirm results of this pilot study.

Prolactin response to suckling and maintenance of postpartum amenorrhea among intensively breastfeeding Nepali women

The aim of the study was to determine the association between PRL responses to suckling and maintenance of postpartum amenorrhea among breastfeeding mothers. Three blood spot samples (5, 30, and 50 min following a timed nursing bout) were collected from 71 intensively breastfeeding Nepali women for PRL determination. Maternal age, BMI (weight/height2), menstrual status, caste, infant age, nursing bout length, and duration of supplementation were recorded at time of sample collection. Independent and paired t tests, linear regression analyses, and general linear models were used to evaluate differences between cycling (n = 36) and amenorrheic (n = 35) women and associations among variables. Logistic regression analyses were used to relate PRL measures to the odds of maintaining lactational amenorrhea. Amenorrheic breastfeeding mothers had higher (P < .001) PRL levels at all 3 collection times than cycling breastfeeding mothers, and PRL levels declined with time since birth (P < 0.05). The odds (OR) of having ceased lactational amenorrhea was significantly higher (OR = 5.0, 95% Cl = 1.3-19.9) among mothers with lower PRL levels (< or = 10 ng/mL) at 50 min post-sucking, and PRL at 50 min showed a significant dose response relationship with menstrual status. The association between 50 min PRL levels and lactational amenorrhea appears to be independent of time postpartum, maternal age, BMI, nursing bout length, and duration of supplementation. Among intensively nursing women, maintenance of elevated PRL levels across the interbout interval increases the odds of maintaining lactational amenorrhea.

Effects of chronic alcohol administration on lactational performance in the rat

Lactating rats, with litters adjusted to eight pups on day 2, were implanted with an atrial catheter on day 3 of lactation. Alcohol in doses of 0.0, 1.0, or 2.0 g/kg BW was infused from day 5 to 12. The blood alcohol levels (BALs) achieved following infusion of the initial doses were maintained for 4 hours daily by infusion. To control for the reduced food intake in alcohol administered groups, rats receiving alcohol doses of 0.0 and 1.0 g/kg BW were pairfed to 2.0 g/kg BW alcohol group. For infusion, combinations of 50% dextrose, 30% alcohol in saline and saline solutions were used for 0.0 and 1.0 g/kg BW alcohol groups whereas the 2.0 g/kg BW alcohol group received 30% alcohol in saline thereby equilizing the calorie intake of the three experimental groups. On day 12, pups were separated from the dams at 0800 h, a catheter extension was attached at 0900 h and baseline blood samples for prolactin level were taken at 1000 h. Following infusion of initial alcohol doses, samples were taken for BALs. Additional samples for BALs were removed 2 h after continuing the infusion. At the end of 4-h infusion, blood samples were taken for alcohol and postinfusion prolactin levels. In groups designed to study the suckling-induced prolactin release, pups were weighed and returned to the dams. Subsequent blood samples were taken 30 min after initiation of suckling. In nonsuckled groups, blood samples were obtained at corresponding time periods. BALs were determined by head space gas chromatography and plasma prolactin by a double antibody radioimmunoassay. Suckling latency and milk consumption during the 30 min of suckling were measured. Dams' and litter weights were determined on days 2, 5, and 12 of lactation. Infusion of alcohol for 8 days from day 5 to 12 of lactation did not affect maternal body weight. However, litters nursed by dams receiving 2.0 g/kg BW alcohol weighted less on day 12 compared to all other groups. Suckling latencies did not differ among groups. Milk consumed during the 30 min of suckling was lower for the alcohol administered groups. The inhibitory effect on milk consumption was greater for the 2.0 g/kg BW group than in the 1.0 g/kg BW alcohol group. Alcohol infusion did not affect the basal prolactin, whereas, the higher dose (2.0 g/kg BW) inhibited suckling-induced prolactin release.(ABSTRACT TRUNCATED AT 400 WORDS)

Serum lactogens possessed normal bioactivity in patients with lactation insufficiency

OBJECTIVE

Insufficient breast milk is the most common reason for premature termination of breast-feeding. The causes of lactation insufficiency are usually multifactorial; in a small percentage of cases it is due to primary lactation failure of unknown origin. The aim of this study was to investigate whether lactation insufficiency of unknown origin could be caused by serum lactogens that had reduced biological activity.

DESIGN

Women with lactation insufficiency of unknown origin and normal lactating controls were subjected to a standardized breast-feeding test for assessment of milk production. Thirty minutes later, serum samples were obtained for determination of total lactogen bioactivity, using an in-vitro bioassay, and levels of prolactin (PRL) and growth hormone (GH) using radioimmunoassay (RIA).

PATIENTS

Twelve lactating mothers with a clinical diagnosis of lactation insufficiency of unknown origin were compared with 12 matched mothers with normal lactation.

MEASUREMENTS

The Nb2 lymphoma cell bioassay was used to measure total lactogen bioactivity in sera. Conventional RIA kits were used to estimate serum PRL and GH concentrations.

RESULTS

Mean milk yield on standardized test feed was 21.6 ml for patients and 146.5 ml for controls. In both patient and control groups the total serum lactogen bioactivity ranged from about 150 to 5000 mIU/l, while the serum RIA (PRL+GH) levels ranged from about 350 to over 7000 mIU/l. There was no evidence of lactogens with reduced bioactivity in the patients' sera.

CONCLUSION

Lactation insufficiency in the women studied cannot be explained by serum lactogens that possess unusually low bioactivity.

The role of breast-feeding beyond postpartum amenorrhoea on the return of fertility in India: a life table and hazards model analysis

This paper investigates the effects of continued breast-feeding after resumption of menses on fertility, using data from two retrospective surveys in India and single decrement life table and multivariate time-dependent hazards analyses. Breast-feeding even after the return of menses is found to be associated with longer birth intervals. The interaction of breast-feeding duration after resumption of menses and postpartum amenorrhoea has a significant effect on the risk of conception after return of menses.

Physiological mechanisms underlying lactational amenorrhea

Breastfeeding delays the resumption of normal ovarian cycles by disrupting the pattern of pulsatile release of GnRH from the hypothalamus and hence LH from the pituitary. The plasma concentrations of FSH during lactation are sufficient to induce follicle growth, but the inadequate pulsatile LH signal results in a reduced estradiol production by these follicles. When follicle growth and estradiol secretion does increase to normal, the suckling stimulus prevents the generation of a normal preovulatory LH surge and follicles either fail to rupture, or become atretic or cystic. Only when the suckling stimulus declines sufficiently to allow generation of a normal preovulatory LH surge to occur will ovulation take place with the formation of a corpus luteum of variable normality. Thus suckling delays the resumption of normal ovarian cyclicity by disrupting but not totally inhibiting, the normal pattern of release of GnRH by the hypothalamus. The mechanism of suckling-induced disruption of GnRH release remains unknown. It does not appear to involve prolactin, dopamine or opiates although a combination of these factors might be involved. Prolactin is the major hormone responsible for milk production and is present in sufficient quantities in almost all women to allow the establishment of normal lactation. Oxytocin is essential for milk let down and is susceptible to inhibition of release by stress. The successful initiation of lactation which would lead to the potential of utilizing breastfeeding as contraceptive may require more attention to be paid to the establishment of non-stress release of oxytocin.

Breastfeeding after pituitary resection: support for a theory of autocrine control of milk supply?

A 20-year-old woman with a history of pituitary resection complicated by diabetes insipidus was able to fully breastfeed for three months despite apparent hyposecretion of pituitary hormones. This case report adds to the growing body of evidence that control of milk production shifts from endocrine to autocrine control shortly after delivery. Autocrine control allows efficient regulation of milk supply to match the needs of the infant. A recently discovered factor in human milk that inhibits lactose and casein synthesis in vitro is believed to be responsible for local, short term control of milk production. This study suggests that practices which result in infrequent or incomplete removal of milk from the breast lead to decreased milk production and should be abandoned.

Thyrotrophin-releasing hormone--a lactation-promoting agent?

OBJECTIVE

To study the lactational and hormonal responses to nasal administration of thyrotrophin-releasing hormone (TRH) in puerperal women with inadequate lactation.

DESIGN

Prospective randomized double-blind placebo-controlled study.

SUBJECTS

19 puerperal women with inadequate lactation (less than 50% of normal milk yield) on the 5th day postpartum.

INTERVENTIONS

10 women were allocated to receive TRH administered by a nasal spray of 1 mg, four times daily, between suckling episodes, for 10 consecutive days starting on day 6 postpartum. Nine women were allocated to receive placebo sprays.

MAIN OUTCOME MEASURES

Daily milk yield, serum levels of prolactin and thyroid hormones.

RESULTS

Before treatment all the women had significant prolactin responses to TRH and suckling stimuli. At the end of 10 days of treatment, milk yield increased significantly in the TRH group from a mean of 142.0 (SD 33.9) to 253.0 (SD 105.3) g/day (P = 0.014). There was no significant change in the placebo group. Basal prolactin levels increased from a mean of 117.4 micrograms/l (SD 45.2) to 173.3 micrograms/l (SD 55.5) (P less than 0.001) in the TRH group whereas in the placebo group prolactin levels decreased from 137.2 (SD 69.5) to 82.0 (SD 37.7) micrograms/l. A further rise in prolactin levels and milk yield was seen in seven women in the TRH group who received a second 10-day course of TRH treatment at their own request. There was no significant change in levels of thyroid stimulating hormone, thyroxine and triiodothyronine during treatment in either of the two treatment groups and no signs of hyperthyroidism.

CONCLUSION

Repeated nasal TRH administration between suckling episodes may improve defective lactation.

The effect of ergometrine on breast feeding

A randomised, controlled trial of 1429 women was carried out to compare 'active' management of the third stage of labour, using i.v. Ergometrine 0.5 mgs, with a method of 'physiological' management, in women at 'low risk' to haemorrhage. A separate sub-study, with 168 women in each of the two groups, examined the possible effects of Ergometrine on serum prolactin levels and the duration of breast feeding. No difference was found in peak (post-suckling) serum prolactin levels taken from 126 women between 48 and 72 hours postnatal. Further studies with larger sample sizes would give a more dependable result. Women who did not receive the drug Ergometrine were more likely to continue breast feeding for longer than four weeks than those who did (p less than 0.05). It is recommended that this drug should not be given routinely to women intending to breast feed.

Thoracic stimulation and prolactin secretion

Although galactorrhea and/or enhanced prolactin (PRL) secretion have been reported with a variety of thoracic stimuli, the effect of thoracic stimulation on dynamic prolactin secretion is not clear. A 49-year-old woman with ventilatory muscle weakness from polio presented with galactorrhea, and intermittent hyperprolactinemia but regular menses. The galactorrhea was noted following the use of a new, tight fitting cuirass (thoracic apparatus which assists ventilation). To determine if the new, "tight" cuirass elicited enhanced PRL secretion, and to assess more extensively the effect of such thoracic stimulation on PRL secretion, serum PRL was measured during brief and prolonged stimulation, sleep, and pharmacological manipulation of PRL. Basal PRL was normal (less than 25 ng/ml) and increased during brief stimulation (1 hour) with the "tight" (137%) and "loose" cuirass (140%). Although the absolute increments were similar, the "tight" cuirass elicited an earlier PRL peak than the "loose" cuirass and the PRL began to decrease while the "tight" cuirass was still functioning. Several hours of thoracic stimulation resulted in a transient rise in PRL and a fall to normal, prestimulatory levels despite persistent stimulation. During this stimulation, PRL did not rise after sleep nor after insulin-induced hypoglycemia despite normal cortisol and GH increments, but the PRL response after TRH was exaggerated.(ABSTRACT TRUNCATED AT 250 WORDS)

Diminution in energy expenditure during lactation

Energy expenditure at rest and in response to a meal and to an infusion of noradrenaline was measured in 12 lactating women and compared with that in seven bottle feeding women and seven non-pregnant, non-lactating controls. The energy response of the lactating women was remeasured after lactation stopped. During lactation the resting metabolic rate was unaltered but there was a reduced response to infusion of noradrenaline and to a meal, which increased to normal control values after lactation stopped. Such reductions in expenditure were not found in women who had been bottle feeding and were tested at a similar six to eight weeks post partum. These findings suggest that metabolic efficiency is enhanced in lactating women, who may not need to increase energy intake to the extent suggested by current recommended dietary allowances.

Patterns of variation in breast-feeding behaviors

This paper describes the range and patterning of variation in specific breast-feeding behaviors among a sample of 62 American mothers, as well as the relationship of the patterns to duration of exclusive breast feeding. Infant feeding data were collected using 24-hr records completed by mothers every 8 days through the first 6 months post partum. Behaviors examined were: number of daily feedings, minimum and maximum intervals between feedings, length of feedings and total daily nursing duration. Variation in magnitude of these behaviors ranged from three- to eight-fold. Principal components analysis found this variation patterned in two dimensions, relating to feeding frequency and length of time spent breast feeding. These dimensions accounted for approximately equal proportions of variance in the breast-feeding behaviors, totaling about 80% of all variance at 4 and 8 weeks. There was significant continuity of breast-feeding styles practiced by any one woman from 4 to 8 weeks. The feeding frequency dimension was strongly associated with duration of exclusive breast feeding. Three explanations--cultural, biological and biocultural--are proposed to account for this association. It is argued that the intracultural variation in breast-feeding styles in this sample may be sufficient to cause corresponding variation in breast milk production, in part accounting for variation in duration of exclusive breast feeding. Predictions of exclusive breast-feeding duration will be most accurate for women with a breast-feeding style of infrequent feedings, while predictions for women with a style of frequent feeding will be confounded by cultural factors which have an independent effect on breast-feeding supplementation.

Domperidone in defective and insufficient lactation

The clinical use of anti-dopaminergic drugs to stimulate plasma PRL levels, to induce lactogenesis and maintain an adequate lactation has been widely suggested, taking into consideration the main inhibitory role of hypothalamic dopamine on PRL secretion. We therefore studied the effects of domperidone (DOM), a direct anti-dopaminergic drug with a low tendency to be secreted in the milk and which does not cross the blood-brain barrier, on inducing lactogenesis in 8 puerperal women with a history of defective lactogenesis (group A) and inducing galactopoiesis in 9 puerperal women who showed 2 weeks after delivery an insufficient lactation (group B). A placebo treatment was performed in 7 and 8 puerperal women with the same characteristics of group A and B, respectively. PRL plasma levels were assayed in basal conditions and after suckling from the 2nd to the 5th day of puerperium in group A and through a 10-day treatment in group B. In both groups domperidone-treated subjects always showed baseline PRL levels and daily milk yield significantly higher than those of the placebo group (P less than 0.01). The lack of any side-effects and the positive results suggest a high usefulness of such a drug in inducing and/or maintaining successful breast feeding, which is at present considered so important for a healthy development of infants.

The prolactin response to suckling

Changes in prolactin concentration during single suckling episodes in twenty breast-feeding women from four to 40 weeks post partum have been investigated. Basal prolactin concentration and the increase in prolactin secretion in response to single suckling episodes and amount of milk taken by the infant were both independent of time post partum until the introduction of supplementary feeds, when a significant decrease with time was apparent. Basal concentrations of prolactin were dependent upon the interval between suckling episodes, and the magnitude of the prolactin response varied with the time of day when suckling took place. The relationship between acute suckling episodes and the long term pattern of prolactin secretion over time post partum is discussed.

Effects of combined oral contraceptive steroids on pituitary-ovarian function during the menstrual cycle of lactating women

The object of this study was to investigate the effects of combined oral contraceptives on pituitary-ovarian function during the menstrual cycle of lactating women whose prolactin levels were usually elevated. Five of six lactating women studied were considered to have the normal menstrual cycle which was comparable to the presumptive ovulatory cycle of non-puerperal women. The patterns of serum LH and FSH as well as estradiol and progesterone during the menstrual cycle of lactating women were quantitatively and qualitatively, similar to those of non-puerperal women. Prolactin levels, however, were elevated throughout the cycle of lactating women as compared with those of non-puerperal women. Treatment with combined oral contraceptive steroids abolished a midcycle surge of LH and decreased ovarian steroids during the menstrual cycle of lactating women. Serum prolactin levels were also decreased throughout the cycle treated with contraceptives in lactating women.

The place of PRL in human lactation

Plasma PRL levels were measured during an episode of breast feeding in fourteen women on the eighth and 42nd post-partum days. The results show that as lactation continues so the importance of absolute values of PRL diminishes, but the capability to secrete PRL in response to the suckling stimulus is maintained.

Release of oxytocin and prolactin in response to suckling

The oxytocin and prolactin responses to suckling were measured in 10 women in early (n = 5) and established lactation (n = 5). Oxytocin was released in a pulsatile manner during suckling in all women, but the response was not related to milk volume, prolactin response, or parity of the mother. In all 10 women plasma oxytocin concentrations increased three to 10 minutes before suckling began. In five women this occurred in response to the baby crying, in three it coincided with the baby becoming restless in expectation of the feed, while in two it corresponded with the mother preparing for the feed. There was no prolactin response to stimuli other than stimulation of the nipple associated with suckling. These results clearly indicate that the milk ejection reflex, with release of oxytocin, occurs in most women before the tactile stimulus of suckling. A second release of oxytocin follows in response to the suckling stimulus itself. Thus it is important that care is taken to protect breast feeding mothers from stress not only during suckling but also immediately before nursing, when conditioned releases of oxytocin will occur.

Suppressed prolactin but normal neurophysin levels in cigarette smoking breast-feeding women

The hormonal responses to breast-feeding were studied during the first 3 post-partum weeks in ten women smoking more than fifteen cigarettes/day and in a control group. Basal PRL levels were significantly lower in smokers compared with non-smokers, but suckling induced acute increments in serum PRL and oxytocin-linked neurophysin, which were not influenced by smoking. The lactational pattern was normal, but smokers weaned their babies significantly earlier compared with non-smokers. Heavy cigarette smoking women have lower basal PRL levels and this may shorten the period of lactation.

Food for the suckling: revolution and development

The 1970's saw a renaissance in child nutrition, a major revision of infant feeding practice and substantial changes in food for the suckling. Many more babies are breast fed, those who are not receive an infant formula specifically designed for this period of life, and solid foods are no longer introduced in the early weeks. These changes have contributed to the improvement in the suckling's health, particularly the reduction in neonatal tetany, and in deaths from gastroenteritis. Developments in the 1980's should improve our knowledge of breast milk and its properties, advisable intakes of specific nutrients and their interrelationships, and the immunology of infant feeding. Meanwhile, practice will be directed towards the enhancement of successful lactation, the processing of donor human milk, the establishment of standards for infant formulas and the special problems of the low birth weight baby.

A dose response relation between improved lactation and metoclopramide

In a placebo-controlled, cross-over study, thirty-seven puerperal women with inadequate production of breast-milk were treated with 5, 10, or 15 mg of metoclopramide three times a day for 2 weeks. Doses of 10 or 15 mg significantly raised maternal serum prolactin; they also increased breast-milk secretion by 42.5 +/- 34.7 (SD) ml and 50.0 + 35.9 ml per feed, respectively. This effect was unrelated to the phase of the puerperium during which treatment was started. The increase in milk secretion was associated with a decreased need for supplementary feeds, and 33% of the infants of these mothers needed no supplementary feeds during treatment. 5 mg doses did not stimulate prolactin milk secretion. Although placebo had no objective effect on the milk yield, 24% of the women judged its effect to be good, and 89% of women on metoclopramide reported a good effect. Seven women on metoclopramide and three women on the placebo complained of slight side-effects. No adverse effects upon the infants were observed. Metoclopramide therapy may be useful for improving poor lactation.

Comparison of prolactin response to suckling and breast pump aspiration in lactating mothers

Prolactin release following breast pump aspiration is less than that following suckling. The long-term effects of this decreased prolactin response are not yet known and therefore the use of the breast pump should be limited to selected cases and for the shortest possible time.