Oxytocin effects in mothers and infants during breastfeeding

1 VOLUME 9 ISSUE 6 2013201infantREVIEW 2013 SNL All rights reserved Oxytocin a system activatorOxytocin, a small peptide of just nineamino acids, is normally associatedwith labour and the milk ejection , Oxytocin is not only a hormonebut also a neurotransmitter and aparacrine substance in the brain1,2. Duringbreastfeeding it is released into the brain ofboth mother and infant where it induces agreat variety of functional three different release pathways(FIGURE 1), Oxytocin functions rather like asystem activator and often influences therelease of other signalling substances suchas opioids, serotonin, dopamine andnoradrenaline. Through these activations,different behavioural and physiologicaleffects are facilitated and coordinated intoadaptive patterns, which are influenced bythe type of stimuli and the endogenous release ofoxytocin or its administration, for exampleby nasal spray in humans, various types ofsocially interactive behaviours can bestimulated.

2 These include maternal andsexual behaviours as well as the develop-ment of bonding and stimulates well-being, it inducesanti-stress effects , decreases sensitivity topain, decreases inflammation andstimulates processes related to growth andhealing. In addition, repeated exposure tooxytocin may give rise to long-term effectsby influencing the production or functionof other signalling systems. For example,noradrenergic activity in the brainmay decrease as a consequence of theOxytocin effects in mothers and infantsduring breastfeedingOxytocin integrates the function of several body systems and exerts many effects in mothersand infants during breastfeeding . This article explains the pathways of Oxytocin release andreviews how Oxytocin can affect behaviour due to its parallel release into the blood circulationand the brain. Oxytocin levels are higher in the infant than in the mother and these levels areaffected by mode of birth.

3 The importance of skin-to-skin contact and its association withbreastfeeding and mother-infant bonding is discussed. Kerstin Uvn s MobergMD, PhDProfessor of PhysiologySwedish University of K. PrimePhD breastfeeding Research AssociateMedela AG, Baar, SwitzerlandKeywordsoxytocin; breastfeeding ; skin-to-skin;anti-stress; milk ejection; bondingKey pointsUvn s Moberg K., Prime Oxytocineffects in mothers and infants duringbreastfeeding. Infant2013; 9(6): Oxytocin is released in the mother andinfant during breastfeeding and skin-to-skin Milk ejection patterns vary Oxytocin is released into circulatingblood and brain structures, in Oxytocin levels are higher in the infantthan in the mother and differ withmode of function of inhibitory alpha-2adrenoceptors3. The regulation of the release of oxytocinis complex and can be affected by differenttypes of sensory inputs, by hormones suchas oestrogen and even by the oxytocinmolecule itself.

4 This article will focus onfour major sensory input nervouspathways (FIGURES 2 and 3) activated by: 1. Sucking of the mother s nipple, in whichthe sensory nerves originate in thebreast. 2. Sucking in the infant, in which thesensory nerves originate in the infantoral The presence of food in thegastrointestinal tract, affecting vagalsensory nerves. 4. Skin-to-skin contact in both mothersand infants , in which the sensory nervesthat originate in the skin respond towarmth, touch, stroking and lightpressure. The motherMilk ejection Oxytocin is critical for milk removal in,perhaps, its most renowned role: the milkejection reflex. Following sucking, therelease of Oxytocin causes the contractionof myoepithelial cells in the breast pushingmilk from the alveoli, through the milkducts and toward the nipple. In general, it takes around a minute ofinfant sucking or stimulation with a breastpump before milk ejection occurs5, , the milk ejection reflex can beREVIEW202 VOLUME 9 ISSUE 6 2013infanteasily conditioned and many women canexperience spontaneous milk ejectionsbetween feeds7,8as the sight, thought,sound and smell of the infant (or even abreast pump in pump-dependent mothers )can cause milk ejection and dripping ofmilk from the nipples.

5 Indeed, it iscommon that milk ejection occurs prior tothe physical attachment of the infant or abreast pump7,9. Milk ejection can be associated withdifferent sensations that vary dramaticallybetween women. These may be localised tothe breast such as a drawing pain ortingling, to more systemic sensations suchas nausea, thirst, fainting or even mentalanxiety and depression8. Sucking- and pumping-inducedoxytocin release has been described aspulsatile7,10. On average, Oxytocin pulsesoccur with 90-second intervals over thefirst 10 minutes of breastfeeding in the firstfew days after birth11,12. The amount ofoxytocin that is released within a 10minute breastfeed is much higher at fourmonths when compared to four days afterFIGURE 1 The release of Oxytocin from the supraoptic (SON) and paraventricular (PVN) nucleiof the hypothalamus. Magnocellular neurons in the SON and PVN release Oxytocin centrallyand peripherally from the posterior pituitary, resulting in effects that include milk ejection anduterine contraction.

6 Parvocellular neurons, located in the PVN, project axons directly into brainstructures involved in the regulation of social interaction, anxiety, the activity of thehypothalamic-pituitary-adrenal axis, well-being and the autonomic nervous system (eg theamygdala, hypothalamus, anterior pituitary, nucleus accumbens, nucleus tractus solitarius andthe dorsal vagal motor nucleus). Magnocellular neuronsCentral Oxytocin release:Dendritic extracellular diffusionParvocellular neuronsCentral Oxytocin release:Axons project into brainstructures and spinal cordAxons ofparvocellular neuronsParaventricularnucleus (PVN)Supraopticnucleus (SON)AnteriorpituitaryAxons ofmagnocellularneuronsPosteriorpituitary CapillaryOxytocinPeripheral Oxytocin release:Axonal release into blood totarget distant organsbirth, but there is still a strong correlationbetween the amount of Oxytocin releasedon the two occasions within pulse of Oxytocin is generallyassociated with one milk ejection and thereis a relationship between the amount ofoxytocin released and the number ofoxytocin pulses during the first 10 minutesof breastfeeding12.

7 The number of milkejections during breastfeeding ranges fromone to 17 over a period of up to 25minutes6,7. Similarly, pulsatile patterns oftwo to 14 milk ejections are seen during a15 minute breast expression5. The simil-arity between the milk ejection patternresulting from breastfeeding and breastpumping is demonstrated in FIGURE an individual mother overtime, it appears that her pattern of milkejection repeats throughout the first ninemonths of lactation5. If a mother has twoor three milk ejections she will continuethat pattern, removing all her milk in thesebrief episodes. Other mothers may follow amore constant pulsing profile in that theyhave continuous milk ejections throughoutthe milk removal session. Both of thesepatterns can remove similar volumes ofmilk successfully, but the second scenariowould require more time to reach thatsame level of milk removal5.

8 Similarrepeatability has been observed inindividual infants at successive breast-feeds14; these mother-derived patterns mayexplain why some infants are quick feedersand others take a bit more time. Oxytocin -induced effects in the brainIt is not known why mothers have suchvaried milk ejection patterns but, sinceoxytocin is involved in so many functions,these release patterns may not only impacton milk removal. Systemic Oxytocin releaseand its release into the brain may result inmany other outcomes involvingbreastfeeding and mother-infantinteractions. For example, breastfeeding inmothers is associated with physiologicaland psychological adaptations including: Increased social interaction Decreased anxiety Decreased cortisol levels Decreased blood pressure Increased gastrointestinal effects are exerted in the brain butare associated with circulating oxytocinlevels, supporting the concept thatoxytocin is released systemically and intothe brain in parallel, as has previously beendemonstrated in sheep in response infantInfants produce Oxytocin too and in fact,the production of Oxytocin begins in thefetus.

9 An understanding of the infantoxytocin system is complicated bydifficulties in collecting repeat bloodsamples and measuring circulatingoxytocin levels in the , some studies exist in whichoxytocin levels have been measured in thenewborn while other studies havedemonstrated the release of oxytocinindirectly via expression of Oxytocin -linkedeffect patterns. Information can also bedrawn from animal experiments, asoxytocin exerts similar effect patterns in Oxytocin levels are affected by themode of delivery In infants born by vaginal delivery, Oxytocin levels in umbilical arterial bloodREVIEWVOLUME 9 ISSUE 6 2013203infantwere actually higher than in infantsborn by caesarean section: 69pg/mL(range 20-315pg/mL) vs 33pg/mL(range 9-195pg/mL), respectively. Mothersalso had higher Oxytocin levels if theydelivered vaginally, compared to caesareansection. In the first 30 minutes after birth, infants (born both vaginally and bycaesarean) had higher Oxytocin levels thanthose of mothers : approximately 30pg/mL(range 13-158pg/mL).

10 Over subsequenthours and days the differences due tomode of birth diminish, yet infants willmaintain a higher Oxytocin level than theirmothers (FIGURE 5). In addition, oxytocinlevels recorded postpartum in infants bornvaginally correlate inversely with fetalarterial pH and also with the duration oflabour. This suggests that the elevatedoxytocin levels recorded postpartum arelinked to the stress of being born (Bystrovaet al 2013, unpublished results)19. Ingestion of Oxytocin from maternal milkHuman milk contains many differenthormones and growth factors and it alsocontains small amounts of Oxytocin . Theconcentration of Oxytocin in maternal milkis approximately 8pg/mL in the first fewdays after birth and then decreases withincreased milk production. Even if theingested Oxytocin was able to survive theacid milieu of the stomach and wasabsorbed from the small intestine of thefetus, the dilution within the circulationwould limit any significant rise of oxytocinlevels.