Oxytocin: This one’s for the Ladies

Previously I posted on the general features of oxytocin, what it acts on, and where it basically acts, and what it’s mostly known for. But the reality is that oxytocin is a LOT more complicated than that, and has different effects of your body and your behavior, depending on who you are. It varies from person to person (as all biological things do) as well as between men and women. And today, we’re going to discuss the ladies. Because if there is anything oxytocin is famous for, it’s for its effects on women.
(Yes, yes, we will cover this bit).
You may have noticed lots of links in the previous post. Those links are to the literature which I searched before posting. There will be lots more links in this one to examples of studies which support what I’m going to tell you about. Of course, all of these are in science-ese, and so if you are puzzling over something and can’t make it out, give a shout out in the comments with the particular paper, and Sci will do her best to cover the paper later on. I have a feeling that oxytocin is going to be a recurring topic.
So here we go.
This one’s for the ladies

So as we know from the previous post, oxytocin is a hormone (by definition, a hormone is a chemical that is released from one part of the body that has effects on another part of the body, but that doesn’t really narrow down the function much, does it?) that is secreted from the posterior pituitary (the nutsack of the brain). In women, it is most known for its extensive roles in reproductive function, particularly in parturition (that’s birth), lactation (that’s nursing), and in orgasm. So we’ll cover those bits first, mostly because Sci LOVES the positive feedback loop in parturition. We’ll also talk about the role of oxytocin in maternal bonding, one of the social aspects. I was going to cover the major effects on social bonds as well, but there’s quite a bit on that, so I think we’re going to have to save that for another post. So we’ll stick just to the specifically female stuff for the moment.
Roles of Oxytocin in the body:
Britney_Spears_bear rug.jpg
In pregnant women, oxytocin has one of it’s major roles (you might say it’s the most important, but given the importance of the OTHER roles of oxytocin, it’s a toss-up). Oxytocin is released at the end of fetal development (and sometimes during), and results in uterine contraction, making it one of the most important hormones at birth (the other one is progesterone, which gets HUGE right before birth).
The coolest thing about oxytocin during parturition is that it’s controlled under a positive feedback cycle. Goes like this (in the very, very simplified version):
1) Baby is big and heavy, and presses against the cervix.
2) Cervix feels the burn and stretches a little.
3) The muscle stretching of the cervix triggers receptors which send nerve impulses to the brain.
4) Brain releases oxytocin.
5) Oxytocin further softens and dilates the cervix.
6) Baby weight pushes downward on the softened cervix and stretches it.
7) Lather, rinse, repeat.
8) BABY!!!
“Positive feedback” is the stretching of the cervix which promotes oxytocin, which promotes stretching, which promotes MORE oxytocin. The actions of the hormone trigger the release of more hormone. If you’re like Sci, you will think this is really, really cool.
However, oxytocin is not necessarily NEEDED for birth. There are oxytocin knockout mice that do not have oxytocin and can still reproduce (but these are knockout animals, and so growing up without oxytocin, their bodies could compensate). But it’s very clear that oxytocin is very important in the normal birth process. In fact, it’s SO important that oxytocin analogues (drugs that mimic oxytocin, such as Pitocin) are used to induce labor, and oxytocin receptor antagonists (which block the actions of oxytocin, like the drug Tractocile) are used to stop premature labor and uterine contractions. So, pretty important.


kittens nursing.jpg
Another one of oxytocin’s big roles in women (and in female mammals in general) is in lactation, where it serves a very important role in milk letdown.
To go to HOW this works, we’re going to need a little anatomy
breast anatomy.jpg
(That’s better)
You can see up there the important things for oxytocin, the alveoli (those little frond things), the milk sinus (also known as the sac), and the nipple opening, which is surrounded on the outside by the areola, which is the dark area of the nipple. While other hormones (like prolactin) are involved in actually MAKING milk, oxytocin is very important for releasing it, in what’s known as the let-down reflex.
Goes like this (again, the simplified version, the complicated version involves dopamine and a host of other hormones):
1) Baby sucks at nipple
2) The sensation of suckling heads to the brain (skipping some detailed steps here).
3) The hypothalamus is stimulated and oxytocin is released from the posterior pituitary.
4) Oxytocin in this case acts to contract the muscles around the alveoli in the breast.
5) The squeezed alveoli deliver milk to the milk sinus via the duct.
6) Baby sucks, milk comes out.
And now we get to the third, best part of oxytocin in women:

(um…pic here…um…nah…)
Oxytocin is actually important in sexual arousal for both men and women (I’ll cover more about the men in the next post). During sexual arousal, oxytocin increases rapidly, with a big burst at orgasm. In fact, in women, the strength of orgasm is directly correlated with the amount of oxytocin. Oxytocin levels correlate to sexual arousal in women, as well as the amount of vaginal lubrication present. Not only that, oxytocin fluctuates along with a woman’s menstrual cycle, being highest in the ovulatory phase and follicular phase, and lowest in the luteal phase (The follicular phase and ovulatory phase are the preparation and release of the egg, respectively, and fertility will peak at ovulation for obvious reasons. The luteal phase is the phase after ovulation, as the egg sits around and grows old until the shedding of the uterine lining during menstruation at the end of the month. Sci will probably have to blog about this sometime).
So oxytocin is very important physically, helping us enjoy the procreation of the species and allowing the species to get out of the womb and get fed. Now, we move on to the first of many fuzzier roles for oxytocin:
Maternal bonding
This is the part where some people get antsy. For it’s true, oxytocin DOES influence behavior. Oxytocin DOES promote things like affiliative behavior with one’s young.
Examples: rats, once they give birth, will pick up pups and carry them around. They’ll build a nest for them (if they haven’t already), and lick them and basically associate with them like good rat mommies. However, if you give a rat mom something to block oxytocin, she will not pick up the pups, carry them around, or make a nest. Giving oxytocin to sheep will induce maternal behavior by sheep for lambs that are not their own, even if the sheep has never given birth.
And this pattern appears to hold true in humans as well. Mothers who have secure attachments to their newborns have stronger activation of the pituitary (where oxytocin is released) when they see pictures of their child, than mothers with less secure attachments. Some studies also indicate that women with particular oxytocin gene regulation may show more signs of “sensitive” parenting. It appears that oxytocin release is a significant part of how women react to their babies, and how much they affiliate with them in the first months of life.
And this is where people get squirmy. Because doesn’t this mean that women are the TOOLS of their HORMONES?! And if women are the tools of their hormones, doesn’t this mean they that BIOLOGY has DECREED that they stay indoors, barefoot and pregnant? And of course there’s the even more squirmy question: if some women are better at raising children than others due to their genes, should women be screened for these genes before having children?
In my opinion, heck no. Women (and men) are certainly influenced by their hormones, and certainly influenced by their genes. But hormones and genes do not act in a vacuum. They act within an environment, and very importantly, within a society. A woman is very capable of both affiliating and responding sensitively to her baby and to still maintain a life.
And we are certainly not forced by our hormones to play certain roles. It’s important to remember that societal interactions are as important, and sometimes MORE important, than hormones and genes. Oxytocin never prevented the societal norms of sending rich women’s children to wet nurses and governesses back in the day. Oxytocin genes might help more sensitive parenting from the start, but someone who lacks them is not necessarily an insensitive parent. We are all capable of learning from our surroundings and learning what works best for our children, and it is obvious that fluctuations in oxytocin levels are not the be all end all of parenting. If they WERE, then all parents would have uniformly high oxytocin levels, evolution having weeded out over time the primate females who had low oxytocin levels, and thus did not care for their young effectively and raise successful offspring. As people with high and low oxytocin are still out there and still raising kids, you can be pretty sure there are other factors at work.
So when it comes down to it, yes, we’re influence by our hormones. But we are ALSO under the influence of human society and the environmental influences coming in through our vast prefrontal cortex. And to discount the incredible influences of society and the cortex would be very naive indeed.
So that’s basic actions of oxytocin as related to women. For it is late, and Sci is very tired. Next we move onward, to oxytocin in MEN. Oh yes, it’s there, boys.

33 Responses

  1. “If they WERE, then all parents would have uniformly high oxytocin levels, evolution having weeded out over time the primate females who had low oxytocin levels, and thus did not care for their young effectively and raise successful offspring.”
    Unless there were a counter-selection against too high levels of oxytocin. Like trusting too much makes you easy prey.
    For humor’s sake, a subjective nonscientific description of your lactation process:
    1) “Open wide, wide”
    2) YEEOUCH!
    3) Ah. Ok. Ohh, I’m roasty-toasty.
    4) oh, here’s the tingle. *hmmmhmmmhmmm* “here it comes!”
    5) oh wow, look at the drool. Don’t cough! *baby rechomps*
    6) ok, now we’ve got a rhythm. Hmmm, how long as it been? I’m thirsty.

  2. Dear Sci,
    I really enjoy reading your posts, but there’s something, well, a bit naive here about the evolution. It’s not about developing PERFECT solutions (uniformly high oxytocine levels), but working ones (oxytocine present) with all the natural variation. I think women with relatively low oxytocine levels did and do take care of their children – SOMEHOW. It may be harder for them and their kids, but they survive (in most cases) – and that’s what evolution cares about. Quantity rather than quality, so to speak.
    And the problem with lower oxytocine level in mothers is quite recent – because of more cesarean sections (too often for woman’s comfort reason) and less breastfeeding (as above) – so evolution didn’t have the time to take care of it. Probably it won’t anyway, because of societal factors you’ve mentioned – like support groups, lactation advisers or the possibility of giving the child away for adoption etc.

  3. I think the dog we sit for has an excess of oxytocin. She’s never had pups but never been spayed. Whenever we bring kittens with us she goes nuts as soon as she smells them, starts whining and growling and making a nest out of her toys, and wails if seperated from them. Unfortunately the kittens are not usually very into having a border collie mum.

  4. Please Tracey if you ever get tired of your lovely dog I’ll have her 😉

  5. Really enjoying these posts about oxytocin. I liked the point about evolution and variations in oxytocin levels. Jan, I don’t think Sci intended to give the impression that she believes evolution’s striving for a “perfect” system; I think that interpretation actually conflicts with her point that nature will settle for a Good Enough solution, and apparently mothers are good enough despite some natural variation in oxytocin levels.

  6. This is a great series, Sci. Very cool. Looking forward to the next one.

  7. Jan and Becca: excellent points, and Sci was very tired when she wrote that last bit. It’s definitely not a perfect system, and it won’t ever be. Most likely, oxytocin levels are balanced out at roughly around a level that works for parenting, but doesn’t make us too trusting. My other hypothesis is that in women with lower levels of oxytocin, higher processing (learning in social situations, etc) will most of the time compensate and result in decent parents reflexes.
    Excellent points. It’s really a thorny situation. Everyone is all about taking care of kids in the best possible manner, but when it gets into issues like this, of hormonal control of behavior, it gets…hairy.
    becca: having never nursed a baby herself, your description made Sci LOL. Oxytocin is also known to stimulate painful uterine contractions during nursing over the first few days or weeks following birth, at the uterus is still sensitive to the hormone, but the hormone is needed for milk let down. Extra ouch.

  8. “giving the child away for adoption ” I’ve never liked this phrase. Sounds too much like regifting something one doesn’t like or can’t use. Adoption is a godsend for many and demonstrates how learning is a large part of being a mother.

  9. Is it possible that maternal bonding is also a positive feedback system? As in, mother bonds with baby, more oxytocin released, mother bonds more with baby.

  10. momkat: *eyeroll* Great…I’ll mention it to the overlords…thanks for pointing it out!

  11. Great post Sci!! I loves me some feedback loops too. is oxytocin the hormone associated with “forgetting” labor pains as well (thereby making it seem not-so-bad to go through with the whole thing again later on), or am I confusing it with something else, or is that just a myth?

  12. Is oxytocin involved in male lactation?

  13. sci- yesh, those contractions are bizarre. If you know what’s happening, you can imagine that you can *feel* the uterus shrinking back up in direct reversal of the labor process. Although at least for me, they were only once or twice as painful as the CHOMP part while baby was learning to chomp and I was adjusting to it.
    If you get a chance and I’m remembering things right, I’m rather curious about oxytocin-effects-on-baby.
    Amvivalent academic- I have every reason to believe I am chock full of oxytoxin. I will NEVER forget the pain of labor. N=1, YMMV.

  14. Interesting and instructive – but it has to be a BIG oversimplification, and it is not surprising that people get antsy: Animals who do not produce oxytocin are lousy mouthers. Women who have CS do not produce oxytocin. Therefore… Suggesting that as social creatures we MIGHT be able to compensate isn’t really much of a help. I am happy to accept the importance of oxytocin in reflexes like labour and milk let down, but a long way from convinced that it has much to do with bonding – or mothering. Or at least, if it does, it is not on a simple feed-back loop. Major problems with bonding are, surely, more often psychological than physiological

  15. Oxytocin, my second most favourite hormone (after melatonin, of course)! And positive feedback loops are fun to teach as they all have something to do with….well, areas usually covered by the bikini. Oh, and it does have something to do with the circadian clock though, as they say, ‘more research is needed’.

  16. So I know you have a lot of ground to cover with oxytocin, but I’m kind of surprised you didn’t note that old midwife trick that is meant to hijack the lactation response for the purpose of assisting in birthing.
    … As an aside, does that really release more oxytocin in concentrations that really matter much?

  17. Sci: I was a bit tired, too, writing that comment early in the morning with one of my kids sitting on my lap for nebulization (routine in the cold season).
    Momkat: And as I do not write much in English on regular basis, my vocabulary is not perfect (that’s about this “giving away” phrase). Adoption or foster parenting is a great thing for many kids and many parents who have fertility problems that can’t yet be helped with science. But it still has its dark side – parents who are not able to raise kids themselves, and sometimes it’s for mostly “hormonal” reasons (not economic ones or things like substance abuse etc.)
    Anyway I think that oxytocine is still much undervalued. Low levels of it after birth are probably the cause of baby blues – and a depressed mother not only has a hard time, but can also give her child away (that phrase…) or even abandon her/him (with fatal consequences in many cases). Such things still do happen, so in some women’s brains prefrontal cortex etc. is apparently not able to compensate for low oxytocine.
    Claire: we know more and more about brain, hormones and all this physiology – and it becomes clear that it affects psychology in so many ways that it can’t be separated just like that. Oxytocine is produced also in response to physical contact between partners, parents and babies – it’s sometimes called the “cuddle hormone”. And we all know that holding hands and cuddling feels good and helps with relationship. Problems arise when it’s not so easy – for example if a kid is autistic, with sensory problems that make her/him hypersensitive to touch. Those babies do not like cuddling and parents OFTEN feel less bonding with them (that’s probably how the “iceberg mother” myth arised). It may be because of many factors, but oxytocine seems an important candidate at least.

  18. Claire:
    “Women who have CS do not produce oxytocin.”
    This is actually not true. First of all, a c-section may occur after the onset of labor. (In fact, it *usually* does, except in the case of high-risk situations or immediate peril to the mother’s health where there isn’t time to wait for the baby to finish cooking.) Secondly, a woman who has had a c-section will undergo the same physiological changes as a woman who has just undergone vaginal birth (or had a miscarriage, or had a fetus die in utero), as the absence of a placenta (and the hormones *it* produces) leads the body to stop acting like it is pregnant. Thirdly, lactation still works, and that will also trigger oxytocin release. (It even, rarely, works in women who haven’t given birth, and sometimes, even more rarely, in men!)
    However, as women who’ve had a c-section are more liable to bleed, and as the body doesn’t always notice right away that it needs to do something about the bleeding, hospitals put these new mothers on oxytocin drips after the birth. The body will take care of it eventually, but the contractions to return the uterus to its normal size *also* serve to staunch the bleeding. And it’s a lot of bleeding; the human placenta is almost terrifyingly invasive in its search for blood supply.

  19. Ambivalent academic: oxytocin does have strong effects on memory formation in both men and women, but I’m not sure if it affects the forgetting of labor pains specifically.
    Colin: if males lactate, then yes. 🙂
    Tybo: I didn’t cover that midwife trick because I’ve never HEARD of it! I presume it involves the midwife sucking on (or applying negative pressure to in some fashion) the pregnant woman’s nipples to stimulate further oxytocin release?
    Calli: W00t.

  20. “So I know you have a lot of ground to cover with oxytocin, but I’m kind of surprised you didn’t note that old midwife trick that is meant to hijack the lactation response for the purpose of assisting in birthing.”
    This was one of the funniest lines in “What to expect”
    It was something along the lines of:
    Question: “So, does nipple stimulation work to induce labor?”
    Answer: “Maybe, but think this through… For one thing, do you really want to intensify the contractions? For another, the actual research isn’t all that compelling. One study found that women that started nipple stimulation for three hours daily in their 38th-39th week were less likely to go over term. On the other hand, who has 3 hours daily to devote to this???!!!”
    (note, I’m posting this from memory, and may have the specific amount of time wrong)

  21. The midwives trick is nipple stimulation or orgasm. My midwife mentioned the nipple thing in passing, but went straight for the big O.
    And, for some purely anecdotal evidence, it worked for me. I was on bed rest for preeclampsia, and getting close to the “lets induce labor or cut this baby out” point. Not wanting a C-section, I took myself to bed Friday evening, had a good old time all weekend, and went into labour in the wee hours of Monday morning. BabyBright was two weeks early, and I recovered from the pre-eclampsia beautifully.

  22. Actually, oxytocin antagonists don’t really appear to work all that well at stopping preterm labor, and my understanding is that they’re not widely used in clinical practice. I was a PTL patient in both of my pregnancies, and nothing beyond the standard terbutaline/mag sulfate/nifedipine was ever discussed, even at the academic medical center I used in my first pregnancy.

  23. Very interesting stuff on my favourite hormone!
    It’s some eight years since I breastfed, but I still remember, in an almost physical sense, the feeling of “letdown” which would occur even if I looked at a photo of my daughter. It’s almost like a bodily memory.
    I was as high as a kite on endorphins and oxytocin for days after her birth (drug free, hot tub from heaven).
    I wonder if there’s any research on oxytocin levels in the long term post-pregnancy/childbirth/lactating. Anecdotally, I know there’s a suggestion that women tend to become multiorgasmic as they get older, and it’s certainly been my experience. Maybe that’s really about the body getting somehow primed by childbirth/lactation? It might make evolutionary sense for sexual activity to become more attractive and rewarding once one has demonstrated fitness by having already reproduced.

  24. Don’t forget nitric oxide. NO is involved at multiple levels in oxytocin signaling and also in the pathways that feed into and out of oxytocin signaling.
    Maternal bonding is coupled to maternal nutritional and metabolic status. If she doesn’t have the metabolic capacity to support lactation the “evolutionarily correct” response is to not bond and abandon the infant. Better the mother survive and reproduce later than that both of them die.
    Inhibiting nitric oxide synthase in sheep blocks maternal bonding. I think that basal NO level is the signal that is used to integrate nutritional stress, metabolic stress, and fight-or-flight status and to enhance or inhibit maternal bonding. Because the basal NO level is a continuous parameter that is already being used as a control parameter, any change in the level (for any reason) changes the output of those signaling pathway.
    I think that low NO is the main reason for problems in maternal bonding. It isn’t a “bug”, it is a “feature”, a feature that was essential during evolutionary time and which we still have.

  25. @Jan- About the imperfect solutions of evolution, the way women give birth now is one of them. I think “baby blues” is a small price to pay for increasing your odds of LIVING through that experience of natural childbirth. And doctors who feel too confident in that science to opt for a c-section when it’s strongly indicated can seriously injure a lady. I know someone who was laid up for a long time over that. Humans can do better than nature and ultimately should. Ectogenesis is coming, baby.

  26. So how does the body know what the oxytocin is signalling? How does it know whether it is supposed to start lactate, contract the uterus or have an orgasm?

  27. @CS Shelton – maybe I didn’t state it clearly enough, but baby blues seems to be correlated with CS more than with natural birth. And I know that CS is far from “painless” and “comfortable” solution, for my wife had it twice – for medical reasons, not “on demand” (I mean many women want this and doctors co-operate).
    Jr: it’s just the context. Oxytocin makes some muscles contract, but it results in lactation if there’s milk (prolactine is needed for it first) and in birth if uterine muscles are big enough (it takes some nine months of pregnancy first). If not, then there’s “just” orgasm 😉 Of course it is also probably the question of level – I think that during birth there’s much more oxytocin that during lactation or orgasm.

  28. Jan: Do you have a citation for CS correlating more with baby blues? I don’t know if that’s oxytocin, or the fact that CS has a longer recovery time associated due to the abdominal surgery. Would like to see that study.

  29. The lactivists say that baby blues is likely to be aided by breastfeeding, and I think C-sections are more associated with never breastfeeding.
    That said, I think the CS and postnatal depression link is not well-established, although there are a number of studies looking at it.

  30. Have there been any studies about what, precisely, “bonding” means? Viewing it as some purely biological response linked to feeding alone seems a bit perilous to me. Humans are not animals. Generally, they choose to carry a child for nine months and their feelings about infants are a whole lot more complex than merely reproduction. The few studies I have seen on bonding are laughably vague. Maybe oxytocin does provoke some kind of extra conditioned response, but I find it extremely difficult to believe that its absence has that much effect on mother/child bonding in the sense I mean it – unconditional love and life-long commitment. And as for CS/baby blues, the anxiety following what may have been a perilous birth is, again, not the same as a purely hormonal response. I would concede that the scientific study of hormones is interesting and instructive, but it too easily can be used to feed more ideological than scientific thinking.

  31. I would believe that there is a correlation with C-sections and postpartum depression because I think what causes both is insufficient nitric oxide. Not all C-sections are due to effects of low NO, but enough that there should be a correlation. I think that essentially all postpartum depression is caused by low NO.
    NO is what triggers mitochondrial biogenesis, and with insufficient mitochondria, the operating potential of what mitochondria are present gets pushed to a higher potential (to make more ATP per mitochondrion) which causes increased production of superoxide (to reduce NO levels local to the mitochondria to disinhibit cytochrome c oxidase to increase O2 binding and reduction, to allow the mitochondria to pull the O2 concentration down, so the O2 concentration gradient increases to cause a greater flux of O2 to diffuse down the O2 concentration gradient from the blood vessel to the mitochondrion).
    NO is important for angiogenesis and the proper vascularization of the placenta. If there is insufficient NO early in pregnancy, then the placenta isn’t big enough, there is insufficient mitochondria in the liver to support the Cori cycle, and in peripheral tissues (causing gestational diabetes), and the blood supply doesn’t expand enough (HIF-alpha is triggered by high NO). Gestational diabetes causes the fetus to grow larger than it should (perhaps causing cephalopelvic disproportion). All of these correlate with obesity and polycystic ovarian syndrome.
    Postpartum depression is (I think) caused by insufficient liver metabolic capacity to support gluconeogenesis for lactation. That is caused by insufficient NO to trigger enough mitochondria biogenesis. Without enough mitochondria, the mitochondria potential gets pushed high, where more superoxide is made to acutely increase metabolic capacity. When that gets chronic, then the NO level never gets high enough to support the level of mitochondria biogenesis that is needed. You have to reduce metabolic load enough to reduce mitochondria potential so that NO levels can go up and mitochondria biogenesis can resume. If you don’t, then postpartum depression proceeds to postpartum psychosis.
    I think the initial depression is a “feature” to reduce metabolic load by inducing depressive apathy, so that there can be recovery of mitochondria biogenesis in the liver. If that isn’t enough, then it proceeds to postpartum psychosis. Lowering the production of superoxide isn’t enough to reverse the state of insufficient mitochondria, you also have to increase the NO level.
    I have a blog which discusses the physiology of all of this in some detail (with links). (warning, some of it is disturbing). That is the link under my pseudonym.

  32. Sci, unfortunately I don’t…

  33. Found it at last in “New Scientist” (by accident ;-))
    There is a link to another interesting news in the text.

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