Whether or not some oxytocin makes it into the milk, is immaterial, since
oxytocin doesn't withstand gastric juices. It seems to stand up to saliva,
or the old buccal tablets of synthetic oxytocin would not have worked. They
were on the way out just before I trained as a midwife and frankly I wish we
still had them. If there were signs of uterine overstimulation in labor the
woman could simply spit it out. Of course you couldn't have an infusion pump
with a nice display to show how many ml per hour the woman was getting, you
wouldn't really know anything except whether you were happy with her uterine
contractions, which when it comes down to it is really all that matters, no?
Hartmann's comment about it not being possible to measure oxytocin levels in
women by drawing blood samples is facetious. It is possible, and a Swedish
research team did so, and were able to show that mothers had oxytocin spikes
in response to their infants' hand movements on the breast in the first
hours postpartum when they were observed while skin to skin. I am too lazy
to find the reference to the article in BIRTH in which these and other
findings were published. Babies exposed to ANY pharmaceutical pain relief
given to mother, do not have the characteristic hand movements of
unmedicated babies and the team postulate that this affects the time of
lactogenesis II as well as the total volume of milk produced in the early days.
The half life of oxytocin is the in vivo half life in the blood of a living
organism; oxytocin is stable in vitro or the 10 IU glass ampules of
synthetic oxytocin which are such a huge part of any labor ward's
armamentarium would not keep the way they do, for aeons. Once blood is
removed from a live body and contained in a glass tube, there is a fixed
amount of both oxytocin and the substances in blood that break it down, so
it should be possible to see relative changes in oxytocin level.
Prolactin is indeed the hormone that directly regulates the amount of milk a
mammal makes. But oxytocin, by seeing to it that the milk glands and ducts
are emptied, triggers higher milk production indirectly too.

Rachel Myr
Kristiansand, Norway

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