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From:
Catherine Fetherston <[log in to unmask]>
Reply To:
Lactation Information and Discussion <[log in to unmask]>
Date:
Tue, 17 Apr 2001 11:38:30 +0800
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I have received lots of private emails from people interested in the
prolactin subject. Denise Fisher had some very interesting thoughts on this
issue and for those who are following this thread I am posting my discussion
with her on this subject (but I reserve the right to revise these opinions
in the next few days after having a chat with those that know a lot more
than me!)

Hi Denise,

> When do you feel the literature supports autocrine control as being the
> regulator of milk synthesis.  I realise it would be gradual - is it a
> transition from right after the onset of lactogenesis II to about 6 to 8
> weeks when it is completely autocrine (well, not completely because you do
> still need prolactin present).

My understanding from the research and from discussions with Mark Cregan is
that autocrine control of both short term (between breastfeeds) and long
term (month to month ) rate of milk synthesis is immediate upon the
commencement of lactogenesis II (which is around 36 hours from memory). It
is the immediate rise in prolactin after birth that stimulates the increase
in lactose production which in turn through osmotic effects cause the
initial changes in volume ("coming in" of milk). Presumably the prolactin
levels and their receptors are very important at this time to initiate
Lactogensis II (and lactose production). However thereafter I think
prolactin is considered only to be permissive, as they've shown that changes
in blood prolactin (above a certain threshold which is required to maintain
lactation) do not regulate milk synthesis.
But I will confirm this with Peter this week and post back to the list, in
case I have misunderstood.
Peter also has a real "thing" about the prescription of galactogogues such
as motilium being prescribed for delayed initiation of lactation when nobody
ever bothers to check whether the mother's prolactin levels are within
normal range or not. (I think he has a point!) But (in my ignorance,) I
wonder if its possible that these galatogogues have the capacity to
stimulate an increase in prolactin receptors and that this is why they
appear to work (when the serum prolactin levels have actually always been
normal)????

> And perhaps it's the number of prolactin receptor sites which are laid down
> that actually determine (to a degree) the breast capacity.  The reason I
> have said this is that Peter H was telling me about studies with pigs (what
> else?) where one teat was used by several piglets and how that teat
> hypertrophied - ie increased it's capacity.  In women would a mother of
> twins or triplets lay down extra prolactin receptor sites in those early
> weeks because of the extra suckling stimulus and so develop a greater
> storage capacity?  Is storage capacity a genetically determined factor or
> determined in the first few weeks of each and every lactation???

This seems to be how I would interpret the current research. On current
evidence, I cant see why the breast would not continue to have new growth
throughout lactation, according to stimulus, and that perhaps any
restriction is simply as a result of, as you say,  individual variation.

>During autocrine control is when I was thinking that the prolactin receptor
> theory (if it ever gets substantiated) would be most useful.  women who
> didn't lay down many prolactin receptors in early lactation are now unable
> to synthesis as much milk - this would still work in with the FIL.

 Yes, I agree, What would also be interesting to know is -  Are the number
of prolactin receptors linked to the amount of glandular tissue synthesised
or is it independent? Can you have plenty of glandular growth during
pregnancy but an insufficiency of prolactin receptors which might lead to
delayed or inadequate initiation of lactogenesis II? Or can this be
compensated for after birth with the sudden increase in breast growth that
is seen in some women at this stage? I have seen a couple of women whose
lactation did not establish until around 4 weeks. No breast growth to speak
of in pregnancy, milk never "appeared" to come in, continued to breastfeed
and top up with formula to baby's need, until finally became fully breastfed
weeks later (How many of this type of women would normally have given up and
we wouldn't know that they would have eventually been able to fully
breastfeed?).

Reagrds
Cathy Fetherston. CM MSc IBCLC
Perth Western Australia

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