> I knew that apoptosis occurs during weaning, but I had
> never carried that thought through to the extent that your last post does,
> Cathy.  Am I understanding correctly that the DUCTAL structure disappears
> between lactations and re-generates during a new preg?

An analogy that is sometimes used is that the breast is like a deciduous
tree. In the virgin (never lactated) breast small branches exist of the pre
ductal system (like a very young tree in winter). In summer (lactating) we
see lots of new branches and leaves etc forming. In winter (involution) the
tree will lose all its leaves and some of its littler  branches (and its
fruit!) but be left with a more extensive basic architecture that will
provide the basis for further growth at the next lactation.

The only evidence I believe we have to show that this is an accurate analogy
is from research in rats and mice. I'm not aware of anything having been
done in humans. In mice a virgin breast will have nicely delineated "tidy"
ductal buds. I believe (this is from discussion) that the involuted gland
(in mice) does not look the same as the virgin gland. It has a more
extensive and "messy" architecture of ducts left. So not every thing
disappears, although all functional tissue does (usually) and must be
rebuilt in a new lactation.

But it would be very interesting to know what happens in the breast of the
mother who is breastfeeding while pregnant. And if this makes a lot of
difference to how the forthcoming lactation will function.
    

> be why we sometimes see what we have called 're-canalization' in some women
> who have exper. breast surgery?  Perhaps re-canalization is constantly
> occuring and would explain why lactation is more successful during some
> lactations in the same woman.

I think this is really interesting. The short answer is of course we don¹t
know. However there's a couple of opposing theories. I was having a
discussion with Mark Cregan who has researched expressing and pre term milk
supply and is also looking at apoptosis. Now he leans toward the theory that
all women have the capacity to produce enormous quantities of milk. That
when milk supply increases during lactation it increases because of an
increase in the efficiency of alveoli to produce milk, not due to the
proliferation of new lactocytes. He bases this proposal on work he has done
that has shown that alveoli are not drained equally throughout the breast at
any one time. Some alveoli will be drained fairly thoroughly while others
remain full and then the full ones will be drained etc and a cyclical
sequential removal of milk occurs. So, the more milk removed, and the more
often, the efficiency of production (or the rate of synthesis) will improve
(we all know this basic principle).

An example: is with mastitis when death and damage of milk producing tissue
occurs the milk supply drops. When it picks up again is it due to an
increased efficiency of the remaining undamaged tissue or is there
differentiation of new tissue occurring that picks up the slack?

I like both theories. Perhaps there's a combination of both.

Regards
Cathy Fetherston CM MSc IBCLC
Perth Western Australia

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