Laura,
I presume you have read what Lisa wrote on 13th Feb about Peter Hartmann's
research. He has two papers printed in JHL March 1995 if you would like to
read it all. The basis of "autocrine" control of milk synthesis (more milk
produced as a result of emptying of breast) is the presence of an inhibitor
substance in the milk. This is produced in the milk all the time, and when
it is left to accumulate (breasts not drained), it inhibits milk synthesis
by a biological feedback mechanism. When the milk is removed, either by the
baby or by expressing, the inhibitor is also removed, and the breast goes
into a greater milk synthesis rate. So it is not really that the breast
produces *more* milk with stimulation, rather that it produces *less* with
inhibition from the milk already stored. A neat method nature has devised
to stop us all blowing up and bursting when we are feeding only one baby
instead of triplets?! ;-) Autocrine control also explains differing supply
in each breast, and the ability to completely dry up one breast while
continuing to lactate in the other.

Endocrine (hormone) stimulation of milk production (from prolactin) is very
important in the initiation of lactation, and is in the background as a
maintainer throughout (getting a bit of a boost each time baby feeds), but
after the first few weeks, the autocrine system is the driving force. This
has practical application too, as it can be seen that bromocriptine (that
is still sometimes used here for lactation suppression) would only work
efficiently in the early days since it works to suppress prolactin. It does
not work very well in established lactation.

Joy Anderson IBCLC, NMAA Breastfeeding Counsellor,
Perth, Western Australia,
who is incredibly fascinated by this wonderful system that nature designed
so perfectly. It's just a shame people interfere and mess it up so often!