Kathy wrote
<<We also understand that prolactin is responsible for milk
production and that prolactin is only released in response to the
baby's suckling at the breast>>

While prolactin is important in stimulating the initial production
of milk, levels decreases rapidly after delivery and can return to
non-lactating levels within months. The sucking response to
prolactin is only evident in the first few months and has usually
disappeared by 6 months.

Once lactation is established, milk synthesis (production) is
primarily under autocrine control, ie local control in the breast,
assuming a favourable hormonal milieu.  That is why women can fed
with one breast and dry up the other. The degree and frequency of
emptying are the most important factors controlling the rate of milk
synthesis.

Interestingly, the natural tendency of the breast is to make too
much milk and autocrine control downregulates production. Initially
they thought that the primary mechanism was an inhibitory
(suppressor) peptide in human milk that slowed the rate of synthesis
when milk was stored in the breast, but now there is evidence that
pressure variations from stored milk may also be a factor.  More
pressure, slower production. It has been suggested that *extreme*
back pressure, such as from engorgement, can also prevent oxytocin
contracting the myoepithelial cells.

I am not aware of any studies which show that milk synthesis
increases *during* a feeding, except that the rate may increase as
the breast empties. Peter Hartmann's work showed that synthesis
occurred throughout the 24 hour period, with the rate dependent on
the degree of emptying. Women were rarely making milk at the maximum
rate, suggesting that the breasts had a lot more production in
reserve.

The message?  Frequent feeding, frequent breast emptying will
increase supply. We have known that for a long time, now science has
explained why.

Ros Escott BappSc IBCLC
Tasmania, Australia