Dear Nancy, I believe it is the autocrine supply that keeps the supply
going after the "boost" of metoclopramide (or prolactin, as originally
designed.  This is the system where milk left in the aveoli sends out a
signal for less milk to be made because there was some leftover this feed.
Good emptying then leads to good filling.  See what other answers you get!
I'm not sure anyone totally knows.  Sincerely, Pat in SNJ