[Lotus]

You should checkout this thread when you get time,

Ok people, who's up for a little NBE science?

• Prolactin and progesterone may enhance ductal outgrowth by inducing ERα expression.
  

• Activation of ER-α causes elongation or horizontal growth of mammary duct cells. Progesterone receptor activation causes side-branching of mammary gland cells. Density, areolar gland development, and gland lactation development are caused by prolactin receptor activation.
  

Check pages 5 thru 9
Hormone Action in the Mammary Gland
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2982168/

http://www.breastnexus.com/showthread.php?tid=19582