Prolactin stores breast fat by increasing the production of lipoprotein lipase (LPL, a fat storage enzyme). So we also know prolactin increases the number of ER's, which kind however (ER alpha or beta) is less known.

From what I've seen in scientific literature on the different types of breast receptors it's a mix, being of 20% androgen receptors, 20% estrogen receptors, 20% glucocorticoid receptors, 20% prolactin, the rest I'm thinking its insulin (IGF-1, or IL-1) receptors. Here's the thing, too much estrogen stimulation doesn't address other receptors. It would appear that androgen receptors will inhibit breast growth by way of DHT, which is present in breast tissue, especially in skin fibroblasts. Progesterone cream is a 5 alpha reduction inhibitor, but..it also stores fat too, and helps build ductal side branching. Breast massage agents should address the receptor types. Therapy should include a 5 AR inhibitor 1st, then go with an E2 source followed by a GH source. Prolactin should could by way of nipple stimulation, have fun.