Effect of prolactin on maintenance of prelactating human mammary gland in vitro.

Human mammary tissue from a female at the end of the second trimester of pregnancy was studied in organ culture in a chemically defined medium. Sampling was carried out at 1, 2 and 3 weeks. Without hormones, there was nearly total lobuloalveolar degeneration in all specimens at all times. Addition of insulin, hydrocortisone and ovine prolactin, in combination at a concentration of 5 mug per ml each, did not affect the extent of degeneration. Raising the concentration of prolactin to 50 mug per ml resulted in greatly improved lobulo-alveolar maintenance in all specimens and continued epithelial cell DNA synthesis for up to 3 weeks in vitro.