Abstract: A method for the screening and identification of low molecular weight compounds which interact with lactogenic/somatogenic receptors is claimed. The method is characterized by the use of isolated tissues for in vitro cultivation as organ culture, primary cells, immortalized or transformed cells from transgenic animal that over-express hormones/receptors belonging to the somatic or lactogenic family. Also a transgenic non-human animal that over-express prolactin which cause phenotypic alterations notably in the prostate and/or mammary gland and use thereof is claimed.