Prolactin regulates a wide variety of biological processes in the ovary and uterus. Particular variants of prolactin, one binding to its receptor isoform can stimulate different intracellular signal transduction pathways. This leads to the activation of a specific set of genes for a given tissue, the species and the period of reproduction. Understanding the relationship between the specific biological function of prolactin and the way it impacts the target cell, despite the progress recorded in the last decade, is the current goal of many studies.