However, in spite of having no metabolic alterations under normal conditions, when challenged by pregnancy (9, 46) or STZ-induced diabetes (present findings), C57BL/6 Prlr null mice were unable to maintain whole body glucose homeostasis and β-cell mass and function, indicating that PRL signaling plays a fundamental role in glucose homeostasis regardless of the genetics. This evidence concerns the gene PRLR and diabetes mellitus.