Factors affecting mRNA hepcidin expression in the liver. Hepcidin levels are regulated by iron levels (store regulator), immune mediators (inflammatory regulator), hypoxia (hypoxia regulator), and erythropoietic demand (erythroid regulator). Pointed arrows indicate up-regulation of hepcidin, and blunt arrows inhibition of its mRNA expression. For each regulator, the treatments used in this study to stimulate or suppress hepcidin expression are shown.