Hepcidin concentration declines from the proximal to distal small intestine. Mice (n = 4, each interrupted line representing an individual mouse) received a single dose of radiolabeled hepcidin, were killed 2 hours later, and their organs were perfused with PBS to remove blood. Hepcidin concentration (average shown as a bold line) decreased from proximal to distal position in the intestine (Spearman R = -0.929, P < .001, n = 4).