Atrial natriuretic peptide (
ANP)-preconditioned livers are protected from
ischemia-reperfusion injury.
ANP-treated organs show increased expression of
heme oxygenase (HO)-1. Because HO-1 liberates bound
iron, the aim of our study was to determine whether
ANP affects
iron regulatory protein (IRP) activity and, thus, the levels of
ferritin. Rat livers were perfused with
Krebs-Henseleit buffer [+/-
ANP,
8-bromo-cGMP (8-Br-cGMP), and
tin protoporphyrin, 20 min], stored in University of Wisconsin
solution (4 degrees C, 24 h), and reperfused (120 min). IRP activity was assessed by gel-shift assays, and
ferritin, IRP phosphorylation, and PKC localization were assessed by Western blot. Control livers displayed decreased IRP activity at the end of
ischemia but no change in
ferritin content during
ischemia and reperfusion.
ANP-pretreated livers showed reduced IRP activity, an effect mimicked by 8-Br-cGMP.
Ferritin levels were increased in
ANP-pretreated organs. Simultaneous perfusion of livers with
ANP and
tin protoporphyrin did not reduce
ANP-induced action, arguing against a role for HO-1 in changes in IRP activity.
ANP and 8-Br-cGMP decreased membrane localization of PKC-alpha and
PKC-epsilon, but this modulation of PKC seems unrelated to inhibition of IRP binding. This work shows the cGMP-mediated attenuation of IRP binding activity by
ANP, which results in increased hepatic
ferritin levels. This change in IRPs is independent of
ANP-induced HO-1 and reduced PKC activation.