We investigated whether
atrial natriuretic peptide (
ANP) given just prior to reperfusion reduces
infarction in rabbit hearts and whether protection is related to activation of
protein kinase G (PKG). Isolated rabbit hearts were subjected to a 30-min period of regional
ischemia; treated hearts received a 20-min infusion of
ANP (0.1 microM) starting 5 min before 2 h of reperfusion.
ANP infusion decreased
infarction from 31.5+/-2.4% of the risk zone in untreated hearts to 12.5+/-2.0% (P<0.001). To explore mechanisms of protection ischemic hearts were treated simultaneously with
ANP and
isatin, a blocker of the
natriuretic peptide receptor, shortly before reperfusion.
ANP's protective effect was aborted (36.8+/-2.9%
infarction). There is no acceptable blocker of
protein kinase G that can be used in intact organs. However, 8-(4-chlorophenylthio)-guanosine 3', 5'-cyclic monophosphate (10 microM), a cell-permeable cGMP analog that directly activates PKG, was infused from 5 min before to 15 min after reperfusion. The PKG activator mimicked
ANP's protection with only 18.2+/-3.6%
infarction (P<0.001). 5-Hydroxyde-canoate (5-HD), a putative mitochondrial
KATP channel (mKATP) inhibitor, abrogated
ANP's protection (34.4+/-2.6%
infarction). Unexpectedly, 1H-[1,2,4]
oxadiazole- [4,3-a]quinoxalin-1-one (ODQ), a blocker of
soluble guanylyl cyclase also prevented
ANP's
infarct-sparing effect. It is unclear whether this observation implicated participation of
soluble guanylyl cyclase in the mechanism or simply a lack of selectivity of ODQ. Finally the
reperfusion injury salvage
kinases (RISK),
phosphatidylinositol 3-kinase and
extracellular signal-regulated kinase, were implicated in
ANP's mechanism since either
wortmannin or
PD98059 infused at reperfusion prevented
ANP's
infarct-sparing effect.
ANP administered just prior to reperfusion protects hearts against
infarction, likely by activation of PKG, opening of mKATP, and stimulation of downstream
kinases.