We have shown that the cardioprotective benefits of ischemic preconditionin
g (PC) can be transferred from PC to virgin acceptor hearts via coronary ef
fluent transfusion, implicating the presence of hormonal preconditioning fa
ctor(s). Using isolated buffer-perfused rabbit hearts, our aims were to: (1
) determine whether the protective factor(s) could be concentrated and reco
vered by reverse phase chromatography and (2) whether opioid receptor activ
ation contributes to this transferred cardioprotection. Material released i
nto the coronary effluent during PC ischemia/reperfusion or normoxic perfus
ion was concentrated by reverse phase chromatography. In phase one, hearts
received no intervention (controls), PC ischemia, concentrate generated fro
m normoxic hearts (normoxic acceptors) or concentrate from PC hearts (PC ac
ceptors). All hearts underwent 40 min of global ischemia, and area of necro
sis (AN) was delineated by tetrazolium staining. In phase two, three additi
onal groups of hearts (control, PC and PC acceptors) received the opioid an
tagonist naloxone (2 pm) throughout the intervention phase. Treatment with
normoxic concentrate had no effect on infarct size: (AN: normoxic acceptors
39 +/- 8%; control 42 +/- 8%). In contrast, treatment with PC concentrate
evoked cardioprotection equivalent to that afforded by conventional PC (AN
19 +/- 5% and 21 +/- 6% respectively: P <0.05 v control). Naloxone had no e
ffect on infarct size in controls, and did not inhibit preconditioning. How
ever, naloxone abrogated the protection achieved by transfer of PC concentr
ate (AN: 44 +/- 7%). These results indicate that PC concentrate evokes a ca
rdioprotective effect via a mechanism requiring an intact opioid receptor s
ystem. (C) 2001 Academic Press.