Myocardial ischemia reperfusion results in an increase in intracellular
sodium concentration, which secondarily increases intracellular
calcium via Na(+)-Ca2+ exchange, resulting in cellular injury.
Endoxin is an endogenous medium of
digitalis receptor and can remarkably inhibit Na+/K(+)-
ATPase activity. Although the level of plasma
endoxin is significantly higher during
myocardial ischemia, its practical significance is unclear. This research is to investigate whether
endoxin is one of important factors involved in
myocardial ischemia reperfusion injury.
Ischemia reperfusion injury was induced by 30 min of global
ischemia and 30 min of reperfusion in isolated rat hearts. Heart rate (HR), left ventricular developed pressure (LVDP), and its first derivative (+/-dp/dtmax) were recorded. The
endoxin contents, intramitochondrial Ca2+ contents, and the Na+/K(+)-
ATPase activity in myocardial tissues were measured. Myocardial damages were evaluated by electron microscopy. The
endoxin and intramitochondrial Ca2+ contents in myocardial tissues were remarkably higher, myocardial membrane
ATPase activity was remarkably lower, the cardiac function was significantly deteriorated, and myocardial morphological damages were severe in
myocardial ischemia reperfusion group vs. control. Anti-
digoxin antiserum (10, 30 mg/kg) caused a significant improvement in cardiac function (LVDP and +/-dp/dtmax), Na+/K(+)-
ATPase activity, and myocardial morphology, and caused a reduction of
endoxin and intramitochondrial Ca2+ contents in myocardial tissues. In the present study, the
endoxin antagonist, anti-
digoxin antiserum, protected the myocardium against the damages induced by
ischemia reperfusion in isolated rat hearts. The results suggest that
endoxin might be one of main factors mediating
myocardial ischemia reperfusion injury.