Comparison of the effects of different magnesium administration times on infarct size.
BACKGROUND
The protection of high magnesium on infarct size remains controversial.


OBJECTIVE
To examine the effects of magnesium administered before ischemia or early in reperfusion on infarct size in a rat model of global ischemia


METHODS
Isolated rat hearts were submitted to 40 min of normothermic global ischemia and 2 h of reperfusion. After 20 min of stabilization, four protocols were performed: ischemic control (IC) hearts; 15 mM of magnesium chloride administered 15 min before ischemia (MgI); 15 mM of magnesium chloride administered during the first 15 min of reperfusion (MgR); or 15 mM magnesium plus 5 mM calcium (Mg+Ca) before ischemia. Infarct size was measured by triphenyltetrazolium staining. Contractile function was assessed by left ventricular developed pressure and the maximal velocity of rise of left ventricular presssure.


RESULTS
The infarct size in IC hearts was 44+/-5%. In MgI and MgR hearts, the infarct diminished to 4.5+/-1.5% and 18+/-4%, respectively. In Mg+Ca hearts, the protection was also obtained (19+/-3%). Myocardial function also improved significantly by magnesium treatment. At the end of reperfusion, left ventricular developed pressure and maximal velocity of rise of left ventricular pressure values were 23+/-6% and 22+/-3% in MgI; and 10+/-3% and 9+/-2.6% in MgR versus 2+/-0.7% and 2.3+/-0.8% in IC hearts, respectively.


CONCLUSIONS
The treatment with magnesium either before ischemia or early in reperfusion has an infarct size limiting effect in a model of global ischemia. This protective effect is partially due to its calcium antagonistic action.
Martínez Demaría
Diego R
DR
Fellow in Cardiology, Residencia Hospitalaria Universitaria del Hospital Italiano de La Plata, La Plata; and.
Cingolani
Horacio E
HE
Mosca
Susana M
SM