AJP - Heart and Circulatory Physiology, Vol 242, Issue 1 89-H93, Copyright © 1982 by American Physiological Society
Effect of increased magnesium on recovery from ischemia in rat and rabbit hearts
M. M. Bersohn, K. I. Shine and W. D. Sterman
Perfusates containing high magnesium concentrations have been suggested to
have a protective effect for ischemic myocardium, but the mechanism for
such an effect is unclear. We investigated the recovery of isolated
perfused rabbit and rat hearts from ischemia under varied conditions of
increased Mg. Hearts were made ischemic in the presence of normal 1.2 mM Mg
or elevated 15 mM Mg. Rabbit hearts, which show minimal alteration in
contractility in the presence of 15 mM Mg, were not protected from ischemia
by high Mg perfusate. Rat hearts, which have a large negative inotropic
response to 15 mM Mg, exhibited significantly better recovery of mechanical
function following ischemia in the presence of high Mg than following
ischemia with normal Mg. This protective effect was abolished by increasing
both Ca and Mg in the perfusate to prevent the decline in contractility
that normally occurred with Mg. Reperfusion with 15 mM Mg after ischemia
also had no protective effect if the rat heart had been made ischemic in
the presence of normal Mg. We conclude that elevated Mg protects ischemic
myocardium only under circumstances in which it has a negative inotropic
effect before the onset of ischemia, i.e., in the rat heart perfused with
normal Ca. These results suggest that the mechanism of protection by high
Mg involves sparing of ATP. However, the different responses to Mg of the
species studied in these experiments should be a caution against
extrapolating such results from rat hearts to other species.
