Effect of magnesium on myocardial damage induced by epinephrine. Ultrastructural and cytochemical study.

Magnesium ion is involved in energy metabolism, transport of ions and control of intracellular Ca2+. Catecholamines, intensify cellular Mg2+ depletion and the detrimental effects of catecholamine excess and Mg2+ deficiency are mutually enhancing in the myocardium. To investigate whether Mg2+ supplementation protects the myocardium against damage induced by catecholamines, we examined the ultrastructure and the ultracytochemical localization of Ca2+ in the myocardium of rabbits infused with epinephrine (1 microgram/kg/min intravenously for 2 hours), in rabbits infused simultaneously with epinephrine and MgSO4 (50 mg/kg, intravenously) and in saline-infused controls. Qualitative evaluation showed that Mg2+ supplementation attenuated the mitochondrial alterations induced by epinephrine and decreased intracellular and endothelial swelling. Ultracytochemistry with oxalate-pyroantimonate showed a shift in the localization of Ca2+ from the vicinity of the sarcolemma in the controls into the mitochondria in epinephrine-treated hearts. Mg2+ supplementation had no effect on the changes in Ca2+ localization induced by epinephrine or on the intensity of the cytochemical reaction. In conclusion, Mg2+ supplementation reduces the ultrastructural features of myocardial damage induced by epinephrine without an effect upon changes in intracellular distribution of Ca2+ induced by epinephrine, as shown cytochemically.