Intracellular magnesium and tolerance against hypoxia in immature rat heart.

Abstract

BACKGROUND: Neonatal hearts show greater resistance to hypoxia than adult hearts do, but the mechanism is unclear. In immature rat hearts, we examined the association between high tolerance for hypoxia and the kinetics of magnesium (Mg), which has myocardial protective effects in adult hearts. METHODS: The hearts of 1-, 2-, 3-, and 10-week-old rats were Langendorff perfused and subjected to 45 min hypoxia and 30 min reoxygenation. The myocardial Mg content was measured by atomic absorption spectrophotometry. RESULTS: In 1-week-old rat hearts, the tension-rate product recovered more immediately with reoxygenation than in the other groups, and aspartate aminotransferase release did not increase throughout the experiment. In 10-week-old rat hearts, total tissue Mg content decreased significantly with reoxygenation (607.0 ± 22.9 µg/g dry weight) from its control level (793.2 ± 16.7 µg/g dry weight). However, in neonates, the total tissue Mg did not decrease with reoxygenation. CONCLUSIONS: The high resistance against hypoxia-reoxygenation injury in neonatal rat hearts is caused, at least in part, by a high ability to maintain myocardial Mg.