Abstract
Objective: We have reported that high Mg applied through out the period of hypoxia can protect rat hearts from hypoxia/reoxygenation injury. The purpose of the present study was to examine when and how long high Mg applied during hypoxia is effective. Methods: Langendorff-perfused rat hearts were subjected to 1) control (CT) group: 30 min hypoxia and 30 min reoxygenation. 2) Hypoxic perfusate containing 12 mM Mg was given at the first 5 min, 3) 10 min or 4) 15 min and then perfused with normal hypoxic solution for total 30 min hypoxia and then 30 min reoxygenation. 5) Hypoxic solution containing 12 mM Mg was given at the second 5 min or 6) the last 15 min during hypoxia and the others same as 2 group. Results: Recoveries of pressure-rate product (PRP) in 2, 3, 4 groups were not different from those perfused with high Mg through out hypoxia and were all higher than those of CT at the end of 30 min reoxygenation. Recoveries of PRP in 5, 6 groups were similar as those of in 2, 3, 4 groups at the first 5-10 min of reoxygenation period, but the recovery was suppressed and there was no difference from CT at the end of 30 min reoxygenation. Conclusions: High concentration of Mg applied at the beginning of hypoxia was important and necessary for protecting rat hearts from hypoxia/reoxygenation-induced injury. [Jpn J Physiol 55 Suppl:S96 (2005)]
