Abstract: Objective In order to determine the dose and time of naloxone(NLX) treatment in the acute and repeated anoxia conditioning, the study was carried out using mice hypoxic models, about the effects of β-endorphin (β-EP), the reverse of respiratory depression and the change of hypoxic endurance time in mice injected with NLX in the hypoxic condition． Methods The mice were divided into 3 groups．The first group was injected with NC, The second group was injected with0.4mg/mL NLX, The third group was injected with0.04mg/mL NLX． Results Oxygen exhausting time of mice was significantly longer under hypoxic condition than under sham condition, but the oxygen exhausting time of mice from the second group under the hypoxic condition was significantly longer than the first group after injection of 0.4mg/mL NLX; there was a significant decrease in the 0.04mg/mL NLX mice compared to those in the first-group mice． Conclusion NLX can block the effect of β-EP released, reverse the respiratory depression, but the NLX in different dose make different effect in the endurance of the mice in the acute and repeated anoxia condition． 0.4mg/mL NLX makes the anoxia-endurance of mice higher than the first group, 0.04mg/mL NLX makes the anoxia-endurance of mice lower than the first group.

Key words: acute and repeated anoxia, anoxia-endurance, Naloxone