Daily reoxygenation decreases myocardial injury and improves post-ischaemic recovery after chronic hypoxia §

Objective: In contrast to the clinical evidence, experimental studies showed that chronic hypoxia (CH) confers a certain degree of protection against ischaemia—reperfusion damage. We studied the effects of daily reoxygenation during CH (CHReox) on hearts exposed to ischaemia— reperfusion. We also separated the intrinsic effects on the myocardium of CH and CHReox from those related to circulatory and nervous factors. Methods:Fifty-one Sprague-Dawley rats were maintained for 15 days under CH (10% O2) or CHReox (10% O2 + 1 h day � 1 exposureto air). Normoxic (N, 21% O2) rats were the control. The animals were randomly assigned to one of the three following protocols: (1) protocol A: hearts (n = 7 per group) were subjected to 30-min occlusion of the left anterior descending (LAD) coronary artery followed by 3-h reperfusion, with measurement