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In rats, immobilization stress (24 h) induced involution of the thymus and spleen, adrenal hypertrophy, and pronounced elevation (by 67%) of serum cortisol in comparison with intact animals; the mean number of stomach ulcers in rats subjected to stress was 6.9. Hypoxic preconditioning consisting of 6 sessions of 10-min hypoxia (8% O2) followed by 10-min reoxygenation with atmospheric air induced adrenal hypertrophy and spleen involution, but did not change blood cortisol level; no stomach ulcers were found in preconditioned rats. In rats subjected to both hypoxic preconditioning and immobilization, the weights of the thymus, adrenal glands, and spleen, as well as cortisol level did not differ from the corresponding parameters in rats subjected to immobilization stress alone. The number of stomach ulcers in experimental rats was 1.5-fold lower than in the stress-control ones. Thus, hypoxic preconditioning exerts a pronounced preventive anti-ulcer effect during immobilization, but it does not affect other indices of the stress reaction.

Chronic continuous normobaric hypoxia (CNH) increases cardiac tolerance to acute ischaemia/reperfusion injury. The objective of this study was to find out whether the cardioprotective effect of CNH mediated by opioid receptors is associated with preservation of mitochondrial function. Rats were adapted to CNH (12% oxygen) for 3 weeks. Isolated perfused hearts were subjected to 45 min of global ischaemia and 30 min of reperfusion; subgroups were pretreated with non-selective opioid receptor antagonist naloxone (300 nmol/L) for 10 min. Cardiac contractile function, creatine kinase activity in coronary effluent, mitochondrial respiration rate, and calcium retention capacity were assessed. Adaptation to CNH decreased myocardial creatine kinase release during reperfusion and improved the post-ischaemic recovery of contractile function, mitochondrial state 3 and uncoupled respiration rates, and calcium retention capacity compared to the normoxic group. These protective effects were completely abolished by naloxone. The contractile recovery positively correlated with state 3 respiration and calcium retention capacity. The results suggest that the preserved mitochondrial function contributes to the protected cardiac phenotype afforded by adaptation to CNH and point to an important role of opioid receptor activation., (© 2015 Wiley Publishing Asia Pty Ltd.)

MEK, PI3, p38, tyrosine, and mTOR kinases are not involved in the regulation of heart resistance to the arrhythmogenic action of short-term ischemia/reperfusion in non-adapted rats.

Hypoxic preconditioning produces an infarct-limiting effect both in the early and delayed periods. The increase in heart resistance to ischemia-repefusion was more pronounced after early preconditioning. Hypoxic preconditioning did not change heart resistance to the arrhythmogenic effect of coronary occlusion and reperfusion.