Effect of Hypoxic Preconditioning on Stress Reaction in Rats

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.