Relationship between Hypoxic Resistance and the Phase of 4-Day Corticosterone Biorhythm in Adult Male Rats

The relationship between the phase of 4-day serum corticosteroid biorhythm and resistance to acute hypobaric hypoxia was studied in male rats. Single evaluations of hypoxic resistance of Wistar rats during the same time of the day have shown that the lifespan of animals is significantly longer during the 4-day biorhythm acrophase than during the bathyphase. Daily testing for 12 days has detected a 4-day rhythm of hypoxic resistance, synphasic with corticosterone biorhythm, irrespective of the wave-like course of the adaptation process phase from the beginning of daily testing and hypoxic resistance. Experiments on Sprague-Dawley rats have shown that animals highly resistant and medium resistant to hypoxia during the infradian biorhythm acrophase become medium resistant and poorly resistant during the bathyphase. In order to detect the animals with the least hypoxic resistance in the population, the studies should be carried out during the 4-day infradian biorhythm acrophase, while detection of the most resistant animals should be carried out during the bathyphase.