Seasonal variations in rat resistance to hypoxia.

Resistance to acute hypoxia was evaluated by the life span after elevation to a simulated altitude of 11,500 m at 13.00-21.00 in different seasons of the same year. The period of investigation was divided into 3 parts: beginning (13.00-15.00), middle (16.00-18.00), and end (19.00-21.00) of the day. Animal life span decreased by the end of the day (the decrease was more pronounced in summer and autumn) and by the end of the year, i. e. in autumn (more pronounced in the middle and end of the day). The life span was longer in the middle of the day in spring in low- and medium-resistant rats and by the end of the year in medium-resistant rats (at the beginning of the day). Fluctuations in the life span during the day and year were more expressed in low- and medium-resistant rats. Differences in the life span of highly and low-resistant rats were the most pronounced in winter.

Effect of geomagnetic activity on rat resistance to hypoxia.

Resistance to acute hypoxia in rats was evaluated by the life span after elevation to an altitude of 11,500 m at 13.00-21.00 (local time) in different seasons of one year. Geomagnetic activity was evaluated using local K index for Moscow and planetary Kp index. Total 24-h geomagnetic activity had a great impact on the life span of rats. The effects of local and planetary geomagnetic activities coincided in about 70% cases. An increase in geomagnetic activity was responsible for prolongation, decrease (2-3 times more often than prolongation), and phase changes in the life span of rats, which were the most pronounced in the case of medium geomagnetic activity, during the second half of the year (in summer and particularly in autumn), in the middle and end of the day, in rats with low resistance to hypoxia.