Effect of acute hypoxia on resistance to hypoxia in rats

Abstract

The resistance of rats to hypoxia was measured by survival time after exposure to high-altitude (11.5 km) hypoxia. The first exposure to acute hypoxia caused phasic changes in the survival time: short-term in high-resistant rats (about 24 h) and long-term in moderate-and lowresistant rats (38-39 days) starting from 1 h and 6-7 days after the first exposure, respectively. Adaptive reactions were more pronounced in low-and moderate-resistant rats, while disadaptation was typical of high-resistant animals. In all rats, the adaptive effect dominated until days 22-23. Throughout the testing, the initial type of resistance was retained in 79% of high-resistant rats, in 41% of low-resistant and in 33% of moderate-resistant rats, i. e., the initially homogenous groups formed after the first exposure in accordance with the type of resistance became mixed, which reduced the intergroup differences. Key Words: acute hypoxia; resistanceBody resistance to hypoxia depends on a variety of factors: daytime [3,12,16], season [3,13], feeding [ 16], and others. In animals, the resistance to acute hypoxia was tested by exposure to acute hypobaric hypoxia which can change their initial resistance [3,4,13]. The purpose of this study was to assess the effects of shortterm hypoxic exposure on the resistance to acute hypoxia in rats. MATERIALS AND METHODSThe resistance to acute hypoxia was tested in male Wistar rats. They were exposed to acute hypoxia by "lifting" in a pressure chamber to an altitude of 11.5 km above the sea level for 60 sec. The experiments were carried out during daytime (13.00-21.00) in autumn. The resistance to acute hypoxia was measured by the survival time under hypoxic conditions, i. e., time after "ascent" to reversible respiratory arrest, after which the animal was "descended" [3,4]. The first exposure determined the initial resistance to acute hypoxia and served as a short-term conditioning expo-