Combined stimuli of cold, hypoxia, and dehydration status on body temperature in rats: a pilot study with practical implications for humans

OBJECTIVE: As human thermoregulatory responses to maintain core body temperature (T(core)) under multiple stressors such as cold, hypoxia, and dehydration (e.g., exposure to high-altitude) are varied, the combined effects of cold, hypoxia, and dehydration status on T(core) in rats were investigated. The following environmental conditions were constructed: (1) thermoneutral (24 °C) or cold (10 °C), (2) normoxia (21% O(2)) or hypoxia (12% O(2)), and (3) euhydration or dehydration (48 h water deprivation), resulted in eight environmental conditions [2 ambient temperatures (T(a)) × 2 oxygen levels × 2 hydration statuses)]. Each condition lasted for 24 h. RESULTS: Normoxic conditions irrespective of hypoxia or dehydration did not strongly decrease the area under the curve (AUC) in T(core) during the 24 period, whereas, hypoxic conditions caused greater decreases in the AUC in T(core), which was accentuated with cold and dehydration (T(a) × O(2) × hydration, P = 0.040 by three-way ANOVA). In contrast, multiple stressors (T(a) × O(2) × hydration or T(a) × O(2) or O(2) × hydration or T(a) × hydration) did not affect locomotor activity counts (all P > 0.05), but a significant simple main effect for O(2) and T(a) was observed (P < 0.001). Heat loss index was not affected by all environmental conditions (all P > 0.05). In conclusion, decreases in T(core) were most affected by multiple environmental stressors such as cold, hypoxia, and dehydration.