Water exchange in rats exposed to cold, hypoxia, and both combined

Male rats were exposed chronically to cold (5 degrees C air), hypoxia (12% oxygen in nitrogen), and both combined. Intake of water and food, as well as urinary excretion, were measured during both a 5-d pretreatment control period and throughout the first 3 weeks of the treatment period. Regression analysis of water intake on urine output revealed that, at a given water intake, all three treated groups excreted significantly more urine than controls. No significant differences occurred among treated groups. Serum osmolalities of all three treated groups, measured at the end of the 48-d treatment period, were elevated significantly above the level of the control group. All treated groups also manifested a thirst immediately following return to control environment (26 degrees C, 20.9% oxygen). Water intakes of all three treated groups were significantly greater than that of the control group during the first 2 h after return to control environment. Thus, the three treated groups appeared to be dehydrated relative to the control group. The results further suggest that the effect of combined cold (5 degrees C) and hypoxia (12% oxygen) on water exchange is not a summation of that occurring separately during cold and hypoxia. The factors inducing dehydration in cold and hypoxia are apparently related to increased evaporative water loss and to alterations in thirst and renal mechanisms.