Thermoregulatory and metabolic responses of Japanese quail to hypoxia

Abstract

Common responses to hypoxia include decreased body temperature (Tb) and decreased energy metabolism. In this study, the effects of hypoxia and hypercapnia on Tb and metabolic oxygen consumption (VO2) were investigated in Japanese quail (Coturnix japonica). When exposed to hypoxia (15, 13, 11 and 9% O2), Tb decreased only at 11% and 9% O2 compared to normoxia; quail were better able to maintain Tb during acute hypoxia after a one-week acclimation to 10% O2. VO2 also decreased during hypoxia, but at 9% O2 this was partially offset by increased anaerobic metabolism. Tb and VO2 responses to 9% O2 were exaggerated at lower ambient temperature (Ta), reflecting a decreased lower critical temperature during hypoxia. Conversely, hypoxia had little effect on T(b) or VO2 at higher Ta (36 degrees C). We conclude that Japanese quail respond to hypoxia in much the same way as mammals, by reducing both Tb and VO2. No relationship was found between the magnitudes of decreases in Tb and VO2 during 9% O2, however. Since metabolism is the source of heat generation, this suggests that Japanese quail increase thermolysis to reduce Tb. During hypercapnia (3, 6 and 9% CO2), Tb was reduced only at 9% CO2 while VO2 was unchanged.

Fig. 1

Body temperature (T_b) and O₂ consumption (V̇o₂) of quail during normoxia (21% O₂) and during exposure to four levels of hypoxia (15, 13, 11, and 9% O₂) (T_a = 23°C). T_b and V̇o₂ are presented both as the minimum value achieved during the 60-min test gas exposure (A, C) and as the corresponding change from baseline (B, D); see text for details. Values are mean ± SEM; n = 16. Letters denote statistical comparisons: groups with different letters are significantly different (P<0.05). In panel D, one-way repeated measures ANOVA detected a significant effect of hypoxia (P=0.03), but post-hoc tests were unable to determine which groups differed.

Fig. 2

Blood lactate concentrations for quail exposed to normoxia (21% O₂) and two levels of hypoxia (11% and 9% O₂) (T_a = 23°C). Values are mean ± SEM; n=6. Groups with different letters are significantly different (P<0.05).

Fig. 3

Effect of acclimation to chronic hypoxia on the body temperature (T_b) and metabolic (V̇o₂) responses to acute hypoxia (9% O₂). Quail were studied before and immediately after a 7-day exposure to 10% O₂. T_b and V̇o₂ are presented both as the minimum value achieved during the 60-min acute exposure to 9% O₂ (A, C) and as the change from baseline (B, D) (T_a = 23°C). Values are mean ± SEM; n=7 for T_b, n=10 for V̇o₂. * P<0.05 vs. before acclimation values.

Fig. 4

Time course for changes in T_b and V̇o₂ during acute hypoxia (9% O₂) in quail before (●) and after (○) acclimation to chronic hypoxia (7 days, 10% O₂) (T_a = 23°C). Baseline (BL) represents the average value during the preceding 30 min of normoxia. T_b and V̇o₂ are reported at 5- and 10-min intervals after the switch to hypoxia, respectively; to ensure that O₂ levels reached a steady state within the respirometer after the switch to 9% O₂ prior to calculating V̇o₂, V̇o₂ is not reported for the 10 min time point. Values are mean ± SEM; n=7. * P<0.05 vs. before acclimation values at the same time point; † P<0.05 vs. BL.

Fig. 5

Effect of ambient temperature on T_b (A) and V̇o₂ (B) for quail during normoxia (○; 21% O₂) or hypoxia (●; 9% O₂). Values are mean ± SEM; n=16. * P<0.05 vs. normoxia at the same T_a. For the effect of T_a within each treatment (i.e., within normoxia or within hypoxia), groups with different letters differ from one another (P<0.05). Triangles (△ normoxia, ▴ hypoxia) represent a subset of quail (n=6) studied at 30 and 36°C; these data were not included in the overall statistical analysis. In panel C, V̇o₂ during hypoxia has been temperature corrected to the normoxic T_b at the corresponding T_a, assuming a Q₁₀ of 3; see text for details.

Fig. 6

Time-dependent changes in T_b (A) and V̇o₂ (B) of quail maintained in normoxia (21% O₂) for 160 min. Quail were studied at ambient temperatures of either 33°C (○) or 13°C (●). Although quail were exposed to normoxia for the entire 160 min, the arrow at minute 100 indicates the time at which quail would have been switched to hypoxia in a typical experiment. Values are mean ± SEM; n = 6. † P<0.05 vs. baseline (i.e., the average value for min 70–100).

Fig. 7

Effect of acute hypercapnia on body temperature (T_b) and O₂ consumption (V̇o₂) of adult quail. Quail were exposed to normocapnia (0% CO₂) and three levels of hypercapnia (3, 6, and 9% CO₂) (T_a = 23°C). T_b and V̇o₂ are presented both as the minimum value achieved during the 60-min test gas exposure (A, C) and as a change from baseline (B, D). Values are mean ± SEM; n = 10. Groups with different letters are significantly different (P<0.05).