Wood S C, Malvin G M
Oxygen Transport Program, Lovelace Medical Foundation, Albuquerque, NM 87108.
J Exp Biol. 1991 Sep;159:203-15. doi: 10.1242/jeb.159.1.203.
We tested the hypotheses that hypoxic toads (Bufo marinus) in a thermal gradient would select a lower than normal temperature and that this behavioral response would be beneficial. Under normoxic conditions, selected body temperature was 24.2 +/- 3.6 degrees C. When inspired O2 was 10% or less, mean selected temperature decreased to 15.3 +/- 2.4 degrees C. The theoretical advantages of hypoxia-induced hypothermia we tested include (1) a reduction of oxygen uptake (VO2) by a Q10 effect; (2) increased arterial saturation (SaO2), (3) a decreased ventilatory response, and (4) a decreased stress response. Gas exchange, hematocrit, hemoglobin, SaO2, PaO2 and pH were measured at 25 degrees C (normal preferred temperature) and 15 degrees C (hypoxia preferred temperature) in toads breathing normoxic or hypoxic gas mixtures. During graded hypoxia at 15 degrees C, SaO2 was significantly increased and VO2 was significantly reduced compared with 25 degrees C. Graded hypoxia did not significantly affect VO2 at 25 degrees C, despite evidence for increased ventilation at that temperature (increased pH and respiratory exchange ratio, RE). At 15 degrees C, graded hypoxia had a significant effect on VO2 only at an inspired O2 of 4%. Increased RE with hypoxia was significant at 25 degrees C but not at 15 degrees C. Hematocrit and [hemoglobin] rose significantly during graded hypoxia at 25 degrees C but did not change at 15 degrees C. Toads exposed to 10% O2 (the value that elicits behavioral hypothermia) showed a significant respiratory alkalosis at 25 degrees C but not at 15 degrees C. Likewise, hypoxia caused a significant drop in SaO2 and PO2 at 25 degrees C. Cooling to 15 degrees C during hypoxia caused a significant rise in SaO2 but no change in PaO2. In conclusion, behavioral hypothermia is a beneficial response to hypoxia in Bufo marinus.
处于热梯度环境中的低氧蟾蜍（海蟾蜍）会选择低于正常的温度，且这种行为反应是有益的。在常氧条件下，选择的体温为24.2±3.6摄氏度。当吸入氧气含量为10%或更低时，平均选择温度降至15.3±2.4摄氏度。我们所检验的低氧诱导体温过低的理论优势包括：（1）通过Q10效应减少氧气摄取量（VO2）；（2）提高动脉血氧饱和度（SaO2）；（3）降低通气反应；（4）降低应激反应。在25摄氏度（正常偏好温度）和15摄氏度（低氧偏好温度）下，对呼吸常氧或低氧混合气体的蟾蜍测量气体交换、血细胞比容、血红蛋白、SaO2、PaO2和pH值。在15摄氏度下进行分级低氧时，与25摄氏度相比，SaO2显著升高，VO2显著降低。尽管有证据表明在25摄氏度时通气增加（pH值和呼吸交换率升高），但分级低氧对25摄氏度时的VO2没有显著影响。在15摄氏度时，分级低氧仅在吸入氧气含量为4%时对VO2有显著影响。低氧时呼吸交换率升高在25摄氏度时显著，但在15摄氏度时不显著。在25摄氏度下进行分级低氧时，血细胞比容和血红蛋白浓度显著升高，但在15摄氏度时没有变化。暴露于10%氧气（引发行为性体温过低的值）的蟾蜍在25摄氏度时出现显著的呼吸性碱中毒，但在15摄氏度时没有。同样，低氧在25摄氏度时导致SaO2和PO2显著下降。低氧期间冷却至15摄氏度导致SaO2显著升高，但PaO2没有变化。总之，行为性体温过低是海蟾蜍对低氧的一种有益反应。
