Calvert D T, Findlay J D, McLean J A
Q J Exp Physiol. 1981 Oct;66(4):377-90. doi: 10.1113/expphysiol.1981.sp002581.
An attempt has been made to study the quantitative relationship between the temperature of the anterior hypothalamic/preoptic (AH/PO) region and heat balance in the conscious ox (Bos taurus) at a thermoneutral air temperature of 20 degrees C. Heat balance was measured by combined gradient-layer and open-circuit calorimetry and AH/PO temperature was controlled using a water-perfused thermode. Continuous warming or cooling of the AH/PO region caused a transient heat imbalance which shifted core temperature to a new stable level dependent upon the level of stimulation. The heat balance responses to continuous AH/PO warming included peripheral vasodilation and increased respiratory and cutaneous evaporative heat loss; those to AH/PO cooling consisted mainly of decreased heat loss. Heat production was largely unaffected by both AH/PO warming and cooling. The heat balance responses developed only slowly, reaching a peak up to 50 min after the start of stimulation and taking several hours to complete. The change to stability in core temperature during continuous AH/PO stimulation and the additional heat loss prior to that stability were the most sensitive indicators of response of all the variables measured. A significant response was observed in these parameters even at the smallest stimulus level (less than 0.33 degrees C) and correlation of response with stimulus level was precise with a zero threshold for response. This suggests a continuity of operation of the AH/PO mechanism about zero. Several responses showed a curved relationship between slope of response and stimulus level, such that the increment in response per unit increase in stimulus level became greater as stimulus level increased. The results suggest a two-tier form of thermoregulation in the ox with AH/PO sensitivity to warming greater than its sensitivity to cooling. It appears also that AH/PO temperature is at least as dominant in the thermoregulatory mechanisms in the ox as it is in smaller animals.
人们试图研究在20摄氏度的热中性气温下，清醒牛（Bos taurus）下丘脑前部/视前区（AH/PO）的温度与热平衡之间的定量关系。通过梯度层和开路量热法相结合来测量热平衡，并使用水灌注热电极控制AH/PO区域的温度。对AH/PO区域进行持续加热或冷却会导致短暂的热失衡，使核心温度转移到一个取决于刺激水平的新稳定水平。对AH/PO区域持续加热的热平衡反应包括外周血管舒张以及呼吸和皮肤蒸发散热增加；对AH/PO区域冷却的反应主要是散热减少。产热在很大程度上不受AH/PO区域加热和冷却的影响。热平衡反应发展缓慢，在刺激开始后长达50分钟达到峰值，并需要几个小时才能完成。在AH/PO区域持续刺激期间核心温度向稳定性的变化以及该稳定性之前的额外散热是所有测量变量中最敏感的反应指标。即使在最小刺激水平（小于0.33摄氏度）下，这些参数也观察到显著反应，并且反应与刺激水平的相关性精确，反应阈值为零。这表明AH/PO机制在零附近的运作具有连续性。一些反应显示反应斜率与刺激水平之间呈曲线关系，使得随着刺激水平增加，单位刺激水平增加时反应的增量变得更大。结果表明，牛的体温调节存在两层形式，AH/PO区域对加热的敏感性大于对冷却的敏感性。似乎AH/PO区域的温度在牛的体温调节机制中至少与在较小动物中一样占主导地位。
