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QUANTITATIVE ASPECTS OF PREOPTIC THERMOSENSITIVITY IN THE CONSCIOUS OX
Author(s) -
Calvert D. T.,
Findlay J. D.,
McLean J. A.
Publication year - 1981
Publication title -
quarterly journal of experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0144-8757
DOI - 10.1113/expphysiol.1981.sp002581
Subject(s) - chemistry , stimulation , stimulus (psychology) , thermoregulation , core temperature , zoology , thermodynamics , medicine , endocrinology , psychology , physics , biology , psychotherapist
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 °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 °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.