HYPOTHERMIA IN THE UNANESTHETIZED 

 POIKILOTHERMIG DOG 



ALLEN 1). KELLER 



The reason for attempting to reduce large heat regulating laboratory animals to 

 the completely non-heat regulatory status was threefold, h'irst, it was desired to 

 determine if the ability of the homotherni to maintain l)ody core temperature near 

 constancy was dependent upon nerve cells localized to the hypothalamus as first sug- 

 gested by Ott^ on the basis of puncture experiments and later clearly indicated by 

 the brain slicing experiments of Isenschmid and Schnitzler.- Second, if this proved 

 to be so it seemed probable that graded tissue defects in the hypothalamus might 

 permit greater insight into the "whats" and the "hows" of heat regulation. Third, 

 there are many ways in which an ambulatory poikilothermic homotherni could be 

 used as a laboratory "test tube." The effects of thermal variables applied to tissues 

 and organs in their otherwise normal habitat could be determined uncomplicated by 

 superimposed thermal regulatory or anesthesia influences. Tissue chemistry could 

 be "slow motioned" to allow study of changes in intermediary metalxjlism, blood 

 clotting, antibody formation and similar processes. The thermal spectrum for invad- 

 ing pathogens might be delimited. 



The material to follow constitutes a summary-report of progress made toward 

 attaining these objectives. 



THE POIKILOTHERMIC DOG 



The healthy dog is an exceptionally good heat regulator as judged by its ability 

 to prevent a lowering of its core temperature in the presence of an abrupt and heavy 

 cooling load. This is illustrated in the upper portion of figure 1 by the colonic tem- 

 perature curves for a dog when, without any previous conditioning to cold, it was 

 abruptly subjected to an ambient temperature of 3° C. for 6 hours and of —20° C. 

 for a 24-hour period. During the 3° C. exposure, deep colonic temi)erature was 

 maintained at 3S° C. for the period of the exposure. When subjected abruptly to 

 — 20° C. core temperature rose from 38 to 38.7° C. during the first hour of exposure 

 and remained at this elevated level during the remainder of the 24-hour run. Thus, 

 increasing the cooling load had a sustained elevating effect. 



The completely poikilothermic animal. The ability to hold body temperature 

 at or slightly above the homothermic level under such circumstances is due to auto- 

 matic regulatory processes mediated by nerve cells localized to the gray matter in 

 the hypothalamus." This is evidenced by the fact that when the nerve fibers which 

 descend from this area are severed the animals lose all ability to regulate against 

 cold. The colonic temperature curves of two such preparations when subjected to 

 an ambient temperature of 3° C. are shown in the lower portion of figure 1. It was 

 necessary to incubate them at 30° C. to keep the body temperature at the normal 

 38° range; when they were abruptly placed in an environment of 3° C. the colonic 

 temperature fell progressively in a straight line to reach 28° C. at the end of a 3-hour 



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