172 



PHYSIOLOGY OF INDUCED HYPOTHERMIA 



6. Corticoid secretion is reduced in most dogs to less than 2^ per cent of normal 

 at temperatures ranging from 25° to 28° C. In a few cases, suppression of corticoid 

 secretion to this extent did not occur until the temperature was reduced 22°- 

 23° C.-'-' 



7. Similar results were ohtained whether hypothermia was induced by ice water 

 immersion, air cooling, or by cooling an external vascular shunt. 



8. The exposure of normal dogs to temperatures of —10° C. for periods up to 

 34 hours did not produce hypothermia or adrenal activation, and did not alter 

 adrenal response to ACTH.^^ The exposure to —48° or —78° C. produced tem- 

 porary adrenal activation, but did not produce hypothermia or alteration in adrenal 

 function.* 



9. The induction of hypothermia under nembutal anesthesia without surgical 

 trauma produced no significant corticosteroid secretion. •"* 



10. Hypothermia to 26° C. produces a 10-fold, and to 21° C. a 100-fold decrease 

 in the secretion of epinephrine and norepinephrine by the adrenal medulla" (fig. 2). 



Conclusions. 1. Trauma under ether anesthesia produces marked increases in 

 pituitary ACTH and adrenal corticoid secretion. The induction of hypothermia 

 greatly depresses the output of these hormones. Pre-hypothermia ACTH and 

 corticoid levels are again noted when the animal is rewarmed. Adrenal sensitivity 



Dog <f I 3 Kgm 

 Temp, 



Cent. 



33.2 33.0 33.5 



270 20.0 



31.0 37,0 



2.0r 



CONTROL PERIOD 



RE-WARMING 



Fig. 2. — Epinephrine, norepinephrine, and corticoid secretion in the adrenal venous blood of 

 the traumatized dog before, during, and after the induction of hypothermia. A very marked de- 

 crease in ei)inei)hrine and norepiiieplirine outjuit occurs durin.n ]iy]>()tlierniia. 



