180 



PHYSIOLOGY OF INDUCED HYPOTHERMIA 



niilligranis of ACTH. It is interesting" that the fall in the ascorhic acid of the 

 adrenals is greater between 2*-'° and 26° C. than between 25° and 23° C. That means 

 that if we want to suppress the reaction of the adrenal to ACTH, it is necessary to 

 decrease the body temperature below 25° C. 



The proljlem is, what is the reaction of the pituitary-adrenal coupled during 

 stress and hypothermic conditions? These results (fig. 2) are applicable to all meth- 

 ods of hypothermia (artificial hibernation, surface cooling), regardless of which 

 drugs are employed to produce hypothermia. These results are also applicable to 

 any stress (formalin injection, or ligation of the hepatic artery or of the mesenteric 

 vein and artery). A stress between V?° and ZZ° C. is able to depress the ascorbic 

 acid level of the adrenal about 35 per cent, between 32° and 28° C. the fall in the 

 adrenal level is only about 10 per cent, and between 27° and 26° C. there is no fall 

 in the adrenal ascorbic level. 



From experiments on more than 1,000 rats we can conclude that there is a criti- 

 cal temperature at which there exists an inhibition of the pituitary reaction. For 

 this reason we thought that between 28° and 26° C. there exists a physiological 

 state which can be compared with an hypophysectomy. 



When we compare surface cooling and artificial hibernation, we see that in 

 surface cooling the drop in the adrenal ascorbic level is 28 per cent. When adrenalin 

 or ACTH are injected (LP.), another fall of about 4.6 to 9.9 per cent is obtained. 

 In fact, when we compare with the controls we see that the same quantity of 

 ACTH is able to depress the adrenal to about 33 to 36 per cent. This suggests that 

 if the adrenals in surface cooling are not able to react more, it is because they are 

 partly exhausted by the cooling. 



Dr. Henry Szvan: We have been interested in attempting to study hypothermia 



pi 



o 



O 

 9 < 



20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 3^ 37 

 TEMPERATURE CENTRALE 



Fig. 2. 



