PHARMACOLOGY AND TOXICOLOGY OF SUPRARENALS 255 



Epinephrin also produces an action upon the medullary centers. The 

 medulla of dogs was perfused by a mixture of defibrinated blood and 

 Ringer's solution entering the carotid and vertebral arteries (Brown). 

 In a majority of cases epinephrin introduced into the perfusion mix- 

 ture caused a slowing of the heart and a fall in blood pressure. It 

 seems to act directly on the vagus center because the slowing was im- 

 mediate and was not connected with a rise in blood pressure. Occasionally 

 there was a fall of blood pressure without the heart effect. 



Fig. 9. Constriction of the intestine from direct application of 1:1,000 epinephrin 

 to the superior mesenteric ganglion. Dog. (After Hartman, Kilborn and Fraser, Am. 

 J. Physiol.) 



McGuigan and Efyatt have postulated a central locus for a part of 

 the response to epinephrin on the ground that pithing the brain pre- 

 vents the secondary rise of pressure following its injection. 



The respiratory center seemed to be affected also. Small doses of 

 epinephrin often increased both the depth and rate of respiration, while 

 large doses usually diminished the depth or rate or might even stop it. 



In conclusion we may say that epinephrin can act on myoneural junc- 

 tions, sympathetic and dorsal root ganglia and centers in the central 

 nervous system, though the greater part of the effect is due to action 

 on the peripheral neurocellular junctions. 



