PHARMACOLOGY OF EPINEPHRINE 115 



the dilatation of the pupil is a notable exception, for the my- 

 driatic action of epinephrine is still elicited after ergotamine. 

 Yohimbin, hydrastinin, quinine, and apocodeine share with 

 the alkaloids of ergot the property of abolishing the stimulat- 

 ing effects of epinephrine. They do not, however, paralyze 

 the inhibiting effects of epinephrine nor the inhibiting effects 

 of sympathetic excitation. Hence, when either contraction or 

 inhibition can normally be induced under different circum- 

 stances through the sympathetic nerves or by epinephrine, if 

 the normal effect be stimulation, this will be abolished by 

 ergotoxine or apocodeine, and the inhibiting effects alone will 

 appear on subsequent injection of epinephrine. This is spoken 

 of as a reversal action. If the normal effect be inhibition, this 

 remains unaltered. 



Originally it was thought that the reversal effect of ergotox- 

 ine was due to a double innervation from the sympathetic. 

 The capillary dilatation observed by Dale and Richards 243 after 

 epinephrine led them to believe that the reversal is due to the 

 persistence of the capillary dilatation when the constricting 

 effects on the arteries have been paralyzed by ergotoxine. 

 Schafer 550 has, however, criticized this view. 



Where the parasympathetic acts as an antagonist to the 

 sympathetic, paralysis of the former results in an augmented 

 action by epinephrine. Thus the preliminary injection of 

 atropine (by paralyzing the parsympathetics) results in an 

 enhanced response to a subsequent injection of epinephrine. 

 Epinephrine also acts as an antagonist to other parasympathe- 

 tic drugs — pilocarpine, physostigmine, choline, etc. Nicotine, 

 which paralyzes sympathetic ganglia, does not affect epineph- 

 rine action for epinephrine does not act through any effect 

 on the ganglia. 36, 270 



Histamine, by its action in paralyzing smooth muscle, acts 

 as an effective antagonist to epinephrine. Cocaine and novo- 

 caine sensitize organs to the action of epinephrine. Thus the 

 pupil is more widely dilated by epinephrine after a preliminary 



