PHYSIOLOGY OF EPINEPHRINE 89 



though less delicate than the intestinal strip method it is ad- 

 vantageous for many purposes. The spinal animal is more 

 sensitive for the application of this method and hence the animal 

 is pithed and maintained under artificial respiration. Suc- 

 cessive injections may be made, each of which causes a rise 

 proportional to the epinephrine concentration of the sample 

 tested. The pressor response of the unknown solution is com- 

 pared with that elicited by the injection of a known amount of 

 epinephrine. 639 



The method just outlined is vitiated if depressor substances 

 are present in the fluids to be tested. This is particularly 

 true of choline and acetylcholine, which as Hunt 324 showed, 

 antagonize the pressor effects of epinephrine. Since choline 

 may be a constituent of extracts prepared from the adrenals, 

 the use of this method alone for assaying the epinephrine con- 

 tent of such extracts is not justified. 



The contraction of a strip of artery, arranged as in the 

 "intestinal segment method" has also been used for epinephrine 

 assays. This method is relatively insensitive, and not fre- 

 quently employed. 



3. The perfusion method. The assay of epinephrine by 

 determining its effect on the caliber of the blood vessels was 

 described by Lawen 375 and perfected by Trendelenburg 636 as 

 a highly sensitive method. A frog is decapitated and its spinal 

 cord thoroughly destroyed. It is placed on its back and the 

 abdominal wall reflected. The bladder and intestines are 

 removed and the renal vein ligated. The remaining viscera 

 including the heart are removed, care being taken to preserve 

 the abdominal aorta intact. A cannula, connected to a 

 Marriotte bottle containing frog Ringer's solution is introduced 

 cephalwards into the abdominal aorta. An outflow cannula is 

 introduced into the anterior abdominal vein which lies exposed 

 on the reflected abdominal wall. A drop recorder marks the 

 rate of outflow of the perfusing fluid. A sensitive preparation 

 permits the detection of a change in the rate of the perfusion 



