PHARMACOLOGY OF EPINEPHRINE 119 



by the preliminary injection of strychnine. This reflex ac- 

 cording to Heymans 297 is initiated in the carotid sinus. 



In cats and dogs, small doses (.0001 mgm. per second) give 

 a fall in blood pressure of 20 to 40 mms. of mercury. 270 This is 

 due to vasodilatation in the extremities by stimulation of sym- 

 pathetic vasodilator peripheral fibers. 243 Whether the arte- 

 rioles or the capillaries are involved in this reaction is question- 

 able. It does not occur in decerebrate unanesthetized or in 

 normal unanesthetized animals. 639 



The fact that very small doses of epinephrine cause a drop 

 in blood pressure instead of a rise was first noted by Moore 

 and Purinton 270 in 1900. Dale 36 showed that ergotoxin had 

 the property of paralyzing those sympathetic fibers which 

 have a stimulating function while unafTecting those having an 

 inhibitory function. After poisoning with ergotoxin, epineph- 

 rine in a dose which normally evokes a rise in blood pressure 

 produces only a fall. 



The effects of epinephrine on the peripheral blood vessels 

 have usually been determined by direct observation, by ple- 

 thysmography measurements, by determining the rate of per- 

 fusion, or the rate of venous outflow. If the blood pressure 

 rises markedly, passive dilatation of the arteries may result 

 with a consequent increase in the plethysmographic volume. 

 This is, for example, taken to be the case in the kidney where 

 the decrease in size of this organ which follows an injection of 

 epinephrine is sometimes preceded or followed by an increase. 



The action of epinephrine differs as regards its effects on 

 different vessels. Despite its general constricting action, cer- 

 tain vessels, particularly the splanchnics, the arteries of the 

 skeletal muscles, the coronary, and the pulmonary vessels are, 

 under certain circumstances at least, dilated by moderate doses 

 of epinephrine. 113 According to Orahovats and Gotsev, 484 epi- 

 nephrine causes dilatation of the splanchnic vessels in two- 

 thirds of all cases and constriction in the remainder. The 

 arteries of the brain according to Dixon and Halliburton 159 are 



