118 MEDULLA 



of the amount injected; i.e., it follows the Weber-Fechner 

 law. 410 Since repeated injections are reproducible one may- 

 use the pressor response to assay epinephrine. 639 A good pres- 

 sor response is obtained in the cat after an injection of 0.001 

 to 0.002 milligrams of epinephrine. The pressor effect of 

 epinephrine is still elicited after cutting the sympathetics and 

 allowing the nerve fibers to degenerate. Hence the pressor 

 action is not mediated through the nervous system. Oliver 

 and Schafer 480 in their original paper deduced this from their 

 own experiments. Langley 379 postulated that the drug acts 

 on the smooth muscle directly. However, Brodie and Dixon 93 

 showed that after the administration of apocodein (which 

 blocks sympathetic fibers and in large doses causes vasodilation 

 and a drop in blood pressure), epinephrine fails to give a pres- 

 sor response. The smooth muscle is still reactive for the ap- 

 plication of barium chloride elicits a reaction. Hence the 

 point of stimulation lies between the sympathetic nerve termi- 

 nals and the muscle cells; i.e., on the hypothetical "receptive 

 substance" of Langley or, as it is more commonly denoted, 

 the myo-neural junction. 



There is no support for the view that epinephrine exerts its 

 pressor effects through action on the ganglia of the sympa- 

 thetic vasomotors as has been claimed. When applied locally 

 to the cervical ganglion, no sympathetic effects are elicited. 110 - 177 



Subcutaneous injections (even in doses which if administered 

 intravenously would be fatal) do not exert pressor effects on 

 cats, dogs, or rabbits, although a very large dose (37 mgs. per 

 kilo) raises the blood pressure in the dog. 13 



In animals with intact centers, a drop in blood pressure fol- 

 lows the return to normal. In rabbits, after the injection of 

 \ mgm. of epinephrine, this drop persists for several days 639 

 due probably to reflex stimulation of the vasodilator center. 

 This reflex is also held accountable for the notch observed in 

 the ascending limb of the blood pressure curve for it is avoided 

 by deep narcosis or by cutting the cord, and is accentuated 



