774 THE ADRENAL GLANDS 



contains an asymmetric carbon atom (asterisked in formula), which 

 indicates that there must be three varieties of epinephrine, differing 

 from one another in the effect which they produce on the plane of 

 polarized light (i.e.., a dextro- and a levo-rotatory and a racemic form). 

 Epinephrine can be prepared by synthetic means, the first product of 

 this synthesis being the racemic salt, which can then be split by appro- 

 priate methods into dextro- and levo- varieties. The levo- variety ap- 

 pears to be identical in its pharmacological action with the natural product. 

 The dextro- variety on the other hand has only poorly developed physio- 

 logical activities (about seven per cent that of the levo- variety), while 

 the racemic variety comes in between the two in its action. A valuable 

 assay of the amount of epinephrine in tissue extracts can be made by 

 the method of Cannon, Folin and Denis, 10 in which an acid extract of 

 the gland is treated with phosphotungstic acid, and the blue color thereby 

 developed compared colorimetrically with a standard blue. 



Physiological Action 



The physiological effects of the intravenous injection of epinephrine are 

 markedly excitatory and slightly inhibitory in nature. We will consider 

 the excitatory action first. Immediately after the intravenous injection 

 of as small an amount as '00008 milligrams per kilogram of body weight, 

 a distinct rise in arterial blood pressure may be observed. When the 

 rise is distinct, it is accompanied by a slowing of the pulse. This slow- 

 ing is caused by stimulation of the vagus center, as is evidenced by the 

 fact that if the vagus nerves are cut, or sufficient atropine administered 

 to paralyze them, the same dose of epinephrine produces not a slowing 

 but a quickening of the pulse, and consequently a much greater rise in 

 blood pressure. The vagus action is developed not because of an effect 

 of epinephrine on the vagus center, but secondarily because of the rise 

 in blood pressure. 



These preliminary experiments indicate that the locus of action of 

 epinephrine, so far as the circulatory system is concerned, is mainly on 

 the small blood vessels, constricting them and thus raising the peripheral 

 resistance. This conclusion can readily be confirmed by applying the 

 epinephrine directly to the blood vessels of the exposed mesentery, or 

 by enclosing a vascular organ such as the kidney in a plethysmo graph 

 during the injection of epinephrine, when a great diminution in volume, 

 accompanying the rise of arterial blood pressure, will be observed. The 

 vasoconstricting effect of epinephrine does not become developed on the 

 large blood vessels near the heart on account of the deficiency in muscu- 

 lar tissue in their walls. Indeed, these vessels may become passively 

 dilated because of the increased blood pressure. The arterioles of dif- 



