Sympathetic Vasodilators 135 



tical stimulation before atropine, oxygen consumption fell in 

 parallel with the decrease in secretion rate, while the increased 

 blood flow was as great as or greater than before. The enhanced 

 effect of stimulation on the blood flow after atropine was explained 

 by the lack of haemoconcentration when no secretion occurred. 

 From this investigation the following conclusions were drawn: 

 "the vasodilator responses of the gland are not secondary to the 

 secretory metabolism. The metabolic and vasodilator responses 

 can be dissociated with atropine, showing that atropine can pre- 

 ferentially enter those receptor sites in the structure of the gland 

 associated with the secretory response. Dale and Gaddum came 

 to the same conclusion." 



SYMPATHETIC VASODILATORS 



The usually pronounced vasodilatation seen in the submaxillary 

 gland of the cat on stimulation of the sympathetic trunk in the 

 neck induced Carlson (1907) to assume that vasodilator fibres are 

 excited. Barcroft (1907, 19 14), on the other hand, produced 

 evidence to show that the dilatation, obtained on sympathetic 

 stimulation, is due to vasodilator metabolites. Ergotoxine had been 

 shown by Dale (1906) to abolish the effect of stimulation of sym- 

 pathetic vasoconstrictors but not of the dilators assumed to be 

 present in the chorda tympani. Barcroft found the sympathetic 

 vasodilatation to disappear, and the secretion as well, after the 

 administration of ergotoxine. When adrenaline was injected, to 

 imitate sympathetic stimulation, it was shown to increase the 

 oxygen consumption of the gland ; there was a parallelism between 

 this increase and the vasodilatation (Barcroft and Piper, 191 2). 

 Adrenaline could be deprived of its secretory effect by perfusing 

 the gland a couple of hours after the death of the animal with 

 saline; the vasodilator effect was, likewise, lost and the only 

 response was a vasoconstriction. 



It is, on the whole, striking that the sympathetic vasodilatation, 

 contrary to the constriction, is closely linked to the secretion and 

 cannot be separated from it (Emmelin, 19550). By injecting chlor- 

 promazine it is possible to abolish both the secretion and the dila- 

 tation with the constriction retained. A small dose of the drug 

 may only reduce the secretory response ; this is true for the vaso- 

 dilatation also. When the effect of a bigger dose is wearing off, 

 the two effects return concomitantly. In an exceptional cat, in 



