Sympathetic Vasoconstrictors 123 



In many glands the effect of sympathetic stimulation can be 

 seen directly on the exposed gland. When the nerve is excited the 

 gland loses its rosy colour and becomes pale. In some glands, such 

 as the submaxillary gland of the cat, the constriction is usually not 

 maintained on continued stimulation. The same is true for the 

 secretory response, as discussed in Chapter III. In Fig. 3.7 it was 

 shown that the vanishing of the secretory effect to some extent was 

 due to the vasoconstriction, since it could be postponed by block- 

 ing the constrictor action with priscol; but the main reason for 

 the cessation of the secretion was probably shortage of mediator 

 at the high rate of stimulation mostly used. Such a mechanism 

 cannot explain the interruption of the constriction on continued 

 sympathetic stimulation. It is closely related to the secretory 

 response ; when this has died away the constriction may reappear. 

 In the dog submaxillary gland, in which the secretory effect of 

 sympathetic stimulation is much smaller than in the cat, the con- 

 striction is much better retained. The secretory effect may be 

 abolished in the cat by the administration of chlorpromazine in 

 suitable dose (Emmelin, 19550); the vasoconstriction is then more 

 pronounced and can be maintained for a long time. The ordinary 

 disappearance of the constriction in the cat submaxillary gland, 

 therefore, seems to be the result of a strong vasodilator action 

 accompanying the secretion. If the sympathetic trunk is stimulated 

 at a low frequency, the secretory response is small and a well- 

 maintained constriction is obtained, similar to that kept up in the 

 gland with an intact sympathetic supply. 



The constriction elicited by sympathetic stimulation is counter- 

 acted by the vasodilatation produced by chorda stimulation, even 

 in the presence of atropine. In some cases no constriction can 

 then be seen ; it may be possible, in those instances, to get a con- 

 striction by abolishing the vasodilator component of the sym- 

 pathetic by injecting chlorpromazine. Usually, however, the sym- 

 pathetic is able to exert some constrictor effect during chorda 

 stimulation. The effect of constriction on the salivary flow in- 

 duced by chorda stimulation when no atropine is present can 

 then be studied. It is shown in Fig. 7.1 which summarizes experi- 

 ences made by numerous investigators. Stimulation of the chorda 

 causes a quick flow of saliva and a marked vasodilatation. When 

 sympathetic stimulation is added, the flow of blood diminishes, 

 and the secretion as well. Some early investigators have taken such 



