78 Pharmacology of Salivary Secretion 



with subsequent abolishment of the action of the chorda. Usually 

 the effect of chorda stimulation is only reduced but not completely 

 cancelled by nicotine applied to the hilum of the cat's submaxillary 

 gland since some synapses within the gland are not reached by the 

 drug. 



Tetraethylammonium differs from nicotine in lacking the initial 

 stimulating effect on the ganglia of the salivary glands (Burn and 

 Dale, 191 5). The same is true for the more recent synthetic gan- 

 glionic blocking compounds. It is possible that curarine may have 

 some excitatory effect on the ganglia before paralysing them. Some- 

 times curarine may cause a small secretory response, not due to a 

 central action (Emmelin and Muren, io^oa). This may be the 

 cause of the secretion observed by Claude Bernard (1864) on in- 

 jection of curare into the artery of the submaxillary gland; he ex- 

 plained the effect as due to exclusion of an inhibitory influence 

 from the central nervous system. 



PARASYMPATHOMIMETIC DRUGS 



Parasympathomimetic drugs cause a secretion of saliva which 

 may be as rapid as that evoked by maximal stimulation of the para- 

 sympathetic fibres. This is best shown if the drugs are applied in 

 such a way as not to cause any general circulatory effects, for 

 instance, close arterially or through the salivary duct. 



In its action on the gland cells acetylcholine closely imitates the 

 action of parasympathetic stimulation ; this can be seen in the elec- 

 trical responses, as shown with intracellular recording by Lund- 

 berg (1955). The effect of acetylcholine is apparently not only to 

 excite the cell but to increase its excitability to subsequent stimuli 

 as well (Beznak and Farkas, 1936-37). This fact very likely pro- 

 vides the explanation of the phenomenon of "true augmented 

 secretion" (Macintosh and Rawlinson, 1935). When the concen- 

 tration of acetylcholine is raised to a certain level the secretory 

 response tends to decline, as demonstrated by Graham and Stav- 

 raky (1953). At such a concentration these investigators found the 

 vascular effect of acetylcholine to change from dilatation to con- 

 striction, and this might be one of the causes of the diminished 

 secretory response ; but Graham and Stavraky think that in addi- 

 tion an inhibitory action on the gland cell is exerted by acetyl- 

 choline in high concentration. It would be interesting to study the 

 microelectrode response of gland cells to such concentrations. 



