80 Pharmacology of Salivary Secretion 



1957). This is true for synthetic muscarine also (Waser, 1958). 

 Some agents with a similar action will be discussed under the 

 heading ' 'miscellaneous agents" of this chapter. 



Cholinesterase inhibitors increase the secretory effect of acetyl- 

 choline and parasympathetic stimulation; if the dose of acetyl- 

 choline, or the frequency of stimulation, is chosen so as to cause 

 submaximal responses the inhibitors may increase the rate of flow 

 of saliva ; otherwise their effect is to increase the duration of action 

 only. It is well known, however, that the anticholinesterases can 

 evoke a flow of saliva even if the parasympathetic fibres are not 

 stimulated and no acetylcholine injected, and this has been taken 

 as evidence for a continuous release of acetylcholine from the post- 

 ganglionic, parasympathetic terminals (see Chapter III). Two ob- 

 servations by Dirnhuber and Evans (1954) seem to be of particular 

 physiological interest in this connection. It is not possible to cause 

 an inhibition of the secretion, as can be done with large doses of 

 injected acetylcholine, by increasing the dose of the anticholin- 

 esterase ; the reasonable explanation is that the amounts of acetyl- 

 choline constantly released are not big enough for such an inhibi- 

 tion, even if the cholinesterase of the gland has been inactivated to 

 a great extent. Further, when the secretion caused by an anti- 

 cholinesterase has been stopped by a small dose of atropine, a 

 secretion cannot be started again by increasing the dose of the 

 anticholinesterase. Hence there is not the "mutual antagonism" 

 studied by Langley (1880) which makes it possible to restart a 

 secretion, caused by pilocarpine but stopped by atropine by giving 

 a bigger dose of pilocarpine. This second observation further 

 supports the view that the amount of acetylcholine released is 

 limited. 



Anticholinesterases may increase the secretory effect not only of 

 parasympathetic, but sometimes of sympathetic stimulation also. 

 This can, however, not be used as evidence showing that there are 

 cholinergic sympathetic secretory fibres, as done by Seeker (1934). 

 This effect of the anticholinesterases can be regarded as analogous 

 to the augmenting action of previous chorda stimulation (Feldberg 

 and Guimarais, 1935). 



As to the action of different cholinesterase inhibitors on salivary 

 secretion reference may be made to the following authors : Burgen, 

 Keele and Slome (1949); Fernandez and Vinoles (1949); Riker and 

 Wescoe (1949); Verbeke (1949); Dirnhuber and Evans (1954); 



