108 Effects of Denervation 



three weeks. In order to study the development of supersensitivity, 

 the level of sensitivity can be estimated repeatedly with intervals 

 of some days using the following method: A cat is anaesthetized 

 with a short-acting barbiturate, fine glass cannulae are introduced 

 from the mouth into the salivary ducts and secretory agents such 

 as adrenaline, acetylcholine or mecholyl are injected into the heart. 



Supersensitivity following parasympathetic or sympathetic de- 

 nervation is unspecific and can be shown for almost all agents 

 which cause a secretion from the normal gland, e.g. adrenaline, 

 noradrenaline and other sympathomimetic drugs, acetylcholine 

 and other cholinesters, and pilocarpine. Statements to the contrary 

 in the early literature seem mostly to be due to the fact that the 

 doses of the drugs tested were too big; the maximal secretory 

 rate of the denervated gland is not bigger than that of the normal 

 gland but may, on the contrary, be smaller because of atrophy. 

 Furthermore, it must be kept in mind that the denervated gland 

 seems to be more readily exhaustible, and that secretion may be 

 more easily inhibited in a denervated than in a normal gland by a 

 big dose. 



There are, however, undoubtedly some exceptions to the general 

 rule. After postganglionic parasympathetic denervation anticho- 

 linesterases cause a very small secretion only, as shown in Fig. 3.8. 

 A reasonable explanation is that these drugs act, wholly or mainly, 

 by preserving acetylcholine released from the postganglionic fibres 

 and therefore lose their secretory activity when these fibres have 

 degenerated. Similarly, after postganglionic sympathetic denerva- 

 tion tyramine has no secretory effect, suggesting some indirect 

 mode of action of this drug in the normal gland (Stromblad, 

 1956^). After preganglionic parasympathetic denervation, on the 

 other hand, the glands are supersensitive both to anticholine- 

 sterases and tyramine. 



According to the law of denervation preganglionic section ought 

 to sensitize not only the gland cells, but the postganglionic neurone 

 also; further, postganglionic section ought to sensitize the gland 

 cells more than preganglionic section. On the whole, the salivary 

 glands fulfil these requirements. After section of the chorda the 

 dose of nicotine needed to evoke a perceptible secretion is smaller 

 than in a normal gland, showing that the parasympathetic ganglion 

 cells have been sensitized (Emmelin, 19536). The gland cells are 

 usually more sensitized after post- than after preganglionic dener- 



