Drugs that Elicit Secretion Reflexly 73 



order of sensitivity: "nasal, chorda secretory, cardiac vagus, tonus 

 of pyloric sphincter, and small intestine, bladder, oculomotor to 

 pupil, salivary vasodilator, vagus to intestine for rhythmic and 

 peristaltic movements". After a dose of a sympatholytic agent such 

 as dihydroergotamine, chlorpromazine or regitine which abolishes 

 the salivary secretory effect of stimulation of the cervical sym- 

 pathetic trunk contraction of the nictitating membrane, dilatation 

 of the pupil and a rise of blood pressure can still be obtained. The 

 order of decreasing sensitivity to the ganglionic blocking action of 

 hexamethonium is given as follows: parasympathetic salivary 

 ganglia, sympathetic superior cervical ganglion, sympathetic vaso- 

 motor and parasympathetic intestinal ganglia and vagal cardiac 

 ganglia (Goodman and Gilman, 1955). Investigators of salivary 

 secretion in animals have often observed that in most types of 

 anaesthesia there is no flow of saliva and it is difficult or impossible 

 to elicit a salivary reflex, whereas various other reflexes are readily 

 evoked. 



DRUGS THAT ELICIT SECRETION REFLEXLY 



The literature dealing with the effect of various gustatory stimuli 

 on the secretion of saliva has been extensively reviewed by Babkin 

 (1928). The effect of agents exciting the taste buds to evoke secre- 

 tion of saliva has been studied particularly in human beings and 

 in dogs. Chemical agents apparently play a minor role as stimulants 

 of salivary secretion in horses, cattle and sheep ; in these animals 

 the physical properties of the food are of particular importance, as 

 shown for instance by Scheunert and Trautmann (1921). Never- 

 theless, it is sometimes possible to evoke a secretion from the 

 parotid gland of sheep by applying acetic acid or sucrose on the 

 tongue (Coats, Denton, Goding and Wright, 1956). When study- 

 ing species differences as to gustatory stimuli, it is necessary to 

 bear in mind investigations on various animals on action potentials 

 in the taste fibres after application of different substances to the 

 tongue. It is known, for instance, that the tongue of the cat lacks 

 receptors sensitive to sugar (Zotterman, 1935). 



Substances irritating the oral mucosa stimulate secretion of 

 saliva. The excessive salivation characteristic of mercury poisoning 

 is thus probably in part secondary to the stomatitis caused by mer- 

 cury excreted by the saliva. Smoking usually increases the flow of 

 saliva by irritating the mucosa ; the amount of nicotine absorbed 



