160 The Inorganic Components of Saliva 



iodide is greater in the older mice. When a high enough dose of 

 one of these anions is used either in vitro or in vivo the I 131 con- 

 centration ratio asymptotes to a value less than i (usually 0-3-0-7) 

 and cannot be further depressed by increase in anion concentration. 



Evidence is available that this residual secretion of iodide occurs 

 via the duct cells (Burgen, Weiss and Weiss, i960). The relation- 

 ship between concentration of iodide and flow found in the dog 

 parotid saliva when the iodide transport process has been depressed 

 by a high I~ and C10 4 ~ concentration is very similar to that found 

 in the normal submaxillary gland (Fig. 8.1 1). 



It has been known for over a century that thiocyanate is con- 

 centrated in the saliva and is found in the saliva of many species. 

 The thiocyanate appears to be mostly produced endogenously 

 from cyanide; its concentration is considerably increased in 

 smokers. Thiocyanate is less well concentrated by the salivary 

 glands than iodide (Ferguson, Naimark and Hildes, 1957) but 

 otherwise its behaviour is quite similar. Radioautographic studies 

 have shown that thiocyanate is concentrated in the same duct seg- 

 ments as iodide (Logothetopoulos and Myant, 1956). Perchlorate 

 is also concentrated at least tenfold in human parotid saliva 

 (Edwards, Fletcher and Rowlands, 1954), but the difficulty of 

 measuring the concentration of this ion has inhibited further study. 

 Nothing is known of nitrate concentrations in saliva. 



It is probable that iodide, perchlorate, thiocyanate and nitrate 

 can all be transported by the same anion transport system in the 

 salivary duct cells and that the ions can compete for transport by 

 this carrier. A similar transport system exists in the thyroid 

 (Wyngaarden, Wright and Ways, 1952; Wyngaarden, Stanbury 

 and Rapp, 1953), in the gastric mucosa (Lipschitz, 19290; Honour, 

 Myant and Rowlands, 1952; Fletcher, Honour and Rowlands, 

 1956; Howell and Middlesworth, 1956) and in the mammary gland 

 (Brown-Grant, 1957). A study of the effect of X-irradiation of the 

 parotid gland has shown no depression of iodide secretion after 

 doses as great as 3,500 r (Awwad, 1959). Large doses of inorganic 

 iodine have been known for a very long time to lead not infre- 

 quently to swelling and pain in the salivary glands. In man and in 

 the mouse virtually all the iodine secreted in the saliva is in the 

 form of inorganic iodide, but in the dog a considerable proportion 

 is incorporated into proteins. 



