Potassium 



149 



saliva. Clark and Shell (1927) found in a study of a large number 

 of samples of human mixed saliva that the potassium concentration 

 was invariably higher than in the plasma. This is true for all the 

 individual glands in man (Kostlin and Rauch, 1957) and is even 

 the case for those salivary glands that secrete an isotonic saliva 

 (Lundberg, 1957; Schneyer and Schneyer, 1959). Gregersen and 

 Ingalls (1931) claimed that the concentration of potassium in dog 

 parotid saliva was independent of the rate of the saliva secretion 

 except at very low flows where a rise of concentration inversely 

 proportionate to flow occurred. Similar relationships have been 

 reported for cat submaxillary saliva and human parotid saliva 



WO 200 300 400 500 600 100 



Rate of saliva secretion (mg/g J mi n) 



Fig. 8.6. The potassium concentration in dog parotid saliva when small 



samples were collected at different rates of secretion. 

 The relationship is U-shaped, rising at both low and high flow rates (Burgen, 1956a). 



(Langstroth, McRae and Stavraky, 19380; Thaysen, Thorn and 

 Schwartz, 1954; Hildes, 1955; Prader, Gautier, Gautier and Naef, 

 1955). The concentration in the saliva was 1-5-4 times the plasma 

 level ; the higher values being found in man. 



The constancy of the plasma concentration with flow was chal- 

 lenged by Burgen in 1956, who found that in the dog and the cat, 

 the saliva potassium was dependent on the size of the sample col- 

 lected. At the beginning of the period of stimulation, the potassium 

 concentration in the saliva is very high and then gradually falls off 

 to reach a much lower steady level after a few minutes. When 

 small samples of saliva are collected, the concentration of potas- 

 sium shows a pronounced dependence on the flow rate, usually 

 giving a U-shaped curve (Fig. 8.6). This dependence on flow rate 



