148 The Inorganic Components of Saliva 



Wechsler (i960), in a study of the submaxillary secretion of 

 young puppies, has found that up to the age of 10 days the saliva is 

 virtually free of bicarbonate but, thereafter, the bicarbonate con- 

 centration rises to reach the adult level after 3-4 weeks. 



The source of the salivary bicarbonate is of considerable interest 

 because it might be derived in part by transfer from the plasma 

 bicarbonate and in part from endogenous bicarbonate produced 

 by the gland metabolism. A simple calculation shows that in a 

 maximally secreting gland it would not be possible for all the 

 secreted bicarbonate to be derived from metabolism. In an active 

 dog submaxillary gland saliva is secreted at 0-3 ml./g. min with 

 a bicarbonate concentration of approximately 40 mEq/1. — a total 

 of approximately 12 //Eq HC0 3 /g. min. The gland metabolism 

 produces only 5 [iEq HC0 3 /g. min so that even if all the meta- 

 bolic bicarbonate of the gland were directed into the saliva this 

 could account for less than half the total. The discrepancy would 

 naturally become all the greater if the saliva bicarbonate level were 

 raised by increase of the arterial pC0 2 or bicarbonate. Sand (195 1) 

 examined this question by injecting C 14 labelled bicarbonate intra- 

 venously in a rabbit and measuring the specific activity of mixed 

 saliva from the mouth and comparing this with that in the blood. 

 The specific activity of the saliva bicarbonate was a little lower 

 than in the blood. These experiments suffered from the defect 

 that the blood bicarbonate concentration was falling rather rapidly 

 during the experiment and the method of saliva collection led to a 

 relatively large error in timing the sample. Wechsler (1959) has 

 repeated this kind of experiment in the cat, taking care to maintain 

 the serum level constant by continuous infusion of C 14 bicarbonate 

 and has found that the saliva specific activity was 10-20 per cent 

 lower than the arterial. These observations suggest that an appre- 

 ciable proportion of the salivary bicarbonate is indeed derived 

 from metabolism. Further support for this view was provided by 

 Sand, who found that after injection of C 14 -lactate, the specific 

 activity of the saliva bicarbonate was higher than in the arterial 

 blood. 



POTASSIUM 



It has been known since the studies of Tiedemann and Gmelin 

 (1826) that potassium is present in rather high concentrations in 



