Salivary Rest Transients 209 



draining from the gland is measured so that the arteriovenous 

 difference of potassium as well as the salivary output is known. 

 By this method it is found that the potassium loss from the gland 

 proceeds at a very rapid rate during the first minute of stimulation, 

 but soon thereafter, a steady state of potassium content is reached 

 and on cessation of stimulation the gland slowly regains its potas- 

 sium content. The concentration of potassium in the venous blood 

 from the gland rises sharply above the arterial level at the begin- 

 ning of stimulation and during this period potassium is being lost 

 both into the blood and into the saliva, but gradually the venous 

 potassium concentration falls and stabilizes at 40-70 per cent of 

 the arterial level. In this steady state as much potassium is being 

 picked up from the blood going through the gland as is being 

 secreted in the saliva. The time course of the venous transient is 

 very similar to the early phase of the potassium transient in saliva 

 and indeed the initial rates of potassium loss by the two routes 

 are proportionate whatever the flow rate. In the dog submaxillary 

 gland, about one-fifth of the initial potassium loss is into the blood 

 and about four-fifths into the saliva (Burgen, 1956a). In the cat 

 sublingual, the losses are about evenly divided between blood and 

 saliva (Lundberg, 1958). It should be noted that both the ampli- 

 tude of the saliva transient and the rate of potassium loss in it are 

 dependent on the rate of nerve stimulation, the transient being 

 much bigger at higher rates of stimulation. A related phenomenon 

 is illustrated in Fig. 10.10. Here stimulation was started at 2 c/s 

 and when a steady state had been reached, the rate of stimulation 

 was increased to 20 c/s. A second transient ensued in both saliva 

 and venous blood. The steady state gland content of potassium 

 fell by a further 1 1 mEq/kg when the rate of secretion was in- 

 creased. Seeman (1956) has also shown the presence of a negative 

 potassium transient when the reverse experiment is carried out, 

 i.e. initial stimulation at a high rate followed by sudden reduction 

 to a low rate. Evidently, the steady state potassium content reached 

 after stimulation is not a fixed one but is dynamically dependent 

 on the rate of stimulation (and saliva secretion). The behaviour of 

 potassium in the gland in response to abrupt changes in gland 

 activity offers important evidence as to the function of the gland 

 but the published explanations cannot be regarded as adequate. 

 Burgen, Terroux and Gonder (1959) pointed out that since the 

 early phase of the potassium transient had such a brief latency, it 



P.S.G. — P 



