Changes in canine saliva ion concentration induced by increased intraluminal pressure

Hydrostatic pressure was applied to a cannula inserted into Wharton's duct of adult dogs anesthetized with pentobarbital and the effect of pressure on saliva flow rate and ionic composition of saliva was measured. Increasing the back pressure on a secreting gland resulted in a decrease in flow rate. Over the range of 0-100 mmHg back pressure the decrease in flow was proportional to the applied back pressure. The potassium concentration of saliva collected in the absence of back pressure and at raised pressure was similar even though back pressure reduced flow. In contrast, sodium concentration decreased when back pressure caused salivary flow rate to be reduced. However, when examined at the same flow rates the concentration of sodium is increased when back pressure is applied to the gland as compared to absence of back pressure. Under conditions of constant stimulation the total output of sodium and potassium into saliva decreases as back pressure is increased; but when equal flow rates are compared total sodium output increases in the presence of applied back pressure, whereas potassium output remains constant.