The effect of taste adaptation on salivary flow rate and salivary sugar clearance.

To provide an objective measure of the rate of taste adaptation, we measured changes in the flow rate of parotid saliva from 12 subjects while a tastant was infused continuously into their mouths. The tastants employed were sucrose, sodium chloride, and citric acid, each at two different concentrations. With all stimuli, the higher concentration elicited significantly higher initial flow rates, which declined exponentially with time. The half-time for adaptation of flow rate was independent of the nature or concentration of the stimulus and averaged 11.3 sec, which suggests that adaptation follows a single exponential curve. The model of salivary sugar clearance developed by Dawes (1983) predicted that the rate of clearance would be independent of the initial sucrose concentration. However, this model did not take into account the effect of taste adaptation on salivary flow. This process was thus incorporated into the model, which then predicted that the time for clearance would be dependent on the initial sucrose concentration, as found experimentally by Goulet and Brudevold (1984). Hence the process of taste adaptation progressively reduces the stimulated salivary flow rate, which retards the rate of salivary clearance of sugar from the oral cavity.