Effect of flow rate on tissue plasminogen activator activity in human parotid saliva

Parotid saliva from 10 healthy volunteers was collected at rest and at constant flow rates of 0.25, 0.5 and 1.0 ml/min, and its tissue plasminogen activator (tPA) activity assayed on fibrin plates containing plasminogen. In unstimulated salivas the median tPA activity was 0.26 (range 0.03-2.0) IU/ml. During the first 15 min of stimulation, a continuous decrease in tPA activity was found at the three flow rates; thereafter a steady state was obtained. No significant differences in activity were found between the three rates. The initial decrease was on average 0.15 IU/ml, and the activity during the steady state was 38% of the prestimulatory level. Thus, stimulation with citric acid causes a significant decrease in tPA activity of parotid saliva but this decrease, as well as the reduction rate, appears to be independent of flow rate.