Chloride Concentration in Parotid Fluid at Low Rates of Flow

¹ School of Aerospace Medicine, USAF Aerospace Medical Center, Brooks Air Force Base, Texas, and Tufts University School of Dental Medicine, Boston, Massachusetts

Parotid fluid was collected from 527 healthy young adult male subjects under conditions of minimal stimulation. At a mean flow rate of 0.042 ml/minute (S.D.= ±0.030), the chloride mean was 24.78 mEq/liter (S.D.= ±7.64). The mean serum chloride concentration was 101.90 mEq/liter (S.D.= ±2.61). At this low rate of flow a significant (p < 0.01) negative correlation (r= —0.25) was found between flow rate and chloride concentration. A comparison of the results of this study with those from other work on comparable subjects led to the hypothesis that the chloride concentration of the parotid fluid is controlled as follows: Chloride is reabsorbed along with sodium by the duct cells and is, at the same time, secreted into the saliva, along with potassium, by cells of the duct walls. At high rates of flow the reabsorption mechanism is overwhelmed, and the chloride concentration increases along with flow-rate increases. At the low rates of flow the secretion of chloride, along with potassium, into the saliva prevents the then very effective reabsorptive process from decreasing the chloride concentration to the very low levels found for sodium and bicarbonate. Thus parotid fluid chloride concentration appears to be dependent on the movement of sodium and potassium between the duct cells and the saliva.