The bicarbonate concentration in human saliva does not exceed the plasma level under normal physiological conditions

Depending on the secretion rate and nature of the stimulus applied, the bicarbonate concentration ([HCO3-]) in human saliva has been shown to vary from 1 to 60 mM, with the highest values obtained in secretions from the parotid and submandibular glands. We conducted the present study on five healthy young males, in order to determine whether human saliva [HCO3-] can exceed the plasma level under normal physiological conditions, and applied a strategy in which we measured the secretory response to various stimulus intensities. Whole saliva stimulation was initiated by chewing paraffin (50-100 chewing cycles/min), parotid saliva stimulation by citric acid taste (0.2-4% citric acid solutions), and both secretions were also collected during systemic medication using pilocarpine (5 mg). Our results showed that the parotid and whole saliva flow rates were closely correlated to the intensity of the secretion-inducing stimulus applied (taste, chewing, and pilocarpine). This was also the case for saliva [HCO3-], all of which was present in the form of physically dissolved CO2, H2CO3, and HCO3-. The highest mean [HCO3-] (i.e. 37.75 mM) was found in parotid saliva after stimulation by pilocarpine in combination with 4% citric acid taste. Under normal physiological conditions (i.e. without pilocarpine) the saliva [HCO3-] was similar to or below the plasma level in both secretions.