Salivary alpha-amylase secretion in resting and stimulated saliva

Objectives: Alpha-amylase, a major component of saliva, exerts its main function in the digestion of carbohydrates. It is also important as an innate defence factor of the oral cavity, as it inhibits the bacterial adherence. Salivary alpha-amylase has been proposed as a marker of sympathetic nervous system activation triggered by psychological stress. However, it is unclear whether its secretion can specifically be stimulated or if its increased concentration depends on concomitant fluctuations of the salivary flow. This study aimed to examine the secretion of alpha-amylase in resting and stimulated saliva and to relate the enzyme activity to the protein content of the sample.

Methods: Both resting and stimulated saliva was collected from 10 subjects between 10:00 and 11:00 a.m. The subjects were asked not to eat or smoke for 2 h prior to collection. All samples were centrifuged to remove the particles and kept in a deep freezer (-80 °C) until used. The alpha-amylase activity of the samples was determined spectrophotometrically at 405 nm from the hydrolysis rate of the chromogenic substrate 2-chloro-4-nitrophenyl-beta-D-maltotrioside. The total protein content of the sample was determined using a commercially available kit (BCA™ Protein Assay Kit, Pierce, USA). Bovine serum albumin was used to generate the standard curve.

Results: The following mean±SD values were found: Flow rate: 0.43±0.24 ml/min (resting saliva), and 2.48±1.04 ml/min (stimulating saliva). Total protein concentration: 1201±631.8 µg/ml (resting saliva) and 1107.8±414.2 µg/ml (stimulated saliva). Alpha-amylase in resting saliva: 16.36±9.37 U/ml and 0.017±0.012 U/µg protein. Alpha-amylase in stimulated saliva: 18.25±9.13 U/ml, and 0.02±0.013 U/µg protein. Only the difference in the flow rate between the resting and the stimulated saliva was statistically significant (p<0.001).

Conclusion: The flow rate has no influence on the alpha-amylase concentration in saliva samples collected from subjects under no psychological stress.