Abstract:

Objective: To investigate the effect of acid stimulation on salivary flow rate and compositions of human parotid and submandibular glands, so as to provide basis for comprehensive evaluation of salivary gland function in both health and disease status. Methods: In the study, 210 healthy participants’ whole saliva samples were collected under passive drooling, and their parotid gland and submandibular gland secretions were collected by negative pressure suction. 2% citric acid was dropped on the tip of tongue every 1 min for acid stimulation for a total of 5 times to collect stimulated whole saliva, parotid and submandibular gland saliva. The collected saliva was weighed and saliva flow rate was calculated. The K⁺, Na⁺, Cl^-, Ca²⁺, total protein, total phosphorus and α-amylase in saliva samples were detected by biochemical analyzer, and the changing features of flow rate and compositions of different kinds of saliva were compared and analyzed. Results: After acid stimulation, saliva flow rate significantly increased. The increase proportion of parotid gland saliva (10.7 folds) was much higher than that of submandibular gland saliva (2.9 folds). The concentrations of Na ⁺, Cl^-, Ca²⁺, total protein and α-amylase in parotid gland saliva increased significantly (P<0.05), but there was no significant difference in total phosphorus and K ⁺ (P=0.89,P=0.34). The concentration of Na⁺ and Ca²⁺ in saliva of submandibular gland increased significantly(P<0.05), the concentration of total phosphorus decreased significantly(P<0.05), and the concentration of Cl^- increased, but the difference was not significant(P=0.068). There was no significant difference in total protein, K⁺ and α-amylase (P=0.85,P=0.07,P=0.95). The compound secretion rate of total phosphorus in saliva of submandibular gland remained unchanged(P=0.066), while the secretion rate of K ⁺, Na⁺, Cl^-, Ca²⁺, total protein and α-amylase significantly increased(P<0.01). The compound secretion rate of K ⁺, Na⁺, Cl^-, Ca²⁺, total protein and total phosphorus and α-amylase in parotid gland saliva increased(P<0.01). The concentrations of Na ⁺, Cl^-, K⁺, total phosphorus, total protein and α-amylase in parotid were higher than those in submandibular gland (P<0.01), and the concentration of Ca ²⁺ in submandibular gland saliva was significantly higher than that in parotid (P<0.001). Conclusion: The response of parotid to acid stimulation is stronger, and the secretion of submandibular gland is more stable. Acid stimulation significantly influences the concentrations of electrolytes in saliva, and the composited secretion rate is an evaluation index to reflect both flow rate and composition concentration of saliva. The parotid gland plays an important role in the secretion of total protein, total phosphorus and α-amylase in saliva, and the submandibular gland is the main source of Ca²⁺ in saliva.

Key words: Saliva, Saliva flow rate, Parotid gland, Submandibular gland, Composition of saliva