Taste disorders and salivary secretion

Saliva is the principal fluid component of the external environment of the taste receptor cells and, as such, could play a role in taste sensitivity. Its main role includes transport of taste substances to and protection of the taste receptor. In the initial step of taste perception, saliva acts as a solvent for taste substances: taste substances are dissolved in salivary water and diffused to the taste receptor. During this process, some salivary constituents chemically interact with taste substances. For example, salivary buffers decrease the concentration of free hydrogen ions (sour taste). Thus, decrease in salivary secretion or change in salivary constituents will change the normal initial process of taste perception. This may be one cause of taste dysfunction seen in patients with Sjogren's syndrome, an autoimmune disorder characterized by destruction of the salivary and lacrimal glands, commonly complain of dry mouth. The patients with severe dry mouth have also problems in the health of the mucous membrane in the oral cavity. Histological studies in rats show that the surgical removal of the major salivary glands resulted in pathological changes such as hyperkeratosis of the tongue epithelium, shrinkage of taste buds, and penetration of bacteria into the apical portion of the taste cells. These changes may affect the renewal rate of taste cells and their receptor functions: the taste cells are replaced, on the average, every 10 days. The surgical removal of the sublingual and submandibular salivary glands resulted in decrement of taste nerve (chorda tympani) responses in rats. The decrease in taste sensitivity recovered after 1-week infusion of artificial saliva into the oral cavity. It is possible that the sensitivity of the replaced taste receptors is determined by the peri-receptor milieu.