The production of saliva is stimulated both by the sympathetic nervous system and the parasympathetic.
The saliva stimulated by sympathetic innervation is thicker, and saliva stimulated parasympathetically is more watery.
Sympathetic stimulation of saliva is to facilitate respiration, whereas parasympathetic stimulation is to facilitate digestion.
Parasympathetic stimulation leads to acetylcholine (ACh) release onto the salivary acinar cells. ACh binds to muscarinic receptors and causes an increased intracellular calcium ion concentration (through the IP3/DAG second messenger system). Increased calcium causes vesicles within the cells to fuse with the apical cell membrane leading to secretion formation. ACh also causes the salivary gland to release kallikrein, an enzyme that converts kininogen to lysyl-bradykinin. Lysyl-bradykinin acts upons blood vessels and capillaries of the salivary gland to generate vasodilation and increased capillary permeability respectively. The resulting increased blood flow to the acinar allows production of more saliva. Lastly, both parasympathetic and sympathetic nervous stimulation can lead to myoepitheilium contraction which causes the expulsion of secretions from the secretory acinus into the ducts and eventually to the oral cavity.
Saliva production may also be pharmacologically stimulated by so called sialagogues. It can also be suppressed by so called antisialagogues.
Clinicians could detect oral squamous cell carcinoma, a form of oral cancer, using a simple test that detects proteins in saliva, according to a report in the October 1, 2008, issue of Clinical Cancer Research, a journal of the American Association for Cancer Research. This work was led by David T. Wong, D.M.D., D.M.Sc., professor and associate dean for research, at the University of California, Los Angeles School of Dentistry.
Previous studies have shown that saliva can be a useful diagnostic tool, but this is the first study to globally evaluate saliva protein levels from oral cancer patients. Since it is very simple to collect and process saliva fluids, the discovery of these biomarkers may lead to a useful clinical tool for noninvasive diagnosis of oral cancer in the future.
"This test is currently not available, but we are developing point-of-care microfluidic devices to detect these markers that we can use in clinical trials," said Shen Hu, Ph.D., assistant professor of Oral Biology and Proteomics at the University of California, Los Angeles School of Dentistry.
Wong, Hu and colleagues have been working as part of the National Institute of Dental and Craniofacial Research (NIDCR)'s Human Saliva Proteome Project, which focuses on identifying and cataloguing the proteomic components of saliva in healthy subjects. This work, also supported by NIDCR, demonstrates the first translational utility of the salivary proteome for oral cancer detection.
