Fluid and protein secretion from salivary glands are primarily regulated by efferent parasympathetic and sympathetic nerves respectively. The protein concentration of saliva, which is made up of a number of functionally important proteins, can vary depending on the impulse traffic arriving from these nerves. The composition of the proteins secreted by a salivary gland with a mixed population of secretory cells can vary with different secretory stimuli and intensities of stimuli, according to how the individual cell populations respond. Most of the published evidence suggests that the protein composition of saliva secreted form the parotid gland, which has an apparently homogeneous secretory cell population, appears to be similar regardless of the type of nerve stimulus. It is likely that salivary secretory cells can secrete protein by a constitutive route, not involving storage granules, in addition to the regulated secretion of protein from storage granules, and that the constitutive route may operate during parasympathetic nerve stimulation. However the functional significance of this type of protein secretion is as yet unknown. In the longer-term the composition of proteins secreted from salivary glands also depends upon the rates of synthesis of individual proteins. Levels of secretory proteins show differing dependencies on specific nerve-mediated stimuli as shown by the changing compositions of proteins secreted following denervation or chronic pharmacological blockade. The levels of secreted proteins appear to be regulated at both the transcriptional and translational levels of protein synthesis. In rodent salivary glands there is a dependency of secretory proline-rich protein synthesis on β-adrenergically mediated stimuli which is dependent upon putative cAMP regulatory sequences of nucleotides in the gene. Although N-linked glycosylation has been shown to be regulated by β-adrenergically mediated stimuli, it is not known if the composition of sugars on proteins varies with neural stimuli.
Biomedical Reviews 1993; 2: 47-56.
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