Regulation of Salivary Proteins

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Abstract
Previous studies have shown that several factors — such as alloxan-induced diabetes, adrenalectomy, or removal of the thyroid-parathyroid gland complex — can influence the flow rate, protein concentration, and protein composition of rat parotid saliva. The present study was undertaken to explore further the influence of glucocorticoids and thyroxine on rat parotid saliva in hormonally intact animals. As compared with untreated animals, adult male rats treated with 10 μg dexamethasone per 100 g body weight for eight days demonstrated a 75% reduction in volume of parotid saliva secreted in response to a uniform stimulus. The protein concentration of the saliva was increased three-fold. Sodium dodecyl sulfate polyacrylamide gel electrophoresis showed relative decreases in acidic and basic proline-rich proteins and in a protein identified as Fraction V, while amylase was increased. The electron microscopic appearance of the granules was markedly different from that of the control, in that the granules exhibited an electron-dense periphery and core, with the remainder of the granule having an electronlucent appearance. In contrast, rats treated for eight days with 20 μg thyroxine per 100 g body weight exhibited a 50% increase in volume of saliva collected in response to a secretory stimulus. Although the concentration of protein was not different from that of the control, gel electrophoresis showed relative increases in acidic and basic proline-rich proteins and a decrease in Fraction V. Amylase was unchanged. The secretory granules of thyroxine-treated rats were electronlucent and amorphous. The granules appeared to coalesce within the cell. These effects on flow rate, protein concentration, and protein composition which occur in the dexamethasone- or thyroxine-treated groups are opposite those shown to occur following removal of the adrenal or thyroid-parathyroid glands, respectively. In summary, the results indicate that hormones of several endocrine systems are involved in the regulation of salivary flow rate, protein concentration, and protein composition.