Effect of a liquid diet on the protein composition of rat parotid saliva

The object of the present study was to determine of the secretory proteins of rats parotid saliva were altered following parotid gland atrophy induced by feeding rats a liquid stock diet which eliminated mastication. Compared to rats fed the pelleted stock diet, the parotid glands of rats fed liquid stock diet showed 40% to 55% reductions in gland weight and content of RNA, amylase, and protein. Gland DNA content was reduced by 26%. The concentration of protein and the activities of three secretory enzymes in parotid saliva were reduced by 40% to 70%. The secretory enzymes were affected in a nonparallel manner so that per milligram of secretory protein DNase was increased, while RNase and amylase were reduced. Examination of the protein composition by acrylamide gel electrophoresis showed that several secretory proteins were no longer present. This study showed that feeding rats a standard stock diet, but in liquid form to eliminate mastication, results in a reduction in the protein concentration of parotid saliva, a loss of several secretory proteins and nonparallel changes in some of the proteins which remain.