Secretion of calcium and phosphate by the dog parotid gland

¹ Department of Physiology, University of Alabama Medical Center, Birmingham, Alabama

In dog parotid saliva, calcium is two to three times more concentrated than it is in the plasma. Phosphate in the saliva is less than one-fifth that of the plasma. Increasing the plasma phosphate level by a factor of 7 increases the saliva phosphate only twice. Salivary calcium varies almost proportionately with plasma calcium. After parotid secretion begins, the concentrations of both calcium and phosphate progressively decrease until a steady state is reached. Calcium and phosphate concentrations increase slightly in the saliva as the secretion rate decreases. At very slow rates there is a more marked increase. During the stop-flow procedure both calcium and phosphate concentrations increase, but to a strikingly different degree and at different sites in the gland. The increase in phosphate is almost exclusively the organic fraction. It is concluded that water and electrolytes are transferred from plasma to saliva by processes that are not coupled, and that proceed at varying and independent rates. The site of these transfers is distal, probably at the level of the ducts.