The effects of intravenous phosphate loading on salivary phosphate secretion and plasma parathyroid hormone levels in the sheep.

Adult sheep were given intravenous infusions of a solution of Na2HPO4 and the effects on parotid salivary composition and on plasma parathyroid hormone levels were studied. Infusion of the phosphate solution resulted in increases in the concentration of inorganic phosphate in the plasma and to proportional increases in the concentration and amount of phosphate secreted in the saliva. There was, however, no evidence that the salivary response was dependent upon a change in endogenous parathyroid hormone release. In other studies infusion of bovine parathyroid hormone or stimulation of endogenous hormone release through infusion of EDTA both led to a fall in the concentration of inorganic phosphate in the plasma and to a fall in the concentration and amount of phosphate secreted in the saliva. Taken together these results suggest that the major factor affecting salivary phosphate secretion in these studies was the concentration of inorganic phosphate in the plasma. Parathyroid hormone does not appear to have any direct effect on salivary phosphate secretion in the sheep though it may indirectly influence phosphate secretion through its effects on plasma inorganic phosphate level.