THE EFFECTS OF INTRAVENOUS PHOSPHATE LOADING ON SALIVARY PHOSPHATE SECRETION AND PLASMA PARATHYROID HORMONE LEVELS IN THE SHEEP

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Abstract
Adult sheep were given i.v. 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 Pi in the plasma and to proportional increases in the concentration and amount of phosphate secreted in the saliva. There was no evidence that the salivary response was dependent on a change in endogenous parathyroid hormone release. In other studies infusion of bovine parathyroid hormone or stimulation of endogenous hormone release through infusions of EDTA both led to a fall in the concentration of Pi in the plasma and to a fall in the concentration and amount of phosphate secreted in the saliva. The major factor affecting salivary phosphate secretion in these studies apparently was the concentration of Pi in the plasma. Parathyroid hormone did 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 Pi level.