Normal handling of phosphate in the salivary glands of X-linked hypophosphataemic mice.

In X-linked hypophosphataemia (Hyp gene) there is reduced renal tubule re-absorption of phosphate and an osteomalacic bone disorder. To determine whether altered phosphate transport also occurs in the salivary gland, saliva was analysed from normal and Hyp mice at 10 weeks of age. The effect of plasma inorganic phosphate on the composition of saliva was controlled by placing both genotypes on either a control diet or a low-P diet for three days. Inorganic phosphate, total phosphate, calcium, sodium, potassium, chloride, amylase, sialic acid, protein, osmotic pressure, percentage water, percentage inorganic solids and sample volume were measured. The Hyp mice fed the control diet showed a significant decrease in salivary-inorganic phosphate, total phosphate, osmotic pressure and sialic acid. These four variables were similarly lower in the normal mice fed the low-phosphate diet. The changes seem to stem from the low plasma inorganic phosphate and not from expression of the Hyp gene in the salivary gland. The total evidence from various organ systems suggests that the altered phosphate transport in X-linked hypophosphataemia may be restricted to the kidney and is not a generalized phosphate-transport deficiency.