The relationship between the concentration of phosphate in plasma and parotid saliva was studied in six conscious sheep and a goat, either intact or thyroparathyroidectomized (t.x.p.t.x.), under conditions designed to minimize marked fluctuations in flow rate of saliva. A linear relationship between acutely induced changes in plasma phosphate concentration and the phosphate level in saliva has been demonstrated in both intact and t.x.p.t.x. animals. Dietary phosphorus depletion caused adaptation of salivary phosphate concentration so that less was secreted at a given concentration of plasma phosphate. Attention is drawn to the similarity between this phenomenon and that already described for the proximal renal tubule. Parathyroid hormone (PTH) was shown to reduce the salivary phosphate concentration with little or no effect on phosphataemia. The administration of 1,25-dihydroxycholecalciferol (1,25(OH)2CC) also caused a reduction in salivary phosphate concentration despite hyperphosphataemia and hypercalcaemia. It is suggested that salivary phosphate concentration can be influenced directly by the concurrent level of plasma phosphate but that this relationship can be modified by the circulating concentration of 1,25(OH)2CC and indirectly by PTH via increased production of 1,25(OH)2CC.

1. Wether sheep were used, some of which were prepared with a Thiry-Vella loop of jejunum. The long-term use of these loops was ensured by regular perfusion with fresh nutrient solution. 2. The net calcium absorption rate from a Thirty-Vella loop of jejunum increased with increasing intraluminal Ca concentration and was increased by the addition of 1 alpha-hydroxy-cholecalciferol (3 micrograms/l) to the loop fluid. 3. When the diet of sheep was changed from one which was normal in Ca to a diet low in Ca there was an increase in the efficiency of net Ca absorption from the jejunal loop. This dietary change was accompanied by an increase in the circulating concentration of 1,25-dihydroxy-cholecalciferol (1,25(OH)2D3). 4. An intravenous infusion of the Ca chelating agent EDTA increased the efficiency of net Ca absorption from the jejunal loop. The use of 47Ca demonstrated that this reflected an increase in the true absorption rate of Ca. 5. Dietary phosphorus deficiency reduced the efficiency of intestinal Ca absorption and was associated with a reduction in the plasma concentration of 1,25(OH)2D3.