Parathyroid hormone gene expression in Hyp mice fed a low-phosphate diet

Background: The murine analogue of X-linkedhypophosphateaemia is the Hyp mouse; it has chronicphosphate depletion from an inherited defect of renal tubular reabsorption.Phosphate directly regulates the parathyroid (PT) in normal rats and it isof interest whether this regulation is intact in Hypmice. Methods: Hyp mice were fedeither a low-phosphate diet or control diet and PTH mRNA levels weremeasured. In addition changes in NMR-visible kidney and muscleintracellular phosphate potentials in normal and Hypmice were determined. Mice were maintained on a low-phosphate (0.02%) ornormal-phosphate (0.6%) diet for 24 and 72 h. Results:On the normal diet, Hyp mice had hypophosphataemia,normocalcaemia, and normal PTH mRNA levels. Phosphate deprivation for 72 hled to a profound fall in plasma phosphate, a slight but significant risein plasma calcium, and a dramatic decrease in PTH mRNA, similar to that ofnormal mice fed this diet. Changes in kidney and muscle intracellularphosphate measured by NMR spectroscopy were not affected by diet orgenotype. Conclusion: Dietary phosphate deprivationdecreased Hyp mice PTH mRNA levels and caused nochange in intracellular phosphate potentials. ThereforeHyp mice parathyroids' adapt appropriately tophosphate deprivation albeit at a lower threshold compared to normal mice.