The effect of parathyroid hormone (PTH) and dietary phosphate on the sodium-dependent phosphate transport system located in the rat renal brush border membrane.

The effect of two parameters regulating renal phosphate excretion, namely parathyroid hormone application and dietary phosphate intake, on the transport properties of isolated rat renal brush border membrane vesicles was investigated. In the first set of experiments brush border membrane vesicles from young normal rats injected i.m. with 30 USP parathyroid hormone or i.v. with 1 mg dibutyryl cAMP were compared. PTH and dbcAMP injection decreased specifically the Vmax of the sodium-dependent phosphate transport system by appr. 30%. In a second set of experiments rats were kept on phosphate-rich and phosphate-poor diet and after 6-8 weeks the brush border membranes were isolated. The membranes obtained from phosphate-depleted animals showed a markedly (approximately 100%) higher initial sodium-dependent phosphate uptake than membranes isolated from animals kept on phosphate-rich diet. Again only the sodium-dependent phosphate uptake was affected, sodium-independent phosphate permeability, sodium-dependent D-glucose transport, mannitol permeability and sodium permeability remained unchanged.