Increased transport of inorganic phosphate in renal brush borders of spontaneously hypertensive rats

Abstract

Phosphate metabolism was studied in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) by measuring serum phosphate concentrations and 24-h urinary phosphate excretions in rats placed in metabolic cages from 6 to 23 wk of age. Serum phosphate concentrations in SHR were significantly lower than those in WKY at 6, 12, and 20 wk of age. In addition, 24-h urinary phosphate excretion was lower in SHR relative to WKY from 6 through 23 wk of age. The hypophosphaturia in SHR was accompanied with an increase in the maximal transport rate of Na+-dependent phosphate transport in renal brush border membrane vesicles (BBMV) isolated from kidney cortex at 6, 12, and 20 wk of age. The apparent affinity for phosphate did not differ significantly between WKY and SHR at all ages studied. A direct relationship between maximal Na+-dependent phosphate transport rates in BBMV and serum phosphate concentrations was observed in both strains. In SHR, phosphate homeostasis is disturbed from 6 wk of age on.