Effect of parathyroid hormone on renal calbindin‐D28k

The present investigation was conducted to examine the effects of parathyroid hormone (PTH) and parathyroid hormone related peptide (PTHrP) on renal calbindin-D28k in rats. Four groups of studies were performed : (1) parathyroidectomy (PTX) or a sham operation followed by infusion of 1,25-dihydroxyvitamin D (1,25 [OH] 2D) or vehicle ; (2) infusions of PTH(1-34), PTH(1-84), 1,25(OH) 2 D, or vehicle ; (3) infusion of PTHrP(1-34), PTHrP (1-86), PTH(1-34), or vehicle ; and (4) injections of calcium or vehicle. PTX reduced renal calbindin-D28k levels even when plasma concentrations of 1,25(OH) 2 D were kept constant by infusion of 1,25(OH) 2 D. Infusions of PTH(1-34), PTH(1-84), and 1,25(OH) 2 D all increased renal calbindin-D28k and plasma calcium, whereas PTHrP(1-34) and PTHrP(1-86) increased renal calbindin-D28k before an increase of plasma calcium took place. Hypercalcemia induced by the injection of calcium did not affect the levels of renal calbindin-D28k The present data suggest that PTH and PTHrP exert a direct effect on renal calbindin-D28k, which is not mediated by changes of 1,25(OH) 2 D or calcium.