EFFECT OF PARATHYROID-HORMONE ON RENAL CALBINDIN-D28K

The present investigation was conducted to examine the effects of para thyroid hormone (PTH) and parathyroid hormone related peptide (PTHrP) on renal calbindin-D28k in rats. Four soups of studies were performed: (1) parathyroidectomy (PTX) or a sham operation followed by infusion of 1,25-dihydroxyvitamin D (1,25[OH]D-2) or vehicle; (2) infusions of PTH(1-34), PTH(1-84), 1,25(OH),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 incre ased renal calbindin-D28k and plasma calcium, whereas PTHrP(1-34) and PTHrP(1-86) increased renal calbindin-D28k before an increase of plasm a calcium took place. Hypercalcemia induced by the injection of calciu m did not affect the levels of renal calbindin-D28k The present data s uggest that PTH and PTHrP exert a direct effect on renal calbindin-D28 k, which is not mediated by changes of 1,25(OH)(2)D or calcium.