[Effect of parathyroid hormone-related protein on Na(+)-dependent phosphate transport in renal brush border membrane vesicles in rats].

Parathyroid hormone-related protein (PTHrP) has significant homology with parathyroid hormone (PTH) especially in the amino-terminal sequence. We compared some effects of human synthetic analogue of amino terminal PTHrP [hPTHrP (1-34)] with those of human synthetic analogue of amino terminal PTH [hPTH (1-34)]. Intravenous administration of hPTHrP (1-34) in parathyroidectomized rats caused hypercalcemic, hypophosphatemic and phosphaturic effects in the same degree of hPTH (1-34). In the kinetic study, apparent Km and Vmax of phosphate transport in renal brush border membrane vesicles were identical in both peptides (hPTHrP(1-34) Km = 27.6 +/- 0.8 mumol, Vmax = 3.78 +/- 0.04 nmol/mg.protein; hPTH(1-34) Km = 29.6 +/- 0.9 mumol, Vmax = 3.04 +/- 0.9 nmol/mg.protein). hPTHrP(1-34) and hPTH(1-34) were equipotent in eliciting a 9-fold increase of adenosine 3',5'-monophosphate (cAMP) production. These results demonstrate that the effect of hPTHrP (1-34) is similar to hPTH(1-34) on serum calcium, phosphorus and nephrogenous cAMP in vivo, and Na(+)-dependent phosphate transport in brush border membrane vesicles.