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±0.8μmol, Vmax=3.78±0.04 nmol/mg.Eprotein; hPTH (1-34) Km=29.6±0.9μmol, 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 phos phate transport in brush border membrane vesicles.
