Effects of the (1-34) fragment of synthetic parathyroid hormone-related protein on tartrate-resistant acid phosphatase and alkaline phosphatase and alkaline phosphatase activities, and on osteocalcin synthesis, in cultured fetal rat calvaria.

In the last years, a parathyroid hormone (PTH)-related peptide (PTHrP) has been isolated from tumors associated with humoral hypercalcemia with malignancy (HHM). In the present work, we studied the effect of bovine PTH (bPTH)(1-34) and PTHrP(1-34) on tartrate-resistant acid phosphatase (TRAP), a marker of bone resorption, and alkaline phosphatase (AP) activities, and basal and vitamin D-stimulated osteocalcin (BGP) synthesis (markers of bone formation) in fetal rat calvaria cultures. After a 48-hour incubation period, both bPTH(1-34) and PTHrP(1-34) caused an increase in TRAP activity liberated in the medium with respect to control cultured calvaria. On the other hand, while after 2 or 4 h of incubation both bPTH(1-34) and PTHrP(1-34) caused a decrease in the AP activity liberated in the medium, after 48 h of incubation both peptides caused a significant increase in the AP liberated in the medium with respect to control cultures. With respect to BGP synthesis, both bPTH(1-34) and PTHrP(1-34) antagonized the 1,25-dihydroxyvitamin D3 stimulatory effect in calvaria cultures. We conclude that PTHrP(1-34) causes similar effects on bone, in organ cultures, to those caused by bPTH(1-34), namely an increase in both bone resorption and formation and a decrease in the vitamin D-stimulated BGP synthesis.