A COMPARISON OF THE EFFECTS OF PARATHYROID-HORMONE AND PARATHYROID HORMONE-RELATED PROTEIN ON OSTEOCALCIN IN THE RAT

We compared the effects of parathyroid hormone (PTH1-34) and parathyro id hormone-related protein (PTHrp1-34) on osteocalcin release in the i solated rat hindlimb and in intact and thyroparathyroidectomized (TPTX ) rats, PTH1-34 suppressed osteocalcin release from perfused rat hindq uarters, while PTHrp1-34 had no effect on osteocalcin release, despite comparable stimulation of cAMP production, Similarly, serum osteocalc in declined in the intact and TPTX animals by 5 h after a single dose of PTH1-34, while there was no response to PTHrp1-34, Chronic administ ration of PTH1-34 or PTHrp1-34 produced comparable hypercalcemia and h ypophosphatemia in sham-operated and TPTX animals, Chronic PTH1-34 adm inistration produced significant increases in serum osteocalcin both i n the sham-operated rats and in the TPTX animals, However, in animals chronically treated with PTHrp1-34, there was no change at any time po int in osteocalcin in either sham-operated or TPTX rats, These differe nces could be inherent or merely due to potency differences between th e two peptides.