HUMAN PARATHYROID HORMONE(1-34) INCREASES BONE-FORMATION AND STRENGTHOF CORTICAL BONE IN AGED RATS

The effect of parathyroid hormone (PTH(1-34)) on mid-diaphyseal femora l cortical bone was studied in 2-year-old male rats. The rats were tre ated with daily injections of 15 nmol/kg PTH(1-34) or vehicle for 56 d ays, and labelled with tetracycline and calcein on day 15 and day 40, respectively. The PTH(1-34) treatment did not affect the body weights or the lengths of the femora. Fluorescence microscopy showed large int racortical cavities in the old vehicle-treated rats. After PTH treatme nt, double labelling and new bone formation filling in these cavities were found. Furthermore, an increased bone formation rate was observed both at the periosteum and at the endosteum. This resulted in an incr ease in the cross-sectional area and a decrease in the medullary area. Three-point bending analysis revealed an increase in ultimate load, u ltimate stiffness, energy absorption and ultimate stress after the PTH (1-34) treatment. No differences were found between the groups regardi ng the hydroxyproline concentration or apparent and real densities. Th e ash concentration was, however, slightly reduced after PTH(1-34) tre atment. The PTH(1-34) treatment of old rats induced the formation of b one both from the periosteum and endosteum, with a pronounced filling in of intracortical cavities, and, furthermore, a marked increase in t he biomechanical competence of the cortical bone.