HUMAN PARATHYROID-HORMONE (1-34) AND (1-84) INCREASE THE MECHANICAL STRENGTH AND THICKNESS OF CORTICAL BONE IN RATS

An anabolic effect on bone of intermittent parathyroid hormone (PTH) t reatment has been found in patients with osteoporosis and also in expe rimental animals. Controversies exist, however, about whether the posi tive effect on the trabecular bone balance occurs at the expense of th e cortical bone. We examined the biomechanical quality of cortical bon e after intermittent treatment with different doses of PTH and, furthe rmore, compared the effects of PTH-(1-34) and PTH-(1-84). Groups of ra ts were treated with biosynthetic human PTH-(1-34) or PTH-(1-84), 1.1, 3.3, 10, or 30 nmol/kg/day for 30 days. No changes in the body weight s and no changes in the lengths of the femora were observed after the PTH treatments. The biomechanical properties were analyzed by means of a materials-testing machine. A dose-related increase in the bending s trength and stiffness of the femora was found, and this increase in me chanical strength corresponds with a 9-12% increase in the cross-secti onal area of the femoral diaphyses. The deflection capability and ener gy absorption were not influenced by any of the PTH treatments. No dif ferences were found between the effects of PTH-(1-34) or PTH-(1-84) on the biomechanical properties of the femora. Consequently, intermitten t treatment with biosynthetic PTH-(1-34) or PTH-(1-84) increased the f ormation of cortical bone, and the biomechanical competence of the fem ora was found to be preserved.