[Bone changes with long term administration of low dose 1-34 human PTH on adult beagles]

It has been suggested that prolonged administration of low dose PTH could exert an anabolic effect on the bone. The effects of near-physiological dose of PTH injection on trabecular and cortical bones were studied in normal young adult beagles. Twelve 18 month-old male beagle dogs were equally divided into 4 groups by body weight. The 1st group serving as the control was subcutaneously injected with 1 ml of normal saline, and the 2nd, the 3rd and the 4th groups were also subcutaneously injected with 1.25, 5.0, 20.0 unit/kg/day of synthetic 1-34 human PTH respectively everyday for 15 weeks. Then, over the following 8 weeks, administration of all vehicle and drugs was withdrawn. After double bone labeling, iliac bone and rib biopsies were taken before and after the drug administration and after the withdrawal. The effects were evaluated with blood chemical and hormonal analysis and bone histomorphometry. No significant changes were noted in serum Ca, P, PTH, calcitonin and 1,25 (OH)2 vit.D levels and A1-P activities with some exceptions. Bone histomorphometry on trabecular bone showed remarkable and statistically significant elevation of formation surface, active formation surface, mineral appositional rate, labeled surface and bone formation rate. On the other hand, bone resorption rate and some other resorption parameters showed a significant elevation but trabecular bone volume showed no significant increase. In cortical bone, the bone dynamics were essentially equal to trabecular bone. But by the increase of bone turnover rate, cortical porosity rate increased. After withdrawal of drug administration, the bone turnover rate went down and a rate of cortical porosity returned to normal level. From these results it was postulated that PTH was effective in activating low remodeling of the skeleton.