THE INFLUENCE OF GROWTH-HORMONE ON CANCELLOUS AND CORTICAL BONE OF THE VERTEBRAL BODY IN AGED RATS

The influence of growth hormone administration on cancellous and corti cal bone of the vertebral body in 2-year-old male rats has been invest igated. AU rats were injected for 80 days, then killed. Controls were given saline, and three recombinant human growth hormone (rhGH) inject ed groups were given either rhGH (2.7 mg/kg/day) for the first 20 of 4 0 days, followed by saline injection, or rhGH for all 80 days. Tetracy cline labeling was performed on days 41 and 69. In ail groups given rh GH, an increase in the cortical bone volume was found. In the rhGH 40- day group, single labeling corresponding to injection on day 41 was se en all around the anterior surface of the vertebral body wall (toward the abdominal cavity). In the rhGH 80-day group, double labeling was s een all around the anterior surface of the vertebral body, and a subst antial increase in the mineralizing surface/total surface, mineral app osition rate, and mineralized bone formation rate was found. In the co rtical bone of the anterior wall, cavities had developed in the rhGH 4 0- and 80-day groups. In the cancellous bone, no differences in bone v olume, bone volume/total volume, or bone surface/bone volume were seen , but in the middle part of the vertebral body a decrease in the miner alizing surface/total surface was found in the rhGH 80-day group. The height of the vertebral body was not influenced by rhGH administration , whereas the transversal and midsaggital diameters were increased in the rhGH 80-day group. The compressive mechanical strength of the vert ebral body specimens,vas increased in the rhGH 80-day group, and this increase most likely could be explained by formation and deposition of cortical bone.