The influence of growth hormone on cancellous and cortical bone of the vertebral body in aged rats.

Abstract

The influence of growth hormone administration on cancellous and cortical bone of the vertebral body in 2-year-old male rats has been investigated. All rats were injected for 80 days, then killed. Controls were given saline, and three recombinant human growth hormone (rhGH) injected groups were given either rhGH (2.7 mg/kg/day) for the first 20 or 40 days, followed by saline injection, or rhGH for all 80 days. Tetracycline labeling was performed on days 41 and 69. In all groups given rhGH, an increase in the cortical bone volume was found. In the rhGH 40-day group, single labeling corresponding to injection on day 41 was seen all around the anterior surface of the vertebral body wall (toward the abdominal cavity). In the rhGH 80-day group, double labeling was seen all around the anterior surface of the vertebral body, and a substantial increase in the mineralizing surface/total surface, mineral apposition rate, and mineralized bone formation rate was found. In the cortical bone of the anterior wall, cavities had developed in the rhGH 40- and 80-day groups. In the cancellous bone, no differences in bone volume, bone volume/total volume, or bone surface/bone volume were seen, but in the middle part of the vertebral body a decrease in the mineralizing 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 vertebral body specimens was increased in the rhGH 80-day group, and this increase most likely could be explained by formation and deposition of cortical bone.