Growth hormone can reverse glucocorticoid-induced low bone turnover on cortical but not on cancellous bone surfaces in adult Wistar rats

We evaluated the effect of glucocorticoids (GC) and growth hormone (GH) on cortical and cancellous bone turnover in adult rats using random vertical sections giving valid measurements of bone surfaces and bone formation parameters. GH administration could reverse GC-induced osteopenia and low bone turnover of cortical bone. However, GH could not reverse the GC-induced low bone turnover of cancellous bone. Methods: Seventy female Wistar rats, 7 months of age, were divided into five groups: (1) start control, (2) saline, (3) GC 9 mg/kg/day (Solu Medrol), (4) GH 5 mg/kg/day, and (5) GC 9 mg/kg/day + GH 5 mg/kg/day, and injected for 3 months. The vertebral body was examined using dynamic histomorphometry and biomechanical tests. Nonparametric methods were used. Results: Glucocorticoid administration induced a low bone turnover state of both the cortical and cancellous bone of the vertebral body, without altering the absolute amount of bone or the biomechanical competence of the vertebral body. GH administration induced a small increase in longitudinal bone growth and ventral modeling drift. This growth increased the total amount of cortical, endocortical, and cancellous bone in the vertebra. The biomechanical competence of a 3.5-mm-high cylinder of the central vertebral body was also increased due to an increase in the amount of cortical bone, whereas the total amount of cancellous bone in the cylinder was unaltered. The cancellous bone density (CBV) was, however, increased due to thicker trabeculae probably induced by an accelerated mineral appositional rate (MAR) induced by GH. GH also increased longitudinal and ventral modeling drifts in the GC-injected animals. GH increased the amount of cortical bone and also the amount of cancellous bone close to the epiphyseal growth plate, whereas the cancellous bone volume of the central vertebral cylinder was unaffected by GH administration in GC-injected animals. GH could also increase parameters of bone formation (bone mineralizing surface (MS) and MAR) on cortical bone surfaces in GC-injected animals, whereas parameters of bone formation [MS and bone formation rates (BFR)] on cancellous bone surfaces were even lower than those of animals injected with GC alone. Conclusion: GH can reverse GC-induced low bone turnover on cortical but not on cancellous bone surfaces.