Glucocorticoid treatment or food deprivation counteract the stimulating effect of growth hormone on rat cortical bone strength.

Growth hormone (GH) has been found to increase the length, thickness and bending strength of rat femora. The present study was designed to investigate if glucocorticoid treatment or food restriction would interfere with the effect of exogenous GH on bone growth. Male rats treated with GH for 30 days experienced a weight gain of 30-35% and longitudinal and periosteal femoral growth. A dose-related increase in the bending strength of the femora was found and was explained by an increased thickness of the femora. In spite of a reduced real density, biomechanical competence was preserved after GH treatment. GH treatment combined with a relatively small dose of glucocorticoid, which in itself had no significant effect on bone growth and strength, reduced the stimulating effect of GH on body weight gain, femoral growth and strength. GH-treated rats that were food restricted, so as to limit their body weight gain to that of the saline group, experienced significant longitudinal and periosteal femoral growth. Bone strength, however, was not increased, which conforms to a reduced mineralization and increased porosity of the femora. Young's modulus (normalized bone stiffness) was significantly decreased in this group, probably as a result of decreased mineralization. Furthermore, the combination of GH treatment and food restriction resulted in a reduced apparent density indicating increased bone resorption.