ADMINISTRATION OF A GLUCOCORTICOID WITH DEPOT EFFECT COUNTERACTS THE STIMULATING EFFECT OF GROWTH-HORMONE ON CANCELLOUS AND CORTICAL BONE OF THE VERTEBRAL BODY IN RATS

Our earlier studies have shown that growth hormone administration coul d not counteract decreased longitudinal growth and cortical osteopenia of rat femora induced by a glucocorticoid with depot effect. In the p resent study we examined the effects of glucocorticoid on vertebral bo ne as well as the effect of growth hormone on vertebral bone in young growing animals also given glucocorticoid injections. Five groups of f emale rats (3 1/2 months) were treated for 80 days as follows: (1) sal ine, (2) prednisolone: Delcortol 5 mg/kg/day, (3) growth hormone: 5 mg /kg/day, (4) prednisolone and growth hormone, (5) food restriction. Ve rtebral dimensions, histomorphometry, and mechanical competence of the vertebral bone were examined. Growth hormone administration increased body weight, vertebral height, cross-sectional area, and volume. The compressive strength of the L-4-corpus cylinder was also increased due to an increase in cancellous bone volume and an increase in the area of cortical bone surrounding the vertebral body. Glucocorticoid admini stration decreased body weight, height. and volume of the intact verte brae. Histological examination revealed that glucocorticoid administra tion de creased the area of cortical bone surrounding the vertebral bo dy but had no effect on the cancellous bone volume. No effect of gluco corticoid administration on mechanical strength of the L-4-corpus cyli nder could be detected. In agreement with our findings in cortical bon e, we found no effect of growth hormone on vertebral bone when given t o animals also receiving glucocorticoid injections. Growth hormone inc reases longitudinal growth, cortical and cancellous bone mass, and mec hanical competence of the vertebral body. Glucocorticoid administratio n decreases longitudinal growth of the vertebrae and cortical bone mas s without affecting cancellous bone mass of the vertebral body. Despit e this, administration of a glucocorticoid with depot effect totally i nhibits the effect of growth hormone on vertebral bone.