Systemic Over-Secretion of Growth Hormone in Transgenic Mice Results in a Specific Pattern of Skeletal Modeling and Adaptation*

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Abstract

ABSTRACT

The effects of growth hormone (GH) over-secretion on bone modeling and remodeling in transgenic mice were investigated using systematic and hierarchical methods. The results showed that continual systemic stimulation of GH over-secretion in mice resulted in an initial increase in bone mass, but its bone quality was not comparable with that of the littermate controls. Further continual over-stimulation of GH resulted in an increase in bone resorption leading to thinner cortices with inferior tissue mechanical properties. Three biological mechanisms following GH over-production are formulated to explain the observed results: GH over-secretion stimulated the production of inferior bone matrices, i.e., woven bone and cartilage, in addition to the production of normal lamellar bone; the increased bone formation stimulated by GH was followed by an exaggerated bone resorption process, resulting in cortical tissue with inferior mechanical properties; and a cortical shift occurred following GH over-stimulation that appeared to be caused by the combined effects of GH over-secretion and a variation in mechanical stimuli in the metallothionein-1 growth hormone regulating hormone transgenic mice. An "Optimal Strain Environment" model is proposed to help explain the observed results. From the results of the present and previous studies, we believe that the primary goal of bone adaptation to a biological perturbation, at least in mice, is to ensure proper mechanical function by maintaining structural integrity. In the process of maintaining a targeted whole bone structural integrity, the mechanical integrity of tissue may be sacrificed.

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