Additive effect of voluntary exercise and growth hormone treatment on bonestrength assessed at four different skeletal sites in an aged rat model

The aim of the study was to assess the effect of growth hormone (GH), volun tary exercise (Ex), and the combination of GH and Ex on bone strength, mass , and dimensions in aged, intact female rats. In addition, the effect of fo od restriction (FR) was studied. Fourteen-month-old virgin F-344 rats were divided into 6 groups with 13 animals in each: (1) baseline (BSL); (2) cont rol + solvent vehicle (CTRL); (3) GH 2.5 mg/kg/day (GH); (4) exercise, volu ntary: 0.6-0.7 km/day (Ex); (5) GH treatment and voluntary exercise (GH + E x); and (6) FR, Group 1 was killed at the beginning of the study and served as baseline. All the other groups were killed after 18 weeks' treatment. T he effects of aging and treatment regimes were measured at four different s keletal sites: lumbar vertebrae, femoral cortical bone, femoral neck, and t he distal femoral metaphysis, Aging in itself induced a decline in vertebra l body strength and ash density. At the appendicular skeletal sites, bone m ass and strength were unchanged or increased. Treatment with GH alone induc ed a significant increase in the biomechanical parameters at the vertebral body and the femoral diaphysis, but not at the femoral neck or the distal f emoral metaphysis, Voluntary exercise on its own increased load values sign ificantly over CTRL at the vertebral body site, but not at any of the appen dicular skeletal sites, The combination of GH and voluntary exercise result ed in an additive effect at the vertebral site and at the femoral diaphysis , and a synergistic (potentiating) effect at the two femoral metaphyses, FR , on the other hand, had a negative effect on cortical bone area and streng th at the femoral diaphysis, but no significant effect on the other sites t ested. We conclude that GH treatment and voluntary exercise both have skele tal anabolic effects; however, these effects are exerted to differing degre es at different sites. Importantly, when dosed together, GH and Ex have eit her an additive or synergistic anabolic effect on all sites (axial and appe ndicular), (Bone 24:71-80; 1999) (C) 1999 by Elsevier Science Inc. All righ ts reserved.