Skeletal challenge: an experimental study of pharmacologically induced changes in bone density in the distal radius, using gamma-ray computed tomography.

Bone density (BD) at the distal end of the radius was measured serially with gamma-ray computed tomography (gamma-CT) in five groups of healthy postmenopausal women. One group comprised untreated controls; women in the other groups were subjected to pharmacologic challenge with putative activators and/or depressors of bone remodeling. The challenge agents, taken orally, were ergocalciferol (vitamin D2) alone and followed by calcium; calcitriol (1,25(OH)2D3), and prednisone. All of the subjects showed changes in BD following challenge; these changes were significant (P less than 0.05) for the groups receiving vitamin D2 and vitamin D2 plus calcium. Responses to ergocalciferol, calcitriol, and prednisone were similar within groups, whereas the group receiving ergocalciferol then calcium comprised two distinct subgroups: bone density transiently increased in one and decreased in the other. For all five groups, the direction of change in bone density in response to the challenge, and its duration and magnitude, were consistent with reported histomorphometric data. We conclude that gamma-CT assessment of change in bone density after pharmacologic challenge provides a useful noninvasive approach to skeletal investigation.