[Dynamics of immobilization-induced osteoporosis in rats]

Wistar male rats weighing 250-270 g were exposed to hypokinesia for 7, 15, 35 or 60 days. Spongy bone of the metaphysis of long bones, vertebral body, breast bone and iliac bone were examined histomorphometrically. It was found that during hypokinesia osteoporosis developed in two stages: Stage 1 (from hypokinesia day 1 to day 15) was characterized by a drastic bone mass loss due to stress-effects (steroid osteopenia) and Stage 2 (from hypokinesia day 15 to the end) was characterized by adaptive changes which included steady-state development and transition to a lower functional level (immobilization osteoporosis).