Effects of centrifuging at 2g on rat long bone metaphyses

Hypergravity may be considered as a means of counteracting the deleterious effects of microgravity on bone tissue. The effects of exposure to 4 days o f hypergravity provided by centrifuging, on bone tissue were studied using histomorphometry. Young 53-day-old male Sprague Dawley rats were randomly d ivided into a centrifuged group (2g, n = 10), a rotated group (ROTATE, n = 6) of rats exposed to 1.03g placed in cages near the centre of rotation of the centrifuge and a stationary control group (CONTROL, n = 10). The body m ass of the 2g rats was decreased by this experience by 16% compared to CONT ROL. The width of the tibial growth plate of 2g was decreased. In two out o f ten 2g rats, the hypertrophic zone was injured. In both the tibial and hu meral primary (1 degrees) spongiosae, a reduced 1 degrees spongiosa width ( -35% and -24%, ROTATE versus CONTROL respectively; -37% and -41%, 2g versus CONTROL respectively) associated with bone gain (+27% for tibia and humeru s ROTATE versus CONTROL; +16% and +20%, 2g versus CONTROL respectively) was observed in both ROTATE and 2g. In the tibial secondary (2 degrees) spongi osa, bone mass was increased in the 2g (+13% 2g versus CONTROL) rats due to thicker trabeculae, but was decreased in ROTATE rats (-12% versus CONTROL) due to thinner trabeculae. The parameters of formation and resorption acti vities were stimulated in the 2g and ROTATE groups, the formation activity being more enhanced in 2g. No structural changes were observed in the humer al 2 degrees spongiosa in any of the groups. Numeral bone formation paramet ers were decreased in 2g and ROTATE but resorption activity was increased i n 2g and decreased in ROTATE compared to CONTROL. In conclusion, as early a s the 4th day, 2g hypergravity induced reduced endochondral bone formation and increased cancellous bone mass. Rotation led to mixed results including reduced endochondral bone formation, increased bone volume in the 1 degree s spongiosa and bone loss in the 2 degrees spongiosa.