Changes in functional construction of bone in rats under conditions of simulated increased gravity.

Abstract

Alterations in cross-sectional area and shape of the femur of female Sprague-Dawley rats exposed continuously for 810 days to either 2.76 or 4.15 G by centrifugation were studied. Compared with control animals, chronically centrifuged rats showed on the average a smaller body-weight (19.3 and 29.1%), a smaller length of the femur (6.6 and 9.0%), and a smaller cross-sectional area at the midshaft position of the femur (15.1 and 19.1%). It was shown by analysis of covariance that chronic centrifugation at 2.76 and 4.15 G inhibits the longitudinal growth of the femur by the same amount as the overall growth in linear dimensions of the rat. The cross-sectional area of the femur at the midshaft position was the same at earth gravity and at hypergravity, if the comparison was made between animals of the same age and the same overall body-size. However, the shape of the femoral cross-section was altered by centrifugation; the sagittal diameter was increased whereas the frontal diameter was decreased. It was shown that the experiments conducted to date have not given clear evidence of a direct relationship between cross-sectional area of the femur and the G load imposed on animals subjected to chronic centrifugation. The alterations in cross-sectional shape of the bones in the centrifuged animals are likely due to an immobilization effect caused by centrifugation.