The role of body fluid shifts on hindlimb bone loss in tail suspended rats using a novel body fluid alteration device

In space, the mechanical loading of the weight-bearing bone decreases and the body fluid shifts cephalad. However, the correlative researches are rarely reported on how the body fluid shift affects the bone, especially how it affects the weight-bearing bone in space or in bed rest on the ground. In our study, a novel model was designed to investigate the effect of body fluid shifts on the bone loss of the hindlimbs in the tail-suspended rats. The model can keep the rat hindlimb unloaded, and change the distribution of the body fluid by altering rats’ body position. The study was conducted for 21 days. Thirty-six female Sprague-Dawley rats were randomly divided into four groups (n = 9, each): control group (CON), head-down tail-suspension group (HDT), head-horizontal tail-suspension group (HHT), head-up tail-suspension group (HUT). The results indicated that body fluid shifting towards the tail end may inhibit the bone loss of the rat hindlimbs, that means the absence of cephalad body fluid shifting resulted in the positive effect on the bone microstructure parameters and the mechanical properties. The results suggested that the backflow of the body fluid in rat hindlimbs was able to alleviate the disuse osteoporosis in a certain extent.