Abstract
We investigated whether swimming activity associated with a three-week period of hypoactivity could prevent the deleterious effects of disuse on the tibias of tail-suspended rats. Forty Wistar rats were divided into five groups: (HS) permanently hindlimb suspension rats; (HS + Swim) rats submitted to unloading interrupted by swimming exercise; (HS + WB) hindlimb suspension rats with interruption for regular weight bearing for the same length of time as the HS+Swim rats; (Control) control rats that were allowed regular cage activities; and (Control + Swim) control rats that underwent swimming exercise. At the end of the experiment, bone mineral density, bone strength, and trabecular quantification were analyzed. The hindlimb-suspended rats exhibited bone quality loss (significant decrease in BMD, bone strength, and deterioration of trabecular and cortical bone architecture; decrease in BV/TV, TbN, TbTh, ConnD, CtV, and CtTh; and increase in TbSp) when compared to control rats. In contrast, trained rats showed a significant increase of 43% in bone mass, 29% in bone strength, 58% in trabecular thickness, 85% in bone volume, 27% in trabeculae number, and 30% in cortical volume, when compared to the hindlimb-suspended rats. We conclude that swimming activity not only ameliorates but also fully prevents the deleterious effects on bone quality in osteopenic rats.
Highlights
Rat hindlimb suspension was developed as a model to study the effects of hypogravity, experienced by astronauts during space flight, on several organs and systems [1]
Regardless of the cause, bone decay starts as an osteopenic state that can evolve into a final state of osteoporosis, which is characterized by increased bone mineral loss, very low density, and diminished bone strength, leading to a high fracture risk [5]
After one week of acclimatization, the animals were randomly assigned to one of five groups (n = 8 per group): (1) hindlimb suspension rats (HS): permanently unloaded rats; (2) HS + swimming (HS + Swim): rats submitted to unloading interrupted by swimming exercise periods; (3) HS + weight bearing (HS + WB): rats submitted to hindlimb suspension, with interruptions for regular weight bearing for the same length of time as the HS + Swim rats; (4) control (Control): control rats that were not submitted to unloading and were allowed to continue their regular cage activities; and (5) control-swimming (Control + Swim): control rats that were not submitted to unloading and that underwent swimming exercise periods
Summary
Rat hindlimb suspension was developed as a model to study the effects of hypogravity, experienced by astronauts during space flight, on several organs and systems [1]. The model was adapted to investigate bone deterioration secondary to disuse [2,3,4]. Several studies have shown that hypoactivity and the absence of weight bearing are closely associated with poor bone quality [2, 4, 6,7,8,9]. Exercise, antiresorptive drugs, and other techniques, such as electrical muscle stimulation, have been proposed as therapies to improve or prevent bone deterioration [10,11,12,13,14,15,16,17]. Rubin et al studied the effects of periods of unloading, interrupted either by regular weight bearing or vibration therapy, on the bone quality of rats. The authors found that vibration therapy, but not weight bearing, attenuated bone loss secondary to disuse [14]. Which type or regimen of muscular exercise would contribute more to restoring or preventing poor bone quality remains unclear, based on the divergent reports in the literature [18,19,20]
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