Submitted on September 21, 2007
Accepted on April 15, 2008
Jump exercise during remobilization restores integrity of the trabecular architecture after tail-suspension in young rats
Yong-In Ju1, Teruki Sone2*, Takeshi Okamoto3, and Masao Fukunaga4
1 Kawasaki University of Medical Welfare, Health and Sports Sciences, Kurashiki, Okayama, Japan
2 Nuclear Medicine, Kawasaki Medical School, Kurashiki, Japan; , Japan
3 Graduate School of Sport Sciences, Waseda University, Tokorozawa, Japan
4 Nuclear Medicine, Kawasaki Medical School, Kurashiki, Japan
* To whom correspondence should be addressed. E-mail: tsone{at}med.kawasaki-m.ac.jp.
Three-dimensional trabecular architecture was investigated in the femora of tail-suspended young growing rats and the effects of jump exercise during remobilization were examined. Five-week-old male Wistar rats (n=35) were randomly assigned to 5 body weight-matched groups: tail-suspended group (SUS, n=7); sedentary control group for SUS (SCON, n=7); spontaneous recovery group after tail suspension (S+RCON, n=7); jump exercise group after tail suspension (S+RJUM, n=7); and age-matched control group for S+RCON and S+RJUM without tail suspension and exercise (SCON+RCON, n=7). Rats in SUS and SCON were killed immediately after tail suspension for 14 days. The jump exercise protocol consisted of 10 jumps/day, 5 days/week and jump height was 40 cm. Bone mineral density (BMD) of the femur and three-dimensional trabecular bone architecture at the distal femoral metaphysis were measured. Tail suspension induced a 13.6% decrease in total femoral BMD (p<0.001) and marked deterioration of trabecular architecture. After 5 weeks of free remobilization, femoral BMD, calf muscle weight, and body weight returned to age-matched control levels, but trabeculae remained thinner and less connected. On the other hand, S+RJUM rats showed significant increases in trabecular thickness, number and connectivity compared to S+RCON rats (62.8%, 31.6% and 24.7%, respectively; p<0.05), and these parameters of trabecular architecture returned to the levels of SCON+RCON. These results indicate that suspension-induced trabecular deterioration persists after remobilization, but jump exercise during remobilization can restore the integrity of trabecular architecture and bone mass in the femur in young growing rats.
