Journal of Applied Physiology, Vol 79, Issue 6 1889-1894, Copyright © 1995 by American Physiological Society
Electrical stimulation of leg muscles increases tibial trabecular bone formation in unloaded rats
E. Zerath, F. Canon, C. Y. Guezennec, X. Holy, S. Renault and C. Andre
Departement de Physiologie Analytique, Centre d'Etudes et de Recherches en Medecine Aerospatiale, Bretigny-sur-Orge, France.
Rat head-down hindlimb suspension (HS) has been shown to induce hindlimb
cancellous bone loss. As HS is known to associate unloading with
progressive disappearance of hindlimb muscle contractions, we investigated
whether persisting muscle motion could modify suspension-induced bone
disorders or even prevent them. Chronic electrical stimulation (ES) was
applied to leg muscles of rats during 3-wk hindlimb suspension, the lack of
support for hindlimbs maintaining a hypodynamic situation. The
histomorphometric characteristics of the proximal tibial metaphysis were
analyzed. At the end of this protocol of combined suspension and
stimulation, trabecular bone loss remained similar to that of nonstimulated
HS animals. However, trabecular bone cell activity parameters showed
greater bone formation after muscle stimulation in unloaded animals, with
significantly increased osteoblastic, osteoid, and mineralizing surfaces.
In addition, periosteal mineral apposition rate and cancellous bone
formation rate, markedly decreased by suspension, were not significantly
different in suspended stimulated compared with normal loaded animals. This
enhanced formation activity could be related to persistence of muscle
activity, as shown by partial preservation of muscle mass. However, direct
electrical effects on bone cannot be excluded. Thus, despite muscle
stimulation, with enhanced bone formation, isolated suppression of
hypokinesia has not been able to counteract bone effects of unloading. This
finding supports the hypothesis of the importance of mechanical loading to
maintain bone architecture.
