EFFECTS OF GRAVITATIONAL UNLOADING AND RELOADING ON THE PROPERTY OF ADDUCTOR LONGUS IN WISTAR HANNOVER RATS

Abstract

Responses of adductor longus muscle to hindlimb unloading followed by reloading were studied in 5-wk-old male Wistar Hannover rats. Hindlimb suspension was performed for 16 days. Half of the suspened group was sacrificed at the end of suspension and adductor longus was sampled. The remaining half was allowed to recover at 1-G environment for 16 days. Serial transverse cross sections (10-μm thick) were cut in a cryostat at -20 °C for immunohistochenical analyses. The% of each fiber phenotype and specific activities of succinate dehydrogenase and α-glycerophosphate dehydrogenase, as well as the fiber cross-sectional area were analyzed. Significant shift of fibers toward fast-twitch type and atrophy were noted in the suspended groups. The% of pure type I fibers was decreased and type I+II fibers was increased. After 16 days, the atrophy, not the phenotype, of fibers was recovered to the control revel. The responses of enzyme activities to unloading were not prominent. It is suggested that adductor longus of Wistar Hannover rat is very susceptible for gravitational unloading relative to other species, although the precise mechanism is still unclear. [J Physiol Sci. 2007;57 Suppl:S94]