title: Periodic weight support effects on rat soleus fibers after hindlimb suspension.
abstract: The morphological and histochemical properties of the rat soleus were studied after 1 wk of hindlimb suspension, one model that removes the weight-bearing function of the hindlimbs. To examine the effectiveness of weight support activity in maintaining soleus mass, fiber size, and succinate dehydrogenase (SDH) activity, the hindlimbs of adult male Sprague-Dawley rats were suspended (HS) and half of these rats were walked on a treadmill for 40 min/day (10 min every 6 h) at 5 m/min and a 19 degree grade (HS-WS). Significant reductions in soleus mass and fiber size were found after 1 wk of HS. Weight support activity decreased the atrophic response by approximately 50%. In the alkaline myofibrillar adenosine triphosphatase (ATPase) dark-staining fibers, SDH activity was higher in the HS than control rats, whereas it was similar to control in the HS-WS rats. Total SDH activity (SDH activity X cross-sectional area) in fibers staining lightly for ATPase in HS and HS-WS rats was lower than in control rats, whereas in the darkly stained ATPase fibers it was similar among the three groups. No changes were observed in fiber type percentages after 1 wk of HS or HS-WS. The results suggest that short-duration, daily weight support activity can ameliorate, but not prevent, soleus atrophy induced by HS. Furthermore, fiber cross-sectional area is more responsive to periodic weight support in dark than light ATPase fibers. These results also demonstrate that muscle fiber atrophy need not be associated with a loss in SDH activity.
authors.affiliation: Brain Research Institute, Los Angeles, California.
authors.forename: E O
authors.initials: EO
authors.lastname: Hauschka
authors.forename: R R
authors.initials: RR
authors.lastname: Roy
authors.forename: V R
authors.initials: VR
authors.lastname: Edgerton
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D006112:Gravitation; D008297:Male; D009119:Muscle Contraction; D009133:Muscular Atrophy / Q000201:enzymology / Q000209:etiology / Q000517:prevention & control*; D009218:Myosins / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013385:Succinate Dehydrogenase / Q000378:metabolism; D014893:Weightlessness / Q000009:adverse effects*
chemical_list: D013385:Succinate Dehydrogenase; D009218:Myosins