Influence of single hindlimb support during simulated weightlessness in the rat.
Mature male rats (n = 16) were assigned to either 14 days of head-down suspension with one hindlimb supported (HDS) or to control cages (C) of similar dimensions. Hindlimb support during HDS preserved the muscle mass-to-body mass ratio (mg/100g) compared with C conditions for the soleus (48.3 +/- 1.0 to 41.7 +/- 1.0), plantaris (98.4 +/- 3.4 to 103.3 +/- 4.1), and gastrocnemius (484.7 +/- 18.5 to 507.2 +/- 13.9). However, the muscle mass-to-body mass ratio was significantly lower for the soleus (28.9 +/- 1.5), plantaris (83.9 +/- 3.6), and gastrocnemius (411.9 +/- 24.2) muscles from the freely hanging hindlimbs compared with the contralateral muscles from the supported hindlimbs or muscles from C animals. Citrate synthase activity (mumol.g-1.min-1) was significantly lower in soleus muscles from HDS rats in both the supported (19.4 +/- 2.3) and freely hanging (20.0 +/- 1.6) hindlimbs compared with C (28.5 +/- 3.1), whereas soleus muscle glycogen concentration (mg/g) was significantly higher in the freely hanging limbs from HDS rats (5.90 +/- 0.31) but not in the supported limbs (3.80 +/- 0.61) compared with C (4.34 +/- 0.50). Doppler flow probes were used to determine that iliac blood flow to freely hanging hindlimbs was significantly decreased after 48 (-19 +/- 5%) and 72 (-20 +/- 6%)h of HDS compared with presuspension values. In addition, iliac vascular resistance was significantly elevated at most time points during the 72 h of HDS in the freely hanging limbs but not the supported hindlimbs.(ABSTRACT TRUNCATED AT 250 WORDS)
Stump
C S
CS
Department of Exercise and Sport Sciences, School of Health Related Professions, University of Arizona, Tucson 85721.
Overton
J M
JM
Tipton
C M
CM
D000818:Animals; D002950:Citrate (si)-Synthase / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism; D006614:Hindlimb / Q000033:anatomy & histology / Q000098:blood supply / Q000201:enzymology / Q000378:metabolism / Q000502:physiology; D008297:Male; D009132:Muscles / Q000033:anatomy & histology / Q000098:blood supply / Q000201:enzymology / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D014893:Weightlessness
D006003:Glycogen; D002950:Citrate (si)-Synthase