Objectives:Previous studies in this lab using the tail-cast hindlimb suspension model have shown that there are specific changes in protein and carbohydrate metabolism in the soleus muscle as a response to unloading. Also, fresh tissue tyrosine and its in vitro release from the muscle are increased in the unloaded soleus, indicating that this condition causes a more negative protein balance. This study was to investigate the effect of microgravity and suspension on protein and carbohydrate metabolism in a number of rat hindlimb muscles.
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Approach:
Amino acids were assayed in muscles from rats exposed to seven days of microgravity and twelve hours of gravity immediately postflight, and rats exposed to six days of suspension with and without twelve hours of loading. Overall changes in body weight, and changes in mass, protein, tyrosine, and glycogen in the hindlimb muscles were compared in SL-3 and ground control rats. Sliced muscles were placed in KOH for glycogen determination or cold perchloric acid for homogenization. Glucose was assayed enzymatically. Homogenates were then separated by centrifuge, protein was assayed spectrophotometrically, and the supernatant was analyzed fluorometrically for tyrosine and other amino acids.
Results:
Flight and ground control rats grew similarly, while unloaded suspension rats grew slower than loaded suspension rats. In flight, unloaded and loaded suspension rats, the soleus atrophied and the gastrocnemius, plantaris and extensor digitorum longus showed reduced growth. The tibialis anterior showed little response. Changes in mass and protein content correlated in these muscles. Muscles from the flight animals showed dramatic increases in glycogen, the soleus being most responsive. Tail-suspension rats without loading showed a greater glycogen concentration in the soleus only, with an even greater value in the loaded, tail-suspension soleus. Only in flight soleus was tyrosine greater than in the control, suggesting a more negative muscle protein balance. In this study, recovery from suspension decreased soleus tyrosine. These results suggest that the additional stress placed on the flight rats postflight by additional transport may have prevented the soleus from showing evidence of recovery from microgravity.
Henriksen EJ, et al. Muscle Protein and Glycogen Responses to Recovery from Hypogravity and Unloading by Tail-Cast Suspension. Abstract S-193. Proceedings of the Seventh Annual Meeting on the IUPS Commission on Gravitational Physiology; 1985 Oct 13-18; Niagara Falls(NY).
Henriksen EJ, Tischler ME, Jacob S, Cook PH, et al. Muscle Protein and Glycogen Responses to Recovery from Hypogravity and Unloading by Tail-Cast Suspension. Abstract 83.6. 36th Annual Fall Meeting of the American Physiological Society; 1985 Oct 13-18; Buffalo (NY) Physiologist 1985; 28(4):376.
Henriksen EJ, Tischler ME, Jacob S, Cook PH. Possible Mechanism for Changes in Glycogen Metabolism in Unloaded Soleus Muscle. Physiologist 1985; 28(6 Suppl): S131-2.
Tischler ME, et al. Muscle Protein and Glycogen Responses to Recovery from Hypogravity and Unloading by Tail-Cast Suspension. Physiologist 1985; 28(6 Suppl):S193-4.
Content, Glycogen, in muscle (soleus, gastroc, edl, tibialis ant, plantaris), rat, KOH, assay
Content, Protein, extensor digitorum longus, muscle, rat, Spectrophotometry
Content, Protein, gastrocnemius, muscle, rat, Spectrophotometry
Content, Protein, plantaris, muscle, rat, Spectrophotometry
Content, Protein, soleus, muscle, rat, Spectrophotometry
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Content, Protein, tibialis anterior, muscle, rat, Spectrophotometry
Content, Tyrosine, in muscle (soleus, gastroc, edl, tibialis ant, plantaris), rat, Fluorometry
Mass, Muscle, extensor digitorum longus, rat, Weighing (cgs)
Mass, Muscle, gastrocnemius, rat, Weighing (cgs)
Mass, Muscle, plantaris, rat, Weighing (cgs)
Mass, Muscle, soleus, rat, Weighing (cgs)
Mass, Muscle, tibialis anterior, rat, Weighing (cgs)