Abstract
Hind leg muscles of female rats (85-99 g) were unloaded by tail cast suspension for 6 days. In the fresh-frozen unloaded soleus, the significantly greater concentration of glycogen correlated with a lower activity ratio of glycogen phosphorylase (p less than 0.02). The activity ratio of glycogen synthase also was lower (p less than 0.001), possibly due to the higher concentration of glycogen. In isolated unloaded soleus, insulin (0.1 milliunit/ml) increased the oxidation of D-[U-14C]glucose, release of lactate and pyruvate, incorporation of D-[U-14C]glucose into glycogen, and the concentration of glucose 6-phosphate more (p less than 0.05) than in the weight-bearing soleus. At physiological doses of insulin, the percent of maximal uptake of 2-deoxy-D-[1,2-3H]glucose/muscle also was greater in the unloaded soleus. Unloading of the soleus increased by 50% the concentration of insulin receptors, due to no decrease in total receptor number during muscle atrophy. This increase may account for the greater response of glucose metabolism to insulin in this muscle. The extensor digitorum longus, which generally shows little response to unloading, displayed no differential response of glucose metabolism to insulin.
Highlights
Hind leg muscles of female rats (85-99 g) were unloaded by tail cast suspension for 6 days
This higher level of glucose-6-P in the unloaded soleus in before, there was no differential effect of insulin on glucose the presence of insulin was accompanied by a greater release metabolism intheextensor digitorumlongus (datanot of lactateandpyruvate (+51%) andoxidation of glucose shown)
Since the same patternof increased responsiveness to insulin in the unloaded soleus was observed using these muscles as well,differences in degradation of glycogen stores could not be responsible for the faster metabolism of glucose seen in this muscle
Summary
Treatment of Animals-Female rats (85-99 g, Harlan SpragueDawley) maintained on food and water ad libitum were anesthetized with either Innovar-Vet (10 pl/lOO g of body weight) or ether and subjected to tail-cast suspension for 6 days [11]. After 30 min, the muscles were transferred to fresh buffer containing various concentrations of insulin, as indicated, and incubated an additional 2 h. Carbohydrate Metabolism-Oxidation of glucose, synthesis of glycogen, and release of lactate and pyruvate were measured simultaneously in muscles incubated with 5 mM D-[U-‘*C]ghCOSe Glucose Uptake-Muscles were preincubated for 60 min in 1 mM glucose and 1% bovine serum albumin and incubated for 15 min with 1 mM 2-deoxy-n-1 1,2-3H]glucose (300 &i/mmol) substituted for glucose in the absence or presence of insulin. Soleus muscles were preincubated at 22 “C for 60 min in Krebs-Ringer bicarbonate buffer supplemented with 5 mM glucose, 0.2% (w/v) bovine serum albumin, and 2 mg/ml bacitracin to inhibit degradation of insulin. Muscles were incubated for 4 h at 22 “C in fresh buffer containing 2 mM pyruvate, 0.2% bovine serum albumin, 2 mg/.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
