Insulin Administration Associated To Strength Training: Effects On Skeletal Muscle Of Rats

Abstract

PURPOSE: The present study aimed to investigate the strength training effects, associated to insulin administration, on skeletal muscle growth of rats. METHODS: Male Wistar rats (90 days of age) were separated into 4 groups (n=10/group): Sedentary Control (SC); Trained Control (TC); Sedentary Insulin Treated (SIT) and Trained Insulin Treated (TIT). Simple commercial insulin, 30mU/100g of body weight (bw), was administered 3 days/week (alternated days), during 12 weeks. The animals belonging to TIT and TC groups performed a strength training program, consisted by jumps in tank with water, carrying overload equivalent to 50% of bw. The training was composed by 4 series of 10 jumps, 1 min of rest between the series, 5 days/week, during 12 weeks. We determined the total protein and DNA contents as well as the protein/DNA ratio and the protein synthesis and degradation rates of the soleus muscle of the animals. At the end of the experiment, we verified the glycaemia of the animals. ANOVA two way, followed by Bonferroni, was used in order to indicate the statistical differences (P<0.05). RESULTS: There was not difference in the glycaemia (mg/dL) when compared all experimental groups (SC= 105.2 ± 13.2; SIT= 103.1 ± 12.4; TC= 104.4 ± 13.8; TIT= 105.8 ± 13.6). Muscle protein synthesis rates (pmol/mg.h) were higher in the TIT group (71.3 ± 3.6) if compared to the other groups (SC= 44.3 ± 2.1; SIT= 45.2 ± 1.6; TC= 62.3 ± 2.5). TC also showed significantly higher values if compared to SC and SIT groups. No differences were found between the groups when analyzed the protein degradation rates (pmol/mg.h) (SC= 271.4 ± 25.2; SIT= 268.9 ± 23.1; TC= 270.3 ± 20.9; TIT= 269.8 ± 22.4). In addition, an improvement in muscle growth was observed in the TI group in relation to the other groups, as indicated by the total protein (g/100g) and DNA (g/100g) contents and protein/DNA ratio values (Total protein: SC= 3.3 ± 0.2; SIT= 3.4 ± 0.5; TC= 4.7 ± 0.3; TIT= 5.9 ± 0.3 - DNA: SC= 0.148 ± 0.03; SIT= 0.147 ± 0.04; TC= 0.153 ± 0.02; TIT= 0.169 ± 0.05 - Protein/DNA: SC= 22.3 ± 0.1; SIT= 23.1 ± 0.3; TC= 30.7 ± 0.2; TIT= 35.0 ± 0.4). CONCLUSION: Taken together, these results suggest that the efficiency of the strength training protocol in promoting muscle growth was improved by insulin treatment in the conditions of the present study. Supported by CAPES, Fapesp and CNPq (Brazilian Foundations).