Changes in lipid metabolism and capillary density of the skeletal muscle following low-intensity exercise training in a rat model of obesity with hyperinsulinemia.

Naoto Fujita,Kohei Karasaki,Saki Aono,Hidemi Fujino,Tomoyuki Kurose,Fumi Sera,Susumu Urakawa,Michael Bader

doi:10.1371/journal.pone.0196895

Naoto Fujita, Kohei Karasaki + Show 6 more

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https://doi.org/10.1371/journal.pone.0196895

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Journal: PloS one	Publication Date: May 2, 2018
Citations: 8	License type: CC BY 4.0

Affiliation: Hiroshima University, Kobe University

Abstract

Although exercise is effective in improving obesity and hyperinsulinemia, the exact influence of exercise on the capillary density of skeletal muscles remains unknown. The aim of this study was to investigate the effects of low-intensity exercise training on metabolism in obesity with hyperinsulinemia, focusing specifically on the capillary density within the skeletal muscle. Otsuka Long-Evans Tokushima fatty (OLETF) rats were used as animal models of obesity with hyperinsulinemia, whereas Long-Evans Tokushima Otsuka (LETO) rats served as controls (no obesity, no hyperinsulinemia). The animals were randomly assigned to either non-exercise or exercise groups (treadmill running for 60 min/day, for 4 weeks). The exercise groups were further divided into subgroups according to training mode: single bout (60 min, daily) vs. multiple bout (three bouts of 20 min, daily). Fasting insulin levels were significantly higher in OLETF than in LETO rats. Among OLETF rats, there were no significant differences in fasting glucose levels between the exercise and the non-exercise groups, but the fasting insulin levels were significantly lower in the exercise group. Body weight and triacylglycerol levels in the liver were significantly higher in OLETF than in LETO rats; however, among OLETF rats, these levels were significantly lower in the exercise than in the non-exercise group. The capillary-to-fiber ratio of the soleus muscle was significantly higher in OLETF than in LETO rats; however, among OLETF rats, the ratio was lower in the exercise group than in the non-exercise group. No significant differences in any of the studied parameters were noted between the single-bout and multiple-bout exercise training modes among either OLETF or LETO rats. These results suggest that low-intensity exercise training improves insulin sensitivity and fatty liver. Additionally, the fact that attenuation of excessive capillarization in the skeletal muscle of OLETF rats was accompanied by improvement in increased body weight.

Highlights

Exercise improves lipid and glucose metabolism in patients with obesity and type 2 diabetes [1]
The fasting glucose levels did not differ between the Otsuka Long-Evans Tokushima fatty (OLETF) Cont and OLETF Ex groups, fasting hyperinsulinemia was milder in the OLETF Ex group
These results indicate that glucose levels were kept in the OLETF Ex group even though insulin secretions were low

Summary

Introduction

Exercise improves lipid and glucose metabolism in patients with obesity and type 2 diabetes [1]. Exercise involves vasodilation and subsequent increase in blood flow to the skeletal muscle [3], which augments the capillary surface area, thereby increasing the accessibility of energy substrates (fatty acids and glucose) to the muscle fibers, with the final outcome of increased fatty acid and glucose uptake. Vasodilation and increased blood flow to the skeletal muscle are induced by insulin signaling, independent of exercise. Insulin suppresses hepatic gluconeogenesis and promotes glucose uptake to adipose cells and skeletal muscle fibers, which reduces blood glucose levels; insulin promotes the phosphorylation of endothelial nitric oxide synthase (eNOS), resulting in vasodilation [4]. The augmented capillary surface area increases insulin delivery to muscle fibers, promoting glucose uptake

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