Long-term voluntary exercise, representing habitual exercise, lowers visceral fat and alters plasma amino acid levels in mice

Abstract

Objectives: To determine the impact of long-term voluntary exercise, representing habitual exercise for the prevention of lifestyle-related diseases, on glucose, lipid, and amino acid metabolism in mice.

Methods: Twenty-four mice aged 6 weeks were divided into three groups. Two groups (16 mice) were housed individually in either cages equipped with a running wheel (8 mice, exercising, Ex-mice) or without (8 mice, sedentary, Se-mice) for 24 weeks. The remaining group (8 mice) was sacrificed at 6 weeks of age. Biomarkers related to glucose, lipid, and amino acid metabolism were examined.

Results: Ex-mice ran voluntarily, predominantly in the dark. The distance per day peaked at 4 weeks and then decreased until 12 weeks to around the level seen at the beginning of the experimental period, and was maintained at 4.9 ± 0.2 km/day from 12 to 24 weeks. Ex-mice showed a similar adrenal weight and vitamin C content to Se-mice but had a significantly lower body weight and higher food intake. Ex-mice also showed a higher skeletal muscle weight, a lower white adipose tissue and liver weight, associated with lower plasma leptin and insulin-like growth factor-1 levels, and a lower hepatic triglyceride content. Analysis of plasma amino acids showed that Ex-mice had significantly higher phenylalanine, tyrosine, and glutamine levels, resulting in a significantly lower Fischer's ratio.

Conclusions: We present an animal model of long-term voluntary exercise under low stress. Findings related to the effects of long-term voluntary exercise on lipid, and amino acid metabolism in our mouse model indicate that such an exercise regimen may affect pathophysiological states related to appetite and behavior.

Fig. 1

Apparatus for studying long-term voluntary exercise in mice. Both types of cage were equipped with a running wheel as shown. a Plastic cage composed of a running wheel and living area (standard breeding cage), with the bottom covered with wood chips, b cage made entirely of steel

Fig. 2

Voluntary activity, body weight, and food intake during the experimental period. Voluntary activity is expressed as the weekly running distance of the mice in cages equipped with a running wheel (Ex-mice; n = 8; a). Body weight (b), food intake (c), and ratio of food intake/body weight (d) of Ex-mice (closed circle) and mice whose cages were not equipped with a running wheel (Se-mice; (open circle, n = 8) are presented. Data are expressed as the mean ± standard error (SE). b–d Statistical analysis by two-way analysis of variance (ANOVA; exercise and time) for repeated measurements. Statistical significance ^#p < 0.05 in the indicated area, NS not significant

Fig. 3

Real-time PCR analysis of mRNA level in Ex-mice and Se-mice. a fatty acid synthase (FAS), glucose-6-phosphate dehydrogenase (G6PD), lipoprotein lipase (LPL), hormone-sensitive lipase (HSL), adipocyte triglyceride lipase (ATGL), adipsin, fatty acid-binding protein 4 (FABP4), leptin, adiponectin, and insulin-like growth factor 1 (IGF-1) levels in the white adipose tissue (WAT) of Se-mice (open column) and Ex-mice (closed column) as determined by real-time PCR. b FAS, G6PD, glucose transporter 2 (Glut2), glucokinase (GK), phosphoenol pyruvate carboxykinase (PEPCK), and IGF-1 levels in the livers of Se-mice (open column) and Ex-mice (closed column) as determined by real-time PCR. The mRNA levels relative to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were calculated with the value of Se-mice set at 1.0. There were either seven or eight samples. Results are expressed as the mean + SE. Findings were analyzed by Student’s t test. Statistical significance *p < 0.05 versus Se-mice