Purpose

Exercise training reduces lipid content and inflammation, regulates browning and thermogenesis, as well as modulates production of adipokines^1-3. Exercise also reduces fat accumulation in the adipose depots and muscle triglycerides⁴ with increased energy expenditure. The goal of this study was to investigate the role of intense exercise on brown adipose tissue activation and assess the heat and respiratory exchange ratio (RER) in chow diet fed rats.

Methods

All in-vivo experiments were in compliance and approved by institutional animal care and use committee. Male Wistar rats (n=12) fed with chow diet (CD) were randomized into two groups including Gp1: sedentary (n= 6), Gp2: exercise (n= 6). Exercise intervention was performed using animal treadmill (Columbus-1012R-1-E58 modular enclosed metabolic treadmill with shock (7670R-E58 Oxymax Economy System). Rats were habituated for exercise using a low intensity exercise protocol (10 to 20 m/min for 10 min per day) for one week. The high-intensity exercise protocol involved treadmill running at the rate of 24m/min for 45 min/day for 2 weeks. After habituation rats were acclimated for 4 days before the energy expenditure (EE) measurements. Volume of O2, CO2, heat production and RER were estimated by Oxymax software for 4 rats in each group. The body weight, fat fraction (FF) from iBAT and EE were measured before and after 2 weeks of exercise intervention. In vivo imaging experiments were performed using a 7 T Bruker (ClinScan) scanner with motion compensation, using a 72mm volume resonator for RF transmission in combination with 20mm receive-only coil for signal reception. Dixon imaging was performed by using the parameters: FOV 55 x55 mm2, matrix size 256×256, in-plane resolution of 0.214μm x 0.214μm, slice thickness of 1mm, TR 8 ms, averages 1, flip angle 8°, echo bandwidths of 1090 Hz/pixel with out-of-phase (1.0ms) and in-phase (2.5ms) echo times. After terminal experiments tissues were fixed in 10 % neutral buffered solution for 24 hours. Hematoxylin and eosin/ UCP-1 antibody staining was performed on 5µm tissue section and stained images were captured at 20× optical magnification by using Aperio ScanScope instrument⁵.

Results and Discussion

Figure 1A shows representative FF images of iBAT obtained from an exercise and sedentary trained animal. Figure 1B shows the FF values at baseline for all the animals, sedentary group and exercise group. FF in exercise group reduced significantly (P <0.01) compared to sedentary group. Figure 2A shows the volume of O2 consumption of control and exercise groups. The VO2 in exercise (4933.19±301.81 ml/kg/hr) group increased significantly (P <0.001) compared to baseline (2038.24±60.81 ml/kg/hr). Figure 2B shows significant increase CO2 (P <0.001) exhalation from exercise group compared to baseline. Figure 2C shows significant increase of RER (P <0.001) in exercise group compared to baseline. Figure 2D shows the heat value which was also significantly (P <0.001) increased in exercise group (4.85±0.29 kcal/hr) compared to the baseline (1.95±0.05 kcal/hr). Metabolic activity of BAT increases with activation by exercise by reduced fat fraction and increased RER. Figures 3A, B show representative H & E stained images from sedentary and exercising animals. The image from exercising animal shows reduction in size and “white” like droplets within iBAT which is in agreement with reduced FF. Figures 4 A, B show the UCP 1 antibody stained images from iBAT obtained from sedentary and exercise groups. The results are in agreement with the H &E images.

Conclusion

Fat content in iBAT reduced significantly reduced with increased energy expenditure in intense exercise group. The H& E images and UCP 1 antibody stained images show reduction in “white” like lipid droplets and size.

Acknowledgements

No acknowledgement found.

References

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