Exercise does not improve insulin resistance and mitochondrial characteristics together

Area of Science:

• Metabolic research
• Exercise physiology
• Mitochondrial biology

Background:

• High-fat diets (HFD) induce whole-body insulin resistance.
• Mitochondrial dysfunction is often implicated in insulin resistance.
• The direct relationship between mitochondrial function and insulin sensitivity requires further investigation.

Purpose of the Study:

• To investigate the relationship between mitochondrial content, respiratory function, and whole-body insulin resistance in rats fed a high-fat diet.
• To determine the impact of exercise training on these parameters.

Main Methods:

• Male Wistar rats were fed either a chow diet or an HFD for 12 weeks.
• Interval training was introduced for 8 weeks in half of the rats from each dietary group.
• In vivo glucose and insulin tolerance, mitochondrial respiratory function, and mitochondrial content (citrate synthase activity and electron transport system protein expression) were assessed.

Main Results:

• HFD rats exhibited impaired glucose and insulin tolerance, yet paradoxically showed increased mitochondrial respiratory function and electron transport system component expression.
• Exercise training improved glucose and insulin tolerance in HFD rats.
• Exercise training increased mitochondrial respiratory function in chow-fed rats' soleus muscle, but this effect was not observed in HFD rats.

Conclusions:

• Exercise training ameliorates high-fat diet-induced insulin resistance in rats.
• Improvements in insulin sensitivity following exercise training in this model are not mediated by changes in mitochondrial respiratory function or content.
• The study suggests a dissociation between mitochondrial adaptations and improvements in whole-body insulin resistance in response to exercise in HFD rats.