Chronic exercise increases insulin binding in muscles but not liver

Area of Science:

• Exercise Physiology
• Metabolic Regulation
• Endocrinology

Background:

• Improved glucose tolerance with chronic exercise is linked to enhanced insulin binding in skeletal muscle.
• Understanding exercise's impact on insulin sensitivity is crucial for metabolic health.

Purpose of the Study:

• To investigate the effects of a 6-week progressive training program on insulin binding in five hindlimb skeletal muscles and the liver.
• To determine if training-induced changes in insulin binding correlate with glucose transport in different muscle types.

Main Methods:

• Rats underwent a 6-week progressive exercise training program.
• Insulin binding assays were performed on plasma membranes from soleus, plantaris, extensor digitorum longus, red gastrocnemius, white gastrocnemius, and liver tissues.
• Serum insulin levels were measured in fed, fasted, and post-glucose tolerance test states.

Main Results:

• Trained rats exhibited lower resting serum insulin levels and reduced insulin levels after an oral glucose tolerance test.
• Insulin binding to plasma membranes significantly increased in soleus, plantaris, and extensor digitorum longus muscles post-training.
• No significant increase in insulin binding was observed in white gastrocnemius, red gastrocnemius, or liver tissues.
• Significant differences in insulin binding were found among the different skeletal muscles.
• Insulin binding data did not strongly correlate with previously published glucose transport data for these muscles.

Conclusions:

• Skeletal muscle insulin binding is heterogeneous and varies between muscle types.
• Progressive exercise training can enhance insulin binding in specific skeletal muscles, but not in the liver.
• The mechanisms underlying exercise-induced improvements in glucose tolerance may involve more than just changes in insulin binding.