IL-6 increases muscle insulin sensitivity only at superphysiological levels.

Area of Science:

• Exercise Physiology
• Molecular Biology
• Endocrinology

Background:

• Exercise enhances muscle glucose transport and insulin sensitivity.
• Interleukin-6 (IL-6) levels rise with exercise and activate AMP-activated protein kinase (AMPK).
• IL-6's role in exercise-induced metabolic adaptations is unclear.

Purpose of the Study:

• To investigate if IL-6 increases muscle insulin sensitivity.
• To determine if IL-6 activates AMPK in muscle tissue.
• To differentiate between physiological and pharmacological effects of IL-6 on muscle metabolism.

Main Methods:

• Rat epitrochlearis and soleus muscles were incubated with IL-6 (120 ng/ml and 10 ng/ml).
• Glucose transport and insulin sensitivity were measured.
• AMPK phosphorylation was assessed to determine pathway activation.

Main Results:

• A high concentration of IL-6 (120 ng/ml) acutely increased glucose transport and later enhanced insulin sensitivity in fast-twitch epitrochlearis muscle.
• IL-6 also increased AMPK phosphorylation in epitrochlearis muscle.
• A lower, more physiological concentration of IL-6 (10 ng/ml) had no effect on muscle glucose transport or insulin sensitivity.

Conclusions:

• IL-6 increases insulin sensitivity in fast-twitch muscle via AMPK activation, but these effects appear pharmacological at high concentrations.
• The study suggests IL-6 does not mediate exercise-induced increases in muscle glucose uptake or insulin sensitivity.
• Exercise-induced IL-6 elevation may not play a significant role in muscle metabolic adaptations to exercise.