Effect of Oral Lactate Administration on Skeletal Muscle Mass in Mice Under Different Loading Conditions.

Area of Science:

• Muscle physiology and metabolism
• Skeletal muscle adaptation
• Exercise biochemistry

Background:

• Lactate, produced by skeletal muscle, is implicated in muscle mass gain.
• The precise molecular mechanisms driving lactate-induced muscle hypertrophy are not fully understood.
• Investigating lactate's role in muscle growth under various mechanical loads is crucial.

Purpose of the Study:

• To determine if oral lactate administration enhances muscle mass.
• To examine lactate's effects under normal weight-bearing, unloading, and reloading conditions.
• To elucidate the molecular signaling pathways involved in lactate's anabolic effects.

Main Methods:

• Male C57BL/6J mice were assigned to control, lactate, unloading, unloading with lactate, reloading, and reloading with lactate groups.
• Hindlimb suspension (HS) was used to induce unloading for two weeks, followed by a two-week ambulation recovery period.
• Mice received oral sodium lactate five times weekly; muscle mass and intracellular signals were analyzed.

Main Results:

• Lactate supplementation increased muscle mass and reduced AMPK phosphorylation in both plantaris and soleus muscles under normal and unloading conditions.
• During reloading after unloading, lactate increased muscle mass and suppressed AMPK phosphorylation in the fast plantaris muscle.
• The effect of lactate on muscle mass and AMPK phosphorylation was less pronounced in the slow soleus muscle during reloading.

Conclusions:

• Oral lactate administration effectively counteracts skeletal muscle atrophy induced by unloading.
• Lactate demonstrates anabolic effects on skeletal muscle mass, potentially serving as a therapeutic intervention.
• The muscle-type specific responses suggest differential regulation of lactate's anabolic actions.