Muscle contraction increases palmitate esterification and oxidation and triacylglycerol oxidation

We examined the oxidation and esterification of palmitate and the hydrolysis and oxidation of intramuscular lipids in isolated soleus muscles at rest and during tetanic contractions (2-40 tetani/min). Muscles were pulsed with [14C]palmitate to prelabel all intramuscular lipid pools. Muscles remained at rest or were then stimulated to contract at 2, 8, 20, or 40 tetani/min (30 min) in the presence of [3H]palmitate. Palmitate oxidation was increased 412% at 2 tetani/min (P < 0.05) and 880% at 8 tetani/min (P < 0.05). During contraction there was an absolute increase in esterification of palmitate to triacylglycerol in proportion with the increasing rate of palmitate oxidation. Intramuscular lipid oxidation provided approximately 77% of the total muscle energy compared with approximately 3% provided by exogenous palmitate under all conditions, with carbohydrate sources (glycogen and glucose) providing approximately 20% of the total energy. Thus, during muscle contraction, the oxidation rates of both exogenous and intramuscular lipids are increased in proportion to each other, while concomitantly palmitate is esterified in proportion to its oxidation.