| Summary: | We investigated the effect of royal jelly (RJ), a natural secretion from worker bees, on the endurance training-induced mitochondrial adaptations in skeletal muscles of ICR mice. Mice received either RJ (1.0 mg/g body weight) or distilled water for three weeks. The mice in the training group were subjected to endurance training (20 m/min; 60 min; 5 times/week). There was a main effect of endurance training on the maximal activities of the mitochondrial enzymes, citrate synthase (CS), and β-hydroxyacyl coenzyme Adehydrogenase (β-HAD), in the <i>plantaris</i> and <i>tibialis anterior</i> (<i>TA</i>) muscles, while no effect of RJ treatment was observed. In the <i>soleus</i> muscle, CS and β-HAD maximal activities were significantly increased by endurance training in the RJ-treated group, while there was no effect of training in the control group. Furthermore, we investigated the effects of acute RJ treatment on the signaling cascade involved in mitochondrial biogenesis. In the <i>soleus</i>, phosphorylation of 5′-AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase (ACC) were additively increased by a single RJ treatment and endurance exercise, while only an exercise effect was found in the <i>plantaris</i> and <i>TA</i> muscles. These results indicate that the RJ treatment induced mitochondrial adaptation with endurance training by AMPK activation in the soleus muscles of ICR mice.
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