Effects of melatonin on muscle and liver bioenergetic profiles: focus on acylcarnitines following endurance swimming exercise in rats

INTRODUCTION: Melatonin (N-acetyl-5-methoxytryptamine) plays a key role in lipid metabolism regulation, directly influencing fatty acid oxidation and lipid transport and modulating pathways related to energy homeostasis. OBJECTIVE: This study aimed to evaluate its acute effects on tissue bioenergetics during post-exercise recovery. METHODS: ¹) or vehicle immediately after exercise. The animals were euthanized at 1, 3, or 24 h post-exercise. RESULTS: Melatonin did not alter the acylcarnitine pool in the muscle or liver, indicating no synergistic effect on β-oxidation. However, it significantly reduced serum glucose levels (F = 11.01; p < 0.001), increased glycogen levels in the red gastrocnemius (F = 82.81; p < 0.001), gluteus maximus (F = 19.55; p < 0.001), and liver (F = 6.24; p < 0.001), and decreased triglyceride content in several skeletal muscles. The integrated biomarker response (IBR) revealed time-dependent shifts in specific acylcarnitine species, although melatonin did not influence these shifts. CONCLUSION: In conclusion, despite not modulating the acylcarnitine pool, melatonin induced favorable metabolic adaptations by enhancing glycogen replenishment and altering lipid availability in a tissue-specific manner. These findings suggest that melatonin may favor the transport or utilization of larger fatty acid molecules, potentially bypassing the conventional acylcarnitine-mediated oxidation pathways. This highlights its role as a modulator of post-exercise recovery and underscores the need for temporally resolved analyses to unravel its bioenergetic effects.