The effects of melatonin daily supplementation to aged rats on the ability to withstand cold, thermoregulation and body weight.

Investigate the role of melatonin on the regulation of body temperature in aged animals that have impaired melatonin production. Aged Male Wistar rats were randomly assigned to the following groups: 1) control (vehicle added to the water bottles during the dark phase) and 2) melatonin-treated (10 mg/kg melatonin added to the water bottles during the dark phase). Before and after 16 weeks of vehicle or melatonin treatment, control group and melatonin-treated animals were acutely exposed to 18 °C for 2 h for an acute cold challenge and thermal images were obtained using an infrared camera. After 16 weeks, animals were euthanized and brown and beige adipocytes were collected for analysis of genes involved in the thermogenesis process by real-time PCR, and the uncoupling protein expression was evaluated by immunoblotting. Browning intensity of beige adipocytes were quantified by staining with hematoxylin-eosin. Chronic melatonin supplementation induced a minor increase in body mass and increased the animal's thermogenic potential in the cold acute challenge. Brown and beige adipocytes acted in a coordinated and complementary way to ensure adequate heat production. Melatonin plays an important role in the thermoregulatory mechanisms, ensuring greater capacity to withstand cold and, also, participating in the regulation of energy balance.

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