Brown adipose tissue (BAT) influences energy balance through nonshivering thermogenesis, and its metabolism daily and seasonal variations are regulated by melatonin through partially known mechanisms. We evaluated the role of melatonin in BAT molecular machinery of male Control, pinealectomized (PINX), and melatonin‐treated pinealectomized (PINX/Mel) adult rats. BAT was collected either every 3 hours over 24 hours or after cold or high‐fat diet (HFD) acute exposure. HFD PINX animals presented decreased Dio2 expression, while HFD PINX/Mel animals showed increased Dio2, Ucp1, and Cidea expression. Cold‐exposed PINX rats showed decreased Dio2 and Lhs expression, and melatonin treatment augmented Adrβ3, Dio2, Ucp1, and Cidea expression. Daily profiles analyses showed altered Dio2, Lhs, Ucp1, Pgc1α, and Cidea gene and UCP1 protein expression in PINX animals, leading to altered rhythmicity under sub‐thermoneutral conditions, which was partially restored by melatonin treatment. The same was observed for mitochondrial complexes I, II, and IV protein expression and enzyme activity. Melatonin absence seems to impair BAT responses to metabolic challenges, and melatonin replacement reverses this effect, with additional increase in the expression of crucial genes, suggesting that melatonin plays an important role in several key points of the thermogenic activation pathway, influencing both the rhythmic profile of the tissue and its ability to respond to metabolic challenges, which is crucial for the organism homeostasis.

As a chronobiotic molecule, melatonin finely tunes a variety of physiological processes including energy metabolism, reproduction and sleep-wake cycle, collaborating for the survival of the organisms. Since its pineal production occurs exclusively during the night, melatonin is responsible for signaling the circadian and circannual cycles to the organisms. This involves different ways of action that need to be considered when analyzing its effects in a given tissue/organism. Non-shivering thermogenesis (NST) is a crucial process for homeothermic animals and increasing evidences show its importance for the energy metabolic balance due to its influence in body weight control. The highly seasonal brown adipose tissue (BAT) is the site for NST and its metabolism is importantly influenced by melatonin. This review focuses on melatonin actions over BAT and the attention should be given to the relation between this signaling molecule and such a seasonally expressed tissue.

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