Abstract
ObjectiveMelatonin has been shown to increase brown adipose tissue (BAT) mass, which can lead to important metabolic effects, such as bodyweight reduction and glycemic improvement. However, BAT mass can only be measured invasively and. The gold standard for non-invasive measurement of BAT activity is positron emission tomography with 2-deoxy-2-[fluorine-18] fluoro-d-glucose (18F-FDG PET). There is no study, to our knowledge, that has evaluated if melatonin influences BAT activity, measured by this imaging technique in animals.MethodsThree experimental groups of Wistar rats (control, pinealectomy, and pinealectomy replaced with melatonin) had an 18F-FDG PET performed at room temperature and after acute cold exposure. The ratio of increased BAT activity after cold exposure/room temperature was called “acute thermogenic capacity” (ATC) We also measured UCP-1 mRNA expression to correlate with the 18F-FDG PET results.ResultsPinealectomy led to reduced acute thermogenic capacity, compared with the other groups, as well as reduced UCP1 mRNA expression.ConclusionMelatonin deficiency impairs BAT response when exposed to acute cold exposure. These results can lead to future studies of the influence of melatonin on BAT, in animals and humans, without needing an invasive evaluation of BAT.
Highlights
Melatonin is a pineal hormone, produced at night, which has a critical role in the synchronization of circadian rhythms, with known metabolic effects in many animal species [1, 2]
In the Positron emission tomography-computed tomography (PET-CT) test performed at room temperature, there were no significant differences between the groups
When the ratio of increase between the after cold challenge was compared with room temperature, we found that the P group had a statistically significant reduction in this parameter (Fig. 3 and Table 1), compared with both of the other groups
Summary
Melatonin is a pineal hormone, produced at night, which has a critical role in the synchronization of circadian rhythms, with known metabolic effects in many animal species [1, 2]. One of its metabolic effects in rodents is a reduction in body weight with a minimal decrease in food intake, suggesting an action on energy expenditure, which possibly relates to activation of brown adipose. Brown adipose tissue is activated by sympathetic noradrenergic stimuli, and cold is the most important physiological stimulus known [7, 8]. Halpern et al Diabetol Metab Syndr (2020) 12:82 still possess active BAT, especially after cold exposure [9, 10]. In this context, a lack of BAT activation could have a potential role in weight gain in humans. Targeting BAT activation could be promising for the treatment of obesity and/or type 2 diabetes [11]
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