The aim of this work was to investigate the effect of the in vitro circadian-like exposure to melatonin [in the presence or absence of insulin (Ins)] on the metabolism and clock gene expression in adipocytes. To simulate the cyclic characteristics of the daily melatonin profile, isolated rat adipocytes were exposed in a circadian-like pattern to melatonin added to the incubating medium for 12 hr (mimicking the night), followed by an equal period without melatonin (mimicking the day) combined or not with Ins. This intermittent incubation was interrupted when four and a half 24-hr cycles were fulfilled. At the end, either during the induced night (melatonin present) or the induced day (melatonin absent), the rates of lipolysis and D-[U-(14)C]-glucose incorporation into lipids were estimated, in addition to the determination of lipogenic [glucose-6-phosphate dehydrogenase and fatty acid synthase (FAS)] and lipolytic (hormone sensitive lipase) enzymes and clock gene (Bmal-1b, Clock, Per-1 and Cry-1) mRNA expression. The leptin release was also measured. During the induced night, the following effects were observed: an increase in the mRNA expression of Clock, Per-1 and FAS; a rise in lipogenic response and leptin secretion; and a decrease in the lipolytic activity. The intermittent exposure of adipocytes to melatonin temporally and rhythmically synchronized their metabolic and hormonal function in a circadian fashion, mimicking what is observed in vivo in animals during the daily light-dark cycle. Therefore, this work helps to clarify the physiological relevance of the circadian pattern of melatonin secretion and its interactions with Ins, contributing to a better understanding of the adipocyte biology.

中文翻译：

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褪黑素和原代分离的脂肪细胞中代谢和激素活性的昼夜节律性。

这项工作的目的是研究体外昼夜节律暴露于褪黑激素[有无胰岛素（Ins）的情况下）对脂肪细胞代谢和时钟基因表达的影响。为了模拟每日褪黑激素谱的循环特征，将分离的大鼠脂肪细胞以昼夜节律的方式暴露于添加到培养液中的褪黑素中12个小时（模仿夜晚），然后等量不使用褪黑激素（模仿一天）。是否与Ins结合使用。当完成四个半小时的24小时周期后，这种间歇性孵育就会中断。最后，在诱导的夜晚（存在褪黑激素）或诱导的白天（不存在褪黑激素）中，估计脂肪分解的速率和D- [U-（14）C]-葡萄糖掺入脂质的速率，除了测定脂生性[6-磷酸葡萄糖脱氢酶和脂肪酸合酶（FAS）]和脂解（激素敏感性脂酶）酶和时钟基因（Bmal-1b，Clock，Per-1和Cry-1）的mRNA表达之外， 。还测量了瘦蛋白的释放。在诱导的夜晚，观察到以下影响：Clock，Per-1和FAS的mRNA表达增加；脂肪生成反应和瘦素分泌增加；并降低脂解活性。脂肪细胞在时间和节律上间歇性地暴露于褪黑激素使它们的代谢和激素功能以昼夜节律同步，这与动物在每天的明暗周期中体内观察到的情况相似。因此，