Dpto Fisiología, Fisiología Animal II, Facultad de Biología, Universidad Complutense de Madrid, 28040 Madrid, Spain.
Peptides. 2011 May;32(5):989-95. doi: 10.1016/j.peptides.2011.01.028. Epub 2011 Feb 1.
The present study investigates the possible circadian dependence of leptin effects on food intake, locomotor activity, glycemia and plasma cortisol levels in goldfish (Carassius auratus). Fish were maintained under 12L:12D photoperiod and subjected to two different feeding schedules, one group fed during photophase (10:00) and the other one during scotophase (22:00). Leptin or saline were intraperitoneally injected at two different times (10:00 or 22:00), coincident or not with the meal time. To eliminate the entraining effect of the light/dark cycle, goldfish maintained under 24h light (LL) were fed and leptin-injected at 10:00. A reduction in food intake and locomotor activity and an increase in glycemia were found in goldfish fed and leptin-injected at 10:00. No significant changes in circulating cortisol were observed. Those effects were not observed when leptin was administered during the scotophase, regardless the feeding schedule; neither in fish maintained under LL, suggesting that a day/night cycle would be necessary to observe the actions of leptin administered during the photophase. Changes in locomotor activity and glycemia were only observed in goldfish when leptin was injected at daytime, coincident with the feeding schedule, suggesting that these leptin actions could be dependent on the feeding time as zeitgeber. In view of these results it appears that the circadian dependence of leptin actions in goldfish can be determined by the combination of both zeitgebers, light/dark cycle and food. Our results point out the relevance of the administration time when investigating regulatory functions of hormones.
本研究旨在探讨瘦素对鱼类摄食、活动、血糖和皮质醇水平的影响是否存在昼夜节律依赖性。实验用金鱼（Carassius auratus），饲养于 12L:12D 光周期下，并采用两种不同的摄食方案，一组在光照期（10:00）摄食，另一组在暗期（22:00）摄食。瘦素或生理盐水在两个不同时间（10:00 或 22:00）通过腹腔注射，与摄食时间一致或不一致。为了消除光/暗周期的同步作用，24 小时光照（LL）下饲养的金鱼在 10:00 时摄食和注射瘦素。结果发现，在 10:00 时摄食和注射瘦素的金鱼摄食量和活动量减少，血糖升高。循环皮质醇没有明显变化。当瘦素在暗期注射时，无论摄食方案如何，都不会观察到这些影响；在接受 LL 光照的金鱼中也没有观察到这些影响，表明需要昼夜节律才能观察到在光照期注射瘦素的作用。只有当在白天（与摄食方案一致）注射瘦素时，金鱼的活动和血糖才会发生变化，这表明这些瘦素作用可能依赖于作为授时因子的摄食时间。鉴于这些结果，瘦素在金鱼中的作用的昼夜节律依赖性似乎可以通过光/暗周期和食物这两个授时因子的组合来确定。我们的研究结果指出，在研究激素的调节功能时，给药时间是很重要的。
