Morgado Elvira, Gordon M Kathleen, del Carmen Miñana-Solis María, Meza Enrique, Levine Seymour, Escobar Carolina, Caba Mario
Lab. Biol. de la Reproducción, IIB, Universidad Veracruzana, AP 114, Xalapa 91000, Veracruz, Mexico.
Am J Physiol Regul Integr Comp Physiol. 2008 Aug;295(2):R690-5. doi: 10.1152/ajpregu.00162.2008. Epub 2008 May 14.
Young rabbits are nursed every 24 h for a period of 3-5 min. As a consequence, pups are synchronized to this nursing event; this synchronization is characterized by increased locomotor activity and a peaking of core temperature and plasma corticosterone in anticipation of the daily meal. Ghrelin is a hormone suggested to play a role in meal initiation and to promote food intake. The present study explored the role of ghrelin in food-entrained conditions. Newborn rabbits were maintained in constant darkness and nursed once daily at 1000 by the lactating dam. On postnatal day 7, rabbits were killed at six different time points to complete a 24-h cycle. All pups developed locomotor rhythms entrained by mealtime and exhibited anticipatory activity. Food-entrained rhythms in plasma corticosterone and free fatty acids were observed even if two meals were omitted. In contrast, daily food-driven rhythms in stomach weight, plasma glucose, liver glycogen, and ghrelin did not persist when two meals were omitted. Peak ghrelin levels were observed at the moment in the cycle when the stomach weight was lowest, i.e., before initiation of anticipation. The present data are in agreement with previous data from rabbit pups maintained in light-dark conditions and provide evidence that 7- to 9-day-old rabbits in constant darkness can exhibit metabolic and hormonal rhythms mainly driven by the restricted daily nursing.
幼兔每24小时哺乳一次，每次持续3 - 5分钟。因此，幼崽会与这次哺乳事件同步；这种同步的特征是在每日进食前运动活动增加、核心体温和血浆皮质酮达到峰值。胃饥饿素是一种被认为在进食启动中起作用并促进食物摄入的激素。本研究探讨了胃饥饿素在食物诱导条件下的作用。新生兔饲养在持续黑暗环境中，由哺乳母兔每天1000时哺乳一次。在出生后第7天，在六个不同时间点处死兔子以完成一个24小时周期。所有幼崽都形成了由进餐时间诱导的运动节律，并表现出预期活动。即使省略两餐，血浆皮质酮和游离脂肪酸的食物诱导节律仍可观察到。相比之下，当省略两餐时，胃重量、血浆葡萄糖、肝糖原和胃饥饿素的每日食物驱动节律不再持续。在胃重量最低的周期时刻，即预期开始前，观察到胃饥饿素水平峰值。目前的数据与之前在明暗条件下饲养的兔幼崽的数据一致，并提供了证据表明，在持续黑暗环境中7至9日龄的兔子可以表现出主要由受限的每日哺乳驱动的代谢和激素节律。
