Kiani Ali
Animal Sciences Group, Lorestan University, Khoramabad, IR Iran.
Int J Endocrinol Metab. 2013 Winter;11(1):34-40. doi: 10.5812/ijem.6529. Epub 2012 Dec 21.
A fall in plasma concentration of energy status related hormones (leptin, insulin-like growth factor-1 (IGF-1) and insulin) and body energy expenditure occurs in response to short term fasting. Nevertheless, the relations of the fasting-induced changes in energy related hormones and metabolites with fasting energy expenditure (FEE) under extended fasting condition have received little attention so far.
It is not clear how energy status related hormones coordinate to cope with feed deprivation under extended fasting time conditions and how quickly these hormones re-bound to fed-state values in response to re-feeding. Thus the objectives of this study were: 1) to determine the effects of extended fasting on plasma concentration of leptin, IGF-1, insulin, glucose, NEFA, 3-β-hydroxybutyrate (BOHB) and urea; and 2) to study the relations of energy status related hormones with FEE and substrate oxidations under extended fasting conditions.
Eighteen six-month-old growing lambs (9 females and 9 males) were fasted for three days. Blood samples were taken one hour before (-1H) and 48 and 72 hours after fasting (48H and 72H) and two hours after re-feeding (+2H) from jugular vein. During the last 22 hours of fasting, gas exchange (CO2 production and O2 consumption) were measured using an open-circuit indirect calorimeter. Respiratory quotient (RQ), FEE and relative proportions of oxidized protein, fat and carbohydrate were calculated.
Plasma levels of leptin, insulin, IGF-1 and glucose decreased but NEFA and urea levels increased within 48H of fasting. Concentration of insulin significantly increased with extended fasting while leptin and IGF-1 levels remained constant. Glucose was the only blood variable that showed a quick re-bound within two hours after re-feeding. Leptin and IGF-1 showed significant positive relations with glucose and BOHB but negative relations with NEFA and Urea. Carbohydrate, fat and proteins contributed to 17%, 61% and 22% of FEE respectively in three-day-fasted lambs. FEE was negatively correlated with insulin and NEFA concentrations in plasma.
Even though plasma levels of leptin and IGF-1 decreased and remained constant under extended fasting, neither leptin nor IGF1 re-bounded to fed-status values within two hours after re-feeding. Under extended fasting condition, firstly an insulin resistance develops and secondly, a fall in FEE through a switch from carbohydrate- to fat-based metabolism occurs and there is an evident negative correlation between FEE and plasma concentration of NEFA.
短期禁食会导致能量状态相关激素（瘦素、胰岛素样生长因子-1（IGF-1）和胰岛素）的血浆浓度下降以及机体能量消耗减少。然而，在长期禁食条件下，禁食诱导的能量相关激素和代谢产物变化与禁食能量消耗（FEE）之间的关系迄今鲜受关注。
目前尚不清楚在延长禁食时间的条件下，能量状态相关激素如何协同应对食物剥夺，以及这些激素在重新进食后多快能恢复到进食状态的值。因此，本研究的目的是：1）确定延长禁食对瘦素、IGF-1、胰岛素、葡萄糖、非酯化脂肪酸（NEFA）、3-β-羟基丁酸（BOHB）和尿素血浆浓度的影响；2）研究在延长禁食条件下，能量状态相关激素与FEE和底物氧化之间的关系。
18只6月龄生长羔羊（9只雌性和9只雄性）禁食3天。在禁食前1小时（-1H）、禁食后48小时和72小时（48H和72H）以及重新进食后2小时（+2H）从颈静脉采集血样。在禁食的最后22小时，使用开路间接量热仪测量气体交换（二氧化碳产生量和氧气消耗量）。计算呼吸商（RQ）、FEE以及氧化蛋白质、脂肪和碳水化合物的相对比例。
禁食48小时内，瘦素、胰岛素、IGF-1和葡萄糖的血浆水平下降，但NEFA和尿素水平升高。随着禁食时间延长，胰岛素浓度显著增加，而瘦素和IGF-1水平保持不变。葡萄糖是唯一在重新进食后两小时内迅速恢复的血液变量。瘦素和IGF-1与葡萄糖和BOHB呈显著正相关，但与NEFA和尿素呈负相关。在禁食三天的羔羊中，碳水化合物、脂肪和蛋白质分别占FEE的17%、61%和22%。FEE与血浆中胰岛素和NEFA浓度呈负相关。
尽管在延长禁食期间瘦素和IGF-1的血浆水平下降并保持不变，但在重新进食后两小时内，瘦素和IGF-1均未恢复到进食状态的值。在延长禁食条件下，首先会出现胰岛素抵抗，其次，通过从基于碳水化合物的代谢转变为基于脂肪的代谢，FEE会下降，并且FEE与血浆NEFA浓度之间存在明显的负相关。
