温度和高脂食物对黑线仓鼠代谢产热和体脂累积的影响

能量代谢的适应性调节是小型哺乳动物应对环境季节性变化的主要策略之一。为探讨不同温度下动物在代谢产热能量支出与脂肪累积之间的权衡策略,以成年雄性黑线仓鼠为研究对象开展了3 个实验:实验1 将动物驯化于高脂和低脂食物;实验2 将动物暴露于低温(5℃)和暖温(30℃);实验3 将饲喂高脂食物的动物暴露于低温。以食物平衡法测定摄食量、摄入能和消化率,以开放式氧气分析仪测定代谢产热,以索氏抽提法测定脂肪含量。结果发现,取食高脂食物的黑线仓鼠摄食量显著减少,但脂肪累积显著增加;暖温下摄食量显著减少,但体脂含量显著增加,低温下摄食量显著升高,但体脂含量显著减少;饲喂高脂食物的黑线仓鼠在低温下摄入能显著增加,非颤抖性产热增强,但体脂含量显著降低。结果表明高脂食物对黑线仓鼠体脂累积的影响与环境温度有关,低温诱导脂肪动员,暖温促进脂肪贮存;低温下黑线仓鼠增加能量摄入不能完全补偿用于产热的能量支出,导致脂肪动员增加;暖温下代谢产热降低是脂肪累积的主要因素;与能量摄入相比代谢产热的能量支出在体脂累积的适应性变化中发挥更重要的作用。     

黑线仓鼠体重和能量代谢的季节性变化

为阐明小型哺乳动物体重和能量代谢的季节性变化以及生理调节机制,将黑线仓鼠驯化于自然环境下12个月,测定其体重、能量收支、身体组织器官和血清瘦素水平的季节性变化。黑线仓鼠能量摄入和支出的季节性变化显著,冬季摄入能、基础代谢率(BMR)、非颤抖性产热(NST)显著高于夏季。体重季节性变化不显著,但身体组织器官重量呈现显著的季节性变化,冬季肝脏、心脏、肾脏以及消化道重量显著高于夏季。体脂含量夏季最高,冬季最低,冬季显著低于夏、秋和春季(P <0.01)。血清瘦素水平的季节性变化显著,夏季瘦素水平比秋、冬季分别高88.2% 和52.4% (P <0.05)。结果表明,黑线仓鼠体重维持季节性稳定,与“调定点假说”的预测不同;但脂肪含量和血清瘦素季节性变化显著,符合该假说。夏季血清瘦素升高具有抑制能量摄入的作用,冬季血清瘦素可能是促进代谢产热的重要因子,瘦素对能量代谢和体重的调节作用与气候的季节性变化有关。       

环境温度和繁殖经历对黑线仓鼠哺乳期能量收支的影响

为探讨环境温度和繁殖经历对黑线仓鼠哺乳期能量收支的影响,将连续3次繁殖的黑线仓鼠暴露于温度梯度降低的条件下(30—0℃,1℃/4d),使初次、第2和3次繁殖的动物分别暴露于30—20℃、20—10℃、10—0C℃,测定了哺乳期能量收支。与初次繁殖的动物相比,第3次繁殖组动物的摄食量显著增加,静止代谢率、非颤抖性产热、褐色脂肪组织细胞色素c氧化酶(COX)活性和血清T3水平显著增加,而断乳时胎仔重显著降低。结果表明:(1)低温下繁殖的黑线仓鼠处于负能量平衡,在自身维持和哺育后代的能量分配之间存在权衡,低温下产热增加,繁殖输出减少;(2)黑线仓鼠可能感知环境温度的变化,在连续降低温度的条件下降低繁殖投资,符合"季节性投资假说"的预测。     

暖温经历对雌性黑线仓鼠能量代谢、产热和体脂含量的影响

能量代谢的生理调节是小型哺乳动物应对不同环境温度的重要策略之一,为探讨暖温下代谢产热在体重和体脂适应性调节中的作用和机理,本研究将雌性黑线仓鼠(Cricetulus barabensis)暴露于暖温(30°C)1个月、3个月和4个月,测定体重、摄入能、代谢产热、体脂含量、褐色脂肪组织(BAT)细胞色素c氧化酶(COX)活性和解偶联蛋1 (UCP1) mRNA表达等。结果显示,暖温对黑线仓鼠体重无显著影响,但使脂肪含量显著增加。与室温组相比(21°C),暖温组消化率显著升高,但摄入能和消化能显著降低;暖温下非颤抖性产热(NST)显著降低,脑、肝脏和心脏COX活性、BAT COX活性和UCP1 mRNA的表达显著下调。结果表明,暖温下降低代谢产热补偿了能量摄入的减少,机体处于正能量平衡状态,是脂肪含量显著增加的主要原因之一。脑、肝脏、心脏和BAT代谢活性降低是代谢产热降低的主要机制,与脂肪累积有关。     

温度对黑线仓鼠能量代谢及开场行为的影响

形态、生理及行为的季节性变化是动物生存和繁殖的适应性策略。温度可能是影响啮齿动物季节性繁殖和种群波动的重要气候因子。为了验证环境温度能诱导鼠类体重、能量代谢及行为产生适应性变化的假设,并探究其中的相互关系和意义,通过不同温度处理模拟四季温度,以野生雄性黑线仓鼠(Cricetulus barabensis)为研究对象,检测其体重、日食量、静止代谢率(RMR)及开场行为的变化。结果显示:随着处理温度的下降,黑线仓鼠的体重、日食量及静止代谢率均出现显著性或极显著性地增加趋势(P0.05或P0.01);以体重为协变量的协方差分析表明,日食量和静止代谢率的增加不完全是由体重增加而造成的;高温处理降低了黑线仓鼠的爬行格数(P0.01),低温处理降低了黑线仓鼠的爬行格数和后肢站立次数(P0.01或P0.05),并产生明显的颤抖现象。以上研究结果支持环境温度能诱导鼠类体重、能量代谢及行为产生适应性变化的假设。低温同时增加黑线仓鼠能量的摄入水平和维持基本生长的能量支出水平,同时降低动物在陌生环境中的自发活动与探索行为。高温则降低黑线仓鼠能量的摄入和支出水平,同时减少自发活动与探索行为。体重、能量代谢和行为学特征的变化有利于仓鼠度过寒冷的冬季和干热的夏季,同时也与仓鼠的季节性繁殖现象相一致,因此这些特征可能是黑线仓鼠对其寒冷的冬季及干热的夏季生存环境的适应。     

黑线仓鼠繁殖输出与基础代谢率的关系

为了解黑线仓鼠繁殖输出与基础代谢率(BMR)的关系,阐明最大持续能量收支(SusMR)的限制水平, 揭示哺乳期能量收支对策,本文测定了哺乳期黑线仓鼠的体重、摄食量、BMR 和身体组成,以及哺乳期的胎仔数、胎仔重和泌乳能量支出(MEO)。结果显示,黑线仓鼠哺乳期体重降低了15.0 ± 0.8% , 摄食量显著增加, 哺乳高峰期平均摄食量为13.9 ± 0.3 g /d, 摄入能为222.1 ± 5.3 kJ/ d, 比哺乳初期增加121% , 比对照组高288% ;哺乳高峰期MEO 为62.4 ± 2.3 kJ/ d, 哺乳末期BMR 为49.7 ± 1.1 kJ/ d; 断乳时平均胎仔数4.7 ± 0.2、窝胎仔重50.5 ±1.6 g; 哺乳末期BMR 比对照组增加48% ,BMR 与消化系统各器官的相关性高于对照组; BMR 与胎仔数、胎仔重、乳腺重量和MEO 显著正相关。结果表明:初次繁殖的黑线仓鼠哺乳期SusMR 限制为4.47 ×BMR, 在自身维持和繁殖输出之间采取了“权衡分配”的原则,通过体重降低以减少BMR 的增加幅度, 从而有利于繁殖输出。     

生长抑素基因在不同性别和年龄黑线仓鼠哈氏腺的差异表达

哈氏腺作为“视网膜-松果体轴”的候补结构,介导了体外光信号与体内神经内分泌调控过程,具有多样性和复杂的生理功能,并受神经和体液因素的双重调控。生长抑素（somatostatin, SS）是调控动物生长发育的主要因子之一,检测SS基因在黑线仓鼠哈氏腺的差异表达模式,为光信号调控动物的生长发育机制提供理论依据。以野生黑线仓鼠（Cricetulus barabensis）为研究对象,测量了不同性别和年龄个体哈氏腺的形态学指标,克隆了哈氏腺SS cDNA序列,实时荧光定量PCR方法检测了哈氏腺中SS基因的表达变化。结果显示：（1）黑线仓鼠体重无性别差异,随年龄增长而增加;哈氏腺的长度和重量也随年龄增长而增加;调整体重影响后,哈氏腺的重量和长度没有年龄之间的差异,但哈氏腺重量存在性别间差异（P<0.05）。（2）克隆到黑线仓鼠哈氏腺SS cDNA序列489 bp ,并对序列结构进行分析,黑线仓鼠哈氏腺SS cDNA具有典型分泌蛋白cDNA的特征,并在进化上高度保守;（3）检测到SS mRNA在黑线仓鼠哈氏腺中均有表达,表达量存在年龄和性别差异（P<0.05）;（4）随着个体性成熟和衰老,黑线仓鼠哈氏腺中SS mRNA的相对表达量逐渐降低,其表达量分别与哈氏腺长度和重量的发育变化负相关（r=-0.557,P=0.022;r=-0.806,P＜0.001）。结果表明,黑线仓鼠哈氏腺重量和SS表达量均表现出两性异形,可能是对不同繁殖策略的适应;SS基因作为负调控因子参与野生黑线仓鼠哈氏腺的生长发育过程。     

繁殖经历对黑线仓鼠哺乳期能量收支的影响

为探讨繁殖经历与哺乳期最大持续能量收支的关系,对连续4 次繁殖的黑线仓鼠哺乳期的能量收支情况进行了测定。结果显示:1)不同繁殖组哺乳高峰期的摄食量、泌乳能量支出(MEO)、胎仔数和胎仔重差异不显著,静止代谢率(RMR)、非颤抖性产热(NST)、褐色脂肪组织(BAT)线粒体细胞色素c 氧化酶(COX)活性、血清甲状腺激素(T3 、T4 )和催乳素水平也无明显变化;2)摄食量与MEO、胎仔重和RMR 呈显著正相关。结果表明,不同繁殖经历的黑线仓鼠主要通过降低产热和增加能量摄入来满足哺乳高峰期的能量需求;哺乳期最大持续代谢率(SusMR)可能受乳腺组织泌乳能力的限制,与“外周限制假说” 的预测一致,不支持“中心限制假说”;SusMR 限制因素和哺乳期能量收支策略可能与繁殖经历无关。     

食物限制对雄性大绒鼠能量代谢特征的影响

为探讨横断山区大绒鼠适应食物匮乏的适应对策,将成年雄性大绒鼠随机分为自由取食组和饲喂正常摄食量的80% 限食组。测定了自由取食组和限食组雄性大绒鼠的体重、静止代谢率、非颤抖性产热以及体脂含量、血清瘦素含量、肝脏鲜重、褐色脂肪组织重量和消化道形态。结果显示:限食使雄性大绒鼠的体重、体脂含量、静止代谢率、非颤抖性产热、褐色脂肪组织重量和大肠、小肠长度显著降低,使盲肠内容物重量显著增加。血清瘦素含量与体重、体脂含量呈极显著正相关。在限食条件下,大绒鼠主要通过降低体重、基础代谢和产热的能量支出以及动用体内脂肪以应对食物资源短缺的环境条件,瘦素可能参与了能量代谢和体重的适应性调节。     

瘦素在哺乳动物体重调节、繁殖和免疫中的作用

瘦素(Leptin) 主要是由白色脂肪细胞分泌的、肥胖基因编码的、分子量为16 KD 的蛋白类激素。其N 端具有信号肽序列, 引导蛋白质进入分泌途径, 信号肽被切除后成为有生物学功能的成熟蛋白质。瘦素在动物的体重调节、发育与生殖、免疫和糖代谢等方面有重要作用。瘦素已经不仅仅是脂肪细胞分泌的蛋白类激素, 而是一个在许多方面发挥作用的神经内分泌调节因子。本文综述了瘦素在哺乳动物体重调节、繁殖和免疫中的作用及其调控机制, 主要包括: 动物血清瘦素浓度的季节性变化; 光周期、温度和食物等环境因子对瘦素浓度的影响; 瘦素与解偶联蛋白(Uncoupling proteins , UCPs) 在能量代谢和产热中的互作; 瘦素与下丘脑神经肽Y (Hypothalamus neuropeptide Y, NPY) 在体重调节和产热作用中的拮抗; 瘦素与甲状腺激素和胰岛素在能量代谢中的互作以及瘦素在生殖和免疫中的作用。     

Different physiological roles of serum leptin in the regulation of energy intake and thermogenesis between pregnancy and lactation in primiparous Brandt's voles (Lasiopodomys brandtii)

Reproduction, especially lactation, is associated with major metabolic adaptive changes. In this study, we investigated the metabolic changes and the roles of leptin during different periods of reproduction in primiparous Brandt's voles (Lasiopodomys brandtii). Energy intake, thermogenic capacity and serum leptin levels were examined in non-reproductive, mid pregnant, late pregnant, early lactating and peak lactating voles. Voles increased body mass by nearly 70% during late pregnancy compared to the non-breeding controls. The increase in body mass was mainly due to the increase in body fat mass which increased by 56%, and the growth of the reproductive tissues and digestive organs. Lactating voles decreased body fat by nearly 27% at peak lactation compared to the controls, and 53% compared to late pregnant voles. At the same time they increased food intake significantly. Uncoupling protein 1 (UCP1) content in brown adipose tissue (BAT) decreased significantly at peak lactation. Serum leptin increased significantly in the mid pregnancy, at a time when there was no increase in body fat, and remained at this high level in late pregnancy. Leptin levels decreased after parturition and reached a nadir at peak lactation. Serum leptin was negatively correlated with energy intake during lactation, but not during pregnancy. These data suggest that Brandt's voles adjust energy intake, thermogenic capacity and body reserves to match the high energy demands for reproduction. Hyperleptinemia, without decreased energy intake suggests a state of leptin resistance during pregnancy, and hypoleptinemia during lactation might act as a signal to stimulate energy intake.     

Effects of leptin infusion during peak lactation on food intake, body composition, litter growth, and maternal neuroendocrine status in female Brandt's voles (Lasiopodomys brandtii)

During lactation, female small mammals frequently reduce their fat reserves to very low levels. The function of this reduction is unclear, as calculations suggest that the contribution of the withdrawn energy from fat to the total energy balance of lactation is trivial. An alternative hypothesis is that reducing fat leads to a reduction in circulating adipokines, such as leptin, that play a role in stimulating the hyperphagia of lactation. We investigated the role of circulating leptin in lactation by repleting leptin levels using miniosmotic pumps during the last 7 days of lactation in Brandt's voles (Lasiopodomys brandtii), a model small wild mammal we have extensively studied in the context of lactation energy demands. Repletion of leptin resulted in a dose-dependent reduction of body mass and food intake in lactating voles. Comparisons to nonreproducing individuals suggests that the reduced leptin in lactation, due to reduced fat stores, may account for ～16% of the lactational hyperphagia. Reduced leptin in lactation may, in part, cause lactational hyperphagia via stimulatory effects on hypothalamic orexigenic neuropeptides (neuropeptide Y and agouti-related peptide) and inhibition of the anorexigenic neuropeptide (proopiomelanocortin). These effects were reversed by the experimental repletion of leptin. There was no significant effect of leptin treatment on daily energy expenditure, milk production or pup growth, but leptin repletion did result in a reversal of the suppression of uncoupling protein-1 levels in brown adipose tissue, indicating an additional role for reducing body fat and leptin during peak lacation.     

Estimation of food intake and ingested energy in Daubenton’s bats (Myotis daubentonii) during pregnancy and spermatogenesis

We studied food intake of and estimated ingested energy in female and male Myotis daubentonii during the periods of pregnancy (period 1, 8 May–4 June) and of intense spermatogenetic activity (period 2, 24 July–22 August) over 8 years (1996–2003) in central Germany. We used radiotelemetry to determine the time spent foraging and marked animals with chemiluminescent light-sticks to determine prey attack rates. Body length, body mass, moisture content, and caloric content of chironomids, the main prey of Daubenton’s bats, were measured to estimate the nightly food intake and, in consequence, energy intake. Pregnant females spent significantly more time foraging than males during period 1 and females during the post-lactation period. In contrast, male foraged longer during the period of highest spermatogenetic activity than during late spring and also significantly longer than post-lactating females. Based on a mean number of 8.3 prey attacks per minute, the time spent foraging, and a capture success rate of either 50 or 92%, calculated intake values with a feeding rate of 7.6 insects per minute (=92% capture success) were more consistent with literature data for other insectivorous bats than that of values calculated on the basis of a capture success rate of 50%. In the high capture-success model, calculated insect intake of female bats was 8.0 g during pregnancy and 4.9 g per day during post-lactation, providing 5.0 and 3.0 kJ of ingested energy per gram body mass per day. Calculated intake of male bats was 3.6 g insects per day during late spring and 8.0 g during period of intensive spermatogenesis, providing 2.6 and 5.7 kJ of ingested energy per gram body mass.     

禁食和重喂食对大绒鼠体重、产热和血清瘦素的影响

动物行为和生理活动的适应性调节是应对食物资源变化的主要策略。为探讨禁食和重喂食对大绒鼠体重、产热和血清瘦素的影响,测定了禁食和重喂食条件下大绒鼠的体重、体脂重量、静止代谢率、身体组成、血清瘦素含量以及禁食后重喂食期间的摄食量。结果显示:禁食导致大绒鼠体重、体脂重量和静止代谢率显著下降,重喂食后体重和静止代谢率能够恢复到对照组水平,而体脂重量却不能恢复。禁食12 h 后血清瘦素含量快速下降,重喂食后未能恢复到对照水平。此外,大绒鼠在禁食后重喂食期间摄食量没有补偿性增加,血清瘦素含量与体脂重量呈正相关关系。这些结果很可能反映出大绒鼠能调节自身生理状况以适应短期的能量缺乏,主要通过降低体重、血清瘦素含量和代谢活性器官重量以减少能量消耗。禁食后重喂食时大绒鼠没有摄食过量。血清瘦素的下降早于体重和体脂的下降。     

Sexually dimorphic responses to fat loss after caloric restriction or surgical lipectomy

White adipose tissue is the principal site for lipid accumulation. Males and females maintain distinctive white adipose tissue distribution patterns. Specifically, males tend to accumulate relatively more visceral fat, whereas females accumulate relatively more subcutaneous fat. The phenomenon of maintaining typical sex-specific fat distributions suggests sex-specific mechanisms that regulate energy balance and adiposity. We used two distinct approaches to reduce fat mass, caloric restriction (CR), and surgical fat removal (termed lipectomy) and assessed parameters involved in the regulation of energy balance. We found that male and female mice responded differentially to CR- and to lipectomy-induced fat loss. Females decreased energy expenditure during CR or after lipectomy. In contrast, males responded by eating more food during food return after CR or after lipectomy. Female CR mice conserved subcutaneous fat, whereas male CR mice lost adiposity equally in the subcutaneous and visceral depots. In addition, female mice had a reduced capability to restore visceral fat after fat loss. After CR, plasma leptin levels decreased in male but not in female mice. The failure to increase food intake after returning to ad libitum intake in females could be due to the relatively stable levels of leptin. In summary, we have found sexual dimorphisms in the response to fat loss that point to important underlying differences in the strategies by which male and female mice regulate body weight.     

Perigestational suppression of weight gain with central leptin gene therapy results in lower weight F1 generation

The efficacy of central leptin therapy on weight homeostasis through various phases of reproduction, pregnancy outcome and postnatal, prepubertal and pubertal growth of offspring was assessed. Enhanced leptin transgene expression after a single intracerebroventricular injection of recombinant adeno-associated virus vector encoding the leptin gene (rAAV-lep) decreased calorie intake and weight in adult nulliparous female rats. rAAV-lep treated rats conceived normally, displayed unremarkable pregnancy rate, parturition and delivered normal sized litters. Significantly lower weight was maintained through gestation, lactation, and post-lactation periods. The maintenance of a modest weight reduction was accompanied by voluntarily reduced calorie intake, increased thermogenic energy expenditure, decreased adiposity as reflected by drastically reduced leptin levels, and suppressed insulin and insulin-like growth factor 1 levels through lactation and post-lactation in rAAV-lep treated dams. The offspring at birth weighed significantly less than those of controls and this lower weight range was sustained during postnatal, prepubertal, pubertal and adult (3 months old) periods, contemporaneous with metabolic circulating hormones in the normal range. For the first time we show the persistent efficacy of central leptin gene therapy to suppress weight gain through all phases of reproduction, lactation and post-lactation in dams and reveal the potential imprinting link to producing lower weight in the F1 generation.     

Leptin sensitive neurons in the hypothalamus.

A major paradigm in the field of obesity research is the existence of an adipose tissue-brain endocrine axis for the regulation of body weight. Leptin, the peptide mediator of this axis, is secreted by adipose cells. It lowers food intake and body weight by acting in the hypothalamus, a region expressing an abundance of leptin receptors and a variety of neuropeptides that influence food intake and energy balance. Among the most promising candidates for leptin-sensitive cells in the hypothalamus are arcuate nucleus neurons that co-express the anabolic neuropeptides, neuropeptide Y (NPY) and agouti-related peptide (AGRP), and those that express proopiomelanocortin (POMC), the precursor of the catabolic peptide, alphaMSH. These cell types contain mRNA encoding leptin receptors and show changes in neuropeptide gene expression in response to changes in food intake and circulating leptin levels. Decreased leptin signaling in the arcuate nucleus is hypothesized to increase the expression of NPY and AGRP. Levels of leptin receptor mRNA and leptin binding are increased in the arcuate nucleus during fasting, principally in NPY/AGRP neurons. These findings suggest that changes in leptin receptor expression in the arcuate nucleus are inversely associated with changes in leptin signaling, and that the arcuate nucleus is an important target of leptin action in the brain.     

Leptin and the adaptations of lactation in rodents and ruminants.

Lactation markedly increases nutrient requirements in both rodents and ruminants. This is met mostly by increased food intake, but there are also adaptations to increase metabolic efficiency. Despite such changes, lactating animals usually experience periods of negative energy balance. This is not due to a physical constraint on food intake, at least in the rat. Leptin, a hormone secreted by adipocytes, plays an important role in the regulation of appetite and energy balance. During lactation, serum leptin concentration is decreased in both rodents and ruminants, and the nocturnal rise in concentration is lost in rats. Hypoleptinaemia in lactation is primarily a result of negative energy balance. There is also increased clearance of serum leptin, and the attenuation of the nocturnal rise in leptin in rats is at least partly due to the suckling stimulus. Hypoleptinaemia is not the major factor driving hyperphagia in lactating rats, but it probably facilitates the increased food intake. Leptin may play a more important role in this respect in lactating ruminants. Leptin is probably involved in other adaptations that increase metabolic efficiency during lactation. The ability of hypothalamic neuropeptides to respond to leptin does not appear to be altered by lactation in either rodents or ruminants. The reason why lactating animals do not respond to hypoleptinaemia with a further increase in appetite, thereby achieving energy balance, appears to be due to a failure to respond to changes in neuropeptides which mediate the effects of leptin.     

The tradeoff between torpor use and reproduction in little brown bats (Myotis lucifugus)

In mammals, reproduction, especially for females is energetically demanding. Therefore, during the reproductive period females could potentially adjust patterns of thermoregulation and foraging in concert to minimise the energetic constraints associated with pregnancy and lactation. We assessed the influence of pregnancy, lactation, and post-lactation on torpor use and foraging behaviour by female little brown bats, Myotis lucifugus. We measured thermoregulation by recording skin temperature and foraging by tracking bats which carried temperature-sensitive radio-tags. We found that individuals, regardless of reproductive condition, used torpor, but the patterns of torpor use varied significantly between reproductive (pregnant and lactating) females and post-lactating females. As we predicted, reproductive females entered torpor for shorter bouts than post-lactating females. Although all females used torpor frequently, pregnant females spent less time in torpor, and maintained higher skin temperatures than either lactating or post-lactating females. This result suggests that delayed offspring development which has been associated with torpor use during pregnancy, may pose a higher risk to an individual’s reproductive success than reduced milk production during lactation. Conversely, foraging behaviour of radio-tagged bats did not vary with reproductive condition, suggesting that even short, shallow bouts of torpor produce substantial energy savings, likely obviating the need to spend more time foraging. Our data clearly show that torpor use and reproduction are not mutually exclusive and that torpor use (no matter how short or shallow) is an important means of balancing the costs of reproduction for M. lucifugus.