The detection of 3 leptin receptor isoforms in crucian carp gill and the influence of fasting and hypoxia on their expression

To understand leptin signaling pathway in the crucian carp (Carassius carassius), we cloned 3 leptin receptor isoform complementary DNAs (ie, the long form [cclpr-L], the short form [cclpr-s1], and the secreted form [cclpr-s2]). Variant cclpr-L had a 3,255-bp open reading frame and a complete intracellular domain with box 1 and box 2 consensus sequences. By contrast, cclpr-s1 contained only 4 amino acids in its intracellular domain, without the “box 1” motif, which is conserved among membrane-bound leptin receptor short isoforms in mammals. Variant cclpr-s2 had no transmembrane domain, suggesting that it is a soluble form of the receptor, and alternative splicing of cclpr-s2 mRNA employs a different mechanism for the generation of soluble leptin receptor by intron retention. The fasting-treated fish showed significantly lower cclpr-L mRNA levels in gill tissue than the control group, whereas cclpr-s2 mRNA levels did not vary significantly among the groups. Treatment with hypoxia significantly increased mRNA levels of both cclpr-L and cclpr-s2 in gill tissue. To our knowledge, this is the first study of leptin receptor isoforms expression in teleosts.     

Food deprivation stimulates the luteolytic capacity in the gilt

The aims of this study were to study the effects of fasting on progesterone (P4) production in the pig and to verify whether fasting influences luteal expression of PGF(2alpha) receptor (FPr) and prostaglandin secretion. Superovulated prepubertal gilts were used; half of them were fasted for 72h starting on day 2 (F2) or 9 (F9) of the induced estrous cycle, respectively, while two groups (C2 and C9) served as respective controls. Plasma P4 and PGFM concentrations were determined by RIA while FPr mRNA expression in CLs collected at the end of fasting period was measured by real-time PCR. In experiment 1, plasma P4 concentrations in fasted gilts were significantly (P<0.01) higher than in controls starting from day 3 (F2; n=6) and 10 (F9; n=6). FPr mRNA expression was similar in F2 and C2 (n=6) CLs while it was significantly (P<0.05) higher in F9 than in C9 (n=6) CLs. In experiment 2, cloprostenol administered on day 12 significantly (P<0.05) increased FPr mRNA expression in CLs from both F9 (n=6) and C9 (n=6) gilts. At the time of cloprostenol injection PGFM levels were significantly higher (P<0.05) in the fasted group and cloprostenol-induced luteolysis in fasted but not in normally fed gilts. Results from this study indicate that fasting in prepubertal gilts induced to ovulate stimulates luteal P4 and PGFM production as well as FPr mRNA expression, thus increasing luteolytic susceptibility.     

Effects of fasting on the meat quality and antioxidant defenses of market-size farmed large yellow croaker (Pseudosciaena crocea)

The study was conducted to investigate fasting effect on flesh composition and antioxidant defenses of market-size large yellow croaker (Pseudosciaena crocea). Two hundred fish (main initial weight 380 g) were divided into two groups (control and fasted) and reared in 6 cages. After two weeks of adaptation, group I fasted for 28 days; group II was fed normally as a control. In 3, 7, 14, 21 and 28 days, 6 fish per group were processed for proximate flesh composition, liver antioxidant enzyme activities and malondialdehyden flesh content analyses. In fasted fish, the reduction of lipid content in muscle occurred after day 3, and, compared to controls, the content of protein decreased from day 21, the activities of liver antioxidative enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPX) increased from day 3, and flesh malondialdehyde (MDA) levels increased from day 21. Muscle lipid reduction shows that the fasting technique is effective in end product improvement of large yellow croaker. However, considering flesh protein loss and the subsequent oxidative stress, the fasting technique should be used with precautions.     

Increased degradation of insulin-like growth factor-I in serum from feed-deprived steers

Severe feed restriction decreases serum insulin-like growth factor I (IGF-I) concentration in animals, and this decrease is thought to be due to reduced IGF-I production in the liver. The objective of this study was to determine whether feed deprivation also increases degradation of serum IGF-I and serum levels of IGF binding protein 3 (IGFBP-3) and acid-labile subunit (ALS), which inhibit IGF-I degradation and increase IGF-I retention in the blood by forming a ternary complex with IGF-I, in cattle. Five steers had free access to pasture, and another five were deprived of feed for 60 h. Serum concentration of IGF-I and liver abundance of IGF-I mRNA at the end of the 60-h period were 50% and 80% lower, respectively, in feed-deprived steers than in fed steers. Less ¹²⁵I-labeled IGF-I remained intact after a 45-h incubation in sera of feed-deprived steers than in sera of fed steers, suggesting that serum IGF-I is more quickly degraded in feed-deprived animals. Serum levels of IGFBP-3 and ALS were decreased by 40% and 30%, respectively, in feed-deprived steers compared with fed steers. These decreases were associated with more than 50% reductions in IGFBP-3 and ALS mRNA in the liver, the major source of serum IGFBP-3 and ALS. Taken together, these results suggest that feed deprivation reduces serum concentration of IGF-I in cattle not only by decreasing IGF-I gene expression in the liver, but also by increasing IGF-I degradation and reducing IGF-I retention in the blood through decreasing IGFBP-3 and ALS production in the liver.     

18月龄生长母水牛绝食代谢的研究

用传统开路式牛用呼吸面具对 18 月龄母水牛绝食产热(FHP)进行研究。结果表明:①18 月龄母水牛 FHP 为328 55 kJ/(kgW0 75·d);每天排出EUN为33 19 g;单位代谢体重每天排出EUN为0 46 g;蛋白分解产热占总产热量为16 46%;尿氮(EUN)与FHP比值为1 46 mg/kJ。②18月龄母水牛维持净能需要:NEm=410 69 kJ/(kgW0 75·d)。     

不同海拔高度下生长牦牛绝食代谢的研究

用闭路循环式呼吸面具,分别在海拔高度2261m和4272m处的暖季对绝食5—7天的生长阉牦牛绝食产热(FHP)进行测定,并在海拔高度3250m处的冬、暖两季,测定不同气温下试牛的FHP。用Brouwer(1965)的简化式计算产热量。结果表明:①在海拔2261m和4272m处,1、2、3岁牦牛的FHP(kJ/kgw~(0.75)·日)分别为351.544±25.744,305.344±20.920,298.583±17.910,和376.225±23.518,324.787±46.208,281.144±24.410。二者差异不显著(P>0.05),其方程为FHP(kJ/日)=920w~(0.52),n=25,r=0.8469。②环境气温显著影响FHP。当气温为8—15℃时,FHP相对恒定P>0.1);高于15℃时,每升高1℃,FHP(kJ/kgw~(0.52)·日)增加10.5(P<0.05);低于8℃时,每下降1℃,FHP减少14.6(P<0.05);低于-20℃时,每下降1℃,FHP增加18.4(P<0.05)。试验指出:①牦牛较低的FHP及它在不同海拔高度FHP的恒定性,是其适应青藏高原缺氧环境及冬春缺草环境的特点;它奇特的自我保护功能是适应严寒环境的特点,这些特点是长期自然选择的结果。②在高海拔地区世代生活的家畜,其代谢值低,而且在其适应的海拔高度范围内相对恒定;未获得遗传性适应的家畜,其代谢值随海拔高度的升高而升高。③生长牦牛代谢体重为w~(0.52)。     

Effects of short- and long-term fasting on plasma and stomach ghrelin,and the growth hormone/insulin-like growth factor I axis in the tilapia, Oreochromis mossambicus

Ghrelin is a highly conserved peptide hormone secreted by the stomach, which is involved in the regulation of food intake and energy expenditure. Ghrelin stimulates growth hormone (GH) release, and increases appetite in a variety of mammalian and non-mammalian vertebrates, including several fish species. Studies were conducted to investigate the effect of feeding and fasting on plasma and stomach ghrelin, and the growth hormone/insulin-like growth factor I (IGF-I) axis in the Mozambique tilapia, a euryhaline teleost. No postprandial changes in plasma and stomach ghrelin levels or stomach ghrelin mRNA levels were observed. Plasma levels of GH, IGF-I and glucose all increased postprandially which agrees with the anabolic roles of these factors. Fasting for 4 and 8 d did not affect ghrelin levels in plasma or stomach. Plasma GH was elevated significantly after 4 and 8 d of fasting, while plasma IGF-I levels were reduced. Plasma ghrelin levels were elevated significantly after 2 and 4 wk of fasting, but no change was detected in stomach ghrelin mRNA levels. Four weeks of fasting did not affect plasma GH levels, although plasma IGF-I and glucose were reduced significantly, indicating that GH resistance exists during a prolonged nutrient deficit (catabolic state). These results indicate that ghrelin may not be acting as a meal-initiated signal in tilapia, although it may be acting as a long-term indicator of negative energy balance.