Glycogenolytic action of glucagon-family peptides and epinephrine on catfish hepatocytes

Glycogenolytic effects of salmon and mammalian glucagons, salmon glucagon-like peptide (GLP) and epinephrine were studied on liver cells isolated from catfish (Ictalurus melas). In spring and summer, salmo-glucagon (3×10^–10 to 3×10^–8 M) was more effective than its mammalian counterpart in the stimulation of glucose release and cAMP synthesis in hepatocytes. GLP was less potent as compared to both glucagons. -amylase activity was not affected by the treatment with either glucagon-family peptides or epinephrine.The comparison of the glycogenolytic effects of salmon glucagon to those of epinephrine reveals a greater potency of the latter hormone in the stimulation of cAMP synthesis, glycogen-phosphorylase activity and glucose release. Glycogen content in the liver cells was equally depleted after treatment with both of the two hormones.     

Effects of cortisol on hepatic carbohydrate metabolism and responsiveness to hormones in the sea raven,Hemitripterus americanus

The sea raven, Hemitripterus americanus, is a sit-and-wait, low metabolic rate, marine teleost. The objective of this study was to determine i) whether cortisol implantation (50 mg. kg^-1) for 7 days altered hepatocyte metabolism, and hepatocyte responsiveness to epinephrine, glucagon and insulin, and ii) whether 8 weeks of food-deprivation modified the above response. Cortisol implantation significantly increased hepatocyte total glucose production and oxidation from alanine compared to the sham group. There was no cortisol effect on glycogen breakdown, suggesting that the activation of other pathways, including gluconeogenesis, are required to account for the increased glucose production. Epinephrine-mediated (10^-5M) glycogen breakdown and insulin-mediated (10^-8M) total glucose production were enhanced in hepatocytes of cortisol implanted sea ravens, but there were no change in any glucagon (10^-7M) effects. The enhanced glycogen breakdown in the absence of similar increases in total glucose production with epinephrine indicates mobilization of carbohydrate reserves for endogenous use by the liver. Food-deprivation for 8 weeks significantly decreased condition factor, plasma cortisol concentration and liver glycogen content in the sea raven, but had no effect on plasma glucose concentration. Hepatocyte total glucose production and flux rates from alanine increased significantly with food-deprivation. Moreover, food-deprivation increased responsiveness of total hepatocyte glucose production to the actions of glucagon and insulin, but not to epinephrine; none of these effects were modified by cortisol implantation. Our results indicate that cortisol in the sea raven exerts both a direct and an indirect or permissive effect on hepatocyte metabolism by modifying hepatocyte responsiveness to epinephrine and insulin stimulation. Cortisol implantation did not modify the effects of glucagon or food-deprivation in this species.     

Hormonal regulation of metabolism in hepatocytes of the ureogenic teleostopsanus beta

Short-term exposure of isolated toadfish hepatocytes to high concentrations (100 nM) of glucagon, glucagon-like peptide (GLP) or epinephrine significantly increases the rate of lactate gluconeogenesis (1.3-fold) and glycogenolysis (5- to 7-fold). Half-maximal responsiveness to GLP is reached at about 2 nM for gluconeogenesis and 6 nM for glycogenolysis, while the value for glycogenolysis activated by catfish glucagon is 28 nM. Cells do not to respond to 5 nM epinephrine. Norepinephrine, urotensin II and leucine-enkephalin, each applied at 100 nM, increase the rate of glycogenolysis by 1.3 to 1.5-fold. All other hormones tested (vasotocin, isotocin, VIP, methionine-enkephalin, ovine prolactin, -endorphin, APY, salmon insulin) failed to affect metabolic flux through glycogenolysis or gluconeogenesis. None of the hormones altered the rate of urea synthesis or the rate of lactate oxidation by hepatocytes. Although toadfish hepatocytes are responsive to hormonal stimuli, they do not appear to be a useful model to study evolutionary trends in short-term hormonal regulation of urea synthesis. However, the obvious differences in mechanisms of control of urea synthesis in this species compared with ureogenic amphibians and mammals open an intriguing avenue for research.     

Carbohydrate metabolism and hepatic zonation in the Atlantic hagfish,Myxine glutinosa liver: effects of hormones

Viable Atlantic hagfish (Myxine glutinosa) hepatocytes were isolated from combined or separated large and small lobes and carbohydrate metabolism was studied. Cells had low levels of glycogen (16–30 μmol·g⁻¹), and low rates of total glucose production (TGP; 0–480 nmol·h⁻¹·g⁻¹ cells). Lactate flux to glucose (5.5 nmol·h⁻¹·g⁻¹) and CO₂ (76 nmol·h⁻¹·g⁻¹) was lower than reported values for teleosts, with a low percentage (30%) of the lactate carbon reaching glucose. Insulin significantly increased total glucose production and gluconeogenesis and decreased 6-phosphofructo 1-kinase (PFK-1) activities and glucose oxidation, while glucagon was without effect on any parameter studied. Forskolin significantly increased TGP. Epinephrine (Epi), norepinephrine (NEpi), isoproterenol (Iso), and phenylephrine (Phe) all decreased CO₂ production from lactate; propanolol blocked the effects of Epi, NEpi, and Iso. The large lobe, accounting for 65% of total liver mass, had a higher glycogen content and higher CO₂ production from lactate compared to the small lobe. Furthermore, enzyme activities in the large lobe were greater than in the small lobe, with the exception of glycogen phosphorylase (GPase) which exhibited smaller %a values in the large lobe. These data indicate the presence of a hormonally-responsive carbohydrate metabolism in hagfish hepatocytes, which is qualitatively and quantitatively different between the two liver lobes.     

Plasma levels of insulin,glucagon and glucagon-like peptide in salmonids of different weights

Plasma levels of insulin in rainbow trout,Oncorhynchus mykiss, Atlantic salmon,Salmo salar, and Pacific coho salmon,Oncorhynchus kisutch and plasma circulating levels of glucagon and glucagon-like peptide, in rainbow trout and Atlantic salmon, were measured by homologous radioimmunoassays. Hormonal levels were compared against the average body weight of the same group of fish. Plasma insulin levels were significantly correlated (r=0.56, 0.46 and 0.42 respectively) with body weight in all three salmonid species. Moreover, rainbow trout from fast-growing families had significantly higher (p<0.005) plasma insulin levels than did fish from slow-growing families. Plasma titres of glucagon and glucagon-like peptide were always lower than insulin titres and did not correlate with body weight.Reported in part at Satellite Symposium on Applications of Comparative Endocrinology to Fish Culture, Almunecar, Spain (Sundby, 1989).     

Response of enzyme activities and metabolic intermediate concentrations to epinephrine administration in hepatopancreas and muscle of carp

SUMMARY: Common carp Cyprinus carpio were administered intraperitoneally with 10 μmol epinephrine per 100 g bodyweight, and enzyme activities and metabolic intermediate concentrations were determined in the hepatopancreas and muscle. Glycogen phosphorylase a (GPase a) activity together with cyclic AMP (cAMP) concentration was increased, and glycogen content was decreased in the hepatopancreas and muscle at 2 h after the administration. The epinephrine administration also increased hepatopancreatic glucose-6-phosphatase and fructose-1,6-biphosphatase activities as well as serum glucose, lactate, and free amino acid concentrations. Furthermore, its administration increased phosphofructokinase activity together with lactate, fructose-6-phosphate, adenosine-5'-monophosphate, and adenosine-5'-diphosphate concentrations and decreased citrate concentration in the muscle. Thereafter, almost all parameter concentrations in the hepatopancreas and muscle recovered to the pre-administered levels during 24 h after the administration. These results suggest that epinephrine administration enhanced glycogenolysis and gluconeogenesis in the hepatopancreas, and released glucose into the bloodstream to supply it to the muscle. The blood glucose together with muscle glycogen seems to be metabolized through enhanced glycolysis in the muscle.     

The role of glycogen phosphorylase in the regulation of glycogenolysis by insulin and glucagon in isolated eel (Anguilla rostrata) hepatocytes

The effects of porcine, scombroid, and salmon insulins, and bovine and anglerfish glucagons on glycogen depletion and glycogen phosphorylase (GPase) activities were examined in freshly isolated American eel (Anguilla rostrata) hepatocytes. Eel liver GPase in crude homogenates was activated (increase in % GPase a) by phosphorylating conditions and was rapidly inactivated (less than 1 h) when a phosphatase inhibitor (fluoride) was absent. Caffeine inhibits, and AMP activates, the b form of GPase consistent with their effects on rat liver GPase. Both mammalian and fish glucagons increased glucose production in eel hepatocytes, but had more ambiguous effects on glycogen levels and GPase activities. The magnitude of bovine glucagon effects were dependent on the initial glycogen content of the cells; only at glycogen concentrations less than approximately 70 μmoles.g⁻¹ did glucagon significantly increase % GPase a. Anglerfish glucagon significantly increased cyclic AMP (cAMP) concentrations by 90% at 10⁻⁷ M, but had no effects at 10⁻⁹ M and 10⁻⁸ M. Scombroid and salmon insulins maintained hepatocyte glycogen concentrations and decreased glucose production, with these effects more pronounced at low (10⁻⁹ to 10⁻⁸ M) rather than high (10⁻⁷ M) hormone concentrations. Porcine and salmon insulins decreased total GPase and % GPase a activities, and salmon insulin decreased CAMP levels, but only at 10⁻⁸ M (by 44%). Glycogen is, therefore, depleted by glucagon and maintained by insulin in freshly isolated American eel hepatocytes, and these changes are accomplished, at least in part, by changes in the activities of GPase. Changes in cAMP do not explain all of the observed hormone effects.     

Vascular actions of neurohypophysial peptides in the flounder

Free swimming, chronically cannulated flounder have been used to study the blood pressure effects of arginine vasotocin (AVT) and isotocin. The initial fall in dorsal aortic blood pressure following AVT injection coincided with an increase in ventral aortic blood pressure, suggesting AVT caused constriction of the arterio-arterial pathway. Ventral aortic blood pressure increased in a dose dependent manner with increasing AVT dose. Dorsal aortic blood pressure also increased following the initial fall but not in a dose dependent manner, the effect at higher doses being off set by branchial vasoconstriction. Isotocin also caused dorsal aortic blood pressure to fall due to branchial vasoconstriction, but no subsequent pressor effect was seen. Branchial vasoconstriction caused by both teleost neurohypophysial peptides suggests the presence of neurohypophysial peptide receptor(s) in the gill, although it is unclear as to whether this is a single common receptor or different populations for each peptide. The dorsal aortic pressor effect of AVT and its absence following isotocin injection suggests there may be other types of neurohypophysial receptors in post-branchial vascular beds. The vascular actions of AVT and isotocin suggest that these peptides may play some role in the regulation of blood pressure or regional blood flow distribution.     

氨氮胁迫对锦绣龙虾代谢酶和抗氧化酶活力的影响

为了研究急性氨氮胁迫对锦绣龙虾(Panulirus ornatus)抗氧化系统及氨氮代谢机制的影响,通过设置对照[(0.24±0.07)mg/L]、低浓度[(1.04±0.08)mg/L]、中浓度[(9.75±0.21)mg/L]和高浓度[(19.87±0.46)mg/L]氨氮胁迫方法对锦绣龙虾进行48 h急性实验,测...     

Metabolic enzyme activities in larvae of the African catfish,Clarias gariepinus: changes in relation to age and nutrition

The influence of ontogeny and nutrition on metabolic enzyme activities in larvae of the African catfish, Clarias gariepinus, was studied. After start of exogenous feeding, the larvae were reared for 10 days under three different nutritional conditions: Artemia nauplii, a dry starter diet, and starvation. The live feed gave the best growth (96 mg within 10 days) whereas the dry diet resulted in low growth (33 mg). This growth difference was reflected in larval RNA and DNA concentrations, but not in the levels of soluble protein. Enzymes representing the following aspects of metabolism have been analysed: NADPH generation (G6PDH, ME), glycolysis (PFK, PK), gluconeogenesis (FDPase), amino acid catabolism (GOT, GPT) and oxidative catabolism (CS). All enzymes were present from the start of exogenous feeding onwards, but their maximum specific activities displayed different developmental patterns. In catfish larvae fed on Artemia, G6PDH and ME activities steadily increased with age and weight of the larvae. CS levels remained, after an immediate enhancement upon onset of exogenous feeding, on a rather stable plateau. The amino acid-degrading enzymes GOT and GPT showed maximum levels at days 3–5 of feeding or at a body weight of 10–20 mg, but decreased thereafter. Activities of PFK, PK and FDPase showed low initial levels, and increased significantly with age and size. Based on the ontogenetic patterns of metabolic enzymes, in C. gariepinus larvae an early and a late developmental phase can be distinguished. During the early phase, the glycolytic and gluconeogenetic capacities are low, whereas they are enforced during the later phase. The oxidative capacity is high both during the early and the late phase. The metabolic changes in catfish development coincide with other major ontogenetic events, e.g., alterations of muscle organization, gill morphology, respiration and stomach structure and function. Rearing catfish larvae on a dry diet instead of Artemia partly altered the developmental pattern described: The ontogenetic elevation of CS, PFK and FDPase was delayed and the early peak in GOT and GPT activities was not realized. Particularly during the early developmental phase, the enzyme behaviour of the larvae fed on dry food was similar to that of starved larvae.Abbreviations CS citrate synthase - FDPase fructose-1,6-diphosphatase - GOT glutamate oxaloacetate transaminase - GPT glutamate pyruvate transaminase - G6PDH glucose-6-phosphate dehydrogenase - ME malic enzyme - PFK phosphofructokinase - PK pyruvate kinase     

鱼类生长抑素调控垂体生长激素分泌的作用机制

生长抑素是一个多基因、多功能的家族。通过其受体的介导参与机体的生长、发育、代谢、生殖以及免疫等生理过程。本文简要概括鱼类生长抑素及其受体的研究进展,重点对生长抑素调控垂体生长激素分泌的信号转导机制进行概括讨论,旨在加深对鱼类生长抑素作用机制的认识和了解。迄今,在鱼类中已经鉴定出六种生长抑素基因和四种生长抑素受体。由于存在多种生长抑素基因以及不同的加工过程,一种鱼可能产生多种形式的生长抑素多肽。鱼类进化过程中存在基因组复制,导致一种受体又有多种亚型。鱼类生长抑素调控垂体生长激素分泌的作用机制主要源自金鱼中的研究,结果表明cAMP通路、钙离子通道以及PKC通路可能参与了金鱼生长抑素抑制垂体生长激素分泌的过程。生长抑素调控垂体生长激素分泌的作用机制是一个复杂的网络结构,多种信号通路参与其中;不同的物种间其作用机制不尽相同。鱼类生长抑素基因、受体及其调控垂体生长激素分泌的作用机制仍有待进一步研究。     

不同糖及糖水平对松浦镜鲤养殖过程中糖代谢相关基因表达的影响

为探讨在养殖不同阶段,不同糖及糖水平对松浦镜鲤肝脏糖酵解酶(GK和HK)、糖异生酶(G6Pase和PEPCK)和糖代谢相关基因(IGF-Ⅰ和GHR)m RNA表达水平的影响,实验采用2×2双因素设计实验,选择淀粉和葡萄糖2种糖源,2个糖水平(25%和50%),共4个实验组,分别为低淀粉组(LS)、高淀粉组(HS)、低葡萄糖组(LG)和高葡萄糖组(HG)。选用初始体质量为(8.30±0.15)g的松浦镜鲤420尾,随机分为4组,每组3个重复,每个重复35尾鱼。实验周期为7周。结果显示,不同养殖阶段,HK基因和IGF-Ⅰ基因在不同实验组中的表达趋势基本一致,HK基因在养殖1周时表达量显著升高,之后开始降低,IGF-Ⅰ基因在养殖3周时表达量显著升高。在不同养殖阶段,GK、PEPCK、G6Pase和GHR基因的表达趋势受糖水平和糖种类的影响。在低糖水平下(LS组和LG组),这些基因表现了相同的变化趋势,GK和GHR基因在1周时表达量最高,之后开始下降;PEPCK基因在3周时表达量最高;G6Pase在1周时表达量升高,之后下降,在7周时表达量又有上升趋势。在高糖水平下,HS组的GK基因的表达量在各个养殖阶段差异不显著,而HG组的GK基因则在1周时表达量显著升高;HS组和HG组的PEPCK基因的表达量在各个养殖阶段差异不显著;HS组的G6Pase基因的表达量在各个养殖阶段差异不显著,而HG组的G6Pase基因则在3周时表达量显著升高;HG组的GHR基因的表达量在各个养殖阶段差异不显著,而HS组的GHR基因则在3周时表达量显著升高。在养殖初期(1周),高糖饲料显著促进了HK基因的表达,并抑制了PEPCK、G6Pase和GHR基因的表达。     

铜对刀鲚幼鱼的急性毒性及对肝抗氧化酶活性与组织结构的影响

采用静水生物测试法研究铜(Cu²⁺)对刀鲚(Coilia nasus)幼鱼的急性毒性并进行安全性评价。根据预实验结果, 设定0.3、0.54、0.96、1.68 和3 mg/L 5个CuSO₄浓度梯度进行急性暴露实验, 以肝组织超氧化物歧化酶(SOD)、过氧化氢酶(CAT)活性为指标, 并通过观察肝、鳃组织病理变化来研究Cu²⁺污染对刀鲚幼鱼的毒性效应。结果表明, 刀鲚幼鱼随Cu^{2 +} 浓度升高毒性效应逐渐增强, 24、48、72和96 h LC₅₀分别为1.087、1.062、1.042和0.967 mg/L, 安全质量浓度为0.009 67 mg/L。刀鲚幼鱼暴露24 h之后, 各Cu²⁺浓度处理组(0.1, 0.2, 0.3 mg/L) CAT活性、SOD活性显著提高(P<0.05); 暴露48 h后, 各组CAT活性下降, CAT活性均低于对照组, 下降幅度与Cu^{2 +}质量浓度呈正相关, SOD活性提高显著(P<0.05); 暴露72 h后, SOD活性有所下降, SOD活性均低于对照组(P<0.05)。1.68 mg/L和3 mg/L的Cu²⁺浓度对刀鲚幼鱼的鳃和肝都造成严重的损伤, 暴露在高浓度组(3 mg/L)中的刀鲚, 其鳃上皮细胞肿大变性, 鳃小片几乎全部脱落; 肝呈黄色, 超微结构发现肝细胞明显增大, 线粒体空泡化, 胞质中出现空泡和大量脂滴, 表明Cu²⁺可诱发刀鲚出现脂肪肝综合征。SOD、CAT活性变化以及鳃、肝结构变化都反映刀鲚幼鱼受伤害的程度, 可用作安全性风险评价的参考依据。     

低盐胁迫对黄姑鱼幼鱼肝脏抗氧化功能的影响

该实验设置3个盐度梯度（9、16、23,分别记为S9、S16、S23）,其中S23为对照组,对黄姑鱼（Nibea albiflora）幼鱼进行低盐度胁迫,于第0、第1、第3和第7天进行取样。通过检测肝脏超氧化物歧化酶（SOD）、过氧化氢酶（CAT）、谷胱甘肽过氧化酶（GSH-Px）和总抗氧化能力（T-AOC）,以及肝脏和血清的丙二醛（MDA）质量摩尔浓度,研究低盐度对黄姑鱼抗氧化系统的影响。结果显示,肝脏SOD活力呈上升后下降变化,而CAT活力呈减弱后增强而后再减弱的变化。肝脏GSH-Px活力出现了显著增强（P 0.05）。且盐度越低,活力变化越剧烈。肝脏T-AOC在盐度16下呈现显著增强后减弱变化（P 0.05）,而S9组T-AOC显著减弱后维持在较低水平（P 0.05）。S9组肝脏与血清b(MDA)有显著升高（P 0.05）,而S16组肝脏b（MDA）呈上下波动变化,血清b(MDA)则略有下降。实验表明,盐度降低可显著影响黄姑鱼肝脏的抗氧化功能,而黄姑鱼对低盐度有较强适应能力,但胁迫过强会消耗机体储备,降低机体抵抗力,损伤鱼体。     

Osmoregulatory actions of growth hormone and its mode of action in salmonids: A review

Osmoregulatory actions of growth hormone (GH) and its mode of action in salmonids are reviewed. We present evidence suggesting that insulin-like growth factor I (IGF-I) mediates some of the actions of GH on seawater acclimation. Plasma concentration and turnover of GH rise following exposure to seawater. Exogenous GH (in vivo) increases gill Na⁺,K⁺-ATPase activity and the number of gill chloride cells, and inhibits an increase in plasma osmolarity and ions following transfer of fish to seawater. A single class of high affinity GH receptors is present in the liver, gill, intestine, and kidney. The levels of IGF-I mRNA in the liver, gill and kidney increased after GH-injection. After transfer to seawater, IGF-I mRNA increased in the gill and kidney following the rise in plasma GH, although no significant change was seen in the liver. Injection of IGF-I improved the ability of the fish to maintain plasma sodium levels after transfer to seawater. GH treatment also sensitizes the interrenal to adrenocorticotropin (ACTH), increasing cortisol secretion. Both cortisol and IGF-I may be involved in mediating the action of GH in seawater adaptation, although studies on the effect of GH on osmoregulatory physiology of non-salmonid species are limited. An integrated model of the osmoregulatory actions of GH is presented, and areas in need of research are outlined.

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Résumé Cet article est une revue des effets osmorégulateurs de l'hormone de croissance et de son mode d'action. Nous présentons des résultats qui suggèrent que le facteur de croissance de type insuline (IGF-I) est un médiateur de certaines des actions de la GH sur l'adaptation à l'eau de mer. Les concentrations plasmatiques et le renouvellement de la GH augmentent après transfert en eau de mer. La GH exogène stimule (in vivo) l'activité Na⁺,K⁺-ATPase et le nombre de cellules à chlorure branchialeset inhibe les augmentations de l'osmolarité et des concentrations ioniques du plasma observées après transfert en eau de mer. Une seule classe de récepteurs à haute affinité pour la GH est présent dans le foie, les branchies, l'intestin et le rein. Les niveaux d'ARNm d'IGF dans le foie, les branchies et le rein augmentent après injection de la GH. Après transfert en eau de mer, les ARNm de l'IGF augmentent dans les branchies et dans le rein en suivant l'augmentation de GH plasmatique, bien qu'aucune modification ne soit observée au niveau du foie. L'injection d'IGF augmente la capacité du poisson à maintenir ses niveaux de sodium plasmatique après transfert en eau de mer. Le traitement à la GH augmente la sensibilité à l'adrenocorticotropine (ACTH) et stimule donc les niveaux de cortisol. A la fois le cortisol et l'IGF-I semblent impliqués comme médiateurs des effets de la GH dans l'adaptation à l'eau de mer, bien que les études sur les effets de la GH sur la physiologie de l'osmorégulation chez les espèces non-salmonidés restent encore limitées. Un modèle intégré des actions de la GH sur l'osmorégulation est présenté et les domaines de recherche à développer sont soulignés.

     

Gluconeogenesis in trout (Oncorhynchus mykiss) white muscle: purification and characterization of fructose-1,6-bisphosphatase activity in vitro

Studies of the enzyme fructose-1,6-bisphosphatase (FBPase) of rainbow trout (Oncorhynchus mykiss) have been undertaken in order to illuminate aspects of skeletal muscle gluconeogenesis in these animals. Maximal activities in crude homogenates of several organs suggest that the liver possesses the greatest FBPase activity on a unit g^–1 tissue basis but that the white muscle, owing to its bulk, contributes substantially to whole body FBPase activity. Studies of fructose-6-phosphate-1-kinase (PFK) and FBPase in crude homogenates of several organs suggests an important role for intracellular pH in regulating the relative carbon flux through the FBPase/PFK locus in vivo. Furthermore, a three-step purification scheme is described for trout white muscle FBPase by which a stable and homogeneous (by SDS PAGE) enzyme preparation (isoelectric point = 7.2; molecular weight = 37.6 kd) was obtained. Kinetic studies of the purified enzyme were undertaken at 20°C under conditions reflective of "rest" and "exercise/recovery" intramuscular pH in vivo. Affinity for substrate (F-1,6-P₂) was increased (Km = 6.88 versus 2.44 mol 1-^–1 as was enzyme activity when pH was lowered from 7.0 to 6.5. Various inhibitor metabolites are identified including F-2,6-P₂ (mixed-type inhibitor, K_i = 0.201 mol 1^–1, pH 7.0) and AMP (non-competitive inhibitor, K_i = 0.438 mol 1^–1, pH 7.0). Inhibition by F-2,6-P₂ was strongly alleviated by a reduction in pH from 7.0 to 6.5 (I₅₀ increased from 0.14 to 0.32 mol 1^–1). AMP on the other hand was a more potent inhibitor at pH 6.5 but this inhibition was totally reversed under conditions of citrate, NH₄ ⁺ and AMP typical of muscle during recovery from exercise in vivo. In purified white muscle enzyme preparations, FBPase demonstrated maximal activity at pH 6.5 whereas the optimal pH of PFK was 7.0 or greater. Indeed, it appears from these in vitro data that regulation by metabolite levels as well as pH are required for net FBPase flux in vivo. It is concluded, therefore that trout white muscle FBPase demonstrates the potential to play an important enzymatic role in the control of intramuscular gluconeogenesis in these animals. The results are discussed in relation to present knowledge regarding the metabolic responses of trout white muscle to, and its subsequent recovery from, exhaustive exercise.     

低温胁迫对点篮子鱼幼鱼肝脏抗氧化酶活性及丙二醛含量的影响

将点篮子鱼(Siganus guttatus)幼鱼由25℃转移至14℃、15℃、16℃、17℃和18℃条件下处理96h,测定在不同温度下、不同时间点点篮子鱼幼鱼肝脏抗氧化酶活性和丙二醛(MDA)含量变化,探讨了温度骤降对点篮子鱼幼鱼肝脏抗氧化酶活性的影响。结果显示:随着温度的降低和处理时间的延长,除14℃组外,其余各组超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和谷胱甘肽过氧化物酶(GPX)活性均呈现先升后降的趋势;14℃组,SOD和GPX活性在3 h时达到最高值,随着处理时间的延长,酶活性持续下降,在96 h时达到最低;14℃组CAT活性在处理后持续降低,在12 h时达到最低,之后逐渐升高并在96 h时显著高于对照组。所有处理组中MDA含量随着处理时间的延长呈现出先升高后降低的趋势,最终各组MDA含量均显著高于对照组(P0.05)。实验表明,温度骤降能激活点篮子鱼幼鱼肝脏中抗氧化酶活性,消除低温应激产生的活性氧自由基(ROS),但肝脏内MDA含量显著增加,表明点篮子鱼仍处于氧化应激状态。在14℃时,抗氧化酶活性变化趋势与25℃及其余温度处理组间均存在明显差异,表明此实验条件下鱼体不能适应14℃的温度。     

蓝点马鲛鱼皮抗氧化肽FractionⅡ对D-Gal诱导氧化损伤大鼠肝脏的保护作用

研究蓝点马鲛鱼皮抗氧化肽FractionⅡ(1~4 ku)对氧化损伤Wistar大鼠肝脏的保护作用。采用D-半乳糖(D-gal)建立衰老模型,实验大鼠随机分为6组:空白对照组;D-Gal模型阴性对照组;D-Gal+维生素E(VE)阳性对照组;抗氧化肽低、中、高剂量组。通过检测血清中谷草转氨酶(AST)、谷丙转氨酶(ALT)和单胺氧化酶(MAO)活性及肝组织匀浆液中超氧化物岐化酶(SOD)、谷胱甘肽过氧化物酶(GSH-Px)、过氧化氢酶(CAT)活性,丙二醛(MDA)、一氧化氮(NO)含量和总抗氧化能力(T-AOC),并结合组织形态学来评价FractionⅡ对氧化损伤肝脏的作用效果。结果显示,与阴性对照相比,各剂量组的FractionⅡ能够显著降低大鼠血清中的AST和ALT活性,提高肝脏组织的SOD、GSH-Px、CAT活性和T-AOC能力,降低MDA和NO含量及MAO水平,并成一定的量效依赖关系。其中效果较好的高剂量(200 mg/kg)多肽处理组SOD、GSH-Px活性分别为236.27、182.23 U/mg蛋白,达到了正常对照及阳性对照组水平;AST、ALT分别降低至302.47和220.43 U/L,MDA含量降低至138.83 nmol/mg蛋白,也达到正常对照组水平。H.E.染色结果也证实,FractionⅡ在保护肝细胞完整性、维持结构清晰、抑制坏死等方面都有一定的效果。研究表明,蓝点马鲛鱼皮抗氧化肽FractionⅡ对D-Gal诱导的氧化损伤大鼠肝脏具有较好的保护作用。     

Seasonal changes of hormones and muscle enzymes in adult lacustrine masu (Oncorhynchus masou) and sockeye salmon (O. nerka)

The upstream migration of adult anadromous fishes is characterized by physiological changes in responses to reproductive and energetic challenges. This study analyzed the physiological responses of lake-resident anadromous masu salmon (Oncorhynchus masou) and sockeye salmon (O. nerka) to migration in order to determine if these fish might serve as a suitable model for ocean-running populations and to differentiate between physiological responses to reproduction and to exercise-linked aspects of migration. Reproductive (estradiol, testosterone, 11-ketotestosterone, 17α,20β-dihydroxy-4-pregnen-3-one) and metabolically-linked (thyroxine, triiodothyronine) hormones showed similar patterns to ocean-running anadromous populations. White muscle pyruvate kinase, lactate dehydrogenase and malate dehydrogenase decreased with the onset of spawning season while white muscle citrate synthase, β-hydroxyacetyl CoA dehydrogenase, phosphofructokinase and glutamate oxaloacetate transaminase did not, suggesting that the former group of enzymes are responding to reproductive or food intake signals while the second group, which typically change during anadromous migration, may be responding to exercise-linked aspects of migration. This revised version was published online in August 2006 with corrections to the Cover Date.