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At least 163 records · Page 9Linked to original sources
PubMed2002

Citrate carrier activity and cardiolipin level in eel (Anguilla anguilla) liver mitochondria.

The activity of the tricarboxylate (citrate) carrier has been assayed in intact liver mitochondria from yellow eel (Anguilla anguilla) and compared to that from rat. The eel-citrate carrier specific activity was approximately 1.7-fold higher than that assayed in rat-liver mitochondria. The content of the main mitochondrial phospholipids, phosphatidylethanolamine and phosphatidylcholine, did not show a significant difference between the two species, while in eel a higher cardiolipin level was observed. Fatty acid composition of eel-liver mitochondrial phospholipids was characterised by a large amount of unsaturated fatty acids, dominated by octadecaenoic acid (C(18:1) (n-9)) and docosahexaenoic acid (C(22:6) (n-3)). The cardiolipin fatty acid pattern of eel-liver mitochondria showed, with respect to the rat, a higher C(20:5) (n-3) and C(22:6) (n-3) content and a lower amount of C(18:2) (n-6) and C(20:4) (n-6). A noticeable activity of lipogenic enzymes was also detected in eel liver cytosol. The results of this study suggest that the remarkable activity of the citrate carrier in eel-liver mitochondria can most likely be ascribed to a considerable cardiolipin level. A covariance of citrate carrier and lipogenic enzyme activities was observed.

Animals↗
PubMed2004

Applying DNA techniques to the identification of the species of dressed toasted eel products.

To differentiate the species of processed eel products, the gene identification of four fresh eel species was first established and the species of eel products collected from markets were investigated. Polymerase Chain Reaction (PCR) and sequence analysis were used to determine the genetic variation in a 362-nucleotide region of the mitochondrial cytochrome b gene in four fresh eels including Anguilla japonica, Anguilla anguilla, Anguilla rostrata, and Muraenesox cinereus. It was found that each eel species had a unique genotype, which was no different among fresh, frozen, and sterilized meats. The restriction enzyme HinfI could differentiate the species of A. japonica and A. rostrata but could not differentiate A. anguilla and M. cinereus. Another restriction enzyme, Sau96 I, was valuable in the differentiation of M. cinereus from the other three species of Anguilla. By applying PCR and restriction enzymes, the species of 12 commercial eel products were identified as A. japonica (9 samples), A. anguilla (2), and A. rostrata (1). This indicated that the sequence and restriction enzyme cutting site analyses were very usable to authenticate species of different processed eel products.

Anguilla↗
PubMed1976

Eel esophagus as an osmoregulatory organ.

Ion and water permeabilities were measured in the isolated esophagus of the eel (Anguilla anguilla and A. japonica), and compared with those in the stomach and the intestine. The freshwater eel esophagus was impermeable both to Na+ and Cl- ions and to water, whereas permeabilities to the ions increased selectively after seawater adaptation. The ion permeabilities of both the freshwater and the seawater eel stomach were lower than in the seawater eel esophagus, although water permeability was greater than in the esophagus. Sea water enclosed in the lumen was diluted three times more efficiently in the seawater eel esophagus than in the stomach. The intestinal permeabilities were greater than those of the esophagus and the stomach, and increased after seawater adaptation. In the eel, ingested sea water seems to be diluted mainly in the esophagus by passive diffusion of the ions into the blood without addition of water. After further but less important dilution in the stomach with salt removal and with water addition, the water is absorbed by the intestine, following active absorption of the ions. Thus the eel in sea water is able to replace water lost osmotically by drinking hypertonic sea water.

Animals↗
PubMed1995

Cloning, properties, site-directed mutagenesis analysis of the subunit structure, tissue distribution and regulation of expression of the type-C eel natriuretic peptide receptor.

Eel natriuretic peptide receptor C (NPR-C) was cloned, characterized and found to have a unique interchain disulfide linkage when compared to that of mammalian NPR-C. The NPR-C cDNA was obtained from an eel gill cDNA library; the open reading frame codes for a polypeptide of 502 amino acids exhibiting the known features of NPR-C, including a weak ligand specificity and a disulfide-linked homodimeric structure. The deduced amino acid sequence shares approximately 60% similarity with the mammalian NPR-C but it lacks the Gly-rich prosequence present in the mammalian counterparts. Site-directed mutagenesis revealed that eel and mammalian NPR-C are quite different in their interchain disulfide-bonding pattern; eel uses the second Cys residue and mammals the fifth Cys residue for the covalent dimerization. The ligand-binding activity of the extracellular domain is not independent of the short cytoplasmic tail. RNase protection analysis revealed that the eel receptor is highly expressed in the gill and heart and, to a much lesser extent, in other tissues including the brain and intestine. The NPR-C mRNA levels were found to be down-regulated in most tissues when eels were transferred from fresh water to seawater; however, in the anterior intestine, the levels were up-regulated, suggesting that NPR-C plays a role in the adaptation to salinity changes in the euryhaline eel.

Amino Acid Sequence↗
PubMed2005

Roles of Slc13a1 and Slc26a1 sulfate transporters of eel kidney in sulfate homeostasis and osmoregulation in freshwater.

Sulfate is required for proper cell growth and development of all organisms. We have shown that the renal sulfate transport system has dual roles in euryhaline eel, namely, maintenance of sulfate homeostasis and osmoregulation of body fluids. To clarify the physiological roles of sulfate transporters in teleost fish, we cloned orthologs of the mammalian renal sulfate transporters Slc13a1 (NaSi-1) and Slc26a1 (Sat-1) from eel (Anguilla japonica) and assessed their functional characteristics, tissue localization, and regulated expression. Full-length cDNAs coding for ajSlc13a1 and ajSlc26a1 were isolated from a freshwater eel kidney cDNA library. Functional expression in Xenopus oocytes revealed the expected sulfate transport characteristics; furthermore, both transporters were inhibited by mercuric chloride. Northern blot analysis, in situ hybridization, and immunohistochemistry demonstrated robust apical and basolateral expression of ajSlc13a1 and ajSlc26a1, respectively, within the proximal tubule of freshwater eel kidney. Expression was dramatically reduced after the transfer of eels from freshwater to seawater; the circulating sulfate concentration in eels was in turn markedly elevated in freshwater compared with seawater conditions (19 mM vs. 1 mM). The reabsorption of sulfate via the apical ajSlc13a1 and basolateral ajSlc26a1 transporters may thus contribute to freshwater osmoregulation in euryhaline eels, via the regulation of circulating sulfate concentration.

Amino Acid Sequence↗
PubMed1997

Characterisation of natriuretic peptide receptors in eel gill.

A radioligand-binding assay was established for eel atrial natriuretic peptide (eANP), and ANP receptors were characterised in the eel gill. ANP binding to the gill membrane fraction was saturable with increasing ligand concentrations and was specific to ANP peptides, i.e. eANP, ventricular natriuretic peptide (VNP) and C-type natriuretic peptide (CNP). A Scatchard analysis revealed a single class of high-affinity receptors with a Kd of 59.2 pM and a Bmax of 67.9 fmol/mg protein. The Kd value is within the range of plasma ANP concentration of the eel. Kd and Bmax did not differ between freshwater (FW)- and seawater (SW)-adapted fish. The gill receptors exhibited similar affinity for eANP, eVNP and eCNP, and ANP binding was almost completely displaced by C-ANF, a specific ligand for guanylate cyclase-uncoupled receptors. The presence of this type of receptor (natriuretic peptide receptor (NPR)-C and NPR-D) was also indicated in eel gill by affinity labelling. cGMP production was stimulated by the addition of eCNP but not by eANP and eVNP, and this was observed only in FW eels. Thus, most ANP receptors in eel gill are NPR-C and NPR-D, but a small number of the NPR-B type are also present in FW eels. In addition to the gill, specific ANP receptors were detected in the red body of the swim bladder, the brain, digestive tracts, kidney, head kidney and urinary bladder, in most of which ANP action has been reported. The density of ANP receptors decreased in most tissues after adaptation to SW except the gill, brain, atrium and spleen.

Adaptation, Physiological↗
PubMed1999

Indole-positive Vibrio vulnificus isolated from disease outbreaks on a Danish eel farm.

Vibrio vulnificus was isolated in 1996 from 2 disease outbreaks on a Danish eel farm which used brackish water. A characteristic clinical sign was extensive, deep muscle necrosis in the head region. V. vulnificus was isolated from kidney, mucus, spleen, gill and intestine of diseased eels. Thirty-two isolates were examined phenotypically and serologically for pathogenicity to eels and for correlation to ribotype and plasmid profile. Biochemically, the isolates showed properties similar to those described previously for eel-pathogenic strains of V. vulnificus, with the exception of indole production. Virulence was evaluated by LD50 (the 50% lethal dose), which ranged from < 9.4 x 10(3) to 2.3 x 10(5) CFU (colony-forming units) per fish. The isolates which were lethal for eels showed identical ribotypes and serotypes. A relationship between certain plasmids and virulence was not found. A serotyping system based on lipopolysaccharide (LPS)-associated O antigen type and on carbohydrate capsule antigens showed that the eel-virulent isolates shared a common LPS-based homogeneous O serogroup and a capsule antigen. V. vulnificus serovar O4 and capsule type 9 was identical serologically to the Japanese isolate ATCC 33149 and was the agent responsible for the disease outbreaks that occurred on the Danish eel farm. Despite absence of antibiotic resistance, treatment had little effect and disease reoccurred.

Animals↗
PubMed2001

Field testing of a vaccine against eel diseases caused by Vibrio vulnificus.

The field results of a vaccination programme against Vibrio vulnificus serovar E (biotype 2) in a Spanish eel farm are reported. A total of 9.5 million glass eels were vaccinated from January 1998 to March 2000 by prolonged immersion followed by 2 subsequent reimmunisations after 12 to 14 and 24 to 28 d, respectively. The acquired protection and the immune response against serovar E were estimated over a period of 6 mo after vaccination. A similar vaccination schedule was conducted with elvers in a Danish eel farm. In this case, the acquired protection and the immune response against serovar E and the new eel-pathogenic serovars, recently described in Denmark, were evaluated over a short term. The overall results show that the vaccine against V. vulnificus serovar E induces a satisfactory protective immunity during the main growth period of eels (around 6 mo) with a relative percentage survival of 62 to 86% and protects them against the new eel-pathogenic serovars. Vaccination of eels by immersion seems to be the best strategy to prevent diseases caused by V. vulnificus.

Animals↗
PubMedDate not supplied

Does hydrostatic pressure have an effect on reactive oxygen species in the eel?

Eels are submitted to hydrostatic pressure (HP) during their spawning migration (about 6000 Km). Before migration, they change from the yellow to the silver stage (silvering process). The effects of HP in relation to the silvering process have been studied on aerobic metabolism and more precisely on reactive oxygen species (ROS) metabolism. HP acclimatization of yellow eels improves oxidative phosphorylation together with supposed concomitant changes in electron leak and ROS production. Therefore hydroxyl radical (OH*) production, superoxyde dismutase and catalase activities, malondialdehyde content and in parallel oxygen consumption were measured in the red muscle of long-term pressure exposed and control group yellow and silver eels. At atmospheric pressure, yellow eels exhibited significantly higher oxygen consumption and OH* production than silver eels; and significantly lower malondialdehyde content. This could be due to the increase in membrane fluidity induced by the silvering process. Long-term HP exposure decreases yellow eel oxygen consumption which becomes similar to that of the silver stage. In parallel there is a decrease in OH* production and concomitantly antioxidant enzyme activities follow the same tendency. Thus the respiratory chain improvement in pressure acclimatized yellow eels is accompanied by a ROS production decrease which could mean an electron leak decrease.

Acclimatization↗
PubMed1993

A C-terminal fragment of the hormone stanniocalcin is bioactive in eels.

An in vivo eel bioassay based on 45Ca uptake from the ambient medium was used to compare the activity of native trout and American eel stanniocalcin (STC) with that of a synthetic C-terminal fragment (AA 202-231; peptide W) of Australian eel STC. Qualitatively, the action of peptide W resembled that of purified native rainbow trout (Oncorhynchus mykiss) STC as well as fresh extracts of American eel Stannius corpuscles in that they all inhibited whole animal Ca2+ influx. This inhibition was observed in both intact and stanniectomized eels regardless of whether the eels were exhibiting high or low initial calcium uptake rates. These observations suggest that peptide W activates eel gill STC receptors. Further, as peptide W was previously reported to stimulate Ca2+ influx in intact rainbow trout fry, the present data provides evidence for a difference in the way this fragment functions in various species.

Anguilla↗
PubMed2000

Molecular cloning and tissue-specific expression of a gonadotropin-releasing hormone receptor in the Japanese eel.

Gonadotropin-releasing hormone (GnRH) is a key regulatory neuropeptide involved in the control of reproduction in vertebrates. In the Japanese eel, one of the most primitive teleost species, two molecular forms of GnRH, mammalian-type GnRH and chicken-II-type GnRH (cGnRH-II), have been identified. This study has isolated a full-length cDNA for a GnRH receptor from the pituitary of the eel. The 3233-bp cDNA encodes a 380-amino acid protein which contains seven hydrophobic transmembrane domains and N- and C-terminal regions. The exon/intron organization of the open reading frame of the eel GnRH receptor gene was also determined. The open reading frame consists of three exons and two introns. The exon-intron splice site is similar to that of the GnRH receptor genes of mammals reported so far. Expression of the eel GnRH receptor was detected in various parts of the brain, pituitary, eye, olfactory epithelium, and testis. This result suggests that GnRH has local functions in these tissues in addition to its actions on gonadotropin synthesis and release in the pituitary. This tissue-specific expression pattern is similar to that of the eel cGnRH-II. Furthermore, the present eel receptor shows very high amino acid identity with the catfish and goldfish GnRH receptors, which are highly selective for the cGnRH-II. These results suggest that the cGnRH-II acts through binding to the present receptor in the eel.

Amino Acid Sequence↗
PubMed1983

Effects of steroid hormones on pituitary immunoreactive gonadotropin in European freshwater eel, Anguilla anguilla L.

The low pituitary immunoreactive gonadotropin (IR GTH) contents of immature female or male freshwater eels were strongly increased after intraperitoneal injections of estradiol. Using female eels, the effect was shown to be dose dependent. In neither sex was modification of pituitary IR GTH observed after progesterone treatment; a very small increase (significant in females but not in males) was produced by cortisol. An important sexual difference occurred with testosterone, which strongly stimulated pituitary IR GTH level in male but not in female eels. The possibility of a low central aromatase activity responsible for the lack of effect of testosterone in the female eel is discussed. Circulating IR GTH levels were very low in steroid-treated eels, as in controls, indicating a weak GTH release. Thus, as in juvenile, immature fish from other species, a sexual steroid stimulated eel pituitary GTH content; the peculiarity of the apparent "blockade" of eel sexual development appears not related to a lack of sensitivity of gonadotropin synthesis to the positive feedback of a sexual steroid.

Anguilla↗
PubMed1990

Evidences for the presence of a somatomedin-like plasma factor(s) in the Japanese eel, Anguilla japonica.

The indirect action of growth hormone (GH) through a somatomedin-like plasma factor(s) on the synthesis of mucopolysaccharides in the ceratobranchial cartilages of the Japanese eel, Anguilla japonica, was studied by monitoring the uptake of [35S]sulfate in vitro. Addition of plasma obtained from intact eels significantly stimulated the sulfate uptake by the cartilages of hypophysectomized eel, whereas plasma from hypophysectomized eels had no effect. On the other hand, the plasma from hypophysectomized eels which had been injected with eel GH significantly stimulated the uptake. The maximal stimulating activity was found in the plasma 24 hr after a single injection of eel GH (2 micrograms/g). This stimulatory activity was dependent on the dose of GH injected. These findings indicate that GH elicits its effect on the cartilages indirectly through a GH-dependent plasma factor(s). The system established in the present study can provide as a biological assay for the somatomedin-like plasma factor(s).

Anguilla↗
PubMed1986

Effect of hypophysectomy on absorption of inorganic phosphate by the eel intestine.

Hypophysectomy of freshwater-adapted eels resulted in a marked reduction in net absorption of PO4(3-) in the non-stripped and non-everted intestine. Stanniectomy was without effect on net movements of water and electrolytes in this isolated eel preparation. Repeated injections of eel calcitonin into the eel, kept either in deionized water or 10 mM CaCl2, had no effect on net absorption of water and electrolytes, including Ca2+ and PO4(3-). In the stripped and everted intestine, the net PO4(3-) absorption was significantly greater in the fed eel than in the starved fish. Hypophysectomy of the fed eel resulted in a significant reduction, not only in PO4(3-) absorption, but also in absorption of water and other electrolytes. It is suggested that pituitary hormone is involved in the intestinal PO4(3-) absorption of the eel.

Anguilla↗
PubMed1994

Developmental changes in the content of dopamine in the olfactory bulb of the European eel (Anguilla anguilla).

The concentrations of dopamine (DA) and of its major metabolite, dihydroxyphenylacetic acid (DOPAC), were measured in discrete areas of the eel brain. To investigate the developmental changes in the content of DA and DOPAC, the assays were performed in yellow eels (i.e. at the feeding stage) and silver eels (i.e. at the migratory stage). DA and DOPAC were unevenly distributed in the eel brain. In yellow eels, the concentration of DA was highest (16-19 pmol/mg protein) in the olfactory bulb (OB), mesencephalic tectum-diencephalon (MT-D) and medulla oblongata (MO) and lowest in the cerebellum (CB, 1 pmol/mg protein), whereas intermediate values were measured in the telencephalon (TE; 10 pmol/mg protein). The metabolic rate of DA, as reflected by the DOPAC/DA ratio, was highest in the OB and CB, with progressively smaller values being observed in the TE, MT-D, and MO. A significant increase in the concentrations of DA (+80%) and DOPAC (+122%) was observed in the OB of silver eels compared with yellow eels, whereas no significant differences were detected in the concentrations of DA and DOPAC in the other brain areas as a function of the developmental stage. The results are discussed in terms of the possible involvement of environmental, behavioral and developmental factors.

3,4-Dihydroxyphenylacetic Acid↗
PubMed2005

A quantitative real-time RT-PCR assay for European eel tyrosine hydroxylase.

Dopamine (DA) plays a key inhibitory role in pubertal development of the European eel, but how DAergic neuronal activity is regulated is not known in this species. In order to investigate the regulation of DA inhibition at the molecular level, we developed a quantitative real-time RT-PCR (qrtRT-PCR) assay, using the Light Cycler system, for the expression of eel tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis. Two different reference genes were compared: the previously cloned eel cytochrome b, and eel acidic ribosomal phosphoprotein P0, the latter of which we cloned and partly sequenced. To further validate the assay, different methods of total RNA extraction were tested and compared. When applied to cDNA extracted from dissected brains of juvenile eels, the expression of TH was highest in the olfactory bulb, followed by the telencephalon including preoptic area, and the di-/mesencephalic areas excluding the optic lobes. TH expression in the optic lobes and in the medulla oblongata was low, whereas no expression could be detected in corpus cerebellum. This distribution pattern is in agreement with earlier studies on TH in the eel using immunohistochemistry, RT-PCR, and Northern blotting. The developed qrtRT-PCR assay provides a new tool for understanding the mechanisms regulating central DA inhibition of puberty in juvenile eels.

Algorithms↗
PubMed2003

Internal redistribution of radiolabelled silver among tissues of rainbow trout (Oncorhynchus mykiss) and European eel (Anguilla anguilla): the influence of silver speciation.

Influence of water Ag(I) speciation on pharmacokinetics of Ag(I) during a post-exposure period was investigated in rainbow trout (Oncorhynchus mykiss) and European eel (Anguilla anguilla). The rainbow trout is sensitive to waterborne ionic Ag(+) whereas the eel is tolerant. The fish were acclimated to either of two chloride concentrations, 10 or 1200 microM, in synthetic soft water and then exposed to a sublethal 24-h pulse of 1.3 microgl(-1) of 110mAg(I) added as 110mAgNO(3) in these waters. The protocol provided exposures to mainly the free ion Ag(+) (low chloride water) or mainly AgCl(aq) (high chloride water). Contents and concentrations of 110mAg(I) in tissues and body fluids were then monitored over a 67-day post-exposure period in Ag(I)-free water of the same chloride levels. Changing the speciation of Ag(I) in the water had no effect on the whole body load of 110mAg(I), but did result in differences in internal distribution. In trout, changing water Ag(I) speciation significantly altered elimination or accumulation of Ag(I) in several body compartments. Notably, trout exposed to AgCl(aq) eliminated 110mAg(I) from the kidney more quickly than trout exposed to Ag(I) primarily as Ag(+). This elimination was matched by higher concentrations of 110mAg in liver of trout exposed to Ag(I) primarily as AgCl(aq). In eel, shifting speciation from Ag(+) to AgCl(aq) hastened elimination of 110mAg(I) from mid and posterior intestine and increased 110mAg(I) retention in kidney. While there was no difference between the two fish species in whole body 110mAg(I) load, most internal body compartments of trout had higher 110mAg(I) concentrations than those in eel early in the experiment. Because tissue-specific elimination times were longer in eel than in trout, these differences were generally cancelled by the end of the 67-day depuration period. The only exception was the liver, which in trout continued to accumulate 110mAg(I) throughout the experiment but in eel remained unchanged. The combined effect of 110mAg(I) movements in the two species was that trout retained all their accumulated 110mAg(I) through the 67-day period, whereas the body burden of 110mAg(I) in eel was reduced to half initial values by day 67.

Adaptation, Physiological↗
PubMed2004

Efficacy of a bivalent vaccine against eel diseases caused by Vibrio vulnificus after its administration by four different routes.

Vulnivaccine, a vaccine against vibriosis caused by Vibrio vulnificus serovar E (formerly biotype 2), confers acceptable levels of protection to eels after its administration by prolonged immersion in three doses. Recently, a new pathogenic serovar, named serovar A, has been isolated from vaccinated eels in a Spanish freshwater eel farm. The main objective of this work was to design a bivalent vaccine, and to study its effectiveness against the two pathogenic serovars. With this aim, eels weighing around 20 g were immunised with the bivalent vaccine by oral and anal intubation, intraperitoneal injection (i.p.) and prolonged immersion. The overall results indicated that: (i) the new vaccine delivered by oral and anal intubation induced protection levels higher than 80%, to that achieved after i.p. vaccination; (ii) oral and anal vaccination induced a significant systemic and mucosal immune response; (iii) the protection after vaccination by whichever routes was related to antibody titres in plasma; (iv) mucosal and systemic compartments showed different kinetics of antibody production; (v) evidence for passive transfer of antibodies from plasma to gut mucus were found after i.p. and anal vaccination, and finally, (vi) vaccination did not enhance the production of lysozyme, in plasma or mucus. In conclusion, this new vaccine is effective in protecting eels against vibriosis caused by the two eel-pathogenic serovars of V. vulnificus, the oral delivery system is a promising way which may be used in intensive culture facilities during the whole growth period of eels.

Anguilla↗