Prostaglandins in the kidney, urinary bladder and gills of the rainbow trout and European eel adapted to fresh water and seawater

Gill tissue lipids of salmon (Salmo salar L.) presmolts and smolts from anadromous and landlocked populations

Composition of membrane lipids from the gills of juvenile Atlantic salmon (Salmo salar) in presmolt and smolt phases of development was compared among anadromous and non-anadromous populations. Three stocks migrating from spawning rivers to either lake (landlocked stock), brackish water or full strength sea water were grown under common garden conditions, and gill lipids and their acyl and alkenyl chains were examined in February (presmolts) and at the end of May (smolts) by mass spectrometry and gas-liquid chromatography. The most remarkable changes upon transition from the presmolt phase to the smolt phase were: (i) increase in the cholesterol/phospholipid ratio, (ii) decrease in the abundance of phosphatidylinositol (PI) content, (iii) increase in the amount of sulfatides, (iv) increase in phosphatidylcholine (PC) and phosphatidylethanolamine (PE) species with two highly unsaturated acyl chains, and finally (v) convergence of interstock differences in PC and PE species composition towards a similar lipid composition. Increases in the gill membrane content of cholesterol and sulfatides are discussed as pre-adaptation of salmon gills for salt-secretion, which may occur by increases in membrane microdomains (rafts) harboring ion channels and pumps. The decreases of PI were likely related to adjusting the gill membrane permeability to ions by diminishing prostanoid production. The similarity of those changes among three salmon stocks and the convergence of initially (presmolt phase) different PC and PE species profiles between the stocks towards similar lipid composition suggests that smoltification process of the gill epithelium is largely similar in anadromous and landlocked populations.

Transcriptome and expression profiling analysis of Leuciscus waleckii: an exploration of the alkali-adapted mechanisms of a freshwater teleost

The strategies by which freshwater teleosts maintain acid-base homeostasis under alkaline stress are attractive and have been explored for a long time. In this study, a cyprinid fish that tolerates extremely alkaline environments (pH 9.6), Leuciscus waleckii, was used as a model to explore the molecular mechanisms of acid-base regulation. Using a lab-controlled alkaline challenge test and 454 sequencing, the transcriptomes of their gills and kidney were profiled and compared. mRNA profiling produced 1 826 022 reads, generated 30 606 contigs with an average length of 1022 bp, of which 19 196 were annotated successfully. Comparative analysis of the expression profiles between alkaline and freshwater L. waleckii habitats revealed approximately 4647 and 7184 genes that were differentially expressed (p < 0.05) in gills and kidney, respectively, of which 2398 and 5127 had more than twofold changes in expression. Gene ontology analysis and KEGG enrichment analysis were conducted. Comprehensive analysis found that genes involved in ion transportation, ammonia transportation, and arachidonic acid metabolism pathways changed dramatically and played important roles in acid-base homeostasis in fish under alkaline stress. These results support the existing hypotheses about candidate genes involved in acid-base regulation under alkaline stress and prompt several new hypotheses. The large transcriptome dataset collected in this study is a useful resource for the exploration of homeostasis modulation in other fish species.

Molecular evolutionary and population genomic analysis of the nine-spined stickleback using a modified restriction-site-associated DNA tag approach

In recent years, the explosion of affordable next generation sequencing technology has provided an unprecedented opportunity to conduct genome-wide studies of adaptive evolution in organisms previously lacking extensive genomic resources. Here, we characterize genome-wide patterns of variability and differentiation using pooled DNA from eight populations of the nine-spined stickleback (Pungitius pungitius L.) from marine, lake and pond environments. We developed a novel genome complexity reduction protocol, defined as paired-end double restriction-site-associated DNA (PE dRAD), to maximize read coverage at sequenced locations. This allowed us to identify over 114,000 short consensus sequences and 15,000 SNPs throughout the genome. A total of 6834 SNPs mapped to a single position on the related three-spined stickleback genome, allowing the detection of genomic regions affected by divergent and balancing selection, both between species and between freshwater and marine populations of the nine-spined stickleback. Gene ontology analysis revealed 15 genomic regions with elevated diversity, enriched for genes involved in functions including immunity, chemical stimulus response, lipid metabolism and signalling pathways. Comparisons of marine and freshwater populations identified nine regions with elevated differentiation related to kidney development, immunity and MAP kinase pathways. In addition, our analysis revealed that a large proportion of the identified SNPs mapping to LG XII is likely to represent alternative alleles from divergent X and Y chromosomes, rather than true autosomal markers following Mendelian segregation. Our work demonstrates how population-wide sequencing and combining inter- and intra-specific RAD analysis can uncover genome-wide patterns of differentiation and adaptations in a non-model species.

Molecular characterization of prostaglandin F receptor (FP) and E receptor subtype 1 (EP₁) in zebrafish

Prostaglandins E (PGE) and F (PGF) mediate diverse physiological functions via their cell surface receptors - prostaglandin E receptor (EP) subtypes 1, 2, 3 and 4 (EP(1); EP(2); EP(3); EP(4)) and F receptor (FP). In teleost fishes, PGE was implicated in gill epithelium ion transport, while both PGE and PGF were involved in oocyte maturation, follicular rupture and coordination of reproductive behaviors. However, little is known about the mechanisms behind their actions. In present study, we first identified the full-length ORF cDNA clones of three zebrafish prostaglandin E receptor subtype 1 (zEP(1)) isoforms - zEP(1a), zEP(1b) and zEP(1c) - and FP (zFP) from adult ovary. RT-PCR showed that zEP(1a), zEP(1b) and zFP are widely expressed in adult tissues, while zEP(1c) mRNA expression is mainly confined in brain and kidney. Using a pGL3-NFAT-RE luciferase reporter system, both zEP(1a) and zEP(1b) expressed in DF-1 cells were shown to be activated by PGE(2) potently while zEP(1c) and zFP were activated by PGF(2a) effectively, suggesting that the four receptors are functionally coupled to intracellular Ca(2+)-signaling pathway. Furthermore, EP1a and EP1b, but not EP1c were suggested to couple to cAMP-PKA signaling pathway using a pGL3-CRE luciferase reporter assay. Although zEP(1c) might originate as a paralog to zEP(1a) and zEP(1b), its functional coupling to PGF(2α) instead of PGE(2) suggested that zEP(1) isoforms might have sub-functionalized in their ligand binding and G protein coupling specificity, in addition to differential tissue distribution. Characterization of these receptors undoubtedly furthered our understanding on the diverse yet highly target-specific responses of prostaglandins in teleosts.

The effects of arachidonic acid on the endocrine and osmoregulatory response of tilapia (Oreochromis mossambicus) acclimated to seawater and subjected to confinement stress

In previous studies in freshwater tilapia (Oreochromis mossambicus), dietary supplementation with arachidonic acid (ArA; 20:4n - 6) had considerable, opposing effects on the main ion-transporting enzyme Na(+)/K(+)-ATPase in gills and kidneys and changed the release of osmoregulatory hormones, such as cortisol. The present study was performed to assess the influence of dietary ArA on (1) the osmoregulatory capacity of tilapia acclimated to seawater (SW) (34‰) and (2) the osmoregulatory imbalance associated with acute stress. The increased ambient salinity was associated with significant alterations in the tissue fatty acid composition, particularly the n - 6 polyunsaturated fatty acids (PUFAs). Tissue levels of ArA were further increased as a result of dietary supplementation, whereas docosahexaenoic acid (DHA, 22:6n - 3) and eicosapentaenoic acid (EPA, 20:5n - 3) decreased in gills and kidneys. Basal plasma cortisol as well as lactate levels were elevated in the ArA-supplemented SW-acclimated tilapia compared with the control group. The 5 min of confinement (transient stress) increased plasma cortisol, glucose, and lactate levels with significantly higher levels in ArA-supplemented tilapia. Confinement was also associated with significantly elevated plasma osmolality, sodium, chloride, and potassium levels. ArA-supplemented tilapia showed markedly lower ionic disturbances after confinement, suggesting that dietary ArA can attenuate the hydromineral imbalance associated with acute stress. These results emphasize the involvement of ArA and/or its metabolites in the endocrine and osmoregulatory processes and the response to confinement stress.

The interruption of thyroid and interrenal and the inter-hormonal interference in fish: does it promote physiologic adaptation or maladaptation?

Endocrines, the chief components of chemical centers which produce hormones in tune with intrinsic and extrinsic clues, create a chemical bridge between the organism and the environment. In fishes also hormones integrate and modulate many physiologic functions and its synthesis, release, biological actions and metabolic clearance are well regulated. Consequently, thyroid hormones (THs) and cortisol, the products of thyroid and interrenal axes, have been identified for their common integrative actions on metabolic and osmotic functions in fish. On the other hand, many anthropogenic chemical substances, popularly known as endocrine disrupting chemicals, have been shown to disrupt the hormone-receptor signaling pathways in a number fish species. These chemicals which are known for their ability to induce endocrine disruption particularly on thyroid and interrenals can cause malfunction or maladaptation of many vital processes which are involved in the development, growth and reproduction in fish. On the contrary, evidence is presented that the endocrine interrupting agents (EIAs) can cause interruption of thyroid and interrenals, resulting in physiologic compensatory mechanisms which can be adaptive, though such hormonal interactions are less recognized in fishes. The EIAs of physical, chemical and biological origins can specifically interrupt and modify the hormonal interactions between THs and cortisol, resulting in specific patterns of inter-hormonal interference. The physiologic analysis of these inter-hormonal interruptions during acclimation and post-acclimation to intrinsic or extrinsic EIAs reveals that combinations of anti-hormonal, pro-hormonal or stati-hormonal interference may help the fish to fine-tune their metabolic and osmotic performances as part of physiologic adaptation. This novel hypothesis on the phenomenon of inter-hormonal interference and its consequent physiologic interference during thyroid and interrenal interruption thus forms the basis of physiologic acclimation. This interfering action of TH and cortisol during hormonal interruption may subsequently promote ecological adaptation in fish as these physiologic processes ultimately favor them to survive in their hostile environment.

The role of thyroid hormones in stress response of fish

Thyroxine (T(4)) and triiodothyronine (T(3)), the principal thyroid hormones (THs) secreted from the hypothalamic-pituitary-thyroid (HPT) axis, produce a plethora of physiologic actions in fish. The diverse actions of THs in fishes are primarily due to the sensitivity of thyroid axis to many physical, chemical and biological factors of both intrinsic and extrinsic origins. The regulation of THs homeostasis becomes more complex due to extrathyroidal deiodination pathways by which the delivery of biologically active T(3) to target cells has been controlled. As primary stress hormones and the end products of hypothalamic-pituitary-interrenal (HPI) and brain-sympathetic-chromaffin (BSC) axes, cortisol and adrenaline exert its actions on its target tissues where it promote and integrate osmotic and metabolic competence. Despite possessing specific osmoregulatory and metabolic actions at cellular and whole-body levels, THs may fine-tune these processes in accordance with the actions of hormones like cortisol and adrenaline. Evidences are presented that THs can modify the pattern and magnitude of stress response in fishes as it modifies either its own actions or the actions of stress hormones. In addition, multiple lines of evidence indicate that hypothalamic and pituitary hormones of thyroid and interrenal axes can interact with each other which in turn may regulate THs/cortisol-mediated actions. Even though it is hard to define these interactions, the magnitude of stress response in fish has been shown to be modified by the changes in the status of THs, pointing to its functional relationship with endocrine stress axes particularly with the interrenal axis. The fine-tuned mechanism that operates in fish during stressor-challenge drives the THs to play both fundamental and modulator roles in stress response by controlling osmoregulation and metabolic regulation. A major role of THs in stress response is thus evident in fish.

The Multifunctional Fish Gill: Dominant Site of Gas Exchange, Osmoregulation, Acid-Base Regulation, and Excretion of Nitrogenous Waste

The fish gill is a multipurpose organ that, in addition to providing for aquatic gas exchange, plays dominant roles in osmotic and ionic regulation, acid-base regulation, and excretion of nitrogenous wastes. Thus, despite the fact that all fish groups have functional kidneys, the gill epithelium is the site of many processes that are mediated by renal epithelia in terrestrial vertebrates. Indeed, many of the pathways that mediate these processes in mammalian renal epithelial are expressed in the gill, and many of the extrinsic and intrinsic modulators of these processes are also found in fish endocrine tissues and the gill itself. The basic patterns of gill physiology were outlined over a half century ago, but modern immunological and molecular techniques are bringing new insights into this complicated system. Nevertheless, substantial questions about the evolution of these mechanisms and control remain.

NaCl transport across the opercular epithelium ofFundulus heteroclitusis inhibited by an endothelin to NO, superoxide, and prostanoid signaling axis

Recent evidence suggests that paracrine signaling agents, such as endothelin (ET), nitric oxide (NO), superoxide (O2-), and prostanoids can modulate mammalian renal function by affecting both hemodynamic and epithelial ionic transport pathways. Since these signaling pathways have been described in fish blood vessels, we hypothesized that they may control salt transport across the gill epithelium—the primary site of ion excretion in marine teleost fishes. We found that ET, the NO donors sodium nitroprusside and spermine NONOate, and the prostanoid PGE2each can produce a concentration-dependent reduction in the short circuit current ( Isc) across the isolated opercular epithelium of the killifish ( Fundulus heteroclitus), the generally accepted model for the marine teleost gill epithelium. Sarafotoxin S6c was equipotent to ET-1, suggesting that ETBreceptors are involved. Incubation with NG-nitro-l-arginine methyl ester (l-NAME) or indomethacin reduced the effect of subsequent addition of SRXS6c by 17 and 89%, respectively, suggesting the presence of an ET to NO and PGE axis. The effects of l-NAME and indomethacin were not additive, but the superoxide dismutase mimetic 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPOL) reduced the effect of SRXS6c by 34% and preincubation with l-NAME, indomethacin, and TEMPOL reduced the SRXS6c response to zero. This suggests a direct role for O2-in this axis. COX-2 appears to be the major enzyme involved in this axis because the specific COX-2 inhibitor NS-398 was twice as effective as the COX-1 inhibitor SC560 in inhibiting the SRXS6c effect. The Iscwas stimulated by the EP2agonist butaprost and inhibited by the EP1,3agonist sulprostone, suggesting both stimulatory and inhibitory PGE receptors in this tissue. Carbaprostacyclin (PGI2analog), thromboxane A2, PGF2α, and PGD2did not affect the Isc. Our data are the first to suggest the importance of an ET-stimulated and NO-, O2--, and PGE2-mediated signaling axis that can modify active extrusion of NaCl across the killifish opercular epithelium and, by inference, the marine teleost gill epithelium.

Effects of acetylsalicylic acid treatment on thyroid hormones, prolactins, and the stress response of tilapia (Oreochromis mossambicus)

The cyclooxygenase (COX) pathway converts arachidonic acid (ArA) into prostaglandins (PGs), which interact with the stress response in mammals and possibly in fish as well. Acetylsalicylic acid (ASA) is a COX inhibitor and was used to characterize the effects of PGs on the release of several hormones and the stress response of tilapia (Oreochromis mossambicus). Plasma PGE2 was significantly reduced at 100 mg ASA/kg body wt, and both basal PGE2 and cortisol levels correlated negatively with plasma salicylate. Basal plasma 3,5,3'-triiodothyronine (T3) was reduced by ASA treatment, whereas prolactin (PRL)188 increased at 100 mg ASA/kg body wt. ASA depressed the cortisol response to the mild stress of 5 min of net confinement. As expected, glucose and lactate were elevated in the stressed control fish, but the responses were blunted by ASA treatment. Gill Na+-K+-ATPase activity was not affected by ASA. Plasma osmolarity increased after confinement in all treatments, whereas sodium only increased at the high ASA dose. This is the first time ASA has been administered to fish in vivo, and the altered hormone release and the inhibition of the acute stress response indicated the involvement of PGs in these processes.

Cell signaling and ion transport across the fish gill epithelium

A large array of circulating and local signaling agents modulate transport of ions across the gill epithelium of fishes by either affecting transport directly or by altering the size and distribution of transporting cells in the epithelium. In some cases, these transport effects are in addition to cardiovascular effects of the same agents, which may affect the perfusion pathways in the gill vasculature and, in turn, affect epithelial transport indirectly. Prolactin is generally considered to function in freshwater, because it is the only agent that allows survival of some hypophysectomized fish species in freshwater. It appears to function by either reducing branchial permeability, Na,K-activated ATPase activity, or reducing the density of chloride cells. Cortisol was initially considered to produce virtually opposite effects (e.g., stimulation of Na,K-activated ATPase and of chloride cell size and density), but more recent studies have found that this steroid stimulates ionic uptake in freshwater fishes, as well as the activity of H-ATPase, an enzyme thought to be central to ionic uptake. Thus, cortisol may function in both high and low salinities. Growth hormone and insulin-like growth factor appear to act synergistically to affect ion regulation in seawater fishes, stimulating both Na,K-activated ATPase and Na-K-2Cl co-transporter activity, and chloride cell size, independent of their effects on growth. Some of the effects of the GH-IGF axis may be via stimulation of the number of cortisol receptors. Thyroid hormones appear to affect seawater ion regulation indirectly, by stimulating the GH-IGF axis. Natriuretic peptides were initially thought to stimulate gill ionic extrusion, but recent studies have not corroborated this finding, so it appears that the major mode of action of these peptides may be reduction of salt loading by inhibition of oral ingestion and intestinal ionic uptake. Receptors for both arginine vasotocin and angiotensin have been described in the gill epithelium, but their respective roles and importance in fish ion regulation remains unknown. The gill epithelium may be affected by both circulating and local adrenergic agents, and a variety of studies have demonstrated that stimulation of alpha-adrenergic versus beta-adrenergic receptors produces inhibition or stimulation of active salt extrusion, respectively. Local effectors, such as prostaglandins, nitric oxide, and endothelin, may affect active salt extrusion as well as gill perfusion. Recent studies have suggested that the endothelin inhibition of salt extrusion is actually mediated by the release of both NO and prostaglandins. It is hoped that modern molecular techniques, combined with physiological measurements, will allow the dissection of the relative roles in ion transport across the fish gill epithelium of this surprisingly large array of putative signaling agents.

Vasoactivity of the ventral aorta of the American eel (Anguilla rostrata), Atlantic hagfish ( Myxine glutinosa), and sea lamprey (Petromyzon marinus)

To determine if vascular smooth muscle from teleost and agnathan fishes expresses receptors for signaling agents that are important in vascular tension in other vertebrates, we exposed rings of aortic vascular smooth muscle from the eel (Anguilla rostrata), the hagfish (Myxine glutinosa), and the lamprey (Petromyzon marinus) to a suite of putative agonists, including: acetylcholine, endothelin, nitric oxide, natriuretic peptides, and prostanoids. Acetylcholine constricted aortic rings from the eel, but had no effect on the rings from lamprey. On the other hand, endothelin constricted rings from all three species. Use of receptor-specific ET agonists demonstrated that only ET(A) receptors are expressed in the eel and lamprey aorta. The nitric oxide donor sodium nitroprusside or nitric oxide itself dilated rings from the eel, but both agonists constricted rings from the hagfish and NO produced a biphasic response (constriction followed by dilation) in the lamprey. Two natriuretic peptides, eel ANP and porcine CNP, produced marginally significant dilation in the eel aorta, human ANP dilated the hagfish rings, and pCNP and eANP dilated the lamprey rings. The prostanoids PGE(1) and PGE(2) both dilated the eel aortic rings, and PGE(1) and carbaprostacyclin (stable PGI(2) agonist) dilated the hagfish and lamprey rings. Our results suggest that receptors for a variety of vasoactive signaling agents are expressed in the aortic smooth muscle of the earliest vertebrates (lamprey and hagfish), as well as the more advanced teleosts (eel).

Evidence for an intrarenal renin-angiotensin system in the rainbow trout, Oncorhynchus mykiss

Physiological and molecular approaches were used to investigate the existence of an intrarenal renin-angiotensin system (RAS) in rainbow trout. Inhibition of angiotensin-converting enzyme by captopril (5 x 10(-4 )M) rapidly decreased vascular resistance of the trunk of the trout, perfused at 19 mmHg, resulting in an increased perfusate flow rate and a decreased intrarenal dorsal aortic pressure. A profound diuresis occurred in the in situ perfused kidney and reflected both increased glomerular filtration rates and decreased water reabsorption (osmolyte reabsorption was unchanged). Renal and vascular parameters recovered once captopril treatment was stopped. Diuretic and vascular effects of captopril on the in situ trout kidney concur with an inhibition of known vasoconstrictor and antidiuretic actions of angiotensin II. However, at a higher perfusion pressure (28 mmHg), captopril had no effect on intrarenal aortic pressure or perfusate and urine flow rates, suggesting that the trout intrarenal RAS is activated by low perfusion pressures/flows. Existence of the renal RAS in trout was further supported by evidence for angiotensinogen gene expression in kidney as well as liver.

The eicosanoid generating capacity of isolated cell populations from the gills of the rainbow trout, Oncorhynchus mykiss

Rainbow trout gill filaments generated a wide range of eicosanoid products following calcium ionophore challenge. The putative lipoxygenase products were separated by reverse phase high performance liquid chromatography (RP-HPLC), while prostanoids were quantified by enzyme immunoassay. Three main monohydroxy compounds containing conjugated dienes were observed after RP-HPLC namely 12-(S) hydroxyeicosatetraenoic acid (12-HETE), 12-(S) hydroxyeicosapentaenoic acid (12-HEPE) and 14-(S) hydroxydocosahexaenoic acid (14-HDHE), derived from endogenous arachidonic, eicosapentaenoic and docosahexaenoic acids, respectively. Their identification was confirmed by mass spectrometry. A further five compounds containing conjugated trienes were also observed but in lesser amounts. One of these products was identified as 8,15-dihydroxyeicosatetraenoic acid (8,15-DiHETE) based on its UV spectrum, co-elution with authentic standard on RP-HPLC and mass spectrometry. Overall, the generation of these products suggests the presence of 12- and possibly 15-lipoxygenase activities in trout gill acting on endogenous sources of fatty acid. To determine if the various cell types in trout gill had differing eicosanoid generating potential, gills were disrupted and the resultant cell suspensions separated by density gradient centrifugation. Following this three bands were formed on the gradients and the cell populations from these were characterised using periodic acid Schiff's (PAS) reactivity for mucosubstances, haematoxylin and eosin staining, and immunoreactivity with both monoclonal and polyclonal antibodies. The first band consisted of polygonal cells and other more minor cell types, the second cell band contained mainly polygonal and PAS-positive goblet epithelial cells, while the third band consisted of mainly erythrocytes. There were significant differences in the eicosanoid generating potential of the isolated cells, with cells from the second band generating significantly more 12-HETE and 8,15-DiHETE than those from both the first band and unfractionated populations. The eicosanoid generating activity of the trout gill epithelial cell line, RTG-W1, was also elucidated. It proved to be a modest generator of eicosanoids in that only low levels of thromboxane B2 and prostaglandin E2 were detected while no lipoxygenase products were observed.

Prostanoid synthesis in whole blood cells from fish of the Arabian Gulf

The ability to synthesise prostaglandins and thromboxane from 14C-labelled arachidonic acid was investigated in 11 species of fish from the Arabian Gulf. Cyclooxygenase activity was assessed in washed whole blood cells. Arachidonic acid and its metabolites were extracted and separated on silicic acid columns and thin layer chromatography (silica gel G). Total capacity to convert [14C]arachidonic acid to prostanoids varied from 1 to 35% among the 11 fish species studied. Gray shark (Chiloscyllium griseum) blood cells had the highest capacity (37 +/- 0.4%) to convert arachidonate into prostanoids and two species of catfish (Arius bilineatus and A. thalassinus) exhibited greater than 10% capacity to convert [14C]arachidonate into prostanoids. The major prostanoid synthesised by the two catfish (A. bilineatus and A thalassinus) was 6-keto PGF1 alpha, a stable metabolite of prostacyclin, PGI2. In contrast, A. teunispinis synthesised thromboxane B2, a stable metabolite of thromboxane A2. Thromboxane B2 (TXB2) was the major product synthesised by all three species of shark studied (Chil. griseum, Carcharhinus plumbeus, Carch. melanopterus), with 6-keto PGF1 alpha a minor product. Other fish studied showed a varied pattern of prostanoid synthesis. The synthesis of these prostanoids was almost completely blocked by preincubation of the whole blood cells from catfish and shark with indomethacin (0.5 microM) suggesting the involvement of cyclooxygenase-mediated prostanoid synthesis.

Effects of dietary gamma-linolenic acid-rich borage oil combined with marine fish oils on tissue phospholipid fatty acid composition and production of prostaglandins E and F of the 1-, 2- and 3-series in a marine fish deficient in delta5 fatty acyl desaturase

The effects of gamma-linolenic acid-rich borage oil (BO), in combination with different marine oils, namely an eicosapentaenoic acid (EPA) rich oil (MO) or a DHA-rich oil (TO), on tissue fatty acid composition and prostaglandin production were investigated in turbot, a species which lacks appreciable delta5 fatty acyl desaturase activity. The juvenile turbot grew well on the experimental diets and there were no significant differences in final weights between dietary treatments. Irrespective of the marine oil component, both the BO-containing diets increased tissue phospholipid levels of 18:2n-6 and 18:3n-6, and their respective elongation products, 20:2n-6 and 20:3n-6, compared to fish fed a control diet containing a standard Northern hemisphere fish oil. Both the BO-containing diets increased the production of 1-series prostaglandins (PG), this being observed across all tissues investigated with PGF and especially PGE. The BO/MO diet also reduced 20:4n-6 in tissue phospholipids without affecting 20:5n-3, whereas the BO/TO combination decreased 20:5n-3 but increased 20:4n-6. The production of 2-series and 3-series PGs was also altered by the dietary treatments but the changes were less dependent upon the tissue levels of their respective precursor fatty acids, 20:4n-6 and 20:5n-3. The BO-containing diets had very significant effects on gross fatty acid compositions of the phospholipids including increased proportions of saturated fatty acids and n-6 polyunsaturated fatty acids (PUFA) and decreased proportions of monounsaturated fatty acids and n-3 PUFA. Overall, this study shows that eicosanoid production in turbot tissues can be influenced by dietary fatty acids, not only by changes in the absolute and relative levels of specific eicosanoid precursor PUFA in tissue phospholipids, but also by general effects on membrane composition, structure and function induced by gross fatty acid compositional changes.

Modification of membrane fatty acid composition, eicosanoid production, and phospholipase A activity in Atlantic salmon (Salmo salar) gill and kidney by dietary lipid

Atlantic salmon post-smolts were fed diets containing either fish oils (Fosol, FO and Marinol, MO) rich in long-chain n-3 polyunsaturated fatty acids (PUFA), or plant oils rich in 18:2n-6 (sunflower oil, SO) or 18:3n-3 (linseed oil, LO) for 12 wk. The major PUFA in individual phospholipids from gill and kidney were related to the dietary lipid intake. Levels of n-6 PUFA were highest while levels of n-3 PUFA were lowest in fish fed SO. Fish fed LO generally had lower levels of 20:4n-6 compared to the other treatments while fish fed SO generally had the highest levels of 20:4n-6. In all phospholipid classes except phosphatidylinositol (PI) 20:5n-3 was greatest in fish fed MO followed by FO, LO, and SO. In PI, 20:5n-3 was also highest in fish fed MO but those fed LO contained more 20:5n-3 than those fed FO. This resulted in the ratio of the eicosanoid precursors, 20:4n-6/20:5n-3, being significantly greater in fish fed SO, for all phospholipid classes, compared to fish fed the other three dietary oils. The activity of gill phospholipase A was greatest in fish fed FO and was lowest in fish fed SO. The concentration of PGF3 alpha was significantly increased in gill homogenates from fish fed MO compared to the other three treatments while PGF2 alpha was significantly increased in fish fed SO compared to those fed LO. The concentration of PGE3 was significantly reduced in kidney homogenates from fish fed SO compared to the other three treatments while PGE2 was significantly increased in fish fed SO compared to those fed either FO or LO.

Diets rich in eicosapentaenoic acid and gamma-linolenic acid affect phospholipid fatty acid composition and production of prostaglandins E1, E2 and E3 in turbot (Scophthalmus maximus), a species deficient in delta 5 fatty acid desaturase

Duplicate groups of juvenile turbot, (Scophthalmus maximus), were fed diets containing either Marinol K (MO), a marine fish oil rich in eicosapentaenoic acid (EPA; 20:5, n-3) or borage oil (BO), rich in gamma-linolenic acid (GLA; 18:3, n-6), for a period of 12 weeks. Individual phospholipid fatty acid compositions from hearts of fish fed BO had significantly more 18:2, n-6, GLA, 20:2, n-6, dihomo-gamma-linolenic acid (DHGLA; 20:3, n-6) and total n-6 polyunsaturated fatty acids (PUFA), but significantly less arachidonic acid (AA; 20:4, n-6), compared to fish fed MO. In both phosphatidylcholine (PC) and phosphatidylethanolamine (PE) from heart, the DHGLA was increased by over 50-fold in fish fed BO while AA was reduced by over two-thirds, compared to fish fed MO. In brain, EPA was the major C20 PUFA, i.e. potential eicosanoid precursor in all phospholipids from fish fed MO, with the EPA level being twice that of AA in brain phosphatidylinositol (PI). DHGLA was the major C20 PUFA in all phospholipid classes from fish fed BO. In kidney and gill, EPA was the predominant C20 PUFA in all phospholipid classes, except PI, in fish fed MO. In kidney of fish fed BO, DHGLA was the major C20 PUFA in all phospholipid classes, except PE. In gill of fish fed BO, DHGLA was the major C20 PUFA in all phospholipid classes, including PI, where DHGLA was over 2.5-fold greater than AA. In homogenates of heart, kidney and gill from BO-fed fish the prostaglandin E1 (PGE1) concentration was significantly increased compared to MO-fed fish. In heart and kidney homogenates from fish fed MO the PGE3 concentration was significantly increased compared to fish fed BO. The ratio of PGE2/PGE1 was significantly reduced in brain, heart, kidney and gill homogenates from fish fed BO compared to those fed MO.

Angiotensin II binding to tissues of the rainbow trout, Oncorhynchus mykiss, studied by autoradiography

Tissue slices from seawater-adapted and freshwater-adapted rainbow trout, Oncorhynchus mykiss, were exposed to 125I-angiotensin II (1.01.10(-9) M) and binding sites located by light-microscopic autoradiography. Binding/uptake was significantly inhibited by excess (10(-5) M) unlabelled angiotensin II, suggesting specific binding/uptake of angiotensin II to the ventral and dorsal aorta (smooth muscle), urinary bladder (smooth muscle and epithelial lining), glomeruli and proximal tubules, the gill (lamellae and central filament), skin (epithelium), intestine and oesophagus (mucosal epithelium), liver, heart (ventricular myocytes), adrenocortical tissue and brain (cerebellum and medulla oblongata). The specific binding/uptake of angiotensin II to tissues of freshwater- and seawater-adapted animals were generally similar. However, binding/uptake by the proximal tubules was significantly higher in freshwater-adapted trout than seawater-adapted trout. Specific binding/uptake of angiotensin II by the smooth muscle of the bladder was significantly higher in trout adapted to seawater than trout adapted to freshwater.