Nephrocalcinosis in juvenile farmed Atlantic Salmon (Salmo salar) may be linked to osmoregulatory stress.

Nephrocalcinosis is a widespread challenge in intensive production of salmon smolt. There is however no consensus on its aetiology, which makes it problematic to implement proper measures to limit its development. We performed a survey of nephrocalcinosis prevalence and environmental factors in 11 different hatcheries in Mid-Norway as well as a 6-month monitoring in one of the hatcheries. A multivariate analysis indicated that the most influencing factor for the prevalence of nephrocalcinosis was the supplementation of sea water during smolt production. In the 6-month monitoring, the hatchery introduced salinity in the production water prior to the change in day length. Mismatch in those environmental signals may increase the risk for developing nephrocalcinosis. Salinity fluctuations prior to smoltification can cause osmotic stress and result in unbalanced levels of ions in fish blood. This was clearly illustrated in our study, as the fish experienced chronic hypercalcaemia and hypermagnesaemia. Both magnesium and calcium are excreted over the kidneys and it is possible that their prolonged, elevated levels in plasma resulted in an oversaturation of the urine when finally excreted. This again could have led to the aggregation of calcium deposits within the kidney. This study indicates a relationship between osmotic stress induced by salinity changes in juvenile Atlantic salmon and the development of nephrocalcinosis. Other factors that may affect the severity of nephrocalcinosis are currently subjects for discussion.

Effect of different dietary arachidonic, eicosapentaenoic, and docosahexaenoic acid content on selected immune parameters in gilthead sea bream (Sparus aurata).

The increasing replacement of fish oil (FO) by vegetable oils (VO) in aquafeeds for marine carnivorous species may lead to modifications of the dietary arachidonic (ARA), eicosapentaenoic (EPA) and docosahexaenoic (DHA) levels and ratios that may compromise the fish immune status. Therefore, this study aimed to assess how different dietary ratios of ARA, EPA, and DHA modulate the immune response of gilthead sea bream juveniles. For that purpose, four isoproteic and isolipidic plant-based diets were formulated to include different dietary Long-Chain-Polyunsaturated Fatty Acids (LC-PUFA) ratios (%DM): Diet A (2.0% ARA: 0.2% EPA: 0.1% DHA); Diet B (1.0% ARA: 0.4% EPA: 0.4% DHA); Diet C (0% ARA: 0.6% EPA: 0.6% DHA); Diet D (0% ARA: 0.3% EPA: 1.5% DHA). Fish were fed the experimental diets for 56 days and then the haematological profile, humoral innate immune parameters, and expression of immune-related genes in the gut were determined. Our results showed that fish fed diet B exhibited an increase in the monocyte numbers, alternative complement activity, and bactericidal activity against Photobacterium damselae compared to the values found in fish fed other diets. Contrarily, peroxidase, antiproteases, and proteases activity and nitric oxide levels were not affected by the dietary treatments. Immune-related gene expression in the distal intestine did not show differences between dietary treatments. Overall, a diet with a balanced n-6 (ARA) and n-3 (EPA+DHA) LC-PUFA ratio seemed to better modulate the fish innate immune response, thus better preparing the fish innate immune system against potential immunological insults.

Oxidative status and intestinal health of gilthead sea bream (Sparus aurata) juveniles fed diets with different ARA/EPA/DHA ratios.

The present work assessed the effects of dietary ratios of essential fatty acids, arachidonic (ARA), eicosapentaenoic (EPA) and docosahexaenoic acid (DHA), on liver and intestine oxidative status, intestinal histomorphology and gut microbiota of gilthead sea bream. Four isoproteic and isolipidic plant-based diets were formulated containing a vegetable oil blend as the main lipid source. Diets were supplemented with ARA/EPA/DHA levels (%DM) equivalent to: 2%:0.2%:0.1% (Diet A); 1.0%:0.4%:0.4% (Diet B); 0%:0.6%:0.6% (Diet C); 0%:0.3%:1.5% (Diet D) and tested in triplicate groups for 56 days. Lipid peroxidation was higher in fish fed diets C and D while no differences were reported between diets regarding total, oxidized, and reduced glutathione, and oxidative stress index. Glutathione reductase was higher in fish fed diet A than diets C and D. No histological alterations were observed in the distal intestine. Lower microbiota diversity was observed in intestinal mucosa of fish fed diet C than A, while diets C and D enabled the proliferation of health-promoting bacteria from Bacteroidetes phylum (Asinibacterium sp.) and the absence of pathogenic species like Edwardsiella tarda. Overall, results suggest that a balance between dietary ARA/EPA + DHA promotes gilthead sea bream juveniles' health however higher dietary content of n-3 LC-PUFA might limited the presence of microbial pathogens in intestinal mucosa.

Assessment of a land-locked Atlantic salmon (Salmo salar L.) population as a potential genetic resource with a focus on long-chain polyunsaturated fatty acid biosynthesis.

The natural food for Atlantic salmon (Salmo salar) in freshwater has relatively lower levels of omega-3 (n-3) long-chain polyunsaturated fatty acids (LC-PUFA) than found in prey for post-smolt salmon in seawater. Land-locked salmon such as the Gullspång population feed exclusively on freshwater type lipids during its entire life cycle, a successful adaptation derived from divergent evolution. Studying land-locked populations may provide insights into the molecular and genetic control mechanisms that determine and regulate n-3 LC-PUFA biosynthesis and retention in Atlantic salmon. A two factorial study was performed comparing land-locked and farmed salmon parr fed diets formulated with fish or rapeseed oil for 8 weeks. The land-locked parr had higher capacity to synthesise n-3 LC-PUFA as indicated by higher expression and activity of desaturase and elongase enzymes. The data suggested that the land-locked salmon had reduced sensitivity to dietary fatty acid composition and that dietary docosahexaenoic acid (DHA) did not appear to suppress expression of LC-PUFA biosynthetic genes or activity of the biosynthesis pathway, probably an evolutionary adaptation to a natural diet lower in DHA. Increased biosynthetic activity did not translate to enhanced n-3 LC-PUFA contents in the flesh and diet was the only factor affecting this parameter. Additionally, high lipogenic and glycolytic potentials were found in land-locked salmon, together with decreased lipolysis which in turn could indicate increased use of carbohydrates as an energy source and a sparing of lipid.

Stress and expression of cyclooxygenases (cox1, cox2a, cox2b) and intestinal eicosanoids, in Atlantic salmon, Salmo salar L.

Prostaglandin H synthetases (cyclooxygenases) catalyze the initial reactions leading to prostanoids in animals. They form interesting links between diet and fish physiology as the type and nature of eicosanoids are affected by dietary lipid sources. Their expression is likely to be affected by tissues and environmental conditions leading to altered amount and ratio of eicosanoids. These mechanisms are, however, poorly understood in fish. In the present study, Atlantic salmon Salmo salar L. (1,000 g, 10°C, seawater) were subjected to acute chasing stress. Liver, kidney, spleen, gill, muscle, midgut and hindgut were extracted before and 1 h post-stress and analyzed for mRNA expression of cox1, cox2a and cox2b. Intestinal samples were further sampled over 24 h for both cox expression and analysis of 15 eicosanoids and isoprostanes of the n-3 and n-6 series. Results show a highly variable but consecutively expression of cox1, cox2a and cox2b in most of the tissues analyzed. Low levels were only found for cox2a in liver and cox2b in liver and kidney. The study reveals the general trend that cox1 is about 10 times the level of cox2b, which again is about 10 times the level of cox2a. Cox2b shows the highest level of expression in the gills indicating a possible higher requirement for this protein in gills. Imposing stress to the fish induces a temporal increase in the expression of cox2a in the midgut, while the gene expression of the other genes is not affected in any of the tissues analyzed. There is, however, a general tendency to increased expression of both cox2 genes that merits further studies. Stress had a profound effect on the intestinal eicosanoid content which showed a general decrease in midgut sections after stress that persisted for at least 24 h.

Determination of the magnetic contribution to the heat capacity of cobalt oxide nanoparticles and the thermodynamic properties of the hydration layers.

We present low temperature (11 K) inelastic neutron scattering (INS) data on four hydrated nanoparticle systems: 10 nm CoO·0.10H(2)O (1), 16 nm Co(3)O(4)·0.40H(2)O (2), 25 nm Co(3)O(4)·0.30H(2)O (3) and 40 nm Co(3)O(4)·0.026H(2)O (4). The vibrational densities of states were obtained for all samples and from these the isochoric heat capacity and vibrational energy for the hydration layers confined to the surfaces of these nanoparticle systems have been elucidated. The results show that water on the surface of CoO nanoparticles is more tightly bound than water confined to the surface of Co(3)O(4), and this is reflected in the reduced heat capacity and vibrational entropy for water on CoO relative to water on Co(3)O(4) nanoparticles. This supports the trend, seen previously, for water to be more tightly bound in materials with higher surface energies. The INS spectra for the antiferromagnetic Co(3)O(4) particles (2-4) also show sharp and intense magnetic excitation peaks at 5 meV, and from this the magnetic contribution to the heat capacity of Co(3)O(4) nanoparticles has been calculated; this represents the first example of use of INS data for determining the magnetic contribution to the heat capacity of any magnetic nanoparticle system.

The effect of hyperoxygenation and reduced flow in fresh water and subsequent infectious pancreatic necrosis virus challenge in sea water, on the intestinal barrier integrity in Atlantic salmon, Salmo salar L.

In high intensive fish production systems, hyperoxygenation and reduced flow are often used to save water and increase the holding capacity. This commonly used husbandry practice has been shown to be stressful to fish and increase mortality after infectious pancreatic necrosis virus (IPNV) challenge, but the cause and effect relationship is not known. Salmonids are particularly sensitive to stress during smoltification and the first weeks after seawater (SW) transfer. This work aimed at investigating the impact of hyperoxygenation combined with reduced flow in fresh water (FW), on the intestinal barrier in FW as well as during later life stages in SW. It further aims at investigating the role of the intestinal barrier during IPNV challenge and possible secondary infections. Hyperoxygenation in FW acted as a stressor as shown by significantly elevated plasma cortisol levels. This stressful husbandry condition tended to increase paracellular permeability (P(app)) as well as translocation of Aeromonas salmonicida in the posterior intestine of Atlantic salmon. After transfer to SW and subsequent IPNV challenge, intestinal permeability, as shown by P(app), and translocation rate of A. salmonicida increased in the anterior intestine, concomitant with further elevation in plasma cortisol levels. In the anterior intestine, four of five fish displayed alterations in intestinal appearance. In two of five fish, IPNV caused massive necrosis with significant loss of cell material and in a further two fish, IPNV caused increased infiltration of lymphocytes into the epithelium and granulocytes in the lamina propria. Hyperoxygenation and reduced flow in the FW stage may serve as stressors with impact mainly during later stages of development. Fish with an early history of hyperoxygenation showed a higher stress response concomitant with a disturbed intestinal barrier function, which may be a cause for the increased susceptibility to IPNV infection and increased susceptibility to secondary infections.

Hydrolysis of acyl-homogeneous and fish oil triacylglycerols using desalted midgut extract from atlantic salmon, Salmo salar.

Despite several studies aimed at evaluating the positional and fatty acid specificity of fish triacylglycerol (TAG) digestive lipases, there is still much uncertainty regarding these issues. The aim of the present study was therefore to address these questions in Atlantic salmon (Salmo salar L.). Crude luminal midgut extracts were collected from fed salmon and the hydrolysis studied for various substrates including triolein (Tri-18:1), trilinolein (Tri-18:2), trilinolenin (Tri-18:3), trieicosapentaenoin (Tri-20:5), tridocosahexaenoin (Tri-22:6) and natural fish oil TAG. Using Tri-18:1, in a time-curve model showed an initial high degree of sn-1 or sn-3 specificity where sn-1,2(2,3)-diacylglycerol (1,2(2,3)-DAG) and free fatty acid (FFA) were the main hydrolytic products up to 15 min. Lack of initial sn-2 specificity was confirmed by negligible sn-1,3-diacylglycerol (1,3-DAG) being produced. During the further hydrolysis of DAG, all positions appeared susceptible to attack causing a concomitantly small increase in sn-1(3)-monoacylglycerol (1(3)-MAG) and 2-MAG, but not at the level expected for an exclusively sn-1,3-specific lipase. Oleic acid (18:1n-9) and eicosapentaenoic acid (20:5n-3) were preferred substrates for hydrolysis using both fish oil and acyl-homogeneous TAGs with FFA as the main product of lipolysis. Hydrolysis of the natural fish oil TAG appeared slower yet produced proportionally more MAG and DAG after 5 min, and similar specificities, as for synthetic TAG substrates, were exhibited with 18:1n-9 and 20:5n-3 accumulating in the FFA fraction after 30 min. Notably, 16:0 was particularly conserved in MAG. As TAG resynthesis of absorbed lipid in salmon enterocytes proceeds preferably with 2-MAG as templates, the absorption of 2-MAG, produced during initial stages of TAG hydrolysis, would need to occur rapidly to be effectively utilised via the MAG pathway.

Histological changes in intestine of Atlantic salmon (Salmo salar L.) following in vitro exposure to pathogenic and probiotic bacterial strains.

Furunculosis and vibriosis are diseases that cause severe economic losses in the fish-farming industry. The foregut of the Atlantic salmon (Salmo salar L.) was exposed in vitro to two fish pathogens, Aeromonas salmonicida (causative agent of furunculosis) and Vibrio anguillarum (causative agent of vibriosis), and to one probiotic strain, Carnobacterium divergens, at 6 x 10(4) or 6 x 10(6) viable bacteria per milliliter. Histological changes following bacterial exposure were assessed by light and electron microscopy. Control samples (foregut exposed to Ringer's solution only) and samples exposed only to C. divergens had a similar appearance to intact intestinal mucosal epithelium, with no signs of damage. However, exposure of the foregut to the pathogenic bacteria resulted in damaged epithelial cells, cell debris in the lumen, and disorganization of the microvilli. Co-incubation of the foregut with a pathogen and C. divergens did not reverse the damaging effects caused by the pathogen, although these were alleviated when probiotic bacteria were used. Based on these results, we suggest that the probiotic bacterium, C. divergens, is able to prevent, to some extent, pathogen-induced damage in the Atlantic salmon foregut.

Translocation of viable Aeromonas salmonicida across the intestine of rainbow trout, Oncorhynchus mykiss (Walbaum).

The pathogenic bacterium Aeromonas salmonicida is the causative agent of the destructive disease furunculosis in salmonids. Horizontal transmission in salmonids has been suggested to occur via the skin, gills and/or intestine. Previous reports are contradictory regarding the role of the intestine as a route of infection. The present study therefore investigates the possibility of bacterial translocation across intestinal epithelia using Ussing chamber technology, in vitro. Intestinal segments were exposed for 90 min to fluorescein isothiocyanate-labelled pathogenic A. salmonicida. Sampling from the serosal side of the Ussing chambers showed that bacteria were able to translocate across the intestinal epithelium in both the proximal and distal regions. Plating and subsequent colony counting showed that the bacteria were viable after translocation. During the 90 min exposure to A. salmonicida, the intestinal segments maintained high viability as measured by electrical parameters. The distal region responded to bacterial exposure by increasing the electrical resistance, indicating an increased mucus secretion. This study thus demonstrates translocation of live A. salmonicida through the intestinal epithelium of rainbow trout, suggesting that the intestine is a possible route of infection in salmonids.

Rainbow trout can discriminate between feeds with different oil sources.

The purpose of present two-choice trials was to examine the capacity of groups of juvenile rainbow trout to differentiate between two isolipidic diets containing distinct oils and to detect an eventual preference. The choice was offered by means of two self-feeders per tank. One feeder distributed a standard diet with fish oil (FO), the other a diet containing vegetable oil, either rich in linolenic acid (linseed oil, LO), linoleic acid (sunflower oil, SO), or oleic acid (rapeseed oil, RO). Each 15-day preference test was preceded by a 15-day adaptation period during which both feeders distributed the same diet. The tests were followed by a 10- to 15-day validation period in order to confirm that feeder solicitations were steered by the characteristics of the diets. Preferences were expressed as relative changes in feed demands for a specific feeder. Averaged over all groups, the preference tests demonstrated the capacity of rainbow trout to discriminate between a diet with FO and a diet containing vegetable oil, and indicated a general preference for the diet with FO over the other diets irrespective of whether they received the diet with fish oil (Experiment 1) or with vegetable oil (Experiment 2) prior to the preference test. The tests also indicated a difference in the extent of relative avoidance of each of the three vegetable oil diets. Diet LO was the most avoided, as indicated by the 37-39% decrease in demands for the feeder with diet LO (P<0.05). Diet RO was the best accepted, causing a decrease in feed demands of only 15-17% (P>0.05). The avoidance of diet SO at the end of the preference test was 30% (P>0.05) after an initially higher avoidance of 43% (P<0.05). It is believed that the metabolic consequences of the excess of linolenic or linoleic acid negatively affected the feed acceptances of diets LO and SO. Further work is needed to elucidate a possible interference of differences in palatability. In all groups, the lower demands for the vegetable oil diets were compensated by increased demands for diet FO. Hence, changes in diet selection had no effect on total feed or energy intakes, measured as the sum of both selections.

Identification and characterization of Carnobacteria isolated from fish intestine.

Eleven bacterial strains were isolated from the gastrointestinal tract of four fish species, Atlantic salmon (Salmo salar L.), Arctic charr (Salvelinus alpinus L.), Atlantic cod (Gadus morhua L.) and wolffish (Anarhichas lupus L.). All the strains were Gram-positive rods, non-sporing, catalase and oxidase-negative, able to grow at pH 9.0 but not on acetate containing media (pH < or = 5.4), and were fermentative. They had a high content of oleic acid (18:1 n-9) in cellular lipid, and were found to belong to the genus Carnobacterium by phenotypic criteria. The eleven carnobacteria strains were further identified on the basis of 16S rDNA sequence analysis and AFLP(TM) fingerprinting.

Epithelium-associated bacteria in the gastrointestinal tract of Arctic charr (Salvelinus alpinus L.). An electron microscopical study.

AIMS: The primary aim was to use transmission electron microscopy (TEM) and scanning electron microscopy (SEM) to define the location of epithelium-associated bacteria in the digestive tract of the salmonid fish, Arctic charr (Salvelinus alpinus). METHODS AND RESULTS: TEM and SEM examination of the gastrointestinal tract demonstrated substantial numbers of ovoid and rod-shaped bacterial cells associated with the microvillous brush borders of enterocytes. Bacteria were found at the tips of microvilli as well as between adjacent microvilli. Endocytosis of bacteria by epithelial cells was observed in two regions (pyloric caeca and midgut). CONCLUSION: Electron microscope examination of the gut is an important tool for evaluating the microbial ecology of the fish digestive tract ecosystem. SIGNIFICANCE AND IMPACT OF THE STUDY: The results of the current study clearly demonstrate that the intestine is involved in bacterial endocytosis.

Lactic acid bacteria associated with the digestive tract of Atlantic salmon (Salmo salar L.).

The present study reports the effect of excessive handling stress and starvation on the lactic acid bacteria associated with the digestive tract of Atlantic salmon (Salmo salar L.). A relatively low population level (approximately 2 x 103 bacteria per gram wet tissue) of viable adherent heterotrophic bacteria was associated with the digestive tract (foregut, midgut and hindgut). Of the 752 bacterial isolates isolated from diet, water and the digestive tract, 201 isolates belonged to the carnobacteria. Of these isolates, one from the diet, one from the rearing water and 80 from the gastrointestinal tract, were further identified on the basis of 16S rDNA sequence analysis. All these isolates were identified as being Carnobacterium piscicola-like. Daily repeated stress and starvation of the fish over 11 d had no influence on the total culturable bacterial numbers or population level of C. piscicola associated with the digestive tract. C. piscicola-like isolates colonizing the various intestinal regions (foregut, midgut and hindgut) were also screened for their ability to produce growth inhibitory compounds active against the fish pathogen Aeromonas salmonicida. Of the 199 C. piscicola isolates tested, 139 inhibited growth of the pathogen.

The effect of diet on aerobic bacterial flora associated with intestine of Arctic charr (Salvelinus alpinus L.).

In order to extend the knowledge on the possible effect of diet on the gastrointestinal microbial community of fish, Arctic charr (Salvelinus alpinus L.) were fed diets containing high (23.7%) and low (6.4%) levels of carbohydrate. The number of viable aerobic and facultative aerobic bacteria associated with the digestive tract were not influenced by dietary regimen. A wide range of bacterial species was isolated, and the predominant bacterial species of both rearing groups were identified as Staphylococcus. There were, however, some differences in bacterial composition between the rearing groups, as well as inter-individual variations. For example, atypical Aeromonas salmonicida were isolated from the small and large intestine of two fish fed low dietary carbohydrate, while Aer. caviae-like isolates were found in the small intestine of four fish fed high carbohydrate. Non-motile Aeromonas spp. were found in the rearing group fed high dietary carbohydrate, but at low frequencies. Dietary manipulation seemed to influence the species composition of carnobacteria, Gram-positive rods, oxidase and catalase-negative and fermentative metabolism. Carnobacterium piscicola-like bacteria were only found in the small intestine, while C. mobile-like and Carnobacterium spp. were isolated from the large intestine of fish fed high carbohydrate. On the contrary, C. divergens-like isolates were found associated with the small and large intestine of fish fed low dietary carbohydrate.

The effect of dietary fatty acids on lactic acid bacteria associated with the epithelial mucosa and from faecalia of Arctic charr, Salvelinus alpinus (L.).

Arctic charr, Salvelinus alpinus (L.), held in fresh water, were fed four experimental diets containing different polyunsaturated fatty acids (PUFA). In addition, one group fed a diet containing only coconut oil as sole lipid source served as control. The population of aerobic heterotrophic bacteria associated with the epithelial mucosa and the faecalia was estimated using the dilution plate technique. Generally, the population level of adherent bacteria increased along the digestive tract (stomach, small intestine and large intestine). Adherent Gram-negative and Gram-positive bacteria seemed to be present at equal levels in all parts of the alimentary tract. Lactic acid bacteria dominated among the Gram-positive bacteria, and they were detected in all regions of fish fed the PUFA supplemented diets. The frequency of lactic acid bacteria was highest in the digestive tract of fish fed diets with added 7.0% linolenic acid (18:3 n-3) or 4% of a PUFA mix. A lower frequency of lactic acid bacteria was found in fish fed dietary linoleic acid (18:2 n-6), and they were absent or present in low numbers in fish fed the coconut oil diet. It is suggested that dietary fatty acids affect the attachment sites for the gastrointestinal microbiota, possibly by modifying the fatty acid composition of the intestine wall. Numerical taxonomy procedures showed that the lactic acid bacteria Carnobacterium spp. and a Carnobacterium piscicola-like strain were predominant, with smaller numbers of Lactobacillus plantarum, Streptococcus spp. and Leuconostoc mesenteroides present. Seven strains of Carnobacterium spp. were further identified on the basis of 16S rDNA sequence analysis, and all these strains were identified as Carnobacterium piscicola.

Cross-pin femoral fixation: a new technique for hamstring anterior cruciate ligament reconstruction of the knee.

A new method of femoral fixation for arthroscopic anterior cruciate ligament (ACL) reconstruction using semitendinosus and gracilis (ST/G) tendons is presented. Biomechanical evaluation of the method was performed with pullout tests using animal tissues simulating fixation of ST/G tendons passing around a 2.5-mm pin placed transversely through a femoral tunnel. Clinical assessment of 22 patients was performed according to IKDC, Tegner, Lysholm, isokinetic strength, and KT1000 standards. Fixation strengths ranged from 725 N to 1,600 N for yield and maximal loads to failure for 35-mm to 70-mm cross-pins. Clinical results at mean follow-up of 30 months showed one traumatic failure, IKDC 86% normal or nearly normal, Tegner 6 ave, Lysholm 93 ave, KT1000 86% < 3 mm side-to-side difference on maximal manual evaluation, and isokinetic strength testing of quadriceps 8% deficit with hamstrings 8% deficit. Cross-pin fixation of ST/G tendons may be one of the strongest modes of femoral graft attachment yet devised. Our clinical outcomes in this initial series compare well with previous reports of ACL reconstruction regardless of graft or technique.

The development of suture anchors for use in soft tissue fixation to bone.

Soft tissue fixation to bone is a basic technique of orthopaedic surgery for which a multitude of devices have been developed. A new class of orthopaedic devices termed "suture anchors" has been developed to secure soft tissues to bone using suture material. The suture anchor is designed to allow quick and secure fixation without the need for extensive exposure. This device was tested using in vitro and in vivo models and found to be comparable with standard transosseous and two-pronged stable techniques. This device should prove useful in allowing the versatility of suture fixation of soft tissues to bone without the technical requirements of constructing transosseous suture tunnels.

Lipids of arctic charr,Salvelinus alpinus (L.) II. Influence of dietary fatty acids on the elongation and desaturation of linoleic and linolenic acid.

Arctic charr,Salvelinus alpinus L. were fed five test diets containing 0% or 1% of different polyunsaturated fatty acids (PUFA) for 93 days. The fish were injected intraperitoneally with (1-(14)C)-18:2(n-6) or (1-(14)C)-18:3(n-3), and the bioconversion to longer chain PUFA studied. The conversion rate in neutral lipids was slow, with most label found as the fatty acid injected, while extensive modification took place prior to or during incorporation into polar lipids. Linolenic acid was preferred over linoleic acid as substrate for elongation and desaturation regardless of diet. In polar lipids, the predominant products of (1-(14)C)-18:2(n-6) metabolism were generally 20:3(n-6) and 20:4(n-6), while 18:4(n-3), 20:5(n-3) and 22:6(n-3) were the major products of (1-(14)C)-18:3(n-3) metabolism. The lack of radioactivity in 22:5(n-6) suggests that Δ 4 desaturation is specific for (n-3) PUFA. Feeding the PUFA deficient diet reduced the Δ 5 desaturation compared to fish maintained on PUFA supplemented diets. The Δ 6 desaturation was only reduced in fish fed C18 PUFA and injected with (1-(14)C)-18:3(n-3). Longer chain C20 and C22 PUFA, particularly those of the (n-3) family, exerted some inhibition on the elongation and desaturation of injected fatty acids compared to those fed C18 PUFA. The incorporation of radiolabelled fatty acids into polar lipids of fish fed a commercial diet was very low, and the desaturation neglectible in both polar and neutral lipids, showing that Arctic charr under culture conditions do not convert short chain PUFA to longer chain metabolites.

Effect of prior infection with virulent Shigella flexneri 2a on the resistance of monkeys to subsequent infection with Shigella sonnei.

All virulent shigellae have large plasmids. Plasmid-associated genes encode the expression of membrane-associated proteins (MAP), some of which correlate with the ability to invade susceptible epithelial cells. These MAP are serologically related in all of the shigella serotypes and evoke an antibody response after infection. To determine whether the MAP have a significant role in protection, 24 monkeys were infected with virulent Shigella flexneri 2a. After recovery, one group (with controls) was rechallenged with S. flexneri 2a; another group (with controls) was fed Shigella sonnei. The animals that were rechallenged with S. flexneri 2a were protected, while those that were fed S. sonnei experienced the same incidence of disease as controls. No differences in serum immune response to MAP after primary infection with S. flexneri were detected in immunoblots using lysates of S. flexneri or S. sonnei or in ELISA using water extracts of these strains.