Estradiol and triiodothyronine differentially modulate reproductive and thyroidal genes in male goldfish.

While the reproductive and thyroidal systems are extensively studied in fish, they are largely studied in isolation from one another, but there is evidence supporting cross-regulation between these two systems. To better understand hormone action and the potential cross-regulation between estrogen and thyroid hormones, we examined gene expression changes in estrogen receptor (ER) and thyroid receptor (TR) subtypes and key enzymes responsible for the local synthesis and availability of estrogen and thyroid hormones (aromatase B and deiodinase, respectively) in sexually regressed, adult, male goldfish in response to 3 days waterborne exposures to 17ß-estradiol (E2; 1 nM), triiodothyronine (T3; 20 and 100 nM), and co-treatments thereof. Treatments with E2 alone did not effect ER subtype transcripts in the liver, telencephalon, or testis; however, in the testis, 1 nM T3 decreased ERα and ERß1 and co-treatments of T3 and E2 decreased ERß1 levels. TRα-1 and TRß transcripts were not auto-regulated by T3 or cross-regulated by E2. Although deiodinase type I levels were also unaffected, deiodinase type II decreased in response to T3 treatments. Liver deiodinase type III transcripts increased in response to T3 treatments, while E2 exhibited antagonistic effects on this T3-mediated induction. These results provide novel evidence of cross-talk between the reproductive and thyroid endocrine axes in a model teleost.

Glucose homeostasis in rainbow trout fed a high-carbohydrate diet: metformin and insulin interact in a tissue-dependent manner.

Carnivorous fish species such as the rainbow trout (Oncorhynchus mykiss) are considered to be "glucose intolerant" because of the prolonged hyperglycemia experienced after intake of a carbohydrate-enriched meal. In the present study, we use this species to study glucose homeostasis in fish chronically infused with the hypoglycemic agents, insulin, and metformin, and fed with a high proportion of carbohydrates (30%). We analyzed liver, skeletal muscle, and white adipose tissue (WAT), which are insulin- and metformin-specific targets at both the biochemical and molecular levels. Trout infused with the combination of insulin and metformin can effectively utilize dietary glucose at the liver, resulting in lowered glycemia, increased insulin sensitivity, and glucose storage capacity, combined with reduced glucose output. However, in both WAT and skeletal muscle, we observed decreased insulin sensitivity with the combined insulin + metformin treatment, resulting in the absence of changes at the metabolic level in the skeletal muscle and an increased potential for glucose uptake and storage in the WAT. Thus, the poor utilization by rainbow trout of a diet with a high proportion of carbohydrate can at least be partially improved by a combined treatment with insulin and metformin, and the glucose intolerance observed in this species could be, in part, due to some of the downstream components of the insulin and metformin signaling pathways. However, the predominant effects of metformin treatment on the action of insulin in these three tissues thought to be involved in glucose homeostasis remain exclusive in this species.

Effects of insulin infusion on glucose homeostasis and glucose metabolism in rainbow trout fed a high-carbohydrate diet.

The origin for the poor glucose utilization in carnivorous fish species fed high carbohydrate diets remains under debate. In the present study, we have fed rainbow trout a diet containing 30% carbohydrate for 1 or 5 days. In both cases, fish were implanted with mini-osmotic pumps releasing 0.7 i.u. kg(-1) day(-1) bovine insulin, and mRNA transcripts and the protein phosphorylation status of proteins controlling glycemia and glucose-related metabolism were studied in fish killed 6 h after the last meal. We demonstrate that when the exposure occurs over a short term (30 h), insulin exerts beneficial actions on trout glucose homeostasis, including a lowered glycemia and increased hepatic lipogenic and glycogenic potentials. However, when trout were fed for 5 days, these beneficial actions of insulin infusion were no longer observed. Thus, the increased lipogenic potential observed after one single meal was not present, and this together with the increased glycogenesis and the decreased glucose exported to the blood from the liver explains the lack of hypoglycemic action of insulin. The fact that insulin improved glucose homeostasis when administrated over a short time period implies that endogenous insulin secretion is inadequate in trout to deal with this amount of dietary carbohydrates. Moreover, the fact that a longer exposure to insulin resulted in a reduced response indicates that the rainbow trout is sensitive to insulin, re-enforcing the hypothesis that the hyperglycemia observed following a high carbohydrate meal is an insulin secretion issue rather an insulin action issue.

Metformin improves postprandial glucose homeostasis in rainbow trout fed dietary carbohydrates: a link with the induction of hepatic lipogenic capacities?

Carnivorous fish are poor users of dietary carbohydrates and are considered to be glucose intolerant. In this context, we have tested, for the first time in rainbow trout, metformin, a common anti-diabetic drug, known to modify muscle and liver metabolism and to control hyperglycemia in mammals. In the present study, juvenile trout were fed with very high levels of carbohydrates (30% of the diet) for this species during 10 days followed by feeding with pellets supplemented with metformin (0.25% of the diet) for three additional days. Dietary metformin led to a significant reduction in postprandial glycemia in trout, demonstrating unambiguously the hypoglycemic effect of this drug. No effect of metformin was detected on mRNA levels for glucose transporter type 4 (GLUT4), or enzymes involved in glycolysis, mitochondrial energy metabolism, or on glycogen level in the white muscle. Expected inhibition of hepatic gluconeogenic (glucose-6-phosphatase, fructose-1,6-bisphosphatase, and phosphoenolpyruvate carboxykinase) mRNA levels was not found, showing instead paradoxically higher mRNA levels for these genes after drug treatment. Finally, metformin treatment was associated with higher mRNA levels and activities for lipogenic enzymes (fatty acid synthase and glucose-6-phosphate dehydrogenase). Overall, this study strongly supports that the induction of hepatic lipogenesis by dietary glucose may permit a more efficient control of postprandial glycemia in carnivorous fish fed with high carbohydrate diets.

50 years of comparative biochemistry: The legacy of Peter Hochachka.

Peter Hochachka was an early pioneer in the field of comparative biochemistry. He passed away in 2002 after 4 decades of research in the discipline. To celebrate his contributions and to coincide with what would have been his 80th birthday, a group of his former students organized a symposium that ran as a satellite to the 2017 Canadian Society of Zoologists annual meeting in Winnipeg, Manitoba (Canada). This Special Issue of CBP brings together manuscripts from symposium attendees and other authors who recognize the role Peter played in the evolution of the discipline. In this article, the symposium organizers and guest editors look back on his career, celebrating his many contributions to research, acknowledging his role in training of generations of graduate students and post-doctoral fellows in comparative biochemistry and physiology.

Waterborne gemfibrozil challenges the hepatic antioxidant defense system and down-regulates peroxisome proliferator-activated receptor beta (PPARbeta) mRNA levels in male goldfish (Carassius auratus).

The lipid regulator gemfibrozil (GEM) is one of many human pharmaceuticals found in the aquatic environment. We previously demonstrated that GEM bioconcentrates in blood and reduces plasma testosterone levels in goldfish (Carassius auratus). In this study, we address the potential of an environmentally relevant waterborne concentration of GEM (1.5 microg/l) to induce oxidative stress in goldfish liver and whether this may be linked to GEM acting as a peroxisome proliferator (PP). We also investigate the autoregulation of the peroxisome proliferator-activated receptors (PPARs) as a potential index of exposure. The three PPAR subtypes (alpha, beta, and gamma) were amplified from goldfish liver cDNA. Goldfish exposed to a concentration higher (1500 microg/l) than environmentally relevant for 14 and 28 days significantly reduce hepatic PPARbeta mRNA levels (p<0.001). Levels of CYP1A1 mRNA were unchanged. GEM exposure significantly induced the antioxidant defense enzymes catalase (p<0.001), glutathione peroxidase (p<0.001) and glutathione-S-transferase (p=0.006) but not acyl-CoA oxidase or glutathione reductase. As GEM exposure failed to increase levels of thiobarbituric reactive substances (TBARS), we conclude that a sub-chronic exposure to GEM upregulates the antioxidant defense status of the goldfish as an adaptive response to this human pharmaceutical.

Integrated responses of Na+/HCO3- cotransporters and V-type H+-ATPases in the fish gill and kidney during respiratory acidosis.

Using degenerate primers, followed by 3' and 5' RACE and "long" PCR, a continuous 4050-bp cDNA was obtained and sequenced from rainbow trout (Oncorhynchus mykiss) gill. The cDNA included an open reading frame encoding a deduced protein of 1088 amino acids. A BLAST search of the GenBank protein database demonstrated that the trout gene shared high sequence similarity with several vertebrate Na(+)/HCO(3)(-) cotransporters (NBCs) and in particular, NBC1. Protein alignment revealed that the trout NBC is >80% identical to vertebrate NBC1s and phylogenetic analysis provided additional evidence that the trout NBC is indeed a homolog of NBC1. Using the same degenerate primers, a partial cDNA (404 bp) for NBC was obtained from eel (Anguilla rostrata) kidney. Analysis of the tissue distribution of trout NBC, as determined by Northern blot analysis and real-time PCR, indicated high transcript levels in several absorptive/secretory epithelia including gill, kidney and intestine and significant levels in liver. NBC mRNA was undetectable in eel gill by real-time PCR. In trout, the levels of gill NBC1 mRNA were increased markedly during respiratory acidosis induced by exposure to hypercarbia; this response was accompanied by a transient increase in branchial V-type H(+)-ATPase mRNA levels. Assuming that the branchial NBC1 is localised to basolateral membranes of gill cells and operates in the influx mode (HCO(3)(-) and Na(+) entry into the cell), it would appear that in trout, the expression of branchial NBC1 is transcriptionally regulated to match the requirements of gill pHi regulation rather than to match trans-epithelial HCO(3)(-) efflux requirements for systemic acid-base balance. By analogy with mammalian systems, NBC1 in the kidney probably plays a role in the tubular reabsorption of both Na(+) and HCO(3)(-). During periods of respiratory acidosis, levels of renal NBC1 mRNA increased (after a transient reduction) in both trout and eel, presumably to increase HCO(3)(-) reabsorption. This strategy, when coupled with increased urinary acidification associated with increased vacuolar H(+)-ATPase activity, ensures that HCO(3)(-) levels accumulate in the body fluids to restore pH.

Stress elevates corticotropin-releasing factor (CRF) and CRF-binding protein mRNA levels in rainbow trout (Oncorhynchus mykiss).

The objectives of this study were to characterize rainbow trout (Oncorhynchus mykiss) corticotropin-releasing factor (CRF)-binding protein (CRF-BP) cDNA and to examine the variations in CRF-BP and CRF mRNA levels in response to different intensities of stress. Trout were physically disturbed by a single or three consecutive periods of chasing until exhaustion followed by 2 h of recovery. The pituitary CRF-BP and preoptic area CRF1 mRNA contents were significantly increased only after repeated chasing events. Physical disturbance increased plasma cortisol levels with the largest change occurring in the group of trout that were exposed to repeated chasing events. Trout were also individually isolated in 120 l tanks or confined to 1.5 l boxes for 4, 24 or 72 h. CRF-BP mRNA levels in confined fish were greater than those of isolated fish at 72 h although there were no differences compared with the control group. CRF1 mRNA levels in the preoptic area were greater and remained elevated for a longer period in confined compared with isolated trout. Isolation led to a transient increase in plasma cortisol levels, but the higher cortisol values developed in the confined fish suggest that this treatment was more stressful than isolation. These results demonstrate that the intensity and duration of stress are important factors regulating CRF and CRF-BP mRNA levels in rainbow trout. We hypothesize that pituitary CRF-BP is involved in regulating the activity of the stress axis, possibly by reducing access to CRF1 receptors in the corticotropes.

The human lipid regulator, gemfibrozil bioconcentrates and reduces testosterone in the goldfish, Carassius auratus.

Human and veterinarian pharmaceuticals have been detected in the aquatic environment for a number of years, but the potential for biological effects in exposed aquatic organism is only now being reported. The lipid regulator, gemfibrozil (GEM) is detected at microg/L concentrations in domestic wastewater and ng/L concentrations in surface waters. We investigated the uptake of GEM in goldfish (Carassius auratus) over a 96 h time period by measuring GEM in blood plasma using LC-MS/MS. Results indicated that GEM can be taken up from water through the gills. In goldfish exposed to GEM by a single intraperitoneal injection, concentrations of GEM in the blood plasma declined rapidly over 96 h post-injection, with a half-life estimated at approximately 19 h. Exposure of goldfish to waterborne GEM at an environmentally relevant concentration over 14 days resulted in a plasma bioconcentration factor of 113. In goldfish exposed to aqueous concentrations of GEM for 96 h or 14 days, plasma testosterone (T) was reduced by over 50% in fish from all treatments. As a possible mechanistic explanation for the observed reduction in T, levels of steroid acute regulatory (StAR) protein transcript in goldfish testes were assessed by RT-PCR. StAR protein is involved in the transport of cholesterol from the outer to the inner mitochondrial membrane for transformation by the first enzyme in steroidogenesis. After exposure to GEM for 96 h, a 50% decrease in StAR mRNA levels was observed in goldfish. Gonadal StAR mRNA levels were not affected in the 14 days exposure, indicating that the observed decreases in plasma testosterone were not solely due to impaired delivery of cholesterol to the inner mitochondrial membrane. Our results demonstrate that exposure to environmental levels of GEM leads to bioconcentration of the drug in plasma and the potential for endocrine disruption in fish.

Increased basal expression of hepatic Cyp1a1 and Cyp1a2 genes in inbred mice selected for susceptibility to acetaminophen-induced hepatotoxicity.

Susceptibility to acetaminophen-induced hepatotoxicity was found to vary widely in an outbred colony of Swiss Webster mice. Some acetaminophen-treated male mice showed a significant elevation in serum levels of the hepatic enzyme alanine aminotransferase at a normally non-hepatotoxic oral dose. A selective breeding program over 17 generations produced inbred mice which were either susceptible or nonsusceptible to the hepatotoxic effects of acetaminophen. Liver microsomes from the susceptible group showed a statistically significant increase in the ability to metabolize acetaminophen to a reactive intermediate which covalently binds N-acetylcysteine. Microsomal cytochrome P450 activities associated with CYP1A2 (acetanilide 4-hydroxylation and methoxyresorufin O-demethylase) were significantly increased in the susceptible group. Ethoxyresorufin O-deethylase activity, associated with both CYP1A1 and CYP1A2, was also significantly elevated in this group. Further examination of both CYP1A isoforms revealed that hepatic CYP1A1 and CYP1A2 mRNA and protein levels were significantly elevated in animals from the susceptible group. In vivo caffeine 3-demethylation, which is associated with CYP1A2 activity, co-segregated with acetaminophen susceptibility and showed a significant positive correlation (r = 0.626, p < 0.005) with CYP1A2 mRNA expression in animals from both the susceptible and nonsusceptible groups. The co-segregation of elevated basal Cyp1a1 and CYP1a2 gene expression levels in animals selected for susceptibility to acetaminophen-induced hepatotoxicity suggested a common heritable basis for regulation of basal expression of both of these CYP1A isoforms. This was supported by the correlated expression of both CYP1A mRNAs within individual mice (r = 0.644, p < 0.02).

Metabolic response of teleost hepatocytes to glucagon-like peptide and glucagon.

Salmon glucagon-like peptide (GLP), bovine glucagon (B-glucagon) and anglerfish glucagon (AF-glucagon), all activate glucose production in teleost hepatocytes through gluconeogenesis and glycogenolysis, but notable species differences exist in their respective effectiveness. In trout hepatocytes, gluconeogenesis appears to be the main target of hormone action. In eel cells, sampled in November, glycogenolysis was activated threefold, while gluconeogenesis was increased by 12% only. In March, glycogenolytic activation was 1.7-fold, while gluconeogenesis was increased by about 1.7-fold after exposure to B-glucagon. In brown bullhead cells, increases in glycogenolysis from seven- (GLP) to tenfold (B- and AF-glucagon) were noted, while activation of gluconeogenesis was slight. Fragments of two AF-glucagons (19-29) revealed only insignificant metabolic activity. Treatment of eel cells with B-glucagon led to large (up to 20-fold) increases in intracellular cyclic AMP (cAMP) concentrations, while exposure to GLP was accompanied by a modest (less than twofold) increase in cAMP, although metabolic effectiveness (gluconeogenesis and glycogenolysis) was similar for the two treatments. Under identical conditions, brown bullhead cellular cAMP responded poorly. Levels of cAMP peaked within 15 min following hormone application. The results imply that no simple or direct relationship exists between the amount of intracellular cAMP and the metabolic action of the glucagon family of hormones. It can further be concluded that GLPs are important regulators of hepatic metabolism, influencing identical targets as glucagon, while the mechanisms of action seem to differ.

Glucagon binding to hepatocytes isolated from two teleost fishes, the American eel and the brown bullhead.

We have characterized the specific binding of glucagon in hepatocytes isolated from two teleost species, the American eel (Anguilla rostrata) and the brown bullhead (Ictalurus nebulosus). Specific glucagon binding was 9.3 and 10.7% in bullhead and eel hepatocytes respectively, after a 2-h incubation at 12 degrees C. Curvilinear Scatchard plots suggest the presence of two classes of binding sites with apparent dissociation constants (Kd) of 1.97 nM (high affinity) and 17.3 nM (low affinity) for bullhead and 2.68 and 22.9 nM for eel cells. The number of high-affinity binding sites per cell was significantly higher in the eel (10,413) than in the bullhead (3811). The number of high-affinity insulin-binding sites was approximately two times higher than that for glucagon in bullheads and the opposite in the eel hepatocytes. In competition experiments, insulin did not displace 125I-labelled glucagon binding in the hepatocytes of either species, while glucagon-like peptide-1(7-37) (GLP-1) displaced glucagon but only at high concentrations, suggesting separate glucagon- and GLP-1-binding sites. The rate of dissociation of hepatocyte-bound 125I-labelled glucagon was similar for both species. Preincubation of hepatocytes in 100 nM glucagon decreased the number of high-affinity glucagon-binding sites by approximately 55% in both species, while the Kd values remained unchanged. Glucagon bound to the cell surface is internalized by fish hepatocytes. These properties indicate that the glucagon binding to hepatocytes of these two teleost species is similar to that reported for mammalian hepatocytes.

beta-Naphthoflavone abolishes interrenal sensitivity to ACTH stimulation in rainbow trout.

We report for the first time that beta-naphthoflavone (BNF) abolishes ACTH stimulation of cortisol production in rainbow trout (Oncorhynchus mykiss). There was significantly higher hepatic cytochrome P450 content and ethoxyresorufin O-de-ethylase and uridine-5'-diphosphoglucuronic acid transferase activities in BNF-treated fish than in sham-treated controls. BNF did not significantly affect either plasma turnover or tissue distribution of [3H]cortisol-derived radioactivity. Hepatic membrane fluidity and hepatocyte capacity for cortisol uptake were not altered by BNF as compared with the sham-treated fish. These results taken together suggest that BNF does not affect cortisol-clearance mechanisms in trout. A 3 min handling disturbance period elicited a plasma cortisol response in the sham-treated fish; however, the response in the BNF-treated fish was muted and significantly lower than in the sham fish. This in vivo response corroborates the lack of interrenal sensitivity to ACTH in vitro in the BNF-treated fish, suggesting that BNF affects the ACTH pathway in trout. Our results suggest the possibility that cytochrome P450-inducing compounds may affect cortisol dynamics by decreasing interrenal responsiveness to ACTH stimulation in fish, thereby impairing the physiological responses that are necessary for the animal to cope with the stressor.

Relationships between environmental organochlorine contaminant residues, plasma corticosterone concentrations, and intermediary metabolic enzyme activities in Great Lakes herring gull embryos.

Experiments were conducted to survey and detect differences in plasma corticosterone concentrations and intermediary metabolic enzyme activities in herring gull (Larus argentatus) embryos environmentally exposed to organochlorine contaminants in ovo. Unincubated fertile herring gull eggs were collected from an Atlantic coast control site and various Great Lakes sites in 1997 and artificially incubated in the laboratory. Liver and/or kidney tissues from approximately half of the late-stage embryos were analyzed for the activities of various intermediary metabolic enzymes known to be regulated, at least in part, by corticosteroids. Basal plasma corticosterone concentrations were determined for the remaining embryos. Yolk sacs were collected from each embryo and a subset was analyzed for organochlorine contaminants. Regression analysis of individual yolk sac organochlorine residue concentrations, or 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs), with individual basal plasma corticosterone concentrations indicated statistically significant inverse relationships for polychlorinated dibenzo-p-dioxins/polychlorinated dibenzofurans (PCDDs/PCDFs), total polychlorinated biphenyls (PCBs), non-ortho PCBs, and TEQs. Similarly, inverse relationships were observed for the activities of two intermediary metabolic enzymes (phosphoenolpyruvate carboxykinase and malic enzyme) when regressed against PCDDs/PCDFs. Overall, these data suggest that current levels of organochlorine contamination may be affecting the hypothalamo-pituitary-adrenal axis and associated intermediary metabolic pathways in environmentally exposed herring gull embryos in the Great Lakes.

Neuropeptide Y-related peptides from the pancreas of a teleostean (eel), holostean (bowfin) and elasmobranch (skate) fish.

Homologous peptides belonging to the pancreatic polypeptide (PP) family were isolated from the pancreas of a teleostean fish, the American eel (Anguilla rostrata), an holostean fish, the bowfin (Amia calva) and an elasmobranch fish, the skate (Raja rhina), and their primary structures were determined. The peptides show stronger homology to neuropeptide Y, particularly in their COOH-terminal regions, than to peptide YY or pancreatic polypeptide and contain an alpha-amidated COOH-terminal tyrosine residue. The skate peptide Tyr-Pro-Pro-Lys-Pro-Glu-Asn-Pro-Gly-Asp10-Asp-Ala-Ala-Pro-Glu-Glu- Leu-Ala-Lys- Tyr20-Tyr-Ser-Ala-Leu-Arg-His-Tyr-Ile-Asn-Leu30-Ile-Thr-Arg- Gln-Arg-Tyr-NH2 represents the first member of the PP family to be isolated from a cartilaginous fish. The primary structure of the pancreatic PP family peptide has been more strongly conserved among the phylogenetically more ancient holostean and elasmobranch fishes than among the teleosts. A comparison of the primary structures of all PP family peptides supports the hypothesis and evolution has acted to conserve features of tertiiary structure in the molecules (e.g., the polyproline- and alpha-helices) rather than individual amino acid residues.

Insulin and insulin-like growth factor-I (IGF-I) binding in fish red muscle: regulation by high insulin levels.

Insulin and IGF-I binding to semi-purified red muscle receptors was characterized in brown trout, Salmo trutta and the common carp. Cyprinus carpio. The yield of glycoprotein obtained after semipurification of receptors with WGA-agarose affinity chromatography in microgram g-1 initial tissue was 210.6 +/- 21 micrograms g-1 in trout and 108.5 +/- 2.5 micrograms g-1 in carp. IGF-I specific binding (4.72 +/- 0.64%/10 micrograms glycoprotein) was 4-5-times higher than insulin binding (1.04 +/- 0.12%/10 micrograms glycoprotein) in trout red muscle. This difference in binding was due to a higher number and a greater affinity of the IGF-I (Kd, 0.21 +/- 0.03 nM) compared with the insulin (Kd, 0.67 +/- 0.06 nM) receptors in this tissue. Carp red muscle IGF-I binding (9.14 +/- 0.55%/10 micrograms glycoprotein) surpassed insulin binding (2.59 +/- 0.094%/10 micrograms glycoprotein) mainly because of a greater affinity of the IGF-I (Kd, 0.092 +/- 0.027 nM) compared with the insulin (Kd, 0.1515 +/- 0.0285 nM) receptor. IGF-I and insulin binding in carp red muscle were higher than in trout, as a consequence of a higher affinity of carp red muscle receptors. Arginine injection provoked acute hyperinsulinemia in both trout (23.3 +/- 1.01 ng ml-1) and carp (24.3 +/- 1.34 ng ml-1. Specific binding of insulin and IGF-I to the red muscle decreased 4 h after injection. In trout, a decrease of insulin and IGF-I binding of 47.0% and 63.3%, respectively was observed compared with controls, in carp, these values were 44.0% and 45.0%. The number of insulin and IGF-I receptors decreased (42-55%) but affinities did not change suggesting that receptor down-regulation is a consequence of high insulin levels.

Ultraviolet-B radiation effects on antioxidant status and survival in the zebrafish, Brachydanio rerio.

Direct impact of ambient (1.95 W/m2) and subambient doses of UV-B radiation on muscle/skin tissue antioxidant status was assessed in mature zebrafish (Brachydanio rerio). The influence of these doses on hatching success and survival in earlier life stages was also examined. Subambient doses of UV-B radiation in the presence (1.28 W/m2) and absence (1.72 W/m2) of a cellulose acetate filter significantly depressed muscle/skin total glutathione (TGSH) levels compared with controls (0.15 W/m2) and low (0.19 W/m2) UV-B-treated fish after 6 and 12 h cumulative exposure. Ambient UV-B exposure significantly decreased muscle/skin glutathione peroxidase (GPx) activity after a 6 h exposure; activities of glutathione reductase (GR) were unchanged over this exposure period. Superoxide dismutase (SOD) and catalase activities peaked after 6 and 12 h cumulative exposure, respectively, but fell back to control levels by the end of the exposure period. The changes in tissue antioxidant status suggested UV-B-mediated increases in cytosolic superoxide anion radicals (O2-) and hydrogen peroxide (H2O2). This apparent UV-B-mediated increase in oxidative stress is further supported by a significant increase in muscle/skin thiobarbituric acid reactive substances (TBARS). Hatching success of newly fertilized eggs continuously exposed to ambient UV-B was only 2% of the control value. Even at 30 and 50% of ambient UV-B, hatching success was only 80 and 20%, respectively, of the control. Newly hatched larvae exposed to an ambient dose of UV-B, experienced 100% mortality after a 12 h cumulative exposure period. This study supports a major impact of UV-B on both the mature and embryonic zebrafish.

Transglycosylation of naringin by Bacillus stearothermophilusMaltogenic amylase to give glycosylated naringin.

Naringin, a bitter compound in citrus fruits, was transglycosylated by Bacillus stearothermophilus maltogenic amylase reaction with maltotriose to give a series of mono-, di-, and triglycosylnaringins. Glycosylation products of naringin were observed by TLC and HPLC. The major glycosylation product was purified by using a Sephadex LH-20 column. The sturcture was determined by using MALDI-TOF MS, methylation analysis, and (1)H and (13)C NMR. The major transglycosylation product was maltosylnaringin, in which the maltose unit was attached by an alpha-1-->6 glycosidic linkage to the D-glucose moiety of naringin. This product was 250 times more soluble in water and 10 times less bitter than naringin.

Glucose intolerance in teleost fish: fact or fiction?

Teleost fish are generally considered to be glucose intolerant. This mini-review examines some of the background and the possible mechanistic bases for this statement. Glucose intolerance is a clinical mammalian term meaning that a glucose load results in persistent hyperglycemia. Teleost fish show persistent hyperglycemia that is generally coincident with transient hyperinsulinemia. The fact that teleost generally have high plasma insulin compared with mammals implies insulin-deficiency is not a suitable explanation for this persistent hyperglycemia. Instead, peripheral utilization of glucose is probably the principle cause of hyperglycemia. Recent evidence for muscle insulin receptors, glucose transporters and hexokinase/glucokinase is reviewed and future experimental directions are suggested. If by altering peripheral glucose utilization fish could become more glucose tolerant, costs to the aquaculture industry may be substantially reduced.