Heavy metal levels in fish from coastal waters of Uruguay.

Copper, mercury, and zinc levels were determined in muscle and liver (N = 163) of seven fish species caught in coastal waters off Montevideo and Piriapolis (control site): Odontesthes spp., Mugil platanus, Micropogonias furnieri, Urophycis brasiliensis, Cynoscion guatucupa, Menticirrhus americanus, and Mustelus schmitti. The local population commonly uses these species for consumption. Heavy metal concentrations determined in this study were generally below those obtained for fish caught in Argentinean and Brazilian coastal waters, with some exceptions in the case of mercury and zinc. Based on copper, mercury, and zinc levels in muscle tissue, we conclude that the fish studied here are acceptable for human consumption. Nevertheless, it is recommended not to consume the fish liver (up to 466 microg Zn g(-1) dry weight in liver) nor large specimens of the investigated species. Regional programs involving the neighboring countries should be established to assess the fisheries resources and potential risks for human health.

Metabolic actions of glucagon and dexamethasone in liver of the ureogenic teleost Opsanus beta.

Injection with pharmacological doses of dexamethasone (5 mg/kg) and/or bovine glucagon (1 mg/kg) exerts pronounced effects on toadfish liver compared with vehicle-treated control fish. Affected parameters include hepatic levels of glycogen and the activities of glutamate dehydrogenase, aspartate aminotransferase, malate dehydrogenase, and enzymes involved in NADPH generation as well as the kinetics of pyruvate kinase. Activities of tyrosine aminotransferase, however, a prime target for hormonal induction in mammals, remain unchanged in Opsanus. In subsequently isolated toadfish hepatocytes, metabolite concentrations and flux through gluconeogenesis are altered as are in vitro responses to epinephrine and catfish glucagon in previously injected fish. Contrary to existing mammalian models, short-term regulation of urea cycle activity can be ruled out for toadfish, since hormone treatments fail to influence the activity of two ornithine-urea cycle enzymes or the rate of hepatocyte-urea synthesis. Treatment-dependent increases in hepatic glutamine synthetase, the unique feeder enzyme for ammonia "nitrogen" in fish urea cycle, indicate a potentially pivotal role for this enzyme in longer-term regulation of ureogenesis.

Nitrogenous waste excretion and accumulation of urea and ammonia inChalcalburnus tarichi (Cyprinidae), endemic to the extremely alkaline Lake Van (Eastern Turkey).

The endemic, anadromous cyprinidChalcalburnus tarichi is the only fish species known to occur in alkaline Lake Van (Eastern Anatolia, Turkey). EightC. tarichi were maintained individually in Lake Van water (17 - 19°C; pH 9.8; 153 mEq·I(-1) total alkalinity; 22‰ total salinity) and tank water samples analyzed for 24 h in 2 to 4 h intervals. At zero time, < 1µM ammonia was present and urea was undetectable in the tank water; at 24 h, total ammonia and urea made up 114±32 and 35±25µM, respectively. Over the experimental period, ammonia-N and urea-N excretion averaged 1041±494 and 607±169µmoles·kg(-1) fish·h(-1), respectively. The extent of urea excretion was highly variable between specimens. Uric acid excretion was not detectable.Urea was present at high concentrations in all tissues and plasma (25 - 35µmoles·g(-1)·ml(-1)) of freshly caughtC. tarichi; total ammonia content of the tissues was by a factor of 1.9 (liver) to 3.0 (brain) lower. High arginase activity (2.4±0.2 U·min(-1)·g(-1)) was detected in the liver ofC. tarichi but ornithine carbamoylphosphate transferase, a key enzyme of the ornithine-urea-cycle, was absent. Ureagenesis is likely through degradation of arginine and/or uricolysis. High glutamine synthetase activity (11±0.6 U·min(-1)·g(-1)) and low ammonia content in brain suggest that, like other teleosts,C. tarichi has an efficient ammonia detoxification in the brain, but in no other tissue.Nitrogenous waste excretion at alkaline pH is discussed. The ability ofC. tarichi to excrete high levels of ammonia at extremely alkaline pH is unique among teleosts studied so far. The mechanism of ammonia excretion under Lake Van conditions remains to be elucidated.

Hormonal regulation of metabolism in hepatocytes of the ureogenic teleostopsanus beta.

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

Norepinephrine: a potent activator of glycogenolysis and gluconeogenesis in rockfish hepatocytes.

Norepinephrine (NOR) is a potent activator of carbohydrate metabolism in isolated hepatocytes from copper rockfish (Sebastes caurinus), increasing rates of glycogenolysis fourfold with an EC50 of 6.3 nM. Nanomolar concentrations of NOR also enhance gluconeogenesis. Epinephrine (EPI) activates both pathways to a smaller extent; the corresponding EC50 for glycogenolysis is 320 nM. There is no significant difference between the magnitude of glucose production in response to comparable doses of NOR, bovine glucagon, and catfish glucagon-like peptide. Experiments with an adrenergic agonist (isoproterenol) and antagonists (propranolol, prazosin, atenolol) indicate that NOR effects are mediated through beta-adrenoceptors. Catecholamine-activated glycogenolysis measured at 100 nM EPI or NOR is poorly correlated with a 30-50% rise in intracellular cAMP. Glucose production following catecholamine administration is not linear: 50% of the hourly glucose output is released within the first 17 min (NOR) and 5 min (EPI), respectively. During hepatocyte incubation (60 min at 15 degrees), added NOR and EPI (100 nM) were not degraded to any significant extent. In the absence of added hormones, rockfish hepatocytes produce 7.41 +/- 0.89 mumol glucose x g-1 packed cells x hr-1 at 15 degrees, with gluconeogenesis accounting for 35.0% of the total production. The rate of glucose output, which is linear for at least 60 min, is not correlated with the initial hepatocyte glycogen level.

Creatine turnover in the starry flounder,Platichthys stellatus.

Starry flounder (Platichthys stellatus) were cannulated and a bolus of 9 µCi(14)C-creatine in saline was injected into the caudal vein. The fish were sacrificed at intervals ranging from 1h to 36d after label injection. Creatine pool size (PCr+Cr) and creatinine (Crn) content in blood, muscle, gills and liver were analyzed and specific activities (SA) determined.Mean concentrations of PCr+Cr/Crn in PCA-extracts of muscle, gills, liver and blood of experimental fish (at rest) were 38.1/2.40, 4.1/0.25, 5.6/0.45 and 0.3/n.d. µmol.g(-1) respectively.Within 10 min, plasma SA had decreased by approximately 90%. In white muscle, the rate of(14)C-Cr appearance as well as label disappearance was slow compared to gills and liver. In fish examined 36d postinjection, mean SA in muscle had decreased to 23% of maximum SA which occurred 24h after injection.(14)C-Cr was incorporated into the liver tissue at a very high rate, SA being two orders of magnitude higher in liver than in white muscle. Over the first 6d, retention of label was observed in liver; after 36d only 3% of the original label was detected.Creatine pool size (PCr+Cr) in white muscle decreased with food deprivation. In flounder sacrificed after 36d, PCr+Cr was only 52% that of fed control fish, suggesting that creatine or precursors for its biosynthesis are supplied with the diet.

Activities of chitinase and protease and concentration of fluoride in the digestive tract of Antarctic fishes feeding on krill (Euphausia superba Dana).

Studies on the digestion of krill by Notothenia rossii marmorata, Notothenia neglecta, Champsocephalus gunnari and Chaenocephalus aceratus showed that these Antarctic fish species are well equipped to feed on krill, as indicated by their high levels of chitinase and protease activity. Very high chitinolytic activities were determined in the stomach of the fish species. However, activities that were measured in intestine samples can be substantial, as well. Very strong protease activities were determined in samples of the stomach tissue and the intestinal contents. When krill were present in the guts, the concentrations of fluoride in the stomach and intestinal contents of N. rossii marmorata and Ch. gunnari were extremely high, while the tissues were practically devoid of fluoride.