Showing papers in "Comparative Biochemistry and Physiology A-molecular & Integrative Physiology in 1998"
TL;DR: It is argued that animal physiological ecologists can benefit from including the measurement of naturally occurring stable isotopes in their battery of techniques, and can make an important contribution to the emerging field of stable isotope in biology by testing experimentally the plethora of assumptions upon which the techniques rely.
Abstract: Chemical, biological, and physical processes lead to distinctive “isotopic signatures” in biological materials that allow tracing of the origins of organic substances. Isotopic variation has been extensively used by plant physiological ecologists and by paleontologists, and recently ecologists have adopted the use of stable isotopes to measure ecosystem patterns and processes. To date, animal physiological ecologists have made minimal use of naturally occurring stable isotopes as tracers. Here we provide a review of the current and potential uses of naturally occurring stable isotopes in animal physiological ecology. We outline the physical and biological processes that lead to variation in isotopic abundance in plants and animals. We summarize current uses in animal physiological ecology (diet reconstruction and animal movement patterns), and suggest areas of research where the use of stable isotopes can be fruitful (protein balance and turnover and the allocation of dietary nutrients). We argue that animal physiological ecologists can benefit from including the measurement of naturally occurring stable isotopes in their battery of techniques. We also argue that animal physiologists can make an important contribution to the emerging field of stable isotopes in biology by testing experimentally the plethora of assumptions upon which the techniques rely.
608 citations
TL;DR: Use of the same approach showed that fish metabolise pentachlorophenol (PCP) and benzo[a]pyrene (BaP) faster than certain aquatic invertebrates, viz. molluscan species and crustacean species, and the higher rate of biotransformation of BaP in fish is consistent with higher levels of total cytochrome P450 and inducible cy tochrome P4501A (CYP1A) activity.
Abstract: Biotransformation of natural and man-made foreign compounds (xenobiotics) proceeds via introduction of a functional group (phase I metabolism) and subsequent attachment of a polar moiety to the group (phase II metabolism). The biotransformation fate of xenobiotics depends on the activities, complement and inducibility of the biotransformation enzymes. Previous analysis of the dependence of in vivo rates of biotransformation on tissue parent compound concentration for marine invertebrates revealed that hydrocarbons are metabolised more slowly than xenobiotics already containing functional groups, and crustaceans metabolise both types of xenobiotics faster than molluscs (Livingstone D.R., Persistent pollutants in marine ecosystems, pp. 3–34, Pergamon, Oxford). Use of the same approach showed that fish metabolise pentachlorophenol (PCP) and benzo[a]pyrene (BaP) faster than certain aquatic invertebrates, viz. rates of biotransformation to total metabolites (pmol min−1 g−1 wet wt.) at a tissue parent compound concentration of 10 nmol g−1 were, respectively, 19.2±3.7 (Carassius auratus) and 4.8±6.6 (molluscan species) (PCP), and 19.1±6.3 (fish species) and 2.1±0.2 (crustacean species) (BaP). The higher rate of biotransformation of BaP in fish is consistent with higher levels of total cytochrome P450 and inducible cytochrome P4501A (CYP1A) activity. The similar rate of metabolism of a hydrocarbon (BaP) (requires initial metabolism by cytochrome P450) and a functional group compound (PCP) by fish may also be due to the high levels of cytochrome P450, compared with the situation in invertebrates where rate-limiting cytochrome P450 may be responsible for the lower rates of hydrocarbon compared with functional group compound metabolism.
486 citations
TL;DR: Relationships among the transport systems are presented to suggest that many, if not all, of these systems may be operating simultaneously in individual, multifunctional chloride cells.
Abstract: This review assembles recent information on seawater-type chloride cells of marine teleost fish and evaluates the secretion of Na+, Cl−, K+, H+ and NH4+ and the absorption of Ca2+. The evidence for the distribution (apical vs basolateral) and the abundance of the various ion pumps, cotransporters, channels and exchangers is assessed and an inclusive model is constructed. Relationships among the transport systems are presented to suggest that many, if not all, of these systems may be operating simultaneously in individual, multifunctional chloride cells.
185 citations
TL;DR: The cultured sturgeon did not seem susceptible to crowding and prolonged handling stress, since neither the serum cortisol and glucose levels nor the other blood parameters were affected by these stressors.
Abstract: Data on the concentrations of some blood constituents of captive Adriatic sturgeon, Acipenser naccarii, a primitive bony fish, are reported. Serum osmolality, Na+, K+, Cl−, Ca2+, cortisol, glucose and total protein concentrations were measured. The effects of anaesthesia, temperature, crowding and prolonged handling stress were tested on a group of 12 4-year-old sturgeons sampled repeatedly. The anaesthetic dose of MS 222 (140 mg l−1) induced significant osmolality elevation in the sturgeon. After exposure to colder temperature (17 versus 25°C), cortisol and Cl− concentrations significantly decreased. The cultured sturgeon did not seem susceptible to crowding and prolonged handling stress, since neither the serum cortisol and glucose levels nor the other blood parameters were affected by these stressors. Results are compared with the few available data on other chondrostean fish and with those on teleosts.
183 citations
TL;DR: Evidence is accumulating to support the hypothesis that Na+ uptake/H+ excretion is accomplished by the pavement cell, and specific localization of a V-type H+-ATPase on the pavementcell epithelium and an increased expression during acidosis provides support for the model originally proposed.
Abstract: This review examines the recent advances in our understanding of the mechanisms of ion transport and acid-base regulation in the freshwater fish gill. The application of a combination of morphological, immunocytochemical and biochemical techniques has yielded considerable insight into the field. An important mechanism for regulation of Cl- uptake/base excretion is by morphological modification of the gill epithelium. During acidosis, the chloride cell associated Cl-/HCO3- exchanger is effectively removed from the apical epithelium because of a covering by adjacent pavement cells; this mechanism reduces base excretion and contributes to the compensation of the acidosis. In addition, acidosis induces changes in both the surface structure and ultrastructure of pavement cells. Evidence is accumulating to support the hypothesis that Na+ uptake/H+ excretion is accomplished by the pavement cell. Further, specific localization of a V-type H+-ATPase on the pavement cell epithelium and an increased expression during acidosis provides support for the model originally proposed, that this exchange is accomplished by an electrochemically coupled H+-ATPase/Na+ channel mechanism.
154 citations
TL;DR: The available evidence indicates that these transporters can indeed function as a first line of defense against some toxins, but important questions remain to be answered especially relating to costs of this defense, the inducibility of the defense and whether there might be other types of transport molecules other than the P -glycoprotein example.
Abstract: Multidrug transporters are ATP-dependent transport proteins which efflux a variety of moderately hydrophobic compounds out of cells. This article reviews the biology and chemistry of one member of this family, the P -glycoprotein-like transporters, and the extent to which the activity of these transporters protects aquatic organisms from natural and anthropogenic toxins. Topics covered include measurement of activity, distribution in aquatic organisms, efficacy in protection from toxins, characteristics of substrates of the transporters in aquatic organisms and finally the question of induction of activity in response to toxin load in the environment. The available evidence indicates that these transporters can indeed function as a first line of defense against some toxins, but important questions remain to be answered especially relating to costs of this defense, the inducibility of the defense and whether there might be other types of transport molecules other than the P -glycoprotein example.
139 citations
TL;DR: The absence of a relationship between selected high or low cortisol response lines and growth indicates that differences between experimental animals should also be considered, particularly with respect to the innate stress response.
Abstract: The present paper deals with the effect of abiotic environmental stressors on metabolism and growth of fish. Although generally the effect of environmental stressors on metabolism is apparent, the extrapolation to growth is not always evident. In stress research it is often difficult to establish borderline levels for chronic stress, so that increased levels of cortisol are used instead to determine when an environment becomes stressful. Because of the observed inconsistency between increased cortisol levels and depressed growth, the question can be raised as to whether cortisol is the most suitable parameter for measuring chronic stress in this context. The absence of a relationship between selected high or low cortisol response lines and growth indicates that differences between experimental animals should also be considered, particularly with respect to the innate stress response. Whether, in view of the possible existence of alternative coping styles, this automatically involves growth, is unclear.
132 citations
TL;DR: Much of this information is based on experimental data using unanesthetized fetal sheep with chronic catheterization; however, clinical outcome data and the use of investigative techniques have supported the relevance of this experimental data to the human situation.
Abstract: When oxygenation is compromised the fetus is capable of a number of adaptive responses, both protective and potentially pathologic, which can be categorized as those affecting fetal metabolism and those affecting fetal oxygen transport. However, both the extent and the duration of the impairment in oxygenation will bear on these adaptive responses. While fetal O2 extraction is increased when oxygenation is acutely compromised thus maintaining O2 consumption, with chronic hypoxemia there is a decrease in O2 consumption paralleling that in O2 delivery and contributed to by the resultant fall-off in growth and alterations in behavioural activity. While a redistribution of blood flow to vital organs continues to be evident, this will be less pronounced than that seen with acute hypoxemia reflecting diminished hormonal changes, underlying metabolic alterations, and the extent to which fetal blood gases are normalized. Much of this information is based on experimental data using unanesthetized fetal sheep with chronic catheterization; however, clinical outcome data and the use of investigative techniques including ultrasound scanning and cordocentesis have supported the relevance of this experimental data to the human situation.
127 citations
TL;DR: A. ocellatus was found to be hypoxia tolerant; it survives more than 16 h of severe hypoxiosis (pO 2 ≤ 0.4 mg l −1 ) and even 4 h of complete anoxia at 28°C.
Abstract: As a result of regular flood pulses, the Amazon basin exhibits large annual changes in its chemical and physical parameters. Ecology and distribution of fish communities seem to be directed by seasonal and diurnal oxygen level oscillations. Amazon fish have developed strategies to thrive under these varying conditions. Astronotus ocellatus normally survives large fluctuations in oxygen availability in varzea lakes. Respirometric and metabolic changes in A. ocellatus were studied during exposure to stepwise declining oxygen levels. Respiration rates were continuously recorded. Haematologic and metabolic parameters (lactate, glucose, cortisol and free fatty acids (FFA)) were determined. A. ocellatus was found to be hypoxia tolerant; it survives more than 16 h of severe hypoxia (pO 2 ≤0.4 mg l −1 ) and even 4 h of complete anoxia at 28°C. Its routine metabolic rate is 10.8 mg O 2 h −1 per 100 g fresh weight. A significant decrease in standard metabolic rate (SMR) starts at 20% air saturation, whereas a significant change of blood lactate does not start until 6% air saturation in water. We suggest therefore that A. ocellatus responses to environmental hypoxia are based mainly on suppressed metabolic rate, whereas under deep hypoxia or anoxia partial compensation is obtained from anaerobic glycolysis.
124 citations
TL;DR: Identifying physiological adaptation to environmental variables requires an explicit link with effects on Darwinian fitness; this can be effected by simultaneous observations on physiological and fitness variables; but the relationships are likely to be complex.
Abstract: Identifying physiological adaptation (or absence of it, which we define as stress) to environmental variables requires an explicit link with effects on Darwinian fitness This can be effected by simultaneous observations on physiological and fitness variables; but the relationships are likely to be complex Specific hypotheses on functional links between physiology and fitness need to be formulated (and incorporated into models) and tested The genetic basis of these relationships and the possibility of evolution of tolerance need to be considered
124 citations
TL;DR: The review discusses procedures for isolation and primary culture of teleostean hepatocytes and the influence of different culture conditions on the physiology of the cells in vitro and suggests hepatocyte aggregate cultures are particularly promising.
Abstract: The review discusses procedures for isolation and primary culture of teleostean hepatocytes and the influence of different culture conditions on the physiology of the cells in vitro. As a routine method to isolate fish liver cells, enzymatic dissociation of the tissue, either in situ or after removal from the donor animal, is applied. In primary culture, piscine hepatocytes usually are maintained as monolayer culture in both serum-free or serum-containing media. Under such simple conditions, teleostean liver cells conserve viability and functional differentiation for approximately 5 days. For longer-term culture, in vitro conditions have to be developed which mimic more closely the in vivo situation. Medium composition and particularly the cellular micro-environment, i.e. the presence of extracellular matrix or of homologous and heterologous cell–cell interactions, appear to be of importance for extended conservation of liver-specific gene expression in vitro. Among the various possible alternatives to the monolayer technique, hepatocyte aggregate cultures are particularly promising. Primary cultures are an attractive model to study time-dependent induction processes under defined experimental conditions, however, the potential of this system to extend our understanding of basic aspects of fish liver physiology and its adaptive responses to environmental change has remained largely unexplored.
TL;DR: This review focuses on the potential negative consequences of chloride cell proliferation on gas transfer and possible compensatory mechanisms that might minimise the extent of respiratory impairment in rainbow trout, hormone treatment and exposure to soft water.
Abstract: The gill lamellar epithelium is composed of two predominant cell types, pavement cells and mitochondria-rich chloride cells. The chloride cells play a vital role in ionic regulation because they are the sites of Ca2+ and Cl− uptake from water. Consequently, lamellar chloride cell proliferation occurs in response to ionoregulatory challenges so as to increase the ion-transporting capacity of the gill. It has been argued that such chloride cell proliferation might increase the thickness of the blood-to-water diffusion barrier and thereby impede gas diffusion. This review focuses on the potential negative consequences of chloride cell proliferation on gas transfer and possible compensatory mechanisms that might minimise the extent of respiratory impairment. Two approaches were used to evoke chloride cell proliferation in rainbow trout, hormone treatment (growth hormone/cortisol) and exposure to soft water. In all cases, chloride cell proliferation was associated with a pronounced thickening of the lamellar diffusion barrier. The thickening of the diffusion barrier was associated with a significant impairment of gas transfer. Subsequent studies revealed that several compensatory physiological responses occurred concurrently with the chloride cell proliferation to alleviate or reduce the detrimental consequences of the thickened diffusion barrier. These included hyperventilation, an increased affinity of haemoglobin-oxygen binding and earlier onset of catecholamine release during acute hypoxia.
TL;DR: The results suggest that the higher muscle weight found in the green and blue light groups was due to increased satellite cell proliferation during the first days of age.
Abstract: In this study we addressed the effect of various monochromatic light treatments on muscle growth and satellite cell proliferation in broilers (Gallus domesticus). Broilers were reared under green (560 nm), blue (480 nm) and red (660 nm) monochromatic lights and white light as a control from day one until 35 days of age. At five days of age, satellite cells were prepared from the experimental chicks. The number of satellite cells per gram of breast muscle and total number of satellite cells derived from the experimental broilers was substantially higher in the groups reared under green and blue light, compared to the red and white light groups. Growth hormone receptor gene expression was also higher in the former groups. High correlation was found between the breast muscle weight observed on day 35 and the number of satellite cells per gram of breast muscle (r = 0.915) and total number of satellite cells (r = 0.833), derived from the experimental chicks as early as five days of age. In addition, the protein/DNA ratio found in breast muscle at 35 days of age was significantly lower in chicks that were reared under green and blue lights. The lowest ratio which was found in the green group and was twice as low as in the control group, indicates the highest number of nuclei in the former group. As satellite cells are the only source of additional nuclei in skeletal muscles of postnatal animals, our results suggest that the higher muscle weight found in the green and blue light groups was due to increased satellite cell proliferation during the first days of age.
TL;DR: Findings indicate a metabolic effect on the utilisation of arginine at high dietary levels of lysine, which was also found to inhibit liver arginase of Atlantic salmon in vitro.
Abstract: The aim of the study was to determine the dietary lysine requirement of medium sized Atlantic salmon (376±46 g) given a high energy diet (23.6 KJ g−1) and to see if increased levels of lysine would effect the metabolism of arginine. Zein was used as a major protein source in the experimental diets, which were supplemented with synthetic amino acids to resemble the amino acid pattern of fish meal, with the exception of lysine. Dietary lysine contents ranged from 5.9 to 21.0 g kg−1 dietary dry matter. The requirement of lysine was estimated at 16–18 g kg−1 dry diet or 0.79–0.89g MJ−1 digestible energy. The result was confirmed by a significant increase of free lysine in muscle if excess lysine was added to the diet. Fish fed the highest level of lysine did not increase growth and tended to show reduced levels of arginine and ornithine in plasma and muscle and reduced level of urea in plasma. These findings indicate a metabolic effect on the utilisation of arginine at high dietary levels of lysine. Lysine was also found to inhibit liver arginase of Atlantic salmon in vitro.
TL;DR: The surprisingly high blood glucose concentrations in hummingbirds were accompanied by glycated hemoglobin levels that are the highest ever measured in birds but are lower than those of non-diabetic humans.
Abstract: We measured levels of glucose and glycated hemoglobin in the blood of three of the world's smallest nectarivorous birds, the Anna's (Calypte anna), Costa's (Calypte costae), and ruby-throated hummingbirds (Archilochus colubris). Plasma glucose levels of hummingbirds that were fasted overnight (17 mM) were higher than those in any mammal and are among the highest ever measured in a fasting vertebrate. Glucose levels in hummingbirds just after feeding were extreme, rising as high as 42 mM. The surprisingly high blood glucose concentrations in hummingbirds were accompanied by glycated hemoglobin levels that are the highest ever measured in birds but are lower than those of non-diabetic humans. How hummingbirds tolerate blood glucose levels that cause serious neurological and microvascular pathologies in diabetic humans and animals remains unknown.
TL;DR: This SW adaptation appears to be related to body size, the larger the fish the easier the adaptation process, and the method of transfer directly affected fish survival and the time they took to achieve ionic and osmotic regulation.
Abstract: The salinity tolerance, and hydromineral regulation capabilities of three size groups (small 110–170 g; medium 230–290 g, large 460–700 g; n =48 for each group) of 13-month-old juvenile Gulf of Mexico sturgeon were investigated. Fish ( n =6 for each salinity) were transferred directly from freshwater (FW) to a series of experimental salinity treatments (0, 5, 10, 15, 20, 25, 30, and 35 parts per thousand (ppt)). Fish were also acclimated in brackish water (20 ppt) for 2 weeks and transferred to a salinity of 34 ppt. In this condition juvenile Gulf of Mexico sturgeon adapted to saltwater (SW) and maintained their hydromineral balance. FW adapted sturgeon ( n =6) had an average blood hemotocrit of 28.2±0.8%, plasma osmolality of 260.7±1.6 mOsm kg −1 H 2 O, and plasma ion concentrations of 135.7±1.2 mM l −1 Na + , 106.9±1.9 mEq l −1 Cl − , and 2.9±0.1 mM l −1 K + . In SW adapted sturgeon ( n =8) blood parameters averaged 26.9±0.7% for hematocrit, 294.2±2.3 mOsm kg −1 H 2 O for osmolality, 152.0±1.7 mM l −1 Na + , 149.2±1.4 mEq l −1 for Cl − , and 3.1±0.1 mM l −1 K + . The method of transfer (abrupt or slow acclimation) directly affected fish survival and the time they took to achieve ionic and osmotic regulation. This SW adaptation appears to be related to body size, the larger the fish the easier the adaptation process. A threshold size of about 170 g was apparent for the fish to adapt to saltwater after 2 weeks of acclimation. Chloride cells were present in both FW and SW adapted sturgeon with SW and brackish water fish having chloride cells significantly ( P −2 ) and larger in size (41.0±3.85 and 34.2±4.49 μ m 2 ) than FW adapted sturgeon (10±1.0 cells mm −2 and 22±2.53 μ m 2 ). Few chloride cells were observed in the opercular membrane, however, none were found in the pseudobranch and spiracle.
TL;DR: The demonstration of the uptake of shinorine by human skin cancer cells in culture raises evolutionary questions regarding the organ specificity of the capacity for the cellular transport of MAAs, and indicates that mammals may be incapable of such.
Abstract: To assess whether vertebrates can acquire, from their diet, ultraviolet radiation-absorbing mycosporine-like amino acids (MAAs), medaka fish and hairless mice were maintained for 150 and 130 days, respectively, on diets either including Mastocarpus stellatus (rich in MAAs) or the same diets without this red alga. In medaka, the MAAs palythine and asterina-330, present in trace quantities in the diet with added M. stellatus, were present in significantly greater quantities in the eyes of fish fed this diet than in the eyes of control fish. Only traces of MAAs were present in the skin of medaka fed the diet containing MAAs. Shinorine, the principal MAA in M. stellatus, was not found in any tissues of medaka, which raises questions about the specificity of transport of MAAs. In hairless mice, no dietary MAAs were found in the tissues of the eyes, skin, or liver after maintenance on the experimental diet. Low concentrations of shinorine were present only in the tissues of the small and large intestines. These results indicate that MAAs are acquired from their diet and translocated to superficial tissues by teleost fish, but that mammals may be incapable of such. Thus, dietary supplementation with MAAs may be useful in aquacultured species of fish, but MAAs as 'dietary sunscreens' may not be an option for mammals, including humans. Nevertheless, our demonstration of the uptake of shinorine by human skin cancer cells in culture raises evolutionary questions regarding the organ specificity of the capacity for the cellular transport of MAAs.
TL;DR: In this paper, the effects of prolonged hypoxemia, induced by placental insufficiency of differing severity and duration, on fetal brain structure were investigated. But the effects on brain development were not well understood, and the use of pharmacological agents with the potential to protect neurons from hypoxemic injury is discussed in relation to the developing brain.
Abstract: It is well-established that severe, acute episodes of hypoxemia can damage the brain before birth, but the effects of more sustained hypoxemia are less well understood. We have used fetal sheep in a series of studies aimed at determining the effects of prolonged hypoxemia, induced by placental insufficiency of differing severity and duration, on fetal brain structure. Restriction of placental, and hence fetal, growth by carunclectomy caused impaired development of neural processes and connections in the hippocampus, cerebellum, and visual cortex; neuronal migration and neuronal numbers did not appear to be affected. Twenty days of placental insufficiency during late gestation induced by umbilicoplacental embolisation also caused abnormalities in brain structure; the cerebellum, which develops late in gestation, was particularly affected. In the cortex, there was evidence of white matter lesions, an increase in the size of capillaries and a proliferation of astroglia. We also examined the effects of shorter periods of hypoxemia (6–12 hr) near mid-gestation on brain structure; fetuses were allowed to recover for 7 or 35 days after the hypoxemic challenge. The major changes were mild focal damage in the cortical white matter, a reduction in the number of Purkinje cells, a delay in the growth of neural processes in the cerebellum and proliferation of blood vessels. The hippocampus was also affected, in particular the areal density of pyramidal cells was reduced. The use of several classes of pharmacological agents with the potential to protect neurons from hypoxemic injury is discussed in relation to the developing brain.
TL;DR: In a broad class of biosystems, stress and aging have similar thermodynamic properties and suggests common underlying principles.
Abstract: Recent advances in nonequilibrium thermodynamics leads to the conclusion that similar processes, constrained by the second law of thermodynamics, give rise to the emergence of structure and process in a broad class of dissipative systems. The second law suggests that, in systems moved away from equilibrium, processes can emerge so that the system organizes in a way that reduces the effect of the applied gradient. If dynamic and or kinetic conditions permit, self organization processes can be expected. As biosystems grow and develop, they should increase their total dissipation, and develop more complex structures with more energy flow, increase their cycling activity, develop greater diversity and generate more hierarchical levels. As a corollary to this general statement, biosystems which do not increase their total dissipation, are organisms dedicated to death, like observed during the aging of any biosystem. Species which survive in ecosystems are those that funnel energy into their own production and reproduction and contribute to autocatalytic processes which increase the total dissipation of the ecosystem while at same time surviving within the constraints of their changing environment. In a broad class of biosystems, stress and aging have similar thermodynamic properties and suggests common underlying principles.
TL;DR: It is concluded that the dogfish apical membrane is extremely tight to urea, but the low apparent branchial permeability may also relate to the presence of an active urea transporter on the basolateral membrane that returns urea to the blood and hence reduces the apical urea gradient.
Abstract: We used a perfused gill preparation from dogfish to investigate the origin of low branchial permeability to urea. Urea permeability (C-14 urea) was measured simultaneously with diffusional water pe ...
TL;DR: The laboratory results suggest that fish carrion and aquatic and terrestrial invertebrates are probably essential dietary items of E. macquarii in the wild, because its metabolic requirements cannot be met from aquatic macrophytes alone.
Abstract: We described the diet of Emydura macquarii, an omnivorous turtle from south-eastern Australia, compared its digestive performance on diets of fish or plants at two temperatures, and related how both diet and temperature affect its food selection in nature. Filamentous algae constituted 61% of the stomach content of E. macquarii. The turtles rarely fed on motile prey, but selected carrion from the lagoon bottom and terrestrial insects (Diptera, Hymenoptera and Coleoptera) trapped on the surface of the water. Digestive efficiency of E. macquarii was affected little by body temperature, in contrast to consumption rates and rates of passage which were strongly influenced by both temperature and diet. In combination, these responses resulted in a slower rate of digestion at 20 degrees C than at 30 degrees C. Digestive efficiency of E. macquarii on a herbivorous diet at 30 degrees C (49%) was about half that of turtles on a carnivorous diet (91%), but they had longer transit times (118 h on the plant diet versus 70 h). Lower consumption rates and longer mean retention times in turtles fed plants compared those fed fish relate to slower digestive processing of the plant. Rapid processing and higher consumption rates of fish by E. macquarii resulted in higher energy gains compared to turtles consuming plants (almost 100 times more energy at 30 degrees C). The laboratory results suggest that fish carrion and aquatic and terrestrial invertebrates are probably essential dietary items of E. macquarii in the wild, because its metabolic requirements cannot be met from aquatic macrophytes alone.
TL;DR: An important implication of this study is that aposymbiotic insects exhibit substantial metabolic adjustments to loss of the symbiosis; they are not simply aphids from which the symbiotic bacteria have been removed.
Abstract: Antibiotics are routinely used to eliminate intracellular prokaryotic microorganisms from a wide range of insect species, but concerns about deleterious effects of antibiotic therapy on the insect host are seldom addressed. Here, the impact of antibiotic therapy in the symbiosis between the pea aphid Acyrthosiphon pisum and bacteria of the genus Buchnera is reviewed. Antibiotic-treatment produces aposymbiotic (i.e. symbiont-free) aphids, but does not depress the mitochondrial complement, the assimilation of dietary amino acids or the incorporation of amino acids into protein in these insects and does not impair osmoregulation, feeding rate and the capacity to penetrate plant tissues. It is concluded that the general malaise associated with aposymbiotic aphids is not attributable to a direct effect of the antibiotic. However, an important implication of this study is that aposymbiotic insects exhibit substantial metabolic adjustments to loss of the symbiosis; they are not simply aphids from which the symbiotic bacteria have been removed.
TL;DR: It is hypothesized that the accumulation of ammonia within the body per se under the above stressful conditions is likely the internal modulator for enhanced ureogenesis mainly to avoid any build up of ammonia to a level that can be toxic to these fish.
Abstract: Most of the Indian air-breathing teleosts are primarily ammoniotelic, but appear to have retained the genes for the urea cycle enzymes, since a full complement of urea cycle enzymes have been reported for many of them. The ability to synthesize urea by these fish is probably due to their amphibious nature, and their normal habitat of swamps, where the water ammonia level may to be quite high, is uninhabitable to any typical freshwater teleosts. One of these air-breathing species, the singhi catfish ( Heteropneustes fossilis ), can tolerate very high ambient total ammonia concentrations (up to 75 mM ammonium chloride) for weeks without any deleterious effects. Transition from ammoniotelism to ureotelism occurs in some of these species of air-breathing fish when exposed to apparently stressful conditions such as higher ambient ammonia, to air, and also when they live in semidry condition inside mud during habitat drying. Although the real mechanism(s) of regulation of ureogenesis is not clear in these fish, given available data, it is hypothesized that the accumulation of ammonia within the body per se under the above stressful conditions is likely the internal modulator for enhanced ureogenesis mainly to avoid any build up of ammonia to a level that can be toxic to these fish. An active urea cycle is believed to predominate over uricolysis as a source of urea, even though both pathways are present in these air-breathing fish. The presence of significant levels of both carbamyl phosphate synthetase (CPS), CPS I-like and CPS III activities, reported in some air-breathing catfishes, may represent intermediate scenarios for a proposed evolutionary transition from CPS III to CPS I, or may play an important physiological adaptive role in the tolerance of these fish to high concentrations of ambient ammonia
TL;DR: The results suggest that paddlefish do not exhibit physiological stress responses to physical disturbances similar in magnitude to those previously documented for many teleostean fishes including salmonids, although cortisol was determined to be the principle steroid released during stress.
Abstract: Juvenile paddlefish (Polyodon spathula) subjected to various physical disturbances showed significant increases in plasma cortisol and lactate, but little or no change in plasma glucose, chloride or hematocrit. When paddlefish were given a 30 s aerial emersion handling stressor, plasma cortisol increased from 2.2±0.6 to 11±1.8 ng ml−1 in 1 h but had returned to the prestress level by 3 h. Addition of 0.5% NaCl to the recovery tanks had no effect on plasma cortisol changes. Plasma lactate rose from 26±2.6 to 52±4.5 mg dl−1 within 3 h. Plasma cortisol increased to 14±4.8 ng ml−1 and plasma lactate rose to 67±3.7 mg dl−1 after fish were continuously chased in their home tanks for 1 h; plasma lactate remained elevated for 5 h. In fish severely confined for 6 h in cages with intermittent handling, plasma cortisol rose from 6.2±1.6 ng ml−1 to its peak level of 74±6.3 ng ml−1 by 2 h, but approached the prestress value after 18 h of recovery. Plasma lactate levels in confined fish increased from 27±2.7 to 73±6.9 mg dl−1 by 3 h but had returned to near-resting levels by 24 h. The results suggest that paddlefish do not exhibit physiological stress responses to physical disturbances similar in magnitude to those previously documented for many teleostean fishes including salmonids, although cortisol was determined to be the principle steroid released during stress.
TL;DR: The method of mounting split lamellae of crab gills in modified Ussing chambers offers the advantage that active ion transport can be measured as short-circuit current and:or flux of radioactive tracers in relation to the epithelial surface.
Abstract: The method of mounting split lamellae of crab gills in modified Ussing chambers offers the advantage that active ion transport can be measured as short-circuit current and:or flux of radioactive tracers in relation to the epithelial surface. Moreover, further modern techniques like microelectrode impalements and current-noise analysis can be applied. The epithelium of posterior gills of Chinese crabs (Eriocheir sinensis) acclimated to fresh water actively absorbs Na and Cl independent of each other. The epithelium of the gills of shore crabs (Carcinus maenas) acclimated to brackish water actively absorbs NaCl in a coupled mode. The different osmotic gradients maintained by the two crab species are reflected in the characteristics of their gill epithelia. Chinese crabs, migrating to fresh water, have a tight gill epithelium. The gill epithelium of shore crabs, living in brackish water of at least 6‐8‰ salinity, is an intermediate between tight and leaky. Regulation of NaCl absorption across the gill epithelium of Chinese crabs is achieved in a hormone-independent way by the haemolymph side osmolarity (autoregulation). Moreover, NaCl absorption is regulated by a hormonal factor of so far unknown chemical nature in the eyestalk extract which stimulates the transport rates via a cAMP-dependent signal transduction pathway, activating apical V-ATPase activity and increasing the number of open apical Na channels. © 1998 Elsevier Science Inc. All rights reserved.
TL;DR: Photosynthetic light-response curves of stressed cells showed that the light compensation points were increased and light saturation values were decreased under the different salinity-stress conditions, and photoinhibition of photosynthesis was significantly enhanced under Salinity- stress.
Abstract: Spirulina platensis cells, growing photoautotrophically in optimal media under 100 or 200 μmol m−2 s−1 photon flux densities (PFD), were exposed to different concentrations of sodium chloride, up to 0.75 M. After an initial acclimation phase, in which growth rate, photosynthetic activity and endogenous respiration were inhibited, a new steady state was established and a recovery in the photosynthetic activity was observed. Furthermore an increase in the respiration rate took place, exceeding the initial rate of the non-stressed cells. Photosynthetic light-response curves (P-I) of stressed cells showed that the light compensation points were increased and light saturation values were decreased under the different salinity-stress conditions. Photoinhibition of photosynthesis was significantly enhanced under salinity-stress. Photosystem II activities of cells substantially decreased after a salt-shock. The results show that, cells grown in higher PFD are less tolerant to salinity-stress than those grown in lower PFD.
TL;DR: It is believed that the venous PO2 threshold to support cardiac performance in the absence of a coronary supply was between 7.8 and 9.9 torr, and it is suspect that the low PO2 in coronary-ligated fish effectively lowered their myocardial O2 demand.
Abstract: We performed in vivo studies to examine the idea that cardiac work is impaired in rainbow trout (Oncorhynchus mykiss) below a certain venous Po2 threshold. We hypothesized that coronary-ligated fish, swimming continuously at a reasonably high water velocity (1.5 body lengths · s−1) and exposed to progressive hypoxia, would fatigue at higher venous Po2 and ambient water Po2 compared with sham-operated fish. However, we found that both the lowest venous Po2 that supported hypoxic swimming (9.9 torr for coronary-ligated fish and 11.1 torr for sham-operated fish) and the venous Po2 at fatigue (7.8 torr and 8.6 torr, respectively) were the same for coronary-ligated and sham-operated fish. Also, both groups quit swimming at the same water Po2, heart rate and hematocrit. Nevertheless, significant differences in cardiac performance did exist between the two groups. Whereas ventral aortic blood pressure (Pva) increased significantly with hypoxic swimming in sham-operated fish, there was no such increase in coronary-ligated fish. In addition, cardiac arrhythmias occurred in coronary-ligated fish at fatigue, and these fish were slower to recover from exhaustion. We believe that the venous Po2 threshold to support cardiac performance in the absence of a coronary supply was between 7.8 and 9.9 torr. Furthermore, we suspect that the low Pva in coronary-ligated fish effectively lowered their myocardial O2 demand. Uncertainty still exists regarding whether or not the venous Po2 threshold lies between 8.6 and 11.1 torr in sham-operated fish.
TL;DR: In this article, the importance of glutathione (GSH) for protection of fish cells against heavy metal stress was investigated by means of the neutral red (NR) uptake inhibition assay and the rank order of metal cytotoxicities (in terms of NR50 values) were Hg>Cd>Zn>Cu>Pb>Ni.
Abstract: The study investigates the importance of glutathione (GSH) for protection of fish cells against heavy metal stress. The cytotoxicities of six metal salts to the continuous rainbow trout cell line RTG-2 were determined by means of the neutral red (NR) uptake inhibition assay. The rank order of metal cytotoxicities (in terms of NR50 values) were Hg>Cd>Zn>Cu>Pb>Ni. The importance of GSH in determining metal toxicity was assessed by inhibition of its synthesis. A 20 h pretreatment of RTG-2 cells with 1 mM buthionine sulfoxime caused sustained reduction of cellular GSH level to ≈30% of the control value. The effect of GSH depletion on metal cytotoxicity was found to be related to the chemical softness parameter of the metal cations: Cytotoxicities of the ‘soft’ metals Hg, Cu and Cd were significantly increased in GSH-depleted cells, whereas cytotoxicities of the ‘hard’ metals Zn, Ni and Pb were not significantly altered. Since chemical softness is a determinant for binding of metal ions to sulfhydryl groups as being present in GSH, the findings of this study suggest that the metal-protective effect of GSH in fish cells is, at least partly, due to its action as an intracellular metal chelator.
TL;DR: Molecular studies have revealed that a specialised urea transport protein is present in kidney tissue of elasmobranchs, similar to the facilitated urea transporter found in the mammalian inner medulla of the kidney.
Abstract: Teleosts appear to have retained the genes for the urea cycle enzymes. A few species express the full complement of enzymes and are ureotelic (e.g., Lake Magadi tilapia) or ammoniotelic (e.g., largemouth bass), whereas most species have low or non-detectable enzyme activities in liver tissue and excrete little urea (e.g., adult rainbow trout). It was surprising, therefore, to find the expression of four urea cycle enzymes during early life stages of rainbow trout. The urea cycle may play a role in ammonia detoxification during a critical time of development. Exposure to alkaline water (pH 9.0-9.5) or NH4Cl (0.2 mmol/l) increased urea excretion by several-fold in trout embryos, free embryos and alevin. Urea transport is either by passive simple diffusion or via carried-mediated transport proteins. Molecular studies have revealed that a specialised urea transport protein is present in kidney tissue of elasmobranchs, similar to the facilitated urea transporter found in the mammalian inner medulla of the kidney.
TL;DR: It is concluded that diaphragm muscle fibers express nc-N OS, ec-NOS, or both; passive myocytes produce NOx; and NO or NO-derivatives inhibit force production by modulating excitation-contraction coupling.
Abstract: We investigated the enzymatic source, cellular production, and functional importance of nitric oxide (NO) in rat diaphragm. Neuronal and endothelial isoforms of constituitive nitric oxide synthase (nc-NOS, ec-NOS) were identified by immunostaining. NOS activity measured in diaphragm homogenates averaged 5.1 pmol/min/mg. Passive diaphragm fiber bundles produced NO derivatives (NOx) at the rate of 0.9 pmol/min/mg as measured by the cytochrome c reduction assay; NO production was confirmed by photolysis/ chemiluminescence measurements. Endogenous NO depressed diaphragm contractile function. The force of submaximal contraction was increased by NOS inhibitors, an effect that was stable for up to 60 min and was reversed by NO donors. We conclude that diaphragm muscle fibers express nc-NOS, ec-NOS, or both; passive myocytes produce NOx; and NO or NO-derivatives inhibit force production by modulating excitation-contraction coupling.