Seasonal reorganization of nitrogen metabolism in an Indian air-breathing teleosts,Channa punctatus (Bloch)

Channa punctatus, an air-breathing freshwater teleost, mobilizes more protein for its energy requirement during summer and spawning months, as revealed by the data on endogenous nitrogen excretion in the form of ammonia-N, urea-N, free amino acids, creatinine and creatine.     

The effects of ambient pH on nitrogen excretion in early life stages of the American toad (Bufo americanus)

Acidification of breeding ponds has been identified as a potential threat to the survival and health of North American amphibian populations. The effects of acid exposure on ion and acid-balance are well known, but there is little information on how environmental water pH influences nitrogen balance in amphibians. The aim of this study was to determine the effects of moderately acidic water (pH 6.0) on nitrogen excretion in early life stages of the toad, Bufo americanus. Acid exposure (pH 6.0, 54 h) resulted in a 20–80% increase in ammonia-N excretion rates in embryos and early, middle and late tadpoles stages, whereas there was no significant effect on urea-N excretion. Tissue ammonia concentrations were significantly higher (+ 33%) in the embryos and 35–65% lower in the three groups of tadpoles exposed to water of pH 6.0 compared to control animals (pH 8.5). In embryos, ammonia excretion accounted for greater than 90% of total nitrogen excretion (ammonia-N + urea-N), but by the late tadpole stage this value had decreased to approximately 65%. These findings indicate that exposure of embryonic and larval B. americanus to moderately acidic water disrupts nitrogen balance by increasing nitrogen loss as ammonia, with no compensatory decrease in urea excretion.     

Pulsatile urea excretion in the gulf toadfish: mechanisms and controls

Opsanus beta expresses a full complement of ornithine–urea cycle (OUC) enzymes and is facultatively ureotelic, reducing ammonia-N excretion and maintaining urea-N excretion under conditions of crowding/confinement. The switch to ureotelism is keyed by a modest rise in cortisol associated with a substantial increase in cytosolic glutamine synthetase for trapping of ammonia-N and an upregulation of the capacity of the mitochondrial OUC to use glutamine-N. The entire day's urea-N production is excreted in 1 or 2 short-lasting pulses, which occur exclusively through the gills. The pulse event is not triggered by an internal urea-N threshold, is not due to pulsatile urea-N production, but reflects pulsatile activation of a specific branchial excretion mechanism that rapidly clears urea-N from the body fluids. A bidirectional facilitated diffusion transporter, with pharmacological similarity to the UT-A type transporters of the mammalian kidney, is activated in the gills, associated with an increased trafficking of dense-cored vesicles in the pavement cells. An 1814 kB cDNA (‘tUT’) coding for a 475–amino acid protein with approximately 62% homology to mammalian UT-A's has been cloned and facilitates phloretin-sensitive urea transport when expressed in Xenopus oocytes. tUT occurs only in gill tissue, but tUT mRNA levels do not change over the pulse cycle, suggesting that tUT regulation occurs at a level beyond mRNA. Circulating cortisol levels consistently decline prior to a pulse event and rise thereafter. When cortisol is experimentally clamped at high levels, natural pulse events are suppressed in size but not in frequency, an effect mediated through glucocorticoid receptors. The cortisol decline appears to be permissive, rather than the actual trigger of the pulse event. Fluctuations in circulating AVT levels do not correlate with pulses; and injections of AVT (at supraphysiological levels) elicit only minute urea-N pulses. However, circulating 5-hydroxytryptamine (5-HT) levels fluctuate considerably and physiological doses of 5-HT cause large urea-N pulse events. When the efferent cranial nerves to the gills are sectioned, natural urea pulse events persist, suggesting that direct motor output from the CNS to the gill is not the proximate control.     

Limited potential for adaptation to climate change in a broadly distributed marine crustacean

The extent to which acclimation and genetic adaptation might buffer natural populations against climate change is largely unknown. Most models predicting biological responses to environmental change assume that species' climatic envelopes are homogeneous both in space and time. Although recent discussions have questioned this assumption, few empirical studies have characterized intraspecific patterns of genetic variation in traits directly related to environmental tolerance limits. We test the extent of such variation in the broadly distributed tidepool copepod Tigriopus californicus using laboratory rearing and selection experiments to quantify thermal tolerance and scope for adaptation in eight populations spanning more than 17° of latitude. Tigriopus californicus exhibit striking local adaptation to temperature, with less than 1 per cent of the total quantitative variance for thermal tolerance partitioned within populations. Moreover, heat-tolerant phenotypes observed in low-latitude populations cannot be achieved in high-latitude populations, either through acclimation or 10 generations of strong selection. Finally, in four populations there was no increase in thermal tolerance between generations 5 and 10 of selection, suggesting that standing variation had already been depleted. Thus, plasticity and adaptation appear to have limited capacity to buffer these isolated populations against further increases in temperature. Our results suggest that models assuming a uniform climatic envelope may greatly underestimate extinction risk in species with strong local adaptation.     

中华绒螯蟹在不同pH值环境下的氮排泄

研究不同pH值环境对中华绒螯蟹（Eriocheir sinensis）氮排泄的影响。本研究采用直接浸浴法测定中华绒螯蟹在pH值4．5，6．0，7．5，9．0和10．5条件下的氮排泄。结果表明，在pH值9．0及其以下时，氨氮排泄无显著变化，当pH值升高到10．5时，氨氮排泄急剧下降，其排泄过程具有不连续性；亚硝酸氮、尿素氮和有机氮的排泄随pH值的升高而增加；硝酸氮的排泄同亚硝酸氮类似，但在pH值10．5时，呈下降状态；总氮的排泄随pH值升高而降低。在pH值4．5时，中华绒螯蟹的氨氮排泄量占总氮排泄量的91．0％，随着pH值上升，氨氮占总氮排泄的比例下降，而包括有机氮在内的其它形式的含氮化合物的排泄比例上升。因此．我们认为当环境pH值在9．0以下的范围波动时，不会对中华绒螯蟹的氨氮排泄带来不利影响，但过高的pH值可能会阻碍氮排泄。     

Greatly elevated urea excretion after air exposure appears to be carrier mediated in the slender lungfish (Protopterus dolloi)

Under aquatic conditions, Protopterus dolloi is ammoniotelic, excreting only small amounts of urea-N. However, upon return to water after 30 d estivation in air, the lungfish excretes only small amounts of ammonia-N but massive amounts of urea-N. A similar pattern is seen after 21-30 d of terrestrialization, a treatment in which the lungfish is air exposed but kept moist throughout. After both treatments, the time course of urea-N excretion is biphasic with an immediate increase, then a fall, and finally a second larger increase that peaks at about 12 h and may be prolonged for several days thereafter. Urea-N excretion rates during the second peak reach 2,000-6,000 micromol N kg(-1) h(-1), two to three orders of magnitude greater than rates in most fish and comparable only to rates in species known to employ UT-A type facilitated diffusion urea transporters. Divided chamber studies and measurements of the clearance rates of [3H]-PEG-4000 (a glomerular filtration and paracellular diffusion marker) and two structural analogs of urea ([14C]-acetamide and [14C]-thiourea) were performed to characterize the two peaks of urea-N excretion. The smaller first peak was almost equally partitioned between the head (including internal and external gills) and the body compartment (including urinary opening), was accompanied by only a modest increase in [14C]-acetamide clearance equal to that in [14C]-thiourea clearance, and could be accounted for by a large but short-lasting increase in [3H]-PEG-4000 clearance (to about fivefold the terrestrial rate). The delayed, much larger second peak in urea-N excretion represented an elevated efflux into both compartments but occurred mainly (72%) via the body rather than the head region. This second peak was accompanied by a substantial increase in [14C]-acetamide clearance but only a modest further rise in [14C]-thiourea clearance. The acetamide to thiourea permeability ratio was typical of UT-A type transporters in other fish. [3H]-PEG-4000 clearance was stable at this time at about double the terrestrial rate, and excretion rates of urea and its analogs were many fold greater than could be accounted for by [3H]-PEG-4000 clearance. We conclude that the first peak may be explained by elevated urinary excretion and paracellular diffusion across the gills upon resubmergence, while the second peak is attributable to a delayed and prolonged activation of a UT-A type facilitated diffusion mechanism, primarily in the skin and perhaps also in branchial epithelia.     

Accumulation of urea in the haemolymph and ammonia excretion of Penaeus japonicus exposed to ambient nitrite

Penaeus japonicus (15.7 ± 1.4 g) were exposed individually in 30 ppt seawater to 0.01 (control), 5, 10, 20 and 50 mg/l nitrite-N for 24 hr. Haemolymph ammonia, urea, nitrite and whole shrimp ammonia-N excretion and nitrite-N uptake were then determined. Ammonia excretion of P. japonicus increased with increased ambient nitrite, and with a concomitant decrease of haemolymph ammonia, as occurring increased concentrations of nitrite. Concentrations of nitrite-N and urea-N in the haemolymph of shrimp increased with increased ambient nitrite-N. However, no urea-N excretion was observed for shrimp exposed to any nitrite treatments.     

Cortisol effects on aerobic and anaerobic metabolism, nitrogen excretion, and whole-body composition in juvenile rainbow trout.

The influence of chronic cortisol elevation on metabolism, body composition, and fuel use patterns was examined in juvenile rainbow trout (Oncorhynchus mykiss). Measurements were performed in a control group (day 0) and in two experimental groups at days 3, 10, and 30 after treatment with a cortisol implant or a sham implant. All fish were fed 1% daily ration. Measured plasma cortisol levels were highest at day 3 and returned close to normal values by day 30 in cortisol-implanted fish. No plasma cortisol elevation was observed in the sham group. Growth was depressed in the cortisol-treated fish. Cortisol elevation resulted in increased plasma glucose concentrations during the entire experimental period, elevated CO2 production at day 3 and 30, and an elevated respiratory quotient (RQ) exceeding 1.0 on these days. Nitrogen excretion, estimated as the sum of ammonia-N plus urea-N excretion, and the nitrogen quotient exhibited small decreases at day 30. Total-N excretion, measured with a nitrogen oxidizer, was approximately twice the sum of ammonia-N plus urea-N excretion but exhibited a similar trend. Aerobic metabolism (routine O2 consumption) was higher on day 10 compared to sham-implanted fish, although not relative to day 0 control levels. Anaerobic metabolism increased substantially, as evidenced by pronounced plasma lactate elevations at days 3 and 10, a small increase in whole-body lactate on day 10, and the elevated RQ on days 3 and 30. Body composition exhibited an increase in total carbohydrate at days 3 and 10, mainly reflecting increased glycogen levels. Protein concentration was stable, indicating, in accord with the respirometry data, that protein usage did not fuel the increased metabolism or carbohydrate elevation. Redirection of nutrient uptake from food and/or mobilization of lipid stores (which decreased relative to the control group but not relative to shams) are suggested as possible energy sources for these actions of cortisol.     

Habitat temperature and the temporal scaling of cold hardening in the high Arctic collembolan, Hypogastrura tullbergi (Schäffer)

Abstract.  1. Cold tolerance is a fundamental adaptation of insects to high latitudes. Flexibility in the cold hardening process, in turn, provides a useful indicator of the extent to which polar insects can respond to spatial and temporal variability in habitat temperature.
2. A scaling approach was adopted to investigate flexibility in the cold tolerance of the high Arctic collembolan, Hypogastrura tullbergi , over different time-scales. The cold hardiness of animals was compared from diurnal warming and cooling phases in the field, and controlled acclimation and cooling treatments in the laboratory. Plasticity in acclimation responses was examined using three parameters: low temperature survival, cold shock survival, and supercooling points (SCPs).
3. Over time-scales of 24–48 h, both field animals from warm diurnal phases and laboratory cultures from a 'warm' acclimation regime (18 °C) consistently showed greater or equivalent cold hardiness to animals from cool diurnal phases and acclimation regimes (3 °C).
4. No significant evidence was found of low temperature acclimation after either hours or days of low temperature exposure. The cold hardiness of H. tullbergi remained 'seasonal' in character and mortality throughout was indicative of the summer state of acclimatization.
5. These data suggest that H. tullbergi employs an 'all or nothing' cryoprotective strategy, cold hardening at seasonal but not diel-temporal scales.
6. It is hypothesised that rapid cold hardening offers little advantage to these high Arctic arthropods because sub-zero habitat temperatures during the summer on West Spitsbergen are rare and behavioural migration into soil profiles offers sufficient buffering against low summer temperatures.     

Effects on acid-base balance, methaemoglobinemia and nitrogen excretion of European eel after exposure to elevated ambient nitrite

Haemoglobin, methaemoglobin, blood nitrite concentration and acid-base balance were measured in European eel Anguilla anguilla following exposure to 0 (control), 0·142, 0·356, 0·751 and l·549 mM nitrite in fresh water for 24 h. Blood GOT (glutamate oxaloacetate transaminase) and GPT (glutamate pyruvate transaminase) activities and whole animal ammonia-N and urea-N excretions were also measured. Blood nitrite, methaemoglobin, PO ₂ (oxygen partial pressure), GOT, and whole animal ammonia-N excretion and urea-N excretion increased directly with increasing ambient nitrite concentrations, whereas blood pH, PCO ₂, and HCO⁻₃ were inversely related to ambient nitrite concentration. An accumulation of nitrite in the blood of A. anguilla following 24 h exposure to elevated ambient nitrite as low as 0·751 mM increased its blood methaemoglobin, PO ₂, GOT and nitrogen excretion, but decreased its PCO ₂ (carbon dioxide partial pressure), HCO⁻₃ and functional haemoglobin.     

Effects of thermal acclimation on nervous conduction and muscle contraction in the frog Rana temporaria

The effects of season and acclimation temperature on the latency of the leg withdrawal reflex and three of its components have been studied: conduction velocity in the sciatic nerve, spinal conduction time, and contraction time of gastrocnemius muscle. The latency of the leg withdrawal reflex was markedly shortened by cold acclimation: the reaction times were at 6 degrees C 1.54 s in 4 degrees C acclimated and 3.97 s in 24 degrees C acclimated winter frogs. Also, the temperature dependence of the reflex latency was reduced by cold acclimation. Thus, frogs acclimated to cold responded to external stimuli in cold more rapidly than warm-acclimated ones. This cold adaptation of the reflex could not be explained by changes in its studied components. These made up only one-tenth of the reflex response time, and either did not show significant cold acclimation (muscle contraction and spinal conduction times in summer) or showed inverse acclimation, especially when measured at high temperatures (i.e. conduction velocities were reduced by acclimation to cold). Thus, the cold acclimation of the reflex response probably resides in the sensory component of the response. The inverse temperature adaptation response of conduction velocities may reflect a reduced ion permeability across cellular membranes in cold which decreases metabolic energy expenditure during inactive periods.     

The effects of temperature and swimming speed on instantaneous fuel use and nitrogenous waste excretion of the Nile tilapia.

The effects of acclimation temperature (30 degrees, 20 degrees, and 15 degrees C) and swimming speed on the aerobic fuel use of the Nile tilapia (Oreochromis niloticus; 8-10 g, 8-9-cm fork length) were investigated using a respirometric approach. As acclimation temperature was decreased from 30 degrees C to 15 degrees C, resting oxygen consumption (Mo2) and carbon dioxide excretion (Mco2) decreased approximately twofold, while nitrogenous waste excretion (ammonia-N plus urea-N) decreased approximately fourfold. Instantaneous aerobic fuel usage was calculated from respiratory gas exchange. At 30 degrees C, resting Mo2 was fueled by 42% lipids, 27% carbohydrates, and 31% protein. At 15 degrees C, lipid use decreased to 21%, carbohydrate use increased greatly to 63%, and protein use decreased to 16%. These patterns at 30 degrees C and 15 degrees C in tilapia paralleled fuel use previously reported in rainbow trout acclimated to 15 degrees C and 5 degrees C, respectively. Temperature also had a pronounced effect on critical swimming speed (UCrit). Tilapia acclimated to 30 degrees C had a UCrit of 5.63+/-0. 06 body lengths/s (BL/s), while, at 20 degrees C, UCrit was significantly lower at 4.21+/-0.14 BL/s. Tilapia acclimated to 15 degrees C were unable or unwilling to swim. As tilapia swam at greater speeds, Mo2 increased exponentially; Mo2min and Mo2max were 5.8+/-0.6 and 21.2+/-1.5 micromol O2/g/h, respectively. Nitrogenous waste excretion increased to a lesser extent with swimming speed. At 30 degrees C, instantaneous protein use while swimming at 15 cm/s ( approximately 1.7 BL/s) was 23%, and at UCrit (5.6 BL/s), protein use dropped slightly to 17%. During a 48-h swim at 25 cm/s (2.7 BL/s, approximately 50% UCrit), Mo2 and urea excretion remained unchanged, while ammonia excretion more than doubled by 24 h and remained elevated 24 h later. These results revealed a shift to greater reliance on protein as an aerobic fuel during prolonged swimming.     

Activity of glyceraldehyde-3-phosphate dehydrogenase isozymes during photoperiodic floral induction in spinach leaves

The activity of NAD⁺ and NADP⁺-dependent glyceraldehyde-3-phosphate dehydrogenase isozymes (EC 1.2.1.12 and EC 1.2.1.13, respectively) were measured in spinach ( Spinacia oleracea L. cv. Nobel) leaves grown under different photoperiodic treatments in order to discriminate between the early events of floral induction and processes related to acclimation. Glycolysis-linked isozyme activities were increased not only during floral induction and acclimation, but also during acclimation alone, suggesting that the changes in cytosolic activities were most probably associated with acclimation. In contrast, the chloroplast-linked isozyme activities only increased during flower induction and appeared to be specifically associated with the initiation of the flowering process. The relative activity changes in the chloroplast and cytosol compartments may thus be supposed to be among the first signs of translation of the photoperiodic signal into cytosolic and cellular metabolic adaptation, whereby the leaf moves rapidly into a new metabolic state.     

Mitochondrial function in seasonal acclimatization versus latitudinal adaptation to cold in the lugworm Arenicola marina (L.)

Previous studies in marine ectotherms from a latitudinal cline have led to the hypothesis that eurythermal adaptation to low mean annual temperatures is energetically costly. To obtain more information on the trade-offs and with that the constraints of thermal adaptation, mitochondrial functions were studied in subpolar lugworms (Arenicola marina L.) adapted to summer cold at the White Sea and were compared with those in boreal specimens from the North Sea, either acclimatized to summer temperatures or to winter cold. During summer, a comparison of mitochondria from subpolar and boreal worms revealed higher succinate oxidation rates and reduced Arrhenius activation energies (Ea) in state 3 respiration at low temperatures, as well as higher proton leakage rates in subpolar lugworms. These differences reflect a higher aerobic capacity in subpolar worms, which is required to maintain motor activity at low but variable environmental temperatures--however, at the expense of an elevated metabolic rate. The lower activity of citrate synthase (CS) found in subpolar worms may indicate a shift in metabolic control within mitochondria. In contrast, acclimatization of boreal lugworms to winter conditions elicited elevated mitochondrial CS activities in parallel with enhanced mitochondrial respiration rates. With falling acclimation temperatures, the significant Arrhenius break temperature in state 3 respiration (11 degrees C) became insignificant (5 degrees C) or even disappeared (0 degrees C) at lower levels of Arrhenius activation energies in the cold, similar to a phenomenon known from hibernating vertebrates. The efficiency of aerobic energy production in winter mitochondria rose as proton leakage in relation to state 3 decreased with cold acclimation, indicated by higher respiratory control ratio values and increased adenosine diphosphate/oxygen (ADP/O) ratios. These transitions indicate reduced metabolic flexibility, possibly paralleled by a loss in aerobic scope and metabolic depression during winter cold. Accordingly, these patterns contrast those found in summer-active, cold-adapted eurytherms at high latitudes.     

Effects of temperature and salinity on nitrogenous excretion by Litopenaeus vannamei juveniles

Excretion rates of ammonia-N, nitrite-N, nitrate-N, and dissolved organic nitrogen (DON) for juvenile Litopenaeus vannamei (3.85+/-0.83 g) were quantified in response to nine different combinations of temperature (24, 28, and 32 degrees C) and salinity (10, 25, and 40 ppt) under laboratory conditions. Results indicated that L. vannamei is ammonotelic, with ammonia-N accounting for 61.9-84.3% of total nitrogen (TN) excretion. There were significant effects of temperature and salinity, but no significant interaction between them, on ammonia-N excretion rate (R(AN)). R(AN) increased with increasing temperature, over the interval 24-32 degrees C. R(AN) was lower at 25 ppt than at 10 and 40 ppt, at all temperatures. DON excretion rate (R(DON)) was not significantly influenced by either temperature or salinity; the overall mean R(DON) was about 5.24 μg-N g -1 h -1. However, the percentages of DON in TN (P(DON)) varied from 15.4 to 36.4% under the various temperature-salinity combinations. P(DON) at 28 and 32 degrees C was significantly lower than at 24 degrees C, and P(DON) at 10 ppt was significantly lower than at 25 and 40 ppt. Only very small amounts of nitrogen were excreted by L. vannamei as nitrite-N and nitrate-N.     

Growth,stress, and acclimation responses to fluctuating temperatures in field and domesticated populations of Manduca sexta

Diurnal fluctuations in temperature are ubiquitous in terrestrial environments, and insects and other ectotherms have evolved to tolerate or acclimate to such fluctuations. Few studies have examined whether ectotherms acclimate to diurnal temperature fluctuations, or how natural and domesticated populations differ in their responses to diurnal fluctuations. We examine how diurnally fluctuating temperatures during development affect growth, acclimation, and stress responses for two populations of Manduca sexta: a field population that typically experiences wide variation in mean and fluctuations in temperature, and a laboratory population that has been domesticated in nearly constant temperatures for more than 300 generations. Laboratory experiments showed that diurnal fluctuations throughout larval development reduced pupal mass for the laboratory but not the field population. The differing effects of diurnal fluctuations were greatest at higher mean temperature (30°C): Here diurnal fluctuations reduced pupal mass and increased pupal development time for the laboratory population, but had little effect for the field population. We also evaluated how mean and fluctuations in temperature during early larval development affected growth rate during the final larval instar as a function of test temperature. At an intermediate (25°C) mean temperature, both the laboratory and field population showed a positive acclimation response to diurnal fluctuations, in which subsequent growth rate was significantly higher at most test temperatures. In contrast at higher mean temperature (30°C), diurnal fluctuations significantly reduced subsequent growth rate at most test temperatures for the laboratory population, but not for the field population. These results suggest that during domestication in constant temperatures, the laboratory population has lost the capacity to tolerate or acclimate to high and fluctuating temperatures. Population differences in acclimation capacity in response to temperature fluctuations have not been previously demonstrated, but they may be important for understanding the evolution of reaction norms and performance curves.     

栉孔扇贝耗氧率和排氨率的研究

1999年 4～ 6月 ,采用室内实验生态学方法对栉孔扇贝的耗氧率和排氨率进行了研究 .结果表明 ,在适宜的温度范围内 ,栉孔扇贝的耗氧率和排氨率均与温度成正比 ,而与体重呈负相关关系 .在实验室温度 (8～ 2 8℃ )条件下 ,栉孔扇贝的耗氧率为 0 .48～ 9.0 9mg·g-1·h-1,排氨率为 0 .0 5～ 1 0 1mg·g-1·h-1.其中耗氧率在 2 3℃时达到最高值 ,2 8℃时开始下降 ,而排氨率则呈持续升高趋势 .栉孔扇贝的日常代谢明显高于标准代谢 ,耗氧率和排氨率平均值分别提高约 35 .8%和 75 .9% .     

Adaptation and acclimation of aerobic exercise physiology in Lake Whitefish ecotypes (Coregonus clupeaformis)

The physiological mechanisms underlying local adaptation in natural populations of animals, and whether the same mechanisms contribute to adaptation and acclimation, are largely unknown. Therefore, we tested for evolutionary divergence in aerobic exercise physiology in laboratory bred, size‐matched crosses of ancestral, benthic, normal Lake Whitefish (Coregonus clupeaformis) and derived, limnetic, more actively swimming “dwarf” ecotypes. We acclimated fish to constant swimming (emulating limnetic foraging) and control conditions (emulating normal activity levels) to simultaneously study phenotypic plasticity. We found extensive divergence between ecotypes: dwarf fish generally had constitutively higher values of traits related to oxygen transport (ventricle size) and use by skeletal muscle (percent oxidative muscle, mitochondrial content), and also evolved differential plasticity of mitochondrial function (Complex I activity and flux through Complexes I–IV and IV). The effects of swim training were less pronounced than differences among ecotypes and the traits which had a significant training effect (ventricle protein content, ventricle malate dehydrogenase activity, and muscle Complex V activity) did not differ among ecotypes. Only one trait, ventricle mass, varied in a similar manner with acclimation and adaptation and followed a pattern consistent with genetic accommodation. Overall, the physiological and biochemical mechanisms underlying acclimation and adaptation to swimming activity in Lake Whitefish differ.     

Energy expenditure and metabolic adaptation during winter dormancy in the lizard Lacerta vivipara Jacquin

1. 1.Laceria vivipara were hibernated from October to March. Respiration rates were measured at various times during this period and compared with respiration rates of lizards at the same temperatures in July.

2. 2.Rates of respiration at 10°C soon after entry into hibernation and towards the end of the dormant period did not differ significantly from rates at 10°C in July.

3. 3.After several weeks in hibernation at 10°C a depression of metabolism occurred which produced acclimated respiration rates significantly lowe than 10°C rates measured at other times of year. This is interpreted as a probable case of negative metabolic compensation to temperature (inverse acclimation).

4. 4.No difference in respiration rates at 5°C could be detected between dormant and summer lizards.

5. 5.Energy expenditure during winter dormancy accounts for approximately 5% of the energy assimilated annually from food. Inverse acclimation at 10°C effects an energy saving amounting to about 35% of the total dormancy expenditure.

Expression of ornithine-urea cycle enzymes in early life stages of air-breathing walking catfish Clarias batrachus and induction of ureogenesis under hyper-ammonia stress

The air-breathing walking catfish Clarias batrachus is a potential ureogenic teleost with having a full complement of ornithine-urea cycle (OUC) enzymes expressed in various tissues. The present study was aimed at determining the pattern of nitrogenous waste excretion in the form of ammonia-N and urea-N along with the changes of tissue ammonia and urea levels, and the expression of OUC enzymes and glutamine synthetase (GSase) in early life stages of this teleost, and further, to study the possible induction of ureogenesis in 15-day old fry under hyper-ammonia stress. The ammonia and urea excretion was visible within 12 h post-fertilization (hpf), which increased several-fold until the yolk was completely absorbed by the embryo. Although all the early developing stages were primarily ammoniotelic, they also excreted significant amount of nitrogen (N) in the form of urea-N (about 35-40% of total N). Tissue levels of ammonia and urea also increased along with subsequent developmental stages at least until the yolk absorption stage. All the OUC enzymes and GSase were expressed within 4-12 hpf showing an increasing trend of activity for all the enzymes until 350 hpf. There was a significant increase of activity of GSase, carbamyl phosphate synthetase III (CPSase III) and argininosuccinate lyase enzymes (ASL), accompanied with significant increase of enzyme protein concentration of at least two enzymes (GSase and CPSase III) in the 15-day old fry following exposure to 10 mM NH4Cl as compared to respective controls kept in water over a period of 72 h. Thus, it appears that the OUC enzymes are expressed in early life stages of walking catfish like other teleosts, but at relatively high levels and remain expressed all through the life stages with a potential of stimulation of ureogenesis throughout the life cycle as a sort of physiological adaptation to survive and breed successfully under hyper-ammonia and various other environmental-related stresses.