The effects of cortisol administration on intermediary metabolism in teleost fish

• 1.1. This Mini Review deals with the metabolic consequences of administration of the hormone cortisol on proteins, carbohydrates and lipids in teleost fish.
• 2.2. Many effects of administered cortisol on intermediary metabolism in fish have been reported: inhibition of protein synthesis and/or catabolism of tissue protein which result in higher availability of amino acids, induction of gluconeogenesis and of liver aminotransferases, hyperglycemia and glycogen deposition in the liver, induction of gluconeogenic enzymes, liberation of free fatty acids and deposition of liver lipids. All these effects are observed to a greater or less extent. However, the experimental data show that some effects are inconsistent.
• 3.3. Some explanations for the inconsistencies are given.

     

Scaling of some metabolic enzymes in liver of a freshwater teleost: an adaptive mechanism

The activities of mitochondrial malate dehydrogenase (mMDH) and the total mitochondrial proteins increase as a function of body mass in the freshwater catfish, Clarias batrachus. It clearly indicates an increase in energy production in larger-sized individuals for various purposes including prey-predator interactions. The higher activity of lactate dehydrogenase (LDH) in larger fish may indicate more production of lactate for gluconeogenesis in the liver to meet emergency requirements of increased energy demand. However, the activity of cytoplasmic malate dehydrogenase (cMDH) decreases with the increasing body mass of the fish which reflects reduction in NADPH production and, in turn, reduced lipogenesis in liver of larger individuals. Thus, the present observations suggest an adaptive mechanism dealing with the higher energy budget, and reduced synthetic activities (lipogenesis) in the liver of larger-sized freshwater catfish. This type of biochemical scaling might be also supporting other metabolic pathways in order to adjust some physiological functions for survival in the aquatic environment.     

Scaling of energy metabolism in unicellular organisms: a re-analysis

The database used by Hemmingsen (1960) to compute energy metabolism in unicellular organisms was reassembled and submitted to linear (log-log) analysis. As Hemmingsen noted, this data set includes marine zygotes, which are not unicellular organisms. If no temperature correction factors are applied to the data the best-fit regression line has a slope of 0.698 +/- 0.024. Application of the temperature correction factors assumed to have been used by Hemmingsen gave a slope of 0.756 +/- 0.021, identical to the value he reported. The correlation coefficient is 0.97. The mean scatter about the regression line exceeds 100%. A revised set of temperature correction factors gave a slope of 0.730 +/- 0.021, suggesting that the value of almost exactly three-quarters obtained by Hemmingsen was probably fortuitous. The slope of the best-fit regression line is very sensitive to the inclusion of bacteria and flagellates. When the data points for these organisms are omitted from the calculation the slope decreases to 0.645 +/- 0.045. When the data points for bacteria, flagellates and marine zygotes are omitted, the slope drops to 0.608 +/- 0.025. The correlation coefficient (0.97), compared to the best-fit line reported by Hemmingsen, is unaffected; the mean deviation about the regression line drops to 40% and the points are evenly distributed about the regression line. Because of the small number of species for which measurements have been made, the existing database relating energy metabolism to cell size is not representative of unicellular organisms generally. It is concluded that the case for a three-quarters power rule expressing energy metabolism as a function of size in unicellular organisms generally is not at all persuasive.     

尺度分析对景观格局指标的影响

采用优势规则和随机规则为基础的两种尺度分析方法,对分类的TM数据进行了尺度变换分析。结果表明,随着尺度(粒度)增加,优势规则处理法使景观中优势类型的面积增加,非优势类型的面积减少,随机规则处理法使各景观类型的面积基本上保持不变,随尺度变大,整个景观和多数类型的最大斑块面积指标增加;最小斑块面积等于尺度大小的平方;平均斑块面积都增加;斑块数迅速减少,在优势规则系列中,多样性指标减小,而在随机规则处理中,基本没有变化,聚集度随尺度的增大而减小,但测量尺度固定的情况下,随图分辨率的提高而增大,随尺度的增加,Moran’s Ⅰ指标减小,景观类型在空间上趋于随机分布,但是测量尺度固定的情况下,随图分辨率的提高而增大,景观类型在空间上趋于聚集分布。     

Scaling effects of grazing in a semi-arid grassland

Abstract. Previous studies have demonstrated relationships between spatial scale and spatial pattern and developed general hypotheses of scaling effects. Few studies, however, have examined the interactive relationship between scale and pattern-driving processes such as grazing. The goal of this study is to evaluate scale-dependent patterns across three spatial scales for three grazing intensities over 45 yr and to identify some mechanisms that may be associated with scale related differences. Correlation analysis and analysis of the coefficients of variation indicate that the relationships between units are dependent upon spatial scale and treatment. Across all grazing treatments, the relationship between units of the same scale becomes stronger as the spatial scale is increased. However, the rate of increase in the correlation coefficient is different for each treatment. The coefficient of variation responded inversely across scales with the greatest variation between small-scale units and little difference between the intermediate- and large scales. In addition to different relationships between units at each scale, differences in heterogeneity within treatments over time is illustrated by the relationship between small-scale units within each treatment and their associated larger scale units. The strongest relationship occurred in the heavily grazed treatments where correlation coefficients of small-scale units with intermediate- and large-scale units were ca. 0.60, indicating similar dynamics across scales. For the moderately grazed and ungrazed treatments this relationship varied from 0.40 to 0.47. Results from this study suggest that grazing alters scaling effects. Variability between small-scale units was greatest in the ungrazed treatment which had greater heterogeneity and less predictability than grazed treatments because of the influence of grazing on plant morphology, demography and composition. At the intermediate scale, relationships between units were fairly similar with the least variation occurring in the moderately grazed treatment. Alternatively, variation between large-scale units was greatest in the moderately grazed treatment because of the relationship between rest cycles, weather patterns, and patch grazing. Therefore, grazing can have a positive, a negative, or no influence on heterogeneity between units depending upon the scale of observation. Evaluation of long-term dynamics across these treatments at the same small spatial scale results in different variances within each treatment which may violate assumptions of some statistical and experimental designs. Therefore, evaluations of temporal dynamics should consider scale relative to the relationship between plant size, density and longevity (relative scale).     

Haematological effects of stress on a teleost, Esox lucius L.

Stress produces a haemoconcentration, elevated blood lactate, increased glucose concentrations and alters the plasma electrolyte balance in two groups (brackish- and freshwater) of the northern pike, Esox leucius L., after one month's starvation. A method for dorsal aorta catheterization and a receptacle for cannulating fish is described.
The blood glucose level of the freshwater pike was twice that of the brackish-water group, and the plasma sodium and magnesium concentrations in the brackish-water pike were significantly higher. The haematocrit, haemoglobin and blood lactic acid concentrations were higher in freshwater pike. The plasma potassium and calcium concentrations in the two groups did not differ.
Haemoconcentration due to stress by handling for 1.5 min was shown by changes in haematocrit and haemoglobin values. The haemoglobin concentration returned to normal in freshwater pike after 4 h but in brackish-water pike after 12 h.
As a result of handling, the blood lactic acid level rose steeply and required 12 h to return to normal.
The blood glucose concentration rose to its maximum value within 1 h of handling and required two days to return to normal.
The plasma sodium level remained stable after handling, but the potassium level was erratic. In brackish-water, the potassium concentration of the pike remained high for 12 h after stress, but in the freshwater group, after a rise, the concentration fell to below the initial level within 4 h. The changes of the potassium concentrations in relation to sampling time are discussed. The changes in the divalent ion concentrations were marked and similar in the two groups; with an increase lasting 1–4 h and then a fall below the initial level, which was regained after two days.     

Central and peripheral effects of ghrelin on energy balance, food intake and lipid metabolism in teleost fish

Ghrelin was first identified and characterized from rat stomach as an endogenous ligand for the growth hormone secretagogue receptor. Ghrelin and its receptor system are present not only in peripheral tissues such as stomach and intestine, but also in the central nervous system of mammals. Interestingly, administration of ghrelin induces an orexigenic effect and also modifies locomotor activity, suggesting its involvement in feeding control and the regulation of energy balance, in addition to the regulation of growth hormone release. Information about ghrelin in non-mammals, such as teleost fish, has also been increasing, and important data have been obtained. An understanding of the evolutionary background of the energy regulation system and the central and peripheral roles of ghrelin in teleost fish could provide indications as to their roles in mammals, particularly humans. In this review, we overview the central and peripheral effects of ghrelin on energy balance, locomotor activity, and lipid metabolism in teleost fish.     

Certain aspects of acetylcholine metabolism in teleost retina

Acetylcholine (ACh) synthesis and release from isolated superfused retina of the teleostEugerres plumieri has been studied under different physiological conditions. The retinas were superfused with Krebs-Ringer solutions containing [¹⁴C]choline and the extracellular space of 32% was determined by [³H]inulin. The retina accumulates choline (Ch) from the superfusion medium and this process is mediated by a high affinity transport system with aK _m of 1.82 M. The incorporated Ch is mainly utilized for the synthesis of ACh. The ACh content of the light-adapted retina is not significantly different from that of a dark-adapted one. However, the release of [¹⁴C]ACh from the light-adapted retina was 52% higher as compared to the release from the dark-adapted retina. Flicker stimulation induced a larger increase in ACh release, than from either light or dark adapted retina, proportional to flicker frequency. The results suggest that changes in ACh utilization were related to the function of cellular units responsible for light changes transduction rather than light detection.In partial fulfillment of a MSc degree.     

The effects of calcitonin on plasma calcium levels and bone metabolism in the fresh water teleost Channa punctatus

Administration of salmon calcitonin (sCT) caused significant reduction in total and ultrafiltrable plasma calcium content in the plasma of a fresh water female teleost Channa punctatus. A time-bound analysis on the effect of sCT showed a highly significant short duration reduction in total and ultrafiltrable plasma calcium content in fish kept in normal tap water and low-calcium water and a moderate hypocalcemia in fish kept in high-calcium water. Sexually immature adult fish showed a greater response than the sexually mature ones. Using tartrate-resistant acid phosphatase (TRACP) and alkaline phosphatase (ALP) activities in plasma and hydroxyproline (HYP) excretion in urine, the effect of sCT on the inhibition of bone calcium resorption were examined. In both sexually mature and immature adult fish, kept in normal tap water, sCT significantly suppressed TRACP and ALP activities in plasma and excretion of HYP in urine within 2-6 h with a maximum at 4 h after injection. Salmon CT treatment to sexually immature adult fish caused significant increase in skeletal bone calcium concentration. Taken together, all this information indicates that CT in a fresh water female teleost is an effective regulator of plasma calcium levels, and its action, at least in part, operates through inhibition of bone calcium resorption.     

In vivo and in vitro effects of prolactin and growth hormone on lipid metabolism in a teleost, Anabas testudineus (Bloch)

Prolactin (PRL) has an important role in the regulation of water and electrolyte homeostasis in teleosts. The present study was designed to evaluate the role of PRL and GH on malic enzyme (ME), glucose-6-phosphate dehydrogenase (G6PDH) and isocitrate dehydrogenase (ICDH) in Anabas testudineus. Ovine prolactin significantly inhibited ME, G6PDH and ICDH activities when administered in vivo compared to vehicle treated controls. In vivo administration of PRL reversed the action of bromocryptine on enzyme activities. Ovine growth hormone in vivo also modified the effect of bromocryptine but not to the level of prolactin. Combined action of PRL+GH in vivo was most effective in keeping the enzyme activities at normal level after bromocryptine treatment. Prolactin in vitro also reversed the action of bromocryptine on enzyme activities, while GH in vitro failed to do so. Hence, prolactin seems to have an inhibitory effect on lipid metabolism in this teleost. Combined action of PRL+GH is more prominent in in vivo conditions at low PRL levels. Dopaminergic pathways may be involved in the control of prolactin and to some extent on growth hormone secretion.     

The effects of lowered temperature on spontaneous eye movements in a teleost fish

A new opto-electronic method has been used to measure spontaneous eye movements in a lightly restrained unanaesthetized marine teleost fish (Parore). The normal scanning pattern of eye movement is similar to that previously described in goldfish. The effects of cooling on eye movements were investigated by 2 degrees C step changes down from ambient temperature (13-14 degrees C). Lowered temperature altered the scanning pattern, decreased saccade velocity, increased mean saccade amplitude and impaired the ability of the fish to hold the eye stationary between saccades. All eye movements stopped at temperatures around 6 degrees C, but could be restored by subsequent warming.     

Catecholaminotropic effects of catecholamines in a teleost fish,Anguilla rostrata

Summary Injections of physiological and supraphysiological doses of epinephrine (E) into cardiaccannulated eels cause a dose-related increase of plasma dopamine (DA) and norepineprine (NE) within 3 min. Likewise, both exogenous DA and NE increase the plasma titers of the respective other two catecholamines (CAs). The baseline titers of NE and E are closely correlated. Lack of a correlation of the baseline titers of NE and E with that of DA appears to be due to a faster disappearance rate of DA from the circulation. E is strongly hyperglycemic, and the weaker glycemic action of NE may be mediated via E release. The effects of E seem to depend on a spurt-like increase rather than its titer per se. The ability of the eel to cope with very fast, excessive increases of plasma CAs raises the question of the underlying mechanisms.Abbreviations CA(s) catecholamine(s) - DA dopamine - NE norepinephrine - E epinephrine     

Differential effects of thyroxine on metabolic enzymes and other macromolecules in a freshwater teleost

The effects of thyroxine (T(4)) on citrate synthase (CS), glucose 6-phosphate dehydrogenase (G6-PDH), lactate dehydrogenase (LDH), DNA, RNA, and protein of various tissues were studied to elucidate the hormonal control of metabolism in a freshwater catfish, Clarias batrachus. T(4) did not produce any significant effect on DNA content of the fish. The CS, RNA, and protein contents of brain, liver, and skeletal muscle of the fish exposed to thiourea for 28 days decreased approximately 50-58% as compared to their levels in control individuals. Injection of T(4) to thiourea-exposed fish produced about three-fold increases in CS, RNA, and protein. These macromolecular inductions by T(4) were blocked by actinomycin D or cycloheximide. This suggests T(4)-induced de novo synthesis of macromolecules and stimulation of aerobic capacity. However, the activities of G6-PDH and LDH of brain, liver, and skeletal muscle of the fish exposed to thiourea increased two times that of the activities in control individuals. Administration of T(4) to thiourea-exposed fish reduced LDH and G6-PDH activities by about 64-74%, which reflects T(4)-dependent inhibition in anaerobic power and selective anabolic activities of the HMP pathway. These differential effects of T(4) on some metabolic enzymes and other important macromolecules may be to meet the other T(4)-induced responses in the freshwater catfish.