Influence of diet composition on feeding and water excretion by the tsetse fly, Glossina morsitans

Adult Glossina morsitans fed on aqueous salt solutions containing phagostimulant ATP in an in vitro feeding system gave an optimal feeding response only over a narrow pH range equivalent to that of vertebrate blood. There was much less discrimination on the basis of molar concentration.The rate and extent of water excretion by the fly was found to depend on the concentration of Na⁺ ions in the food medium: an active transport mechanism is indicated which enables water to pass from the meal through the anterior midgut wall and into the haemocoele. A favourable osmotic gradient assisted water transport in the presence of Na⁺ ions: the system could not operate efficiently in the presence of Na⁺ ions if the osmotic pressure of the food medium was higher than that of vertebrate blood, nor could it operate efficiently in any solution lacking Na⁺ ions.Normal transfer of a meal from the crop to the anterior midgut occurred only when the food medium was isotonic with vertebrate blood or in the presence of Na⁺ ions if hypotonic. Normal transfer of isotonic solutions was prevented in the presence of excess K⁺ ions, and hypertonic solutions were not transferred normally even in the presence of Na⁺ ions. Thus the rate of water excretion was reduced.Tsetse flies fed on blood in an in vitro feeding system excreted water at a significantly lower rate than flies fed on a living animal. Evidence suggests that this is due to a combined effect of changes in viscosity, effective ionic composition, and osmotic pressure, upon the normal rate and extent of food uptake and manipulation of the meal prior to digestion. The implications of this are discussed in terms of future developments of in vitro feeding techniques for haematophagous insects.     

The influence of cyclic glucose feeding on a continuous bakers' yeast culture

Conclusions Except for the pronounced adaptation-hysteresis effect, the pulse experiments exhibited the expected trend: deviation from the steady feed reference curve was greatest at lowest dilution rates. Under conditions of lowest glucose level the effect of pulsing would be expected to cause the largest fluctuations in glucose, causing a certain fraction of the cells to ferment. Generally over the entire dilution rate range the biomass production was decreased and the ethanol was increased by pulsing the feed stream. There is, however, some evidence that pulse feeding can trigger quite unexpected results. Point (6) at D=0.3 h^–1 in Fig. 1 exhibit a biomass productivity which was about 20% greater than the continuous feeding reference value (DX=3.6 kg m^–3 h^–1 as compared with 3.0 kg m^–3 h^–1). Such performance would be of significant commercial value, but the poor reproducibility due to adaptation, as seen here, certainly would preclude its application.The results obtained should also be applicable to fed batch operation at the corresponding glucose level. Further experiments including the variation of the glucose feeding period would be necessary to obtain a conclusive picture. The observed phenomena are likely to occur in other fermentations and could eventually explain some of the problems existing with scale up of fermentation processes.Symbols D dilution rate h^–1 - P product (ethanol) concentration kg m^–3 - Q_O2 specific oxygen uptake rate mol kg^–1 s^–1 - Q_CO2 specific CO₂ production rate mol kg^–1 s^–1 - S substrate (glucose) concentration kg m^–3 - X biomass concentration kg m^–3 - Y_P/S yield of ethanol from glucose kg kg^–1 - Y_X/S yield of biomass from glucose kg kg^–1     

Stress-dependent redistribution of abscisic acid (ABA) in Hordeum vulgare L leaves: the role of epidermal ABA metabolism, tonoplastic transport and the cuticle

When ¹⁴C-labelled abscisic acid ([¹⁴C]ABA) was supplied to isolated protoplasts of the barley leaf at pH 6, initial rates of metabolism were about five times higher in epidermal cell protoplasts than in mesophyll cell protoplasts if equal cytosolic volumes were considered. In spite of the fact that epidermal cells make up only about 35% of the total water space in barley leaves, and despite the small cytosolic volume of these cells, in intact leaves all epidermal cells would thus metabolize half as much ABA per unit time as the mesophyll cells (0–27 and 0–51 mmol h^?1 m^?3 leaf water). Therefore, under these conditions epidermal cells seem to be a stronger sink than mesophyll cells for ABA that arrives via the transpiration stream. However, at an apoplastic pH of 7–25, which occurs in stressed leaves, the proportion of total metabolized ABA would be much smaller in epidermal than in mesophyll cells (0–029 and 0–204 mmolh^?l m^?3 leaf water). Our results indicate that under conditions of slightly alkaline apoplastic pH the epidermis may serve as the main source for fast stress-dependent ABA redistribution into the guard cell apoplast. This is partly the result of ABA transport across the epidermal tonoplast, which is dependent on the apoplastic pH and possibly on the cytosolic calcium concentration. The cuticle seems to be of no particular importance in stress-induced apoplastic ABA shifts and cannot be regarded as a significant sink for high ABA concentrations under stress.     

The role of phosphorus release by roach [Rutilus rutilus (L.)] in the water quality changes of a biomanipulated lake

SUMMARY 1. Following fish removal, the water quality in biomanipulated lakes often improves concomitant with decreased phosphorus (P) levels. Because the decrease in P concentrations derives most probably either directly or indirectly from fish, which are the main target of biomanipulation, this study examined the P release of 0+, 1+ and 2+ roach [Rutilus rutilus (L.)] and changes in the P release during summer in a shallow eutrophic lake in Finland. 2. The P release was separated into P derived from benthic and littoral food items and into recycled P derived from feeding on zooplankton, to estimate the contribution of net P additions to the water column by the fish to the increase in P concentrations of the lake water (75–110 mg P m^?3) in summer 1991–96. 3. Individual P release of roach by both egestion and excretion was estimated with a bioenergetics model. The size of the roach population was estimated with a depletion method and the proportions of different age groups from catch samples, using a programme separating mixtures of normal distributions. The sensitivity of the release estimates to variation in the growth data was estimated with the jackknife technique. 4. The biomass‐specific P release by 0+ roach (0.36–0.54 mg P g^?1 day^?1) was higher than that by older roach (0.07–0.16 mg P g^?1 day^?1) throughout the summer. The P release by the whole roach population deriving from benthic and littoral food items (0.7–2.7 mg m^?3 during July to August, representing a net addition to the water column) was 5–19 times lower in 1991–96 than the recycled P release deriving from zooplankton (8.9–25.7 mg m^?3), and too low to explain the increase in the P concentration of the lake water during the summer. Because the biomass‐specific P release and roach diet composition vary with fish age, it is important to consider the age structure of fish populations to obtain correct estimates of P release and net additions to the water column. 5. The removal of roach by fishing diminished the roach stock greatly, but the fish‐mediated P release to the water column changed little. This effect was because of the high compensation capacity of the roach population, leading to high recruitment of young fish with higher biomass‐specific P release rates. 6. External loading is very low during summer months and therefore it cannot explain the increase in the P concentration of water during that time. Internal loading from the sediment might be as high as 10.2 mg P m^?2 day^?1, i.e. 50 times higher than the maximum net P addition by the total roach population.     

Oxalic acid production by Aspergillus niger

Aspergillus niger is able to produce a quite high concentration of oxalic acid using sucrose as carbon and energy source. Operating at pH higher than 6 and an enriched N and P medium is necessary in order to conduct the fermentation towards oxalic acid production. A pH?shift technique, operating at acid pH?in the first two days and then setting pH?to 6, allowed the productivity to slightly increase in shaking flasks cultures up to 3.0?kg/m³?·?d, with a final oxalic acid concentration of 29?kg/m³. When operating at more controlled conditions, in a stirred tank, both productivity and oxalic acid concentration were improved (4.1?kg/m³?·?d and 33.8?kg/m³, respectively). However the main drawback of this fermentation is the low yield attained (about 0.3?kg oxalic acid/kg sucrose) because most of glucose, resulting from the hydrolysis of sucrose by the extracellular enzymes secreted at the beginning of the fermentation, is very quickly oxidised to gluconic acid, a process which is favoured at a pH?close to 6. Milk whey was proved to be a very good substrate as it allows oxalic acid to be produced with a similar productivity (2.5?kg/m³?·?d in shaking flasks) giving excellent yields of almost 0.6?kg oxalic acid/kg lactose.     

HUNGER OVERCOMES FEAR IN NASSARIUS FESTIVUS, A SCAVENGING GASTROPOD ON HONG KONG SHORES

On protected intertidal sand flats, virtually worldwide, nassariidsnails scavenge carrion. Typically, they lie in repose beneaththe sand surface but emerge to feed when chemoreceptors detectcarrion. Distance from the potential food influences whetherthey move towards it and, if they do, whether they obtain ameal before it is consumed by others. This study shows that the rate at which Nassarius festivus movestoward food bait is similar for starved and well-fed individuals.That is, when individuals decide to feed, the rate at whichthey move toward food is always approximately the same. Thisstudy exposes another facet of nassariid nutrition related tothe degree of hunger. Recently fed individuals, i.e., thosewhich have fed for < 14 days, will cease feeding and departpalatable food if crushed conspecifics are added to it. Individualswhich have not fed for > 14 days tend to remain feeding,despite the addition of crushed conspecifics. Another studyhas shown that N. festivus consumes sufficient energy from afed-to-satiation meal to sustain it in repose for 20 days.These experiments clarify the observation. Between 14 to 20days since its last meal, N. festivus will feed when the possibilityarises, despite potentially adverse consequences. That is, hungerovercomes the fear of being consumed at a feeding assemblagebecause, without feeding, the alternative may be death by starvation.Thus, a nassariid makes decisions about whether or not to feed.The fear of predation causes N. festivus to abandon a meal ifthe previous one was obtained within a fortnight but, thereafter,it will risk predation to avoid starvation. (Received 14 March 1994; accepted 7 July 1994)     

Low filtering rates of <Emphasis Type="Italic">Daphnia magna</Emphasis> in a hypertrophic lake: laboratory and in situ experiments using synthetic microspheres

Zooplankton grazing was measured in Albufera of València (Spain), a shallow turbid hypertrophic lagoon dominated by filamentous bluegreens, during the period of Daphnia magna growth, to evaluate the role of this cladoceran in maintaining a clear water phase which takes place after flushing for rice cultivation practices. We found extremely low ingestion and clearance rates (CR) on latex beads in situ, using a Haney trap suggesting potentially strong inhibition of grazing by the filamentous cyanobacteria, still flourishing in the lagoon. To test the effect of filaments, we undertook laboratory feeding experiments using six different dilutions of the lagoon water to vary filament concentrations, and four different bead concentrations. A highly significant power function between CR and water dilution associated with filament concentrations was found, indicating that the ability of Daphnia to exploit smaller edible algae and thereby control phytoplankton growth would depend on filament concentration levels in the lagoon. From our results only the two more diluted treatments, 9 × 10³ and 18 × 10³ filament ml⁻¹ showed CRs not far from the range of what would be normally expected on the basis of the general relationship of feeding rate as a function of total food concentration. This means that at lower food concentrations, filaments reduce D. magna CR by increasing total food concentration beyond the incipient limiting level, as well as by moderate mechanical interference with the animal’s feeding. However, at lagoon water concentrations above 25% (corresponding to filament concentrations of 75 × 10⁵ filaments ml⁻¹), extremely low CR’s, which did not respond to any food addition, were obtained for D. magna. From these results we can infer that at concentrations beyond the above-mentioned critical level, feeding inhibition by filamentous cyanobacteria is most probably due entirely to mechanical interference. Guest editor: Piet Spaak Cladocera: Proceedings of the 7th International Symposium on Cladocera     

Effect of light intensity and eye development on prey capture by larval striped bass Morone saxatilis

The efficacy of visual and non-visual feeding among pelagic striped bass Morone saxatilis larvae adapted to a turbid estuary was determined in the laboratory in clear water. Capture of Artemia salina (density 100 l⁻¹) was significantly affected by the interaction between age of larvae (range: 8–25 days post-hatch, dph) and light intensity (range: 0–10·6 μmol s⁻¹ m⁻² at the water surface). Visual feeding by larvae aged 9–11 dph was highest in dim light (0·086–0·79 μmol s⁻¹ m⁻²), with fish capturing up to 5 prey larva⁻¹ h⁻¹. As the larvae grew, prey capture in brighter light improved, associated with an increasing proportion of twin cone photoreceptors and improving ability of the retina to light- and dark-adapt. By age >22 dph, mean prey capture was greatest at highest light intensities (0·79 and 10·6 μmol s⁻¹ m⁻²) exceeding 100 prey larva⁻¹ h⁻¹. Incidence of feeding larvae generally improved as the larvae grew, reaching >80% in all light intensities from 16 dph onwards. The lower threshold for visual feeding, between 0·0084 and 0·03 μmol s⁻¹ m⁻², remained constant as the larvae grew, despite an increasing density of rod photoreceptors. Below this threshold, non-visual feeding was evident at a low rate (<6 prey larva⁻¹ h⁻¹) that was independent of larval age.     

High yeast concentration in continuous fermentation with cell recycle obtained by tangential microfiltration

Summary Continuous fermentation fed by 150 kg/m³ of glucose with total cell recycling by tangential microfiltration enabled yeasts concentration of 300 kg/m³ (dry weight) to be reached with a dilution rate of 0,5h^–1 and a cell viability greater than 75%. The stability of this system was tested for 50 residence times of the permeate. The method can be used both for the production of cell concentrates and for high rates of metabolite production.Nomenclature D. W. dry weight - X_T (kg/m³) total cell concentration D.W. - X_V (kg/m³) viable cell concentration D.W. - V viability of cell culture in per cent of total cell concentration - S (kg/m³) glucose concentration - P (kg/m³) ethanol concentration - D (h) dilution rate - R (kg/kg) fermentation yield - (h) specific growth rate - vp(kg/kg/h) specific alcohol production rate - (m) yeast size - (kg/kg) kg of intracellular water per kg of dry cells     

Foraging costs and accessibility as determinants of giving-up densities in a swan-pondweed system

We measured the patch use behaviour of Bewick's swans (Cygnus columbianus bewickii) feeding on below ground tubers of fennel pondweed (Potamogeton pectinatus). We compared the swans’ attack rates, foraging costs and giving‐up densities (GUDs) in natural and experimental food patches that differed in water depth. Unlike most studies that attribute habitat‐specific differences in GUDs to predation risk, food quality or foraging substrate, we quantified the relative importance of energetic costs and accessibility. Accessibility is defined as the extent to which the animal's morphology restricts its harvest of all food items within a food patch. Patch use behaviours were measured at shallow (ca 0.4 m) and deep (ca 0.6 m) water depths on sandy sediments. In a laboratory foraging experiment, when harvesting food patches, the swan's attack rate (m³ s^?1) did not differ between depths. In deep water the energetic costs of surfacing, feeding and trampling were 1.13 to 1.21 times higher than in shallow water with a tendency to spend relatively more time trampling, the most expensive activity. Taking time allocation as measured in the field into account, foraging in deep water was 1.26 times as expensive as in shallow water. In the lake the GUD in shallow water was on average 12.9 g m^?2. If differences in energetic costs were the only factor determining differences in GUDs, then the deep water GUD should be 14.2 g m^?2. Instead, the mean GUD in deep water was 20.2 g m^?2, and therefore energetic costs explain just 18% of the difference in GUDs. At deep sites, 24% of tuber biomass was estimated to be out of reach, and we calculated a maximum accessible foraging depth of 0.86 m. This is close to the published 0.84 m based on body measurements. A laboratory experiment with food offered at a depth of 0.89 m confirmed that it was just out of reach. The agreement between calculated and observed maximum accessible foraging depths suggests that accessibility largely explains the remaining difference in GUDs with depth, and it confirms the existence of partial prey refuges in this system.     

Anaerobic digestion of sugar beet pulps

Summary Anaerobic digestion of sugar beet pulps was studied in a 70 l digestor with sequential feeding, after enzymatic hydrolysis by Trichoderma harzianum cellulases. During the 130 days feeding, 3.6 m³ of biogas were produced with an average content of 58% CH₄ from 270 l of hydrolysed pulps at 20 g VS/l. Average yield and production rate were respectively 0.67 m³/kg VS and 0.4 m³/ kg VS and 0.4 m³/m³ of digestor per day.     

Bioenergetic model of planktivorous fish feeding, growth and metabolism: theoretical optimum swimming speed of fish larvae

The feeding activity of an individual fish larva is described by an equation which includes parameters for the area successfully searched, probability of food capture multiplied by the cross-sectional perceptive visual field, larval swimming speed and the time required to consume a unit of food energy. The proportion of ingested food energy used for metabolism increases exponentially with increasing swimming speed. The model predicts that food consumption rate increases asymptotically whereas metabolic rate increases exponentially. This results in a predicted growth rate curve that reaches a maximum at a certain swimming speed and decreases at both higher and lower speeds. The model can be used to predict the influence of type of prey, prey density, water temperature etc. on larval growth. An expression describing how many hours per day fish larvae must forage in order to grow at a certain daily body weight gain allows the limits of environmental conditions for positive, zero and negative growth rate to be set. Results of simulations demonstrated that the optimum swimming speed for maximum growth of coregonid larvae increased with an increase in food density, decrease in water temperature or decrease of prey vulnerability. At optimum ‘theoretical’ swimming speed an increase in water temperature from 5 to 17° C required the food density to be increased from 20 to 80 copepods l^?1 in order to maintain a daily growth increment of 2%. The minimum Artemia density required for maintenance metabolism increased from 10 to 30 items 1¹ over the same temperature increase from 5 to 17° C, and food densities required for 8% growth rates were 26 and 56 Artemia nauplii l^?1 at 5 and 17° C, respectively. Contrary to previous findings, results of the present study suggest that metabolic rates of actively feeding fish larvae may be from 5 to 50 times the standard metabolic rate: earlier studies suggested that a factor of 2–3 may be generally applicable.     

Anaerobic digestion of glycerol derived from biodiesel manufacturing

The anaerobic digestion of glycerol derived from biodiesel manufacturing, in which COD was found to be 1010 g/kg, was studied in batch laboratory-scale reactors at mesophilic temperature using granular and non-granular sludge. Due to the high KOH concentration of this by-product, H₃PO₄ was added to recover this alkaline catalyst as agricultural fertilizer (potassium phosphates). Although it would not be economically viable, a volume of glycerol was distilled and utilised as reference substrate. The anaerobic revalorisation of glycerol using granular sludge achieved a biodegradability of around 100%, while the methane yield coefficient was 0.306 m³ CH₄/kg acidified glycerol. Anaerobic digestion could be a good option for revalorising this available, impure and low priced by-product derived from the surplus of biodiesel companies. The organic loading rate studied was 0.21–0.38 g COD/g VSS d, although an inhibition phenomenon was observed at the highest load.     

The importance of wetlands in the energy balance of an agricultural landscape

Energy fluxes, including net radiation, latent heat flux and sensible heat flux were determined on clear days during the vegetative period in four types of land cover: wet meadow, pasture, arable field, and an artificial concrete surface. The average net radiation ranged between 123 W m^?2 at the concrete surface and 164 W m^?2 at the wet meadow. The mean maximum daytime latent heat ranged between 500 and 600 W m^?2, which corresponds to an evapotranspiration rate of about 0.2 g m^?2 s^?1 under the prevailing conditions of the wet meadow. The results demonstrated that the wet meadow dissipated about 30 % more energy through evapotranspiration than the field or the pasture, and up to 70 % more energy than the concrete surface. The evaporative fraction indicated that more than 100 % of the energy released by the wet meadow was dissipated through evapotranspiration; this was attributed to local heat advection. Wetland evapotranspiration thus contributes significantly to the cooling of agricultural landscapes; the energy released can reach several 100 MW km^?2. Wetland evapotranspiration has a double ‘air conditioning’ effect through which it equalises temperature differences: (1) surplus solar energy is bound into water vapour as latent heat; (2) The vapour moves towards cooler portions of the atmosphere where the energy is released. The air-conditioning effect of wetlands plays an important role in mitigating local climate extremes; this ecosystem service tends to be disregarded in relation to other better-known wetland functions such as nutrient retention and provision of high biodiversity.     

Bottom–up carbon subsidies and top–down predation pressure interact to affect aquatic food web structure

Human impacts such as eutrophication, overexploitation and climate change currently threaten future global food and drinking water supplies. Consequently, it is important that we understand how anthropogenic resource (bottom–up) and consumer (top–down) manipulations affect aquatic food web structure and production. Future climate changes are predicted to increase the inputs of terrestrial dissolved organic carbon to lakes. These carbon subsidies can either increase or decrease total basal production in aquatic food webs, depending on bacterial competition with phytoplankton for nutrients. This study examines the effects of carbon subsidies (bottom–up) on a pelagic community exposed to different levels of top–down predation. We conducted a large scale mesocosm experiment in an oligotrophic clear water lake in northern Sweden, using a natural plankton community exposed to three levels of glucose addition (0, 420 and 2100 μg C l^?1 total added glucose) and three levels of young‐of‐the‐year perch Perca fluviatilis density (0, 0.56 and 2 individuals m^?3). Bacterioplankton production doubled with glucose addition, but phytoplankton production was unaffected, in contrast to previous studies that have manipulated carbon, nutrients or light simultaneously. This suggests that carbon addition alone is not sufficient to reduce autotrophic production, at least in an oligotrophic lake dominated by mixotrophic phytoplankton. Larval perch grazing did not produce a classical trophic cascade, but substantially altered the species composition of crustacean zooplankton and ciliate trophic levels. Glucose addition increased the biomass of rotifers, thus potentially increasing energy transfer through the heterotrophic pathway, but only when fish were absent. This study illustrates that changes in community structure due to selective feeding by top‐predators can determine the influence of bottom–up carbon subsidies.     

Identification of an Obese Eating Style in 4‐year‐old Children Born at High and Low Risk for Obesity

This study tested whether children's eating behavior and parental feeding prompts during a laboratory test meal differ among children born at high risk (HR) or low risk (LR) for obesity and are associated with excess child weight gain. At 4 years of age, 32 HR children (mean maternal prepregnancy BMI = 30.4 kg/m²) and 29 LR children (maternal BMI = 19.6 kg/m²) consumed a test meal in which their eating behavior was assessed, including rate of caloric consumption, mouthfuls/min, and requests for food. Parental prompts for the child to eat also were measured at year 4, and child body composition was measured at ages 4 and 6 years. T‐tests, and logistic and multiple regression analyses tested study aims. Results indicated that HR and LR children did not differ in eating rate or parental feeding prompts. Greater maternal BMI, child mouthfuls of food/min, and total caloric intake/min during the test meal predicted an increased risk of being overweight or obese at age 6, whereas greater active mealtime was associated with a reduced risk of being overweight or obese. Regression analyses indicated that only mouthfuls of food/min predicted changes in BMI from 4 to 6 years, and mouthfuls of food/min and gender predicted 2‐year changes in sum of skinfolds and total body fat. Thus, a rapid eating style, characterized by increased mouthfuls of food/min, may be a behavioral marker for the development of childhood obesity.     

Effect of food conditions on the bacterial feeding of Daphnia galeata

Feeding selectivities of Daphnia galeata were measured using various density combinations of ¹⁴C-labeled Chlamydomonas and ³H-labeled natural bacteria. In all food combinations, D. galeata preferred algae. Selectivity coefficient (bacterial clearance rate: algal clearance rate) was 0.35 at the level of incipient food limitation (1.5 × 10⁶ µm³ ml^–1).However, it increased up to 0.9 with increasing total food concentration. A simple mechanical sieving model alone cannot explain such a change in the selectivity coefficient. A mechanism of clogging suggestively explain the increase of bacterial ingestion efficiency by D. galeata, especially at high food concentrations. The change of selectivity coefficient related to food condition suggests that bacterial feeding by the Daphnia is incidental event associated with the algal feeding.     

Annual energy budget and food requirements of breeding wandering albatrosses (<Emphasis Type="Italic">Diomedea exulans</Emphasis>)

Energy budgets form an integral part of our understanding of animal energetics, particularly when presented in the context of reproduction. In this paper, I created a time-energy budget for a breeding pair of wandering albatrosses (Diomedea exulans) to estimate the annual breeding costs and food requirements of the population at Possession Island, Crozet Archipelago. For a breeding cycle that lasts 356 days on average, a pair uses 2,733 MJ to raise a single chick to fledging. This estimate is 1.21 times higher than previously calculated for wandering albatrosses breeding at Marion Island. Unlike the current analysis, the previous study assumed that foraging costs were constant across all stages of the breeding cycle. Recent evidence shows that foraging costs vary during breeding for wandering albatrosses at Crozet and this is probably true for all populations. Incubation costs have also been shown to be substantially lower than previously determined. Therefore, if a wandering albatross pair at Crozet uses a total of 2,733 MJ to breed, they would need to consume at least 1.7 kg bird^–1 day^–1 of fresh food, on average, to balance their own energy requirements and to provision a single chick for approximately 278 days. At this rate of food consumption, the breeding population at Crozet would consume approximately 340 tonnes of fresh food per breeding season.     

Effect of Acute Negative and Positive Energy Balance on Basal Very-Low Density Lipoprotein Triglyceride Metabolism in Women

Background

Acute reduction in dietary energy intake reduces very low-density lipoprotein triglyceride (VLDL-TG) concentration. Although chronic dietary energy surplus and obesity are associated with hypertriglyceridemia, the effect of acute overfeeding on VLDL-TG metabolism is not known.

Objective

The aim of the present study was to investigate the effects of acute negative and positive energy balance on VLDL-TG metabolism in healthy women.

Design

Ten healthy women (age: 22.0±2.9 years, BMI: 21.2±1.3 kg/m²) underwent a stable isotopically labeled tracer infusion study to determine basal VLDL-TG kinetics after performing, in random order, three experimental trials on the previous day: i) isocaloric feeding (control) ii) hypocaloric feeding with a dietary energy restriction of 2.89±0.42 MJ and iii) hypercaloric feeding with a dietary energy surplus of 2.91±0.32 MJ. The three diets had the same macronutrient composition.

Results

Fasting plasma VLDL-TG concentrations decreased by ∼26% after hypocaloric feeding relative to the control trial (P = 0.037), owing to decreased hepatic VLDL-TG secretion rate (by 21%, P = 0.023) and increased VLDL-TG plasma clearance rate (by ∼12%, P = 0.016). Hypercaloric feeding increased plasma glucose concentration (P = 0.042) but had no effect on VLDL-TG concentration and kinetics compared to the control trial.

Conclusion

Acute dietary energy deficit (∼3MJ) leads to hypotriglyceridemia via a combination of decreased hepatic VLDL-TG secretion and increased VLDL-TG clearance. On the other hand, acute dietary energy surplus (∼3MJ) does not affect basal VLDL-TG metabolism but disrupts glucose homeostasis in healthy women.     

中华鲟仔鱼初次摄食时间与存活及生长的关系

研究了延迟投饵对中华鲟开口仔鱼存活及生长的影响。初次开口摄食在11—12日龄,13日龄卵黄基本吸收完毕,营养完全依靠外界供给。12日龄后,延迟投喂时间在1—10天的范围内,仔鱼成活率在46.67—73.33％之间,各组间无显著差异;延迟投喂时间为11d,成活率下降至13.3％;延迟投喂时间为12d,成活率为0。此外,延迟投喂时间在8d(20日龄)之内,42日龄后测量,仔鱼体长和体重与对照组无明显差异;延迟投喂超过9d,则体长和体重的指标明显低于对照组。仔鱼不摄食可以存活的最长时间是42日龄,但延迟投喂12天(24日龄)以上即发生不可逆转饥饿,故其饥饿的不可逆点(PNR)是24日龄。