Effects of water restriction on digestive function in two macropodid marsupials from divergent habitats and the feral goat

The effects of water restriction on digestive function in the euro (Macropus robustus erubescens) found in the arid zone of inland Australia, the eastern wallaroo (M.r.robustus) from more mesic regions of eastern Australia, and the feral goat (Capra hircus) found throughout the range of M. robustus, were compared in order to examine some physiological adaptations required by herbivores for the exploitation of arid environments. Eight animals of each species were held in individual metabolism cages in temperature-moderated rooms and given a chopped hay diet ad libitum. Half the animals were restricted to 40 ml water·kg^-0.80·day^-1. This was 40%, 32% and 57% of voluntary drinking water intake in the euro, wallaroo and goat, respectively. All species responded to water restriction by reducing faecal, urinary and evaporative water losses in association with reductions in feed intake. All animals increased urine osmolality and electrolyte concentrations but not to maximal levels, while packed-cell volume and plasma osmolality and electrolyte concentrations were unaffected by water restriction. The euro displayed a suite of characteristics that separated it from the wallaroo in terms of physiological adaptation, including lower voluntary water intake, an increase in fibre digestibility and maintenance of nitrogen balance during water restriction, and lower faecal water efflux associated with a consistently lower faecal water content (54% versus 59% water in the wallaroo during water restriction, P<0.05). The euro's colon was 37% longer (P<0.01) than that of the wallaroo. The goat had the lowest faecal water efflux (P<0.05) and the longest colon (P<0.001). Water restriction did not affect water content in digesta, nor short-chain fatty acid concentrations or production rates in vitro. Total body water, as a proportion of body mass, was depressed (P<0.05) in the macropodids, but not in the goat. The reduction in dietary nitrogen intake, which accompanied water restriction, was partially compensated by an increase in urea degradation in the gut from 68% to 76% of urea synthesis water-restricted macropodids. These responses to water restriction are discussed in relation to those reported in other macropodid and ruminant species.Abbreviations BM body mass - SCFA short-chain fatty acids - DM dry matter - PCV packed-cell volume     

牛肾组织及其培养物的不同消化法效果评价

为了比较不同消化液及消化方式对牛肾皮质组织和培养后形成单层细胞的消化分散效果并确定最适消化液和消化方式,分别用0.25%胰蛋白酶和0.25%胰蛋白酶-0.02%EDTA两种消化液,消化牛肾皮质组织及其培养形成的单层牛肾皮质细胞。牛肾皮质组织采用热(37℃)和冷(4℃)两种消化方式;经培养形成单层的牛肾皮质细胞采用室温(25℃)消化。结果显示,用0.25%胰蛋白酶-0.02%EDTA消化液热消化牛肾组织时,分散获得牛肾皮质细胞的活细胞数、存活率、贴壁率均优于其他消化方法,差异显著(P0.05)。培养形成的单层牛肾皮质细胞用0.25%胰蛋白酶-0.02%EDTA消化液的消化速度明显快于用单一0.25%胰蛋白酶消化液的消化速度,统计学分析显示具有显著性差异(P0.01),两种消化液消化所得细胞的存活率及贴壁率前者要更高,差异显著(P0.05)。     

Ingestion without inactivation of bacteriophages by Tetrahymena

Tetrahymena has been shown to ingest and inactivate bacteriophages, such as T4, in co-incubation experiments. In this study, Tetrahymena thermophila failed to inactivate phages PhiX174 and MS2 in co-incubations, although PhiX174 were ingested by T. thermophila, as demonstrated by: (1) recovery at defecation in a pulse-chase experiment, (2) recovery from Tetrahymena by detergent lysis, and (3) transmission electron microscopy. We conclude, therefore, that the phages must be digestion-resistant. Internalized PhiX174 were further shown to be partially protected from lethal damage by ultraviolet (UV) C and UVB irradiation. Finally, ingested PhiX174 were shown to be rapidly transported through buffer in a horizontal swimming, race tube-like assay. The transport and protection of phages may confer evolutionary advantages that explain the acquisition of digestion-resistance by some phages.     

Experimental tests of the mechanism for ant-enhanced growth in an ant-tended lycaenid butterfly

In a previous laboratory study, larvae of the ant-tended lycaenid butterfly Hemiargus isola developed into larger adults when reared with the ant Formica perpilosa than when reared without ants. Ants neither fed butterfly larvae nor significantly delayed developmental duration. We investigated two non-exclusive hypotheses for the mechanism of this effect: larvae tended by F. perpilosa (1) consume more food, and (2) digest the food they consume more efficiently, than those reared without ants. Larvae reared in the laboratory with F. perpilosa ants became significantly heavier adults but produced a significantly lighter fecal mass than their untended counterparts, suggesting that greater food consumption was not the primary mechanism for the higher growth rates of ant-tended larvae. Tended and untended larvae were equally proficient at digesting the contents of pollen (a major natural food source) throughout the tended portion of the life cycle. Taken together, the results suggest that neither greater consumption nor higher assimilation accounts for the larger size of F. perpilosa-tended larvae. We propose that tended larvae may expend less energy than their untended counterparts. Received: 3 January 1997 / Accepted: 18 June 1997     

Influence of Surfactants on Lipase Fat Digestion in a Model Gastro-intestinal System

In the present study, we use a model gastro-intestinal system to study the influence of different food-grade surface-active molecules (Sn-2 monopalmitin, β-lactoglobulin, or lysophosphatodylcholine) on lipase activity. The interfacial activity of lipase and surfactants are assessed with the pendant drop technique, a commonly used tensiometry instrument. A mathematical model is adopted which enables quantitative determination of the composition of the water–oil interface as a function of bulk surfactant concentration in the water–oil mixtures. Our results show a decrease in gastric lipolysis when interfacially active molecules are incorporated into a food matrix. However, only the Sn-2 monopalmitin caused a systematic decrease in triglyceride hydrolysis throughout the gastro-intestinal tract. This effect is most likely due to exclusion of both lipase and triglyceride from the water–oil interface together with a probable saturation of the solubilization capacity of bile with monoglycerides. Addition of β-lactoglobulin or lysophopholipids increased the hydrolysis of fat after the gastric phase. These results can be attributed to an increasing interfacial area with lipase and substrate present at the interface. Otherwise, β-lactoglobulin, or lysophopholipids reduced fat hydrolysis in the stomach. From the mathematical modeling of the interface composition, we can conclude that Sn-2 monopalmitin can desorb lipase from the interface, which, together with exclusion of substrate from the interface, explains the gradually decreased triglyceride hydrolysis that occurs during the digestion. Our results provide a biophysics approach on lipolysis that can bring new insights into the problem of fat uptake.     

Sulfakinin is an important regulator of digestive processes in the migratory locust,Locusta migratoria

Sulfakinin (SK) is a sulfated insect neuropeptide that is best known for its function as a satiety factor. It displays structural and functional similarities with the vertebrate peptides gastrin and cholecystokinin. Peptidomic studies in multiple insects, crustaceans and arachnids have revealed the widespread occurrence of SK in the arthropod phylum. Multiple studies in hemi- and holometabolous insects revealed the pleiotropic nature of this neuropeptide: in addition to its activity as a satiety factor, SK was also reported to affect muscle contraction, digestive enzyme release, odor preference, aggression and metabolism. However, the main site of action seems to be the digestive system of insects. In this study, we have investigated whether SK can intervene in the control of nutrient uptake and digestion in the migratory locust (Locusta migratoria). We provide evidence that sulfakinin reduces food uptake in this species. Furthermore, we discovered that SK has very pronounced effects on the main digestive enzyme secreting parts of the locust gut. It effectively reduced digestive enzyme secretion from both the midgut and gastric caeca. SK injection also elicited a reduction in absorbance and proteolytic activity of the gastric caeca contents. The characteristic sulfation of the tyrosine residue is crucial for the observed effects on digestive enzyme secretion. In an attempt to provide potential leads for the development of peptidomimetic compounds based on SK, we also tested two mimetic analogs of the natural peptide ligand in the digestive enzyme secretion assay. These analogs were able to mimic the effect of the natural SK, but their effects were milder. The results of this study provide new insights into the action of SK on the digestive system in (hemimetabolous) insects.     

Peritrophic matrix of Phlebotomus duboscqi and its kinetics during Leishmania major development

Light microscopy of native preparations, histology, and electron microscopy have revealed that Phlebotomus duboscqi belongs to a class of sand fly species with prompt development of the peritrophic matrix (PM). Secretion of electron-lucent fibrils, presumably chitin, starts immediately after the ingestion of a blood meal and, about 6 h later, is followed by secretion of amorphous electron-dense components, presumably proteins and glycoproteins. The PM matures in less than 12 h and consists of a thin laminar outer layer and a thick amorphous inner layer. No differences have been found in the timing of the disintegration of the PM in females infected with Leishmania major. In both groups of females (infected and uninfected), the disintegration of the PM is initiated at the posterior end. Although parasites are present at high densities in the anterior part of the blood meal bolus, they escape from the PM at the posterior end only. These results suggest that L. major chitinase does not have an important role in parasite escape from the PM. Promastigotes remain in the intraperitrophic space until the PM is broken down by sand-fly-derived chitinases and only then migrate anteriorly. Disintegration of the PM occurs simultaneously with the morphological transformation of parasites from procyclic forms to long nectomonads. A novel role is ascribed to the anterior plug, a component of the PM secreted by the thoracic midgut; this plug functions as a temporary barrier to stop the forward migration of nectomonads to the thoracic midgut. This work was supported by the Ministry of Education of the Czech Republic (projects MSM0021620828 and LC06009).     

Hydrophilic polydopamine‐coated magnetic graphene nanocomposites for highly efficient tryptic immobilization

In this work, polydopamine‐coated magnetic graphene (MG@PDA) nanocomposites were synthesized by a facile method. Trypsin was then directly immobilized on the surface of the nanocomposites through simple PDA chemistry with no need for introducing any other coupling groups. The as‐made MG@PDA nanocomposites inherit not only the large surface area of graphene which makes them capable of immobilizing high amount of trypsin (up to 0.175 mg/mg), but also the good hydrophilicity of PDA which greatly improves their biocompatibility. Moreover, the strong magnetic responsibility makes them easy to be separated from the digested peptide solution when applying a magnetic field. The feasibility of the trypsin‐immobilized MG@PDA (MG@PDA‐trypsin) nanocomposites for protein digestion was investigated and the results indicated their high digestion efficiency in a short digestion time (10 min). In addition, the reusability and stability of the MG@PDA‐trypsin nanocomposites were also tested in our work. To further confirm the efficiency of MG@PDA‐trypsin nanocomposites for proteome analysis, they were applied to digest proteins extracted from skimmed milk, followed by nano RPLC‐ESI‐MS/MS analysis, and a total of 321 proteins were identified, much more than those obtained by 16‐h in‐solution digestion (264 proteins), indicating the great potential of MG@PDA‐trypsin nanocomposites as the supports for high‐throughput proteome study.