Effect of zinc on L-threonine transport across the jejunum of rabbit

Zinc is an essential trace element for life. Many metalloenzymes involved in the metabolism of carbohydrates, lipids, protein, and nucleic acids require zinc for their functions. The aim of this study was to characterize how zinc acts on the intestinal amino acid absorption in rabbit. Results obtained show that zinc inhibits both L-threonine accumulation in the jejunum tissue, and mucosal-to-serosal transepithelial flux of this amino acid in a dose-dependent way. The inhibition does not increase by a 10-min previous intestinal exposure of the mucosa to the heavy metal, and is not reversed by washing the intestinal tissue with saline solution or 10mM EDTA, but is appreciably reversed with 10mM dithioerythritol. Zinc seems not to modify amino acid diffusion across the intestinal epithelium. The inhibition of intestinal amino acid transport by zinc seems to be of a competitive type, and appears to be a result of impairment of the active transport that is altered by its binding to proteins (prevailing to thiol groups) of the brush-border membrane of enterocytes.     

Inhibition of L-threonine intestinal absorption in rabbits by cadmium

Cadmium compounds are widely spread in the environment. Animal exposure to cadmium compounds occurs mainly through foods or drinks contaminated by this metal. Cadmium has been shown to produce several negative effects on the gastrointestinal tract such as inhibition on sugars and amino acids absorption. The aim of the present work was to study the inhibitory characteristics of cadmium on L-threonine intestinal absorption in rabbits in order to understand about this malabsorption of nutrients. Our results show that L-thereonine tissue accumulation as well as mucosal to serosal transepithelial fluxes are decreased in a dose-dependent manner in rabbit jejunum. Amino acid diffusion across the intestinal epithelium was not affected by cadmium. A noncompetitive mechanism and a partial reversion by dithioerythritol (thiol groups protector) is described for this inhibition.     

Alteration in surface substructure of frog urinary bladder by calcium ionophore, verapamil and antidiuretic hormone

The calcium antagonist verapamil and the calcium ionophore A23187 have been shown to inhibit the hydro-osmotic actions of antidiuretic hormone (ADH) presumably by different mechanisms. Presently, urinary bladders of the frog (Rana pipiens) were examined under SEM following exposure to calcium ionophore A23187, verapamil and ADH in the presence and absence of an osmotic gradient. Cells exposed to ADH show marked changes in surface substructure which is accompanied by an expansion of microridges, cell borders and the appearance of microvilli in the granular cells. The microvilli are pronounced and appear at the junction of microridges. In the presence of an osmotic gradient, ADH induces granular cell swelling and some cells show a blistering effect. Calcium ionophore, in the absence of an osmotic gradient, induced pronounced morphological changes in the granular cells, where the microvilli become prominently visible as 'finger-like' projections. This effect may be due to the action of calcium in promoting elongation of microtubules. Cells exposed to ionophore plus ADH are indistinguishable from ionophore alone. The most apparent effect of verapamil on surface substructure was on the elevation of the mitochondrial-rich cells above the surrounding granular cells. These cells show some degree of separation from the granular cells and are accentuated in tissues exposed to verapamil plus ADH. The present observations suggest that these agents, verapamil and calcium ionophore, have marked effects on cellular morphology. These actions are mediated through alterations in calcium movements and reflect the relative importance of cellular calcium in transepithelial water flow and the actions of antidiuretic hormone.     

Study of interaction between calcium and zinc ond-galactose intestinal transport

Zinc is an essential trace element necessary to life. This metal may exert some of its physiological effects by acting directly on cellular membranes, either by altering permeability or by modulating the activity of membrane-bound enzymes. On the other hand, calcium is an essential element in a wide variety of cellular activities. The aim of the present work was to study a possible interaction between zinc and calcium on intestinal transport ofd-galactose in jejunum of rabbit in vitro. In media with Ca²⁺, when ZnCl₂ was present at 0.5 or 1 mM, zinc was found to reduce thed-galactose absorption significantly. In Ca²⁺-free media, where CaCl₂ was omitted and replaced isotonically with choline chloride, the sugar transport was not modified by zinc. Verapamil at 10⁻⁶ M (blocking mainly Ca²⁺ transport) did not modify the inhibitory effect of zinc ond-galactose transport. When 10⁻⁶ M of A 23187 (Ca²⁺-specific ionophore) was added with/without Ca²⁺ to the media, ZnCl₂ produced no change in sugar transport. These results could suggest a possible interaction of calcium and zinc for the same chemical groups of membrane, which could affect the intestinal absorption of sugars.     

Effect of cadmium on enzymatic digestion and sugar transport in the small intestine of rabbit

Cadmium compounds are found widely in our environment: for example, in food, water, soil, and ambient air. The most important exposure route of animals to cadmium in the general environment is via oral exposure. In oral cadmium intoxication, the immediate target organ is the gastrointestinal tract. The aim of the present work was to determine how cadmium acts on the intestinal absorption of sugars and on the sucrase activity through rabbit jejunum, after in vitro administration and/or oral administration of CdCl₂ in drinking water. Results obtained show that cadmium decreasesD-galactose accumulation in the jejunum tissue. This effect seems to be the result of an action mainly located on Na⁺-dependent sugar transport of the mucosal border of the intestinal epithelium, because cadmium seemnnot to modify the sugar diffusion across the intestinal epithelium. Cadmium has also been shown to inhibit the (Na⁺-K⁺)-ATPase activity of the enterocyte, which might explain the inhibition of theD-galactose Na⁺-dependent transport. Nevertheless, a direct action of the cadmium molecule on the Na⁺-dependent carrier cannot be discarded. Cadmium altered the sucrose activity when it was administered in the drinking water for 4 d.     

Effect of serotonin on D-galactose transport across the rabbit jejunum

The patterns of storage and release of serotonin found in the enterochromaffin cells of the intestinal mucosa suggest that this hormone may be an important modulator of intestinal functions. Serotonin has been shown to produce secretion of water and electrolytes in rabbit ileum, but the hormone does not appear to interact significantly with other transport processes. The aim of the present study was to determine the effect of serotonin on D-galactose absorption in rabbit jejunum. The results obtained show that serotonin (10(-8) and 10(-6)M) partially reduced (by 20 and 40% respectively) D-galactose uptake across the mucosal border. This effect was concentration-dependent, and it seemed to be caused by the inhibition of Na+-dependent sugar transport. Methysergide, an antagonist of serotonin which binds with receptor 2 of serotonin, blocked the effect of serotonin. These findings suggest that serotonin may act as a regulator of sugar intestinal absorption, and that this serotonin regulation could be mediated by a direct or indirect action of the complex serotonin-receptor, which may inhibit the Na+-dependent transport system of sugars located in the brush-border membrane.     

Ca2+ ionophores inhibit superoxide generation by chemotactic peptide in rabbit neutrophils and the correlation with intracellular calcium

Summary Effects of Ca²⁺ ionophores, A23187 and lasalocid, on superoxide anion generation by chemotactic peptide, N-formyl-methionyl-leucyl-phenylalanine methyl ester, in rabbit peritoneal exudate neutrophils were studied. The ionophores by themselves did not activate superoxide anion generation in these neutrophils. When preincubated with the cells for 2 min, both the ionophores inhibited superoxide generation induced by chemotactic peptide. The inhibition was present even in the absence of extracellular Ca²⁺ and the inhibition was better then. Lasalocid produces a dose-dependent chlortetracycline fluorescence decrease response in neutrophils loaded with chlortetracycline. This response is independent of extracellular Ca²⁺ concentration and is related to release of Ca²⁺ from intracellular storage sites. The dose-range at which lasalocid gives this response is same as the dose-range at which it causes inhibition of superoxide response. It may be concluded that the inhibition of superoxide generation by these ionophores is correlated to intracellular Ca²⁺ modulation.Abbreviations FMLP Formyl-Methionyl-Leucyl-Phenylalanine methyl ester     

Tannic acid-glutaraldehyde fixation reveals calcium ionophore-induced changes in rabbit polymorphonuclear leukocyte membranes

TAG fixation of normal and Ca²⁺ ionophore-treated rabbit polymorphonuclear leukocytes (PMN) has revealed membrane components not apparent with conventional glutaraldehyde fixation. These included a 30 Å external electron-dense coating on untreated cells. A somewhat thicker coat (40 Å) was observed in ionophore-treated, nondegranulating PMN. In ionophore-treated, degranulating PMN, a 65 Å cell membrane coat was observed. A similar coat was observed on the inner side of the membrane of some azurophil-type granules, but the electron density and thickness were not so pronounced. Cytoplasmic granules were often closely apposed and often protruded outward at the plasma membrane. Extracellular lamellae, sometimes stacked apposed to the plasma membrane, possibly represent remnants of intense granule extrusion. Sequential degranulation of the respective granules was not apparent.     

Effects of calcium and sugars on intestinal manganese absorption

An in vivo luminal perfusion technique was used to investigate the influence of Ca, Mg, lactose, and glucose on Mn absorption in different segments of the rat intestine. Mn absorption was determined by measuring disappearance of⁵⁴Mn activity from the perfusion solution containing 0.1 or 0.01 mmol/L Mn. Na and water absorption were also determined. Mn absorption decreased during the first 30 min of perfusion to reach a steady state thereafter. Ca (1 mmol/L) inhibited Mn absorption in the proximal jejunum and in the colon, whereas Mn absorption was increased by Ca in the distal jejunum. Mg (1 mmol/L), lactose, and glucose (25 mmol/L each) had no effect on Mn absorption in the jejunum. These results can be explained by a direct interaction of Mn and Ca during transcellular Ca transport in the proximal jejunum and colon. The reason for the stimulatory effect of Ca in the distal jejunum is unknown.     

Effects of membrane peroxidation on [3H]acetylcholine release in rat cerebral cortical synaptosomes

[³H]Acetylcholine (ACh) release, malonaldehyde formation and⁴⁵calcium-uptake were measured in rat cerebral cortical nerve terminal that were exposed to various concentrations of ferrous and ascorbate ions. At a constant molar ratio of 25:1, ferrous:ascorbate, these ions increased malonaldehyde (MA) synthesis in a concentration-dependent manner. Treatment with these ions in the same ratio also induced a dose-related inhibition of the K⁺-depolarization-induced release of newly synthesized [³H]ACh. Combined exposure to Fe²⁺/ascorbate also reduced calcium ionophore A23187-induced [³H]ACh release. Neither ferrous nor ascorbate ions alone altered depolarization-or ionophore-induced [³H]ACh release over this concentration range. Depolarization- and A23187-induced⁴⁵calcium uptake were not affected by peroxidation, suggesting that membrane peroxidation influenced some process in the release-process subsequent to calcium influx in a manner similar to what is observed during aging.     

红细胞在钙离子和离子载体A23187作用下的流变特性研究

用新激光衍射法研究了钙离子及离子载体A23187对红细胞流变特性的影响.用不同浓度的钙离子及离子载体A23187分别处理红细胞后,测量其取向指数和小变形指数.结果表明离子载体A23187较细胞外钙离子浓度对红细胞流变特性的影响更大.而且,最大取向指数和最大小变形指数随着钙离子及离子载体A23187浓度的增加而降低.离子载体A23187浓度增加导致红细胞变形能力明显降低.     

Intestinal absorption of biotin and biocytin in the rat

The uptake of biotin and biocytin was investigated in rat intestine using the everted sac technique. It has been shown that at biotin and biocytin concentrations !ess than 40 and 50 nM respectively, absorption proceeds by a saturable process, whereas at higher concentrations uptake by passive diffusion predominates. Fractionation of solublized brush border preparations indicates that biotinidase is the only protein which binds biotin in this preparation.     

A genomic map of clinal variation across the European rabbit hybrid zone

Speciation is a process proceeding from weak to complete reproductive isolation. In this continuum, naturally hybridizing taxa provide a promising avenue for revealing the genetic changes associated with the incipient stages of speciation. To identify such changes between two subspecies of rabbits that display partial reproductive isolation, we studied patterns of allele frequency change across their hybrid zone using whole‐genome sequencing. To connect levels and patterns of genetic differentiation with phenotypic manifestations of subfertility in hybrid rabbits, we further investigated patterns of gene expression in testis. Geographic cline analysis revealed 253 regions characterized by steep changes in allele frequency across their natural region of contact. This catalog of regions is likely to be enriched for loci implicated in reproductive barriers and yielded several insights into the evolution of hybrid dysfunction in rabbits: (i) incomplete reproductive isolation is likely governed by the effects of many loci, (ii) protein–protein interaction analysis suggest that genes within these loci interact more than expected by chance, (iii) regulatory variation is likely the primary driver of incompatibilities, and (iv) large chromosomal rearrangements appear not to be a major mechanism underlying incompatibilities or promoting isolation in the face of gene flow. We detected extensive misregulation of gene expression in testis of hybrid males, but not a statistical overrepresentation of differentially expressed genes in candidate regions. Our results also did not support an X chromosome‐wide disruption of expression as observed in mice and cats, suggesting variation in the mechanistic basis of hybrid male reduced fertility among mammals.     

Effects of glutathione and of cysteine on intestinal absorption of selenium from selenite

The influence of glutathione (1 mmol/L) (GSH) on in vitro mucosal uptake and in vivo absorption of⁷⁵Se-labeled selenite (10 μmol/L) was investigated in rat jejunum. For comparison, the effect ofl-cysteine (1 mmol/L) on in vivo absorption of⁷⁵Se-labeled selenite was also studied. In the in vitro, uptake experiments, only the mucosal surface was exposed to the incubation medium for 3 min. For the in vivo experiments, a luminal perfusion technique was employed. GSH inhibited in vitro mucosal Se uptake, whereas absorption in vivo was stimulated by GSH.l-Cysteine also stimulated in vivo Se absorption, confirming former in vitro mucosal uptake experiments. Thus, unlikel-cysteine, GSH affected in vitro and in vivo absorption of Se from selenite differently. Enzymatic cleavage of products of the reaction of selenite with GSH occuring more efficiently under in vivo than in vitro conditions may be a prerequisite for the stimulatory effect of GSH on Se absorption. This apparently does not apply to the stimulatory effect of cysteine. Since, GSH occurs in the intestinal lumen under physiological conditions, it may contribute to the high bioavailability of Se from selenite.     

Role of vasoactive intestinal polypeptide (VIP) in the neurogenic vasodilatation of the portal vein in the rabbit

A coarse network of nerve fibres displaying immunoreactivity for vasoactive intestinal polypeptide (VIP) was found in the wall of the hepatic portal vein of the rabbit. Electrical field stimulation of the rabbit portal vein in vitro, in the presence of adrenergic and cholinergic blockade, caused a marked relaxation of the vessel and a release of VIP into the perfusate. Addition of VIP to the tissue bath elicited a concentration-dependent inhibition of the mechanical activity of the portal vein. The results suggest that VIP containing neurones might participate in the non-cholinergic, non-adrenergic vasodilatation of the portal vein in the rabbit.     

Gene expression profiles in rat intestine identify pathways for 1,25-dihydroxyvitamin D(3) stimulated calcium absorption and clarify its immunomodulatory properties

Microarray technology has been used to discover 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) induced gene expression changes in rat small intestine in vivo. Here, we report gene expression changes related to intestinal absorption or transport, the immune system and angiogenesis in response to 1,25-(OH)(2)D(3). Vitamin D deficient rats were intrajugularly given vehicle or vehicle containing 730 ng of 1,25-(OH)(2)D(3)/kg of body weight. Intestinal mRNA was harvested from duodenal mucosa at 15 min, 1, 3, and 6 h post-injection and studied by Affymetrix microarrays. Genes significantly affected by 1,25-(OH)(2)D(3) were confirmed by quantitative RT-PCR with remarkable agreement. The most strongly affected gene in intestine was CYP24 with 97-fold increase at 6 h post-1,25-(OH)(2)D(3) treatment. Intestinal calcium absorption genes: TRPV5, TRPV6, calbindin D(9k), and Ca(2+) dependent ATPase all were up-regulated in response to 1,25-(OH)(2)D(3), supporting the currently accepted mechanism of 1,25-(OH)(2)D(3) induced transcellular calcium transport. However, a 1,25-(OH)(2)D(3) suppression of several intra-/intercellular matrix modeling proteins such as sodium/potassium ATPase, claudin 3, aquaporin 8, cadherin 17, and RhoA suggests a vitamin D regulation of tight junction permeability and paracellular calcium transport. Several other genes related to the immune system and angiogenesis whose expression was changed in response to 1,25-(OH)(2)D(3) provided evidence for an immunomodulatory and anti-angiogenic role of 1,25-(OH)(2)D(3).     

Adaptability of the digestive function according to age at weaning in the rabbit: I. Effect on feed intake and digestive functionality

The functional adaptability of the digestive system to the level of feed intake was investigated in the young rabbits by comparing two groups of 12 litters each, weaned at 21 (W21) or 35 (W35) days of age. From 14 days onwards, rabbits were fed a pelleted feed (NDF: 332 g/kg, CP: 177 g/kg, starch: 98 g/kg, as-fed basis). Until 49 days of age, the profile of digestive enzymes was weekly determined in the small intestinal content and mucosa, as well as caecal fermentation traits and fibrolytic activities. In the W21 group, the solid feed intake was increased by 57% between 21 and 35 days (P < 0.01), while the daily body growth was lower from 21 till 42 days (-17%, P < 0.05) when compared with the W35 group. Activities of enzymes of pancreatic origin were only scarcely influenced by the weaning age. In the W21 group, amylase activity tended to be lower at 28 days of age (-36%, P = 0.064), and trypsin activity was decreased by 31% at 49 days of age (P < 0.01). Lipase activity was similar in both weaning groups. Duodenal and jejunal activities of maltase and aminopeptidase N (APN) were higher on day 28 in the W21 group as compared with the W35 group (×1.4 to ×2.4, respectively, P < 0.05). On day 35, duodenal APN activity was twice as higher in the W21 group than in the W35 group (P < 0.01). In caecum, major differences between both weaning groups were observed at 28 days of age with a decrease in ammonia concentration (-43%, P < 0.01) in W21 compared with W35 rabbits. Conversely, the acetate proportion was 5% higher in the W21 group (P < 0.01) on day 28. In conclusion, the digestive tract of early-weaned rabbits showed some adaptative properties in response to nutritional environment changes, but they were insufficient to maintain their growth rate.     

Heterogeneity of tachykinin receptors in the rabbit lung

The tachykinins, substance P (SP) and neurokinin A (NKA), are agonists for the NK₁ and NK₂ receptors, respectively. Tachykinins have various respiratory effects, including bronchoconstriction. This study characterizes tachykinin binding sites in the rabbit lung. We hypothesize that (2-[¹²⁵I]iodohistidyl¹)Neurokinin A ([¹²⁵I]NKA) interacts with NK₁ and NK₂ binding sites in the rabbit lung. The K_d determined from saturation isotherms was 0.69 X/÷1.14 nM (geometic mean X/÷ SEM) and the B_max was 4.15±0.22 femtomole/mg protein (arithmetic mean±SEM). Competitive inhibition studies with NKA, SP and various selective tachykinin agonists showed the rank order of potency: [β-Ala⁸]-Neurokinin A 4–10=SP ≫ NKA ≫ [Sar⁹,Met(O₂)¹¹]-Substance P. [β-Ala⁸]-Neurokinin A 4–10, a selective NK₂ agonist, and SP inhibition of [¹²⁵I]NKA binding were best described using a two-site model. Competitive inhibition studies using the selective nonpeptide NK₂ antagonist (SR 48968) and the selective nonpeptide NK₁ antagonist (CP 96,345) revealed K_i's of 5.5 nM and 8.1 nM, respectively. Our data therefore suggest that [¹²⁵I]NKA binds to both the NK₁ and NK₂ receptors in the lung. Special issue dedicated to Dr. Kinya Kuriyama.     

Transport of neutral and cationic amino acids across the brush-border membrane of the rabbit ileum

Summary The transport of sugars and amino acids across the brush-border membrane of the distal rabbit ileum has been studied. The kinetics of the transport of glucose demonstrated that the data obtained with the present technique are less distorted by unstirred layers than those obtained with the same technique adapted to the use of magnetic stirring. The role of depolarization of the electrical potential difference across the brush-border membrane in mutual inhibition between different classes of amino acids was estimated by measurements of the effects of high concentrations of alanine and lysine on the transport of galactose. It was found that this role would be insignificant in the present study. By measurements of the transport of alanine, leucine and lysine and the inhibitory interactions between these amino acids the function of three transport systems has been delineated. The transport of lysine is resolved in a high- and a low-affinity contribution. At 140mm sodium these transport systems may also function as respectively high- and low-affinity contributors to the transport of neutral amino acids. At 0mm sodium the high-affinity system remains a high-affinity system for cationic and neutral amino acids with reduced capacity especially for the neutral amino acids. At 0mm sodium the low-affinity system's affinity for lysine is reduced and it is inaccessible to neutral amino acids. In addition to the two systems for lysine transport the existence of a lysine-resistant, sodium-dependent, high-affinity system for the transport of neutral amino acids has been confirmed. It seems unlikely that the distal ileum is equipped with a low-affinity, sodium-independent system for the transport of neutral amino acids.     

Stimulation of sex pheromone production by PBAN-like substance in the pine caterpillar moth, Dendrolimus punctatus (Lepidoptera: Lasiocampidae)

Sex pheromone production in the female pine caterpillar moth, Dendrolimus punctatus is controlled by a PBAN-like substance located in the head of female moth. Pheromone titer was significantly decreased by decapitation of female moth, and restored by injection of either Hez-PBAN or head extract prepared from male or female moth. Stimulation of pheromone production by head extract followed a dose-dependent pattern from 0.5 to at least 4 head equivalent. A gland in vitro assay was used to study the relationship between gland incubation time and pheromone production as well as calcium involvement in the stimulation of pheromone production by head extract. Maximum pheromone production was occurred at 60 min after pheromone gland was incubated with two equivalents of head extracts. In vitro experiments showed that the presence of calcium in the incubation medium was necessary for stimulation of pheromone production. The calcium ionophore, A 23187, alone stimulated pheromone production. The pheromone components (Z,E)-5,7-dodecadienol and its acetate and propionate were produced in these experiments but in addition to the aldehyde, (Z,E)-5,7-dodecadienal was also found. This indicates that females are capable of producing four oxygenated functional groups. The PBAN-like substance control of the pheromone biosynthetic pathway was investigated by monitoring the incorporation of the labeled precursor into both pheromone and pheromone intermediates.