A new role for enteric glucagon-37: acute stimulation of glucose absorption in rat small intestine

Glucagon-37 is secreted by intestinal L-cells following carbohydrate uptake. It is known to inhibit gastric acid secretion (hence also named oxyntomodulin) and appears to increase intracellular cyclic AMP concentrations. Since cyclic AMP could enhance intestinal glucose absorption, a possible stimulatory effect of glucagon-37 on glucose transport was examined. Glucagon-37 acutely increased glucose absorption in the isolated, vascularly perfused small intestine and in isolated enterocytes of the rat. In these cells the stimulation by glucagon-37 could be completely blocked by the cAMP antagonist Rp-cAMPS and was therefore mediated by cAMP. The stimulation of intestinal glucose absorption by glucagon-37 appears to be a major new physiological function.     

Specific absorption coefficient and the phytoplankton package effect in Lake Taihu,China

In order to investigate variations of absorption and total chlorophyll-a (TChl-a)-specific absorption coefficient of phytoplankton in Lake Taihu, 57 water samples obtained from Lake Taihu during November 8–22, 2007 were used in this study. Package effect and accessory pigments’ influences on the absorption spectra were also examined. Phytoplankton absorption was measured by quality filter technical, and TChl-a concentration was measured by “hot ethanol” method. Results yielded significant variations in phytoplankton absorption and TChl-a-specific absorption coefficient. Phytoplankton absorption coefficient at 675 nm is highly correlated to TChl-a concentration, while absorption at 440 nm is less correlated to TChl-a concentration because of great package effect and accessory pigments’ influence. There was an inverse relationship between a _ph*(λ) and TChl-a concentration. Four types of absorption spectra are identified by normalizing a _ph*(λ) to a _ph*(440). The a _ph*(λ) variation is mainly due to accessory pigments and package effect, whose influence at 675 nm ranges from 83.2% to 28%, with an average of 65.3%. Meanwhile, the wide varying ratio of a _ph*(440) to a _ph*(675) indicates a large variation range in the ratio of accessory pigment to TChl-a concentration. Those findings are significant to estimate Chl-a concentration based on bio-optical model, estimate primary production from remote sensing, and plan further ecological restoration measures for Lake Taihu. Handling editor: Luigi Naselli-Flores     

Uptake of the components of phenylalanylphenylalanine and maltose by intestinal epithelium

The observed rate of phenylalanine absorption into rat intestinal rings with 0.5 or 5.0 mM phenylalanine is greater than that for absorption of phenylalanine from 0.25 or 2.5 mM Phe-Phe, respectively. With the amino acid phenylalanine, V for absorption is the same whether Na⁺ is present (149 mM) or absent, but the concentration at which the half-maximal transport rate occurred (K_t) is greater in the absence of Na⁺. For Phe-Phe, the V decreases in the absence of Na⁺ whilst K_t is not influenced by the Na⁺ concentration. The different effect of Na⁺ on Phe and Phe-Phe transport indicates that the absorptive mechanism for Phe-Phe is different from that for phenylalanine. Absorption of a mixture of [U-¹⁴C]Phe-Phe and Phe-[G-³H]Phe showed identical rates of uptake of the carboxyl and amino terminal amino acids.Studies of transport of radioactive maltose showed that the rates of uptake of the reducing and non-reducing glucosyl moieties are identical. Radioactive maltose absorption is not inhibited by glucose oxidase.These results provide evidence that in intestinal epithelium, hydrolysis of Phe-Phe and maltose does not occur on the cell surface with release of the hydrolyzed products to the medium. Rather, hydrolysis and release of the reaction products occur at a point on the cytosol side of a diffusion barrier located in the brush border membrane.     

Ausscheidungen der Aminosäuren mit dem Harn und Kot von kolostomierten und nicht operierten Hennen — Beitrag zur Methode der Aminosäurenresorbierbarkeit

Veal calves aged 8 weeks were fed iso‐energetic amounts of milk replacers with either a low (7.1g of calcium/kg of air‐dry diet) or a high concentration of calcium (11.6g of calcium/kg of air‐dry diet) for a period of 10 weeks. The extra calcium was added in the form of calcium formiate. Final body weight of the two dietary groups was similar. Faeces were collected during the final week of the trial. The high calcium diet raised faecal dry matter output by 87% and faecal energy by 70%. The extra output of faecal dry matter was composed of 36% and 37% of crude fat and ash, respectively. The extra faecal energy output was for 75% in the form of crude fat. The high versus low calcium intake not only depressed apparent digestibility of total lipids but also that of crude protein, carbohydrates and ash. It is concluded that a high calcium intake by veal calves reduced energy availability without affecting body weight gain.     

Acute exposure to ergot alkaloids from endophyte-infected tall fescue does not alter absorptive or barrier function of the isolated bovine ruminal epithelium

Ergot alkaloids in endophyte-infected (Neotyphodium coenophialum) tall fescue (Lolium arundinaceum) have been shown to cause a reduction in blood flow to the rumen epithelium as well as a decrease in volatile fatty acids (VFA) absorption from the washed rumen of steers. Previous data also indicates that incubating an extract of endophyte-infected tall fescue seed causes an increase in the amount of VFA absorbed per unit of blood flow, which could result from an alteration in the absorptive or barrier function of the rumen epithelium. An experiment was conducted to determine the acute effects of an endophyte-infected tall fescue seed extract (EXT) on total, passive or facilitated acetate and butyrate flux across the isolated bovine rumen as well as the barrier function measured by inulin flux and tissue conductance (G_t). Flux of ergovaline across the rumen epithelium was also evaluated. Rumen tissue from the caudal dorsal sac of Holstein steers (n=6), fed a common diet, was collected and isolated shortly after slaughter and mounted between two halves of Ussing chambers. In vitro treatments included vehicle control (80% methanol, 0.5% of total volume), Low EXT (50 ng ergovaline/ml) and High EXT (250 ng ergovaline/ml). Results indicate that there is no effect of acute exposure to ergot alkaloids on total, passive or facilitated flux of acetate or butyrate across the isolate bovine rumen epithelium (P>0.51). Inulin flux (P=0.16) and G_t (P>0.17) were not affected by EXT treatment, indicating no alteration in barrier function due to acute ergot alkaloid exposure. Ergovaline was detected in the serosal buffer of the High EXT treatment indicating that the flux rate is ~0.25 to 0.44 ng/cm² per hour. Data indicate that specific pathways for VFA absorption and barrier function of the rumen epithelium are not affected by acute exposure to ergot alkaloids from tall fescue at the concentrations tested. Ergovaline has the potential to be absorbed from the rumen of cattle that could contribute to reduced blood flow and motility and lead to reduced growth rates of cattle.     

Brush border membrane non-esterified fatty acids. Physiological levels and significance for mucosal iron uptake in mouse proximal intestine

Brush border membrane vesicles prepared using divalent cation precipitation methods can contain unphysiological levels of non-esterified fatty acids. Fatty acid production from endogenous lipid during brush border membrane vesicle preparation is effectively prevented by the lipase inhibitor diethyl 4-nitrophenylphosphate plus cooling. Vesicles prepared using this procedure have variable levels of non-esterified fatty acids (range 22-193 nmol mg-1 protein). Changes in non-esterified fatty acid levels in brush border membrane vesicles parallel Fe uptake by vesicles from Fe/ascorbate solutions. Brush border membrane vesicle fatty acids appear to be derived from the diet but hypoxic mice are able to maintain high brush border membrane non-esterified fatty acid levels despite reduced dietary intake. Non-esterified fatty acids in brush border membrane may thus provide a physiological mechanism of mucosal Fe uptake.     

Paracellular nutrient absorption in a gum-feeding new world primate, the common marmoset Callithrix jacchus

The common marmoset is one of the few callitrichid species that is not threatened or endangered in the wild, and is widely used in biomedical research, yet relatively little is understood about its digestive physiology. Dietary specialization on plant exudates has lead to relatively reduced small intestines, yet the common marmoset has exceptional dietary breadth, allowing it to successfully utilize a variety of habitats. We predicted that passive, paracellular nutrient absorption would be used by the common marmoset to a greater extent than in other non-flying mammals. We measured the bioavailability and rates of absorption of two metabolically inert carbohydrates not transported by mediated pathways (L-rhamnose and cellobiose, molecular masses of 164 and 342, respectively) to measure paracellular uptake, and of a non-metabolized D-glucose analog (3-O-methyl-D-glucose) to measure total uptake by both mediated and paracellular pathways. We found high bioavailability of 3-O-methyl-D-glucose (83+/-5%), and much higher bioavailability of the paracellular probes than in similarly sized non-flying mammals (30+/-3% and 19+/-2% for L-rhamnose and cellobiose, respectively). Passive, paracellular nutrient absorption accounts for around 30% of total glucose absorption in common marmosets and intestinal permeability is significantly higher than in humans, the only other species of primate measured to date. This may allow the common marmoset to maintain high digestive efficiency when feeding on higher quality foods (fruit, arthropods, gums with higher proportions of simple sugars), in spite of relatively reduced small intestines correlated with adaptations for fermentative digestion of plant gums. We find no evidence to support, in primates, the hypothesis that reliance on paracellular nutrient absorption should increase with body size in mammals, but suggest instead that it may be associated with small body size and/or taxon-specific adaptations to diet.     

Manipulating Backbone Structure to Enhance Low Band Gap Polymer Photovoltaic Performance

A pair of polymers, PBDTBT and PBDTDTBT , was synthesized for application in polymer solar cells (PSCs). Although these two polymers have similar absorption bands and molecular energy levels, PBDTDTBT exhibits much better photovoltaic performance in polymer solar cell (PSC) devices with power conversion efficiency (PCE) of 7.4%. To understand the differences between PBDTDTBT and PBDTBT , we have investigated the correlations of the molecular structure, morphology, dynamics and efficiency of these two polymers. A theoretical investigation using density functional theory (DFT) and time‐dependent DFT (TDDFT) has been employed to investigate the electron density and electron delocalization extent of the unimers. TEM data showed that PBDTDTBT phase separates from PC₇₁BM, while PBDTBT suffers from having a proper morphology on different processing conditions. Grazing incidence wide angle X‐ray diffraction (GIWAXD) was used to probe the crystal structure of the polymers in thin film. A polymorph crystal structure was observed for PBDTBT . Grazing incidence small angle X‐ray scattering (GISAXS) was used to probe the size scale of phase separation, with an optimized 25 nm feature size observed for PBDTDTBT /PC₇₁BM blends, which agrees well with TEM results. Femtosecond transient absorption (TA) spectroscopy was used to probe the dynamics of the fundamental processes in organic photovoltaic (OPV) materials, such as charge separation and recombination. The enhanced absorption coefficient, good charge separation, optimal phase separation and higher charge mobility all contribute to the high PCE of the PBDTDTBT /PC₇₁BM devices.     

The relationship between iron status and lead absorption in rats

The absorption of lead from loops of small intestinein situ was investigated in rats in which iron absorption was increased by stimuli varying in type, intensity, or duration. Lead absorption was increased by a short period of severe iron restriction before any change in hematological indices became apparent. A period of hypoxia, which markedly increased iron absorption, did not influence absorption of lead. An extended period of moderate iron restriction resulted in a marked reduction in liver iron stores and increased iron absorption throughout the 17-wk experiment. Under these conditions lead absorption was initially also increased, but after 12 wk, when iron intake had become adequate to meet essential requirements, lead absorption was similar to that in iron-supplemented rats. These results are discussed in the light of evidence for a receptor-mediated absorption process for iron.     

Maltobionic acid enhances intestinal absorption of calcium and magnesium in rats

ABSTRACT

In Experiment 1, the effects of calcium maltobionate (MBCa) on calcium and magnesium absorption were examined using male rats. Four diets were designed in which 25%, 50%, and 100% of calcium carbonate (CaCO₃, Control) were substituted with MBCa and were designated as MBCa-25, MBCa-50, and MBCa-100, respectively. The cecal concentration of short-chain fatty acids was significantly higher in groups MBCa-50 and MBCa-100; however, pH of cecal contents did not significantly differ among the groups. Retention rates of calcium and magnesium were significantly higher in all MBCa groups as compared to the Control. In Experiment 2, the efficiency of calcium absorption was compared using everted sacs of jejunum and ileum with CaCO₃ and MBCa as calcium sources. More calcium from MBCa was absorbed as the concentration of calcium increased in comparison to CaCO₃. It was concluded that MBCa is a better calcium source than CaCO₃ in terms of both calcium retention and absorption.

Abbreviations: ANOVA: analysis of variance; Ca: Calcium; CaCO_3: calcium carbonate; ICP-OES: Inductivity coupled plasma optical emission spectrometer; Mg: magnesium; MBCa: calcium maltobionate; OCPC: o-cresolphthalein complexone; SCFAs: short-chain fatty acids; SE: standard error; TRPM6: transient receptor potential melastatin 6.     

多效唑在土壤中的行为研究

本文利用示踪技术研究多效唑在３种土壤中的行为。土壤理化性质对多效唑在土壤中的纵向移动和横向扩散有影响。多效唑在土壤中的纵向移动性较大,且随时间的推移纵向移动性减小．多数唑易被土壤吸附,但仍有部分易随雨水横向扩散和纵向移动。土壤对多效唑的吸附量随浓度增加而提高,在一定浓度范围内,浓度对吸附率的影响不大。     

ACAT2 and ABCG5/G8 are both required for efficient cholesterol absorption in mice: evidence from thoracic lymph duct cannulation

The metabolic fate of newly absorbed cholesterol and phytosterol is orchestrated through adenosine triphosphate-binding cassette transporter G5 and G8 heterodimer (G5G8), and acyl CoA:cholesterol acyltransferase 2 (ACAT2). We hypothesized that intestinal G5G8 limits sterol absorption by reducing substrate availability for ACAT2 esterification and have attempted to define the roles of these two factors using gene deletion studies in mice. Male ACAT2(-/-), G5G8(-/-), ACAT2(-/-)G5G8(-/-) (DKO), and wild-type (WT) control mice were fed a diet with 20% of energy as palm oil and 0.2% (w/w) cholesterol. Sterol absorption efficiency was directly measured by monitoring the appearance of [(3)H]sitosterol and [(14)C]cholesterol tracers in lymph after thoracic lymph duct cannulation. The average percentage (± SEM) absorption of [(14)C]cholesterol after 8 h of lymph collection was 40.55 ± 0.76%, 19.41 ± 1.52%, 32.13 ± 1.60%, and 21.27 ± 1.35% for WT, ACAT2(-/-), G5G8(-/-), and DKO mice, respectively. [(3)H]sitosterol absorption was <2% in WT and ACAT2(-/-) mice, whereas it was up to 6.8% in G5G8(-/-) and DKO mice. G5G8(-/-) mice also produced chylomicrons with ～70% less cholesterol ester mass than WT mice. In contrast to expectations, the data demonstrated that the absence of G5G8 led to decreased intestinal cholesterol esterification and reduced cholesterol transport efficiency. Intestinal G5G8 appeared to limit the absorption of phytosterols; ACAT2 more efficiently esterified cholesterol than phytosterols. The data indicate that handling of sterols by the intestine involves both G5G8 and ACAT2 but that an additional factor (possibly Niemann-Pick C1-like 1) may be key in determining absorption efficiency.     

Optical Saturable Absorption in Gold Nanoparticles

In this work, we present the experimental study of the nonlinear absorption of gold nanospheres and nanorods in aqueous suspension, using picosecond white-light supercontinuum open-aperture Z-scan. We demonstrate a saturable absorption effect in all particle suspensions at low-pulse energy. In the high-pulse energy regime, the apparent reverse-saturable absorption, observed in gold nanorods, was determined to be induced by photodegradation. Using the Lorentzian deconvolution method for the absorption spectra, we explain the variations on nonlinear optical effects and prove that saturable absorption only occurs within the plasmonic bands.     

东北地区城市针叶树冬季滞尘效应研究

对不同种针叶树同一降尘条件及同种针叶树不同降尘条件的滞尘能力进行研究,结果表明,针叶树在东北的冬季有很强的滞尘作用,不同的针叶树滞尘能力排序为沙松冷杉>沙地云杉>红皮云杉>东北红豆杉>白皮松>华山松>油松,不同针叶树叶表面结构不同,滞尘量较小的白皮松、华山松和油松表面平滑,细胞与气孔排列整齐,而滞尘量较大的红皮云杉、沙松冷杉、东北红豆杉的针叶表皮平滑程度较差,细胞与气孔排列较前3种植物差,在红皮云杉叶表面上有大小不等的瘤状物,不同针叶树叶断面形状与滞尘量相关,白皮松和油松叶片的上表面呈弧形,不易附着灰尘;华山松叶片呈三棱形,上表面较窄,附着灰尘的量较小;两种云杉的叶片呈四棱形,上表面较3种松属植物的叶片要宽与平展,因此相对滞尘量要大;沙松冷杉和东北红豆杉的叶断面形状都较扁、平,这种断面正是构成其滞尘量大于3种松属和两种云杉属植物的主要因素。     

Induced absorption band of holotransketolase and its interpretation

It has long been known that formation of a catalytically active holotransketolase from the apoenzyme and thiamine diphosphate (ThDP) is accompanied by appearance, in both the absorption and CD spectra, of a new band. Binding and subsequent conversion of transketolase substrates bring about changes in the intensity of this band. The observation of these changes allows the investigator to monitor the coenzyme-to-apoenzyme binding and the conversion of the substrates during the transketolase reaction and thus to kinetically characterize its individual steps. As regards the new absorption band induced by ThDP binding, its nature, until recently, remained unknown. The reason for its appearance was considered to be either the formation of a charge transfer complex between ThDP and tryptophan (phenylalanine) residue or stacking interaction between the residues of aromatic amino acids. They are thought to be brought together as a result of conformational changes of the apoenzyme during its interaction with the coenzyme. However none of these hypotheses had been substantiated experimentally. According to our hypothesis, the induced absorption band is that of the imino form of ThDP resulting from three contributing features of the ThDP binding site of transketolase: the relative hydrophobicity of this site, hydrogen bonding of the N1"-atom of the ThDP aminopyrimidine ring to Glu418, and base stacking interactions between the aminopyrimidine ring of ThDP and Phe445.     

离体外翻肠囊法研究白及提取物中6种成分的肠吸收特性

为研究白及提取物中4-(葡萄糖氧基)-肉桂酸葡萄糖氧基苄酯(B12)、2-异丁基苹果酸(B6)、1-[4-(葡萄糖氧)苄基]-2-异丁基苹果酸酯(B17)、1,4-二[4-(葡萄糖氧)苄基]-2-异丁基苹果酸酯(B14)、二氢菲1(B19)和1,4-二[4-(葡萄糖氧)苄基]-2-异丁基苹果酸酯-2-[4-O-肉桂酰基-6-O-乙酰基]葡萄糖苷(B23)6个成分在大鼠小肠中的吸收动力学特性。实验采用大鼠离体外翻肠囊模型考察各成分在不同浓度、不同肠段的吸收特性,建立超高效液相色谱-三重四极杆串联质谱联用仪(UPLC-MS/MS)法测定各成分含量,计算累计吸收量和吸收速率常数。结果表明,除B6成分的低浓度外,各成分在不同浓度、不同肠段下均表现为线性吸收,其回归相关系数(R)均达到0.9以上,符合一级吸收速率,且吸收速率常数随着浓度的增加而增加,提示各成分吸收机制为被动吸收;在同一浓度下不同肠段的总体吸收趋势为十二指肠的吸收要大于回肠、结肠和空肠。综上,白及提取物中6种成分在小肠中均有吸收,但小肠对各成分的吸收具有选择性。本研究可为白及提取物的药物临床开发,确定药物剂型方面提供了一定的实验参考。     

Adipose triglyceride lipase is a TG hydrolase of the small intestine and regulates intestinal PPARα signaling

Adipose triglyceride lipase (ATGL) is the rate-limiting enzyme mediating triglyceride (TG) hydrolysis. The lack of ATGL results in TG accumulation in multiple tissues, underscoring the critical role of ATGL in maintaining lipid homeostasis. Recent evidence suggests that ATGL affects TG metabolism via activation of peroxisome proliferator-activated receptor α (PPARα). To investigate specific effects of intestinal ATGL on lipid metabolism we generated mice lacking ATGL exclusively in the intestine (ATGLiKO). We found decreased TG hydrolase activity and increased intracellular TG content in ATGLiKO small intestines. Intragastric administration of [³H]trioleate resulted in the accumulation of radioactive TG in the intestine, whereas absorption into the systemic circulation was unchanged. Intraperitoneally injected [³H]oleate also accumulated within TG in ATGLiKO intestines, indicating that ATGL mobilizes fatty acids from the systemic circulation absorbed by the basolateral side from the blood. Down-regulation of PPARα target genes suggested modulation of cholesterol absorption by intestinal ATGL. Accordingly, ATGL deficiency in the intestine resulted in delayed cholesterol absorption. Importantly, this study provides evidence that ATGL has no impact on intestinal TG absorption but hydrolyzes TGs taken up from the intestinal lumen and systemic circulation. Our data support the role of ATGL in modulating PPARα-dependent processes also in the small intestine.     

Intestinal iron absorption in chickens

Intestinal iron absorption in chickens was studied in vivo, using an intestinal perfusion technique in closed circuit. The results obtained show that iron absorption, at 30 min intervals, is a linear function of test solution iron concentrations of up to 776 μg Fe/20 mL. At higher concentrations, iron saturation occurs. The mucosal epithelial cells seem to be less a limiting factor than in rats. However, in chickens, the binding capacity of plasma might play an important role in the regulation of iron absorption. Iron absorption versus time was analyzed in 15, 30, 60, and 120 min periods for the iron concentration of 14 μg Fe/20 mL. Intestinal iron absorption showed a linear relationship between these two parameters. A period of perfusion of either 30 or 60 min by a solution of 14 μg Fe/20 mL appears suitable since no interference by a saturation process can then occur.     

植物吸收离子动力学综合型模型探讨

本文在前人工作基础上提出了一个离子吸收动力学新模型（综合型抑制作用模型）,并推导出其速率方程．该模型能将现有的离子吸收相互作用模型（竞争性抑制作用模型,反竞争性抑制模型和非竞争性抑制作用模型）统一在该模型之中．笔者用该模型很好地解释了七例有关离子吸收相互作用试验结果．     

Structure of bovine milk calcium phosphate determined by x-ray absorption spectroscopy

Calcium in cow's milk is mainly in the form of calcium phosphate-phosphoprotein complexes known as casein micelles. These micelles, in contrast to other phosphoprotein complexes in bone and other tissues, can be readily isolated and studied, but conventional techniques have given ambiguous and conflicting evidence on the structure of milk calcium phosphate. Extended X-ray absorption fine structure and near-edge structure measurements at the newly commissioned Synchrotron Radiation Source at Daresbury indicate that it closely resembles brushite, CaHPO₄·2H₂O. This result, and chemical analysis, requires that phosphate groups from the matrix phosphoproteins be incorporated in the brushite lattice, probably in the surface, suggesting that these organic phosphate groups act as heterogeneous nucleation sites for phase separation of the calcium phosphate from solution.