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Marine teleost fish continuously ingest seawater to prevent dehydration and their intestines absorb fluid by mechanisms linked to three separate driving forces: 1) cotransport of NaCl from the gut fluid; 2) bicarbonate (HC[O.sup.-.sub.3]) secretion and [Cl.sup.-] absorption via [Cl.sup.-]/HC[O.sup.-.sub.3] exchange fueled by metabolic C[O.sub.2]; and 3) alkaline precipitation of [Ca.sup.2+] as insoluble CaC[O.sub.3], which aids [H.sub.2]O absorption). The latter two processes involve high rates of epithelial HC[O.sup.-.sub.3] secretion stimulated by intestinal [Ca.sup.2+] and can drive a major portion of water absorption. At higher salinities and ambient [Ca.sup.2+] concentrations the osmoregulatory role of intestinal HC[O.sup.-.sub.3] secretion is amplified, but this has repercussions for other physiological processes, in particular, respiratory gas transport (as it is fueled by metabolic CO2) and acid-base regulation (as intestinal cells must export [H.sup.+] into the blood to balance apical HC[O.sup.-.sub.3] secretion). The flounder intestine was perfused in vivo with salines containing 10, 40, or 90 mM [Ca.sup.2+]. Increasing the luminal [Ca.sup.2+] concentration caused a large elevation in intestinal HC[O.sup.-.sub.3] production and excretion. Additionally, blood pH decreased (-0.13 pH units) and plasma partial pressure of C[O.sub.2] (PC[O.sub.2]) levels were elevated (+1.16 mmHg) at the highest Ca perfusate level after 3 days of perfusion. Increasing the perfusate [[Ca.sup.2+]] also produced proportional increases in net acid excretion via the gills. When the net intestinal flux of all ions across the intestine was calculated, there was a greater absorption of anions than cations. This missing cation flux was assumed to be protons, which vary with an almost 1 : 1 relationship with net acid excretion via the gill. This study illustrates the intimate link between intestinal HC[O.sup.-.sub.3] production and osmoregulation with acid-base balance and respiratory gas exchange and the specific controlling role of ingested [Ca.sup.2+] independent of any other ion or overall osmolality in marine teleost fish. carbon dioxide; oxygen; protons; gill; carbonic anhydrase doi: 10.1152/ajpregu.00513.2009.

The intestine of marine teleosts must effectively absorb fluid from ingested seawater to avoid dehydration. This fluid transport has been almost exclusively characterized as driven by NaCl absorption. However, an additional feature of the osmoregulatory role of the intestine is substantial net HC[O.sup.-.sub.3] secretion. This is suggested to drive additional fluid absorption directly (via [Cl.sup.-]/HC[O.sup.-.sub.3] exchange) and indirectly by precipitating ingested [Ca.sup.2+] as CaC[O.sub.3], thus creating the osmotic gradient for additional fluid absorption. The present study tested this hypothesis by perfusing the intestine of the European flounder in vivo with varying [[Ca.sup.2+]]: 10 (control), 40, and 90 mM. Fractional fluid absorption increased from 47% (control) to 73% (90 mM [Ca.sup.2+]), where almost all secreted HC[O.sup.-.sub.3] was excreted as CaC[O.sub.3]. This additional fluid absorption could not be explained by NaCl cotransport. Instead, a significant positive relationship between [Na.sup.+]-independent fluid absorption and total HC[O.sup.-.sub.3] secretion was consistent with the predicted roles for anion exchange and CaC[O.sub.3] precipitation. Further analysis suggested that [Na.sup.+]-independent fluid absorption could be accounted for by net C1 and [H.sup.+] absorption (from [Cl.sup.-]/HC[O.sup.-.sub.3] exchange and CO, hydration, respectively). There was no evidence to suggest that CaC[O.sub.3] alone was responsible for driving fluid absorption. However, by preventing the accumulation of luminal [Ca.sup.2+] it played a vital role by dynamically maintaining a favorable osmotic gradient all along the intestine, which permits substantially higher rates of solute-linked fluid absorption. To overcome the resulting hyperosmotic and highly acidic absorbate, it is proposed that plasma HC[O.sup.-.sub.3] buffers the absorbed [H.sup.+] (from HC[O.sup.-.sub.3] production), and consequently reduces the osmolarity of the absorbed fluid entering the body. osmoregulation; chloride/bicarbonate exchange; in vivo perfusion doi: 10.1152/ajpregu.00545.2009.

Singla A, Dwivedi A, Saksena S, Gill RK, Alrefai WA, Ramaswamy K, Dudeja PK. Mechanisms of lysophosphatidic acid (LPA) mediated stimulation of intestinal apical [C1.sup.-]/[OH.sup.-] exchange. Am J Physiol Gastrointest Liver Physio1298: G 182-G189, 2010. First published November 12, 2009; doi: 10.1152/ajpgi.00345.2009.--Lysophosphatidic acid (LPA), a potent bioactive phospholipid, is a natural component of food products like soy and egg yolk. LPA modulates a number of epithelial functions and has been shown to inhibit cholera toxin-induced diarrhea. Antidiarrheal effects of LPA are known to be mediated by inhibiting chloride secretion. However, the effects of LPA on chloride absorption in the mammalian intestine are not known. The present studies examined the effects of LPA on apical [Cl.sup.-]/[OH.sup.-] exchangers known to be involved in chloride absorption in intestinal epithelial cells. Caco-2 cells were treated with LPA, and [C1.sup.-]/[OH.sup.-] exchange activity was measured as DIDS-sensitive [sup.36][Cl.sup.-] uptake. Cell surface biotinylation studies were performed to evaluate the effect of LPA on cell surface levels of apical [Cl.sup.-]/[OH.sup.-] exchangers, downregulated in adenoma (DRA) (SLC26A3), and putative anion transporter-1 (SLC26A6). Treatment of Caco-2 cells with LPA (100 [micro]M) significantly stimulated [Cl.sup.-]/[OH.sup.-] exchange activity. Specific agonist for LPA2 receptor mimicked the effects of LPA. LPA-mediated stimulation of [C1.sup.-]/[OH.sup.-] exchange activity was dependent on activation of phosphatidylinositol 3-kinase/Akt signaling pathway. Consistent with the functional activity, LPA treatment resulted in increased levels of DRA on the apical membrane. Our results demonstrate that LPA stimulates apical [Cl.sup.-]/[OH.sup.-] exchange activity and surface levels of DRA in intestinal epithelial cells. This increase in [Cl.sup.-]/[OH.sup.-] exchange may contribute to the antidiarrheal effects of LPA. downregulated in adenoma; chloride absorption; human intestine; LPA receptor 2; phosphatidylinositol 3-kinase/Akt doi: 10.1152/ajpgi.00345.2009

Fouillet H, Juillet B, Gaudichon C, Mariotti F, Tome D, Bos C. Absorption kinetics are a key factor regulating postprandial protein metabolism in response to qualitative and quantitative variations in protein intake. Am J Physiol Regul lntegr Comp Physiol 297: R1691-R1705, 2009. First published October 7, 2009; doi: 10.1152/ajpregu.00281.2009.--We have previously demonstrated that increasing the habitual protein intake widened the gap in nutritional quality between proteins through mechanisms that arc not yet fully understood. We hypothesized that the differences in gastrointestinal kinetics between dietary proteins were an important factor affecting their differential response to an increased protein intake. To test this hypothesis, we built a 13-compartment model providing integrative insight into the sequential dynamics of meal nitrogen (Nm) absorption, splanchnic uptake, and metabolism, and subsequent peripheral transfer and deposition. The model was developed from data on postprandial Nm kinetics in certain accessible pools, obtained from subjects having ingested a [sup.5]N-labeled milk or soy protein meal, after adaptation to normal (NP) or high (HP) protein diets. The faster absorption of Nm after soy vs. milk caused its earlier and stronger splanchnic delivery, which favored its local catabolic utilization (up to +30%) and limited its peripheral accretion (down to -20%). Nm absorption was also accelerated after HP vs. NP adaptation, and this kinetic effect accounted for most of the HP-induced increase (up to +20%) in splanchnic Nm catabolic use, and the decrease (down to -25%) in peripheral Nm anabolic utilization. The HP-induced acceleration in Nm absorption was more pronounced with soy than with milk, as were the HP effects on Nm regional metabolism. Our integrative approach identified Nm absorption kinetics, which exert a direct and lasting impact on Nm splanchnic catabolic use and peripheral delivery, as being critical in adaptation to both qualitative and quantitative changes in protein intake. interorgan amino acid metabolism; milk protein; soy protein; highprotein diets; compartmental model doi: 10.1152/ajpregu.00281.2009

Marine teleost fish precipitate divalent cations as carbonate deposits in the intestine to minimize the potential for excessive [Ca.sup.2+] entry and to stimulate water absorption by reducing luminal osmotic pressure. This carbonate deposit formation, therefore, helps maintain osmoregulation in the seawater (SW) environment and requires controlled secretion of HC[O.sup.-.sub.3] to match the amount of [Ca.sup.2+] entering the intestinal lumen. Despite its physiological importance, the process of HC[O.sup.-.sub.3] secretion has not been characterized at the molecular level. We analyzed the expression of two families of HC[O.sup.-.sub.3] transporters, Slc4 and Slc26, in fresh-waterand SW-acclimated euryhaline pufferfish, mefugu (Takifugu obscurus), and obtained the following candidate clones: NBCel (an [Na.sup.+]-HC[O.sup.-.sub.3] cotransporter) and Slc26a6A and Slc26a6B (putative [Cl.sup-]/n HC[O.sup.-.sub.3] exchangers). Heterologous expression in Xenopus oocytes showed that Slc26a6A and Slc26a6B have potent HC[O.sup.-.sub.3]-transporting activity as electrogenic [Cl.sup.-]/nHC[O.sup.-.sub.3] exchangers, whereas mefugu NBCel functions as an electrogenic [Na.sup.+]-nHC[O.sup.-.sub.3] cotransporter. Expression of NBCel and Slc26a6A was highly induced in the intestine in SW and expression of Slc26a6B was high in the intestine in SW and fresh water, suggesting their involvement in HC[O.sup.-.sub.3] secretion and carbonate precipitate formation. Immunohistochemistry showed staining on the apical (Slc26a6A and Slc26a6B) and basolateral (NBCel) membranes of the intestinal epithelial cells in SW. We therefore propose a mechanism for HC[O.sup.-.sub.3] transport across the intestinal epithelial cells of marine fish that includes basolateral HC[O.sup.-.sub.3] uptake (NBCel) and apical HC[O.sup.-.sub.3] secretion (Slc26a6A and Slc26a6B). osmoregulation; NBC; Slc26; intestine; calcium carbonate

Intestinal cholesterol absorption is modulated by transport proteins in enterocytes. Cholesterol uptake from intestinal lumen requires several proteins on apical brush-border membranes, including Niemann-Pick CI-like 1 (NPC1L1), scavenger receptor B-I, and CD36, whereas two ATP-binding cassette half transporters, ABCG5 and ABCG8, on apical membranes work together for cholesterol efflux back to the intestinal lumen to limit cholesterol absorption. NPCIL1 is essential for cholesterol absorption, but its function as a cell surface transporter or an intracellular cholesterol transport protein needs clarification. Another ATP transporter, ABCAI, is present in the basolateral membrane to mediate HDL secretion from enterocytes. Niemann-Pick C1-Like 1 protein; scavenger receptors; ATP-binding cassette proteins

Before cholesterol and fatty acid molecules in the small intestinal lumen can interact with their possible transporters for uptake and absorption, they must pass through a diffusion barrier, which may modify the kinetics of nutrient assimilation. This barrier includes an unstirred water layer and a surface mucous coat, which is located at the intestinal lumen-membrane interface. In the present study, we investigated whether disruption of the mucin gene (Muc)1 may influence intestinal uptake and absorption of cholesterol and fatty acid in male Muc[1.sup.-/-] mice. The wild-type mice displayed relatively high levels of Muc1, Muc2, Muc3, and Muc4 mRNAs and relatively low levels of Muc5ac and Muc5b mRNAs in the small intestine. The absence of Muc1 mRNA and protein in the small intestines of Muc[1.sup.-/-] mice confirmed complete knockout of the Muc1 gene, but the mRNA expression for other mucin genes remained unchanged. Intestinal uptake and absorption of cholesterol but not palmitic acid were significantly reduced in Muc[1.sup.-/-] mice compared with the wild-type mice. However, knockout of the Muc1 gene did not impair either expression levels of the genes that encode intestinal sterol efflux transporters Abcg5 and Abcg8 and fatty acid transporter Fatp4 or small intestinal transit rates. We conclude that physiological levels of the epithelial mucin produced by the Muc1 gene are necessary for normal intestinal uptake and absorption of cholesterol in mice. Our study implies that because cholesterol absorption efficiency is reduced by ~50% in Muc1-deficient mice, there may be one or more additional pathways for cholesterol absorption. ATP-binding cassette (transporter); intestinal uptake; surface mucous coat; mucin gel; micelle; nutrition

NHE3, the apical isoform of the [Na.sup.+]/[H.sup.+] exchanger, is central to the absorption of salt and water across the intestinal epithelium. We report that treatment of epithelial cells with toxin B of Clostridium difficile, a diarrheal pathogen, causes a pronounced inhibition of NHE3 activity, with little effect on the basolateral NHE1 isoform. Depression of NHE3 activity is accompanied by the translocation of apical exchangers to a subapical endomembrane compartment. Treatment of cells with toxin B increased the fraction of exchangers that were solubilized by nonionic detergents and induced dephosphorylation and extensive redistribution of ezrin. The Rho-kinase inhibitor, Y-27632, also altered the distribution and activity of NHE3. We suggest that inactivation of Rho-family GTPases by clostridial toxin B alters the interaction between NHE3 and the microvillar cytoskeleton, possibly by impairing the ability of ezrin to bridge the exchangers to filamentous actin. Detachment of NHE3 from the actin skeleton would facilitate its internalization, resulting in net disappearance from the apical surface. The consequent inhibition of transport is likely to contribute to the diarrheal effects of C. difficile. KEY WORDS: Na/H exchange * antiport * pH regulation * Rho * ezrin

Background: Scavenger receptor class B type I (SR-BI) is known to mediate cellular uptake of cholesterol from high density lipoprotein particles and is particularly abundant in liver and steroidogenic tissues. [...]

Background and aims: Dietary fat plays a role in the pathophysiology of symptoms in functional dyspepsia (FD). In healthy subjects, cognitive factors enhance postprandial fullness; in FD patients, attention increases [...]

Two experiments, Trial 1 (in vitro) and Trial 2 (in vivo), were conducted to examine the effects of ionophores, monensin, laidlomycin, and laidlomycin propionate on whole-animal [O.sub.2] consumption, organ weights, jejunal glucose absorption, and [0.sub.2] utilization, as well as growth, feed and water consumption, and feed efficiency. In Trial 1, 30 male Swiss-Webster mice, 8 wk old, were used to measure the in vitro effects of each of the ionophores at concentrations of 1.62 or 16.2 mM. Six combinations of three ionophores at two concentrations resulted in a total of eight treatments. All eight treatments were exposed to jejunal rings from a single mouse for a total of 30 observations per treatment. Jejunal rings were exposed to each ionophore treatment for 15 min. Laidlomycin propionate (16.2 mM) decreased (P < 0.2) glucose absorption, as estimated by [H.sup.3]-3-O-methyl glucose uptake compared with all other treatments, whereas laidlomycin propionate (1.62 mM) increased (P = 0.032)jejunal DM content compared with 16.2 mM laidlomycin propionate. In Trial 2, 40 5-wk-old mice were allotted into four treatments--control and 16.2 mM each of monensin, laidlomycin, and laidlomycin propionate--for a total of 10 observations per treatment. Ionophores were administered via the drinking water for 14 d. No ionophore treatment had any effect on whole-mouse [O.sub.2] consumption. Monensin increased (P = 0.004) stomach size and decreased (P = 0.049) the efficiency of BW gain compared with controls. Laidlomycin propionate decreased (P = 0.032) the percentage of whole jejunum oxygen consumption due to oubain-sensitive respiration compared with control. The efficiency of intestinal glucose absorption was not changed due to treatment in either trial. Under the conditions of these studies, monensin, laidlomycin, and laidlomycin propionate had minimal and inconsistent effects on jejunal function and energy utilization in mice. This investigation suggests that changes in the energetic requirements of animals treated with ionophores are not an issue in animal production. Key Words: Absorption, Glucose, Intestines, Ionophores, Mice

Background: A large oral dose of iron will reduce the absorption of a subsequent smaller dose of iron in a phenomenon known as mucosal block. Molecular analysis of this process [...]

DNase I in rats is mainly expressed in the parotid gland and the small intestine and functions as a digestive enzyme. Male Wistar rats were deprived of food for 48 h, refed with nonpurified diet for 2 h and killed at 0, 0.33, 0.67, 1, 2, 6 or 12 h. The activity and mRNA of DNase I in the parotid gland and the small intestine were determined. We found that in rats that were not fed for 48 h there was accumulation of DNase I in the parotid gland but not in the small intestine. In the parotid gland, refeeding decreased DNase I activity (P < 0.05), perhaps due to an increase in secretion. The increase in DNase I mRNA probably resulted from the need for protein synthesis. However, in the small intestine, both the enzyme activity and the amount of mRNA were up-regulated by refeeding (P < 0.05). Exposing rats to food in a sealed transparent flask also caused a 2.5-fold increase in DNase I mRNA within 30 min in the parotid gland. These data suggested that the expression of rat parotid DNase I is up-regulated by feeding and that mastication is not essential for the regulation. KEY WORDS: * DNasel * parotid gland * small intestine * starvation * refeeding

Dietary retinyl esters are hydrolyzed in the intestine by the pancreatic enzyme, pancreatic triglyceride lipase (PTL), and intestinal brush border enzyme, phospholipase B. Recent work on the carboxylester lipase (CEL) knockout mouse suggests that CEL may not be involved in dietary retinyl ester digestion. The possible roles of the pancreatic lipase-related proteins (PLRP) 1 and 2 and other enzymes require further investigation. Unesterified retinol is taken up by the enterocytes, perhaps involving both diffusion and protein-mediated facilitated transport. Once in the cell, retinol is complexed with cellular retinol-binding protein type 2 (CRBP2) and the complex serves as a substrate for reesterification of the retinol by the enzyme lecithin:retinol acyltransferase (LRAT). Retinol not bound to CRBP2 is esterified by acyl-CoA acyltransferase (ARAT). The retinyl esters are incorporated into chylomicrons, intestinal lipoproteins that transport other dietary lipids such as triglycerides, phospholipids, and cholesterol. Chylomicrons containing newly absorbed retinyl esters are then secreted into the lymph. J. Nutr. 131: 1405-1408, 2001. KEY WORDS: * retinoids * lipid absorption * pancreatic enzymes * chylomicrons * lipases

An Ussing chamber technique was used to determine the effects of three indigestible disaccharides on net Ca transport from the luminal side to the basolateral side of isolated preparations of jejunal, ileal, cecal and colonic epithelium in rats. Permeability of Lucifer Yellow (LY) and transepithelial electrical resistance (TEER), which are indicators of intercellular passage of the intestinal mucosa, were also determined. The concentrations of Ca in the serosal and mucosal media were 1.25 mmol/L and 10 mmol/L, respectively. After a 30-min incubation, the net Ca transport, LY passage and TEER were determined. In the control experiment, LY permeability was lowest, and TEER value was highest in the colon. The addition of 1-100 mmol/L melibiose, difructose anhydride (DFA)III, or DFAIV to the mucosal medium increased the net Ca absorption and LY permeability dose-dependently in the jejunum, ileum, cecum and colon preparations. Melibiose decreased TEER dose-dependently in the jejunum and cecum, but not in the ileum and colon. DFAIII decreased TEER dose-dependently in the jejunum, cecum and colon, but not in the ileum. DFAIV decreased TEER dose-dependently in all four intestinal portions. Positive linear relationships were found between net Ca transport and LY passage in all portions of the intestine, whereas negative linear relationships were found between net Ca absorption and TEER. We concluded that the three indigestible saccharides directly affect the epithelial tissue and activate the passage of tight junctions, thereby promoting Ca absorption in the small and large intestine in vitro. KEY WORDS: Ca absorption * indigestible saccharide * Ussing chamber * intestine * tight junction

The activity of nitric oxide synthase (NOS) was assayed in enterocytes isolated from human duodenal biopsies to determine its role in celiac disease. Patients were categorized into groups with irritable bowel syndrome, iron-deficiency anemia, [B.sub.12]/folate deficiency, and treated and untreated celiac disease. Enterocytes isolated from all groups showed 1400W-inhibitable [Ca.sup.2+]-independent NOS activity with a pH level and temperature optimum of 9.4 and 37[degrees]C, respectively. Western blotting showed that enterocytes expressed the inducible NOS protein and proteins with nitrated tyrosine residues, the latter being indicative of nitric oxide-driven peroxynitrite and/or free-radical damage. Endothelial NOS was seen only in the lamina propria. Patients with celiac disease had higher NOS activity than other patient groups. Treatment of the condition led to a fall in activity. Enzyme-linked immunosorbent assay demonstrated cGMP production by the enterocyte fraction, but cGMP levels did not correlate with NOS activity. These results suggest that inducible NOS is constitutively expressed in human duodenal enterocytes, is increased in patients with untreated celiac disease, and is partially corrected when such patients are treated. We found no evidence to support a role for nitric oxide in the formation of cGMP within the small intestine. Furthermore, we were unable to demonstrate a role for peroxynitrite/free radical damage in the pathophysiology of celiac disease. small bowel; malabsorption; nitric oxide; peroxynitrite; guanosine 3',5'-cyclic monophosphate

Extracellular ATP regulates a variety of functions in epithelial tissues by activating the membrane P2-receptor. The purpose of this study was to investigate the autocrine/paracrine regulation by luminal ATP of electrogenic amiloride-sensitive [Na.sup.+] absorption in the distal colon from guinea pigs treated with aldosterone by measuring the amiloride-sensitive short-circuit current ([I.sub.sc]) and [sup.22][Na.sup.+] flux in vitro with the Ussing chamber technique. ATP added to the luminal side inhibited the amiloride-sensitive [I.sub.sc] and [sup.22][Na.sup.+] absorption to a similar degree. The concentration dependence of the inhibitory effect of ATP on amiloridesensitive [I.sub.sc] had an I[C.sub.50] value of 20-30 [micro] M, with the maximum inhibition being ~50%. The effects of different nucleotides and of a nucleoside were also studied, the order of potency being ATP = UTP > ADP > adenosine. The effects of ATP were slightly, but significantly, reduced in the presence of suramin in the luminal solution. The inhibitory effect of luminal ATP was more potent in the absence of both [Mg.sup.2+] and [Ca.sup.2+] from the luminal solution. Pretreatment of the tissue with ionomycin or thapsigargin in the absence of serosal [Ca.sup.2+] did not affect the percent inhibition of amiloride-sensitive [I.sub.sc] induced by ATP. Mechanical perturbation with a hypotonic luminal solution caused a reduction in amiloride-sensitive [I.sub.sc], this effect being prevented by the presence of hexokinase, an ATP-scavenging enzyme. These results suggest that ATP released into the luminal side by hypotonic stimulation could exert an inhibitory effect on the electrogenic [Na.sup.+] absorption. This effect was probably mediated by a P2[Y.sub.2] receptor on the apical membrane of colonic epithelial cells, and a change in the intracellular [Ca.sup.2+] concentration may not be necessary for this process. P2Y receptor; UTP; volume regulation; intestinal absorption; intracellular [Ca.sup.2+]

Intestinal epithelial cells (IEC) are located at the strategic interface between the external environment and the most extensive lymphoid compartment in the body. Besides their central role in the absorption of nutrients, they also provide sample information to the immune system on soluble or particulate antigens present in the intestinal lumen. Like professional antigen-presenting cells, IEC have recently been shown to secrete 30- to 90-nm diameter vesicles named exosomes from their apical and basolateral surfaces. These vesicles carry molecules that are implicated in adhesion and antigen presentation, such as major histocompatibility complex (MHC) class I molecules, MHC class II molecules, CD63, CD26/dipeptidyl-peptidase IV, tetraspan proteins, and A33 antigen. IEC exosomes therefore, constitute a link by which IEC may influence antigen presentation in the mucosal or systemic immune system independent of direct cellular contact with effector cells. antigen; absorption; antigen presentation; oral tolerance; mucosal immune system

The effect of the electrical charge on the intestinal absorption of a protein was studied in normal adult rats. Chicken egg lysozyme (Lyz), a basic protein with a molecular weight of 14,300, was selected and several techniques for chemical modification were applied. Then the intestinal absorption of Lyz derivatives was evaluated by measuring the radioactivity in plasma and tissues, after the administration of an [sup.111]In-labeled derivative to an in situ closed loop of the jejunum. After the administration of [sup.111]In-Lyz, the level of radioactivity in plasma was comparable with the lytic activity of Lyz, supporting the fact that the radioactivity represents intact Lyz. [sup.111]In-cationized Lyz showed a 2-3 times higher level of radioactivity in plasma, whereas the radioactivity of [sup.111]In-anionized Lyz was much lower. The absorption rate of [sup.111]In-Lyz derivatives calculated by a deconvolution method was correlated for the strength of their positive net charge. A similar relationship was observed using superoxide dismutase. These findings indicate that the intestinal absorption of a protein is, at least partially, determined by its electrical charge. intestinal absorption; chicken egg lysozyme; pharmacokinetics; chemical modification; superoxide dismutase

This study was done to establish and validate a single-pass perfusion method for measuring the absorption of water and electrolytes by the mouse small intestine. The method was then used to study intestinal absorption in mice whose villin gene had been invalidated (v-/-). The single-pass perfusion of the jejunum measures the absorption of water, [Cl.sub.-], [Na.sub.+], [K.sub.+], [HCO.sup.-.sub.3], and glucose in anesthetized wild-type and v-/- mice in vivo. We measured absorption under basal and stimulated conditions (carbachol, vasoactive intestinal polypeptide, intralumen PG[E.sub.2]). Basal absorption and stimulated secretions were similar to those previously obtained in rats. There was no difference between wild-type and v-/- mice in animals with mixed genetic background or in pure C57BL6 mice. We conclude that this in vivo perfusion method is suitable for studying the absorption/ secretion of electrolytes in the mouse intestine and that a lack of villin does not significantly alter basal and secretagogue-stimulated electrolyte movements across the epithelium of the mouse jejunum in vivo. intestinal hormones; transport; brush-border epithelium; jejunum

This article examines the effects of varying the types and amounts of transportable carbohydrates in cold beverages on gastric emptying rates. Findings indicate that gastric volumes and emptying rates remain constant across carbohydrate solutions and that cold beverages are warmed to stomach temperature within minutes after ingestion.

An increase in intestinal permeability in HIV patients with diarrhea increases the absorption of ganciclovir, according to a study of 42 HIV patients. Ganciclovir is used to prevent and treat cytomegalovirus infections.

Alimet (Novus Inter., Inc., St. Louis, MO) feed supplement (an 88% aqueous solution of 2-hydroxy-4-(methylthio) butanoic acid; HMB) is a source of L-Met commonly used in nonruminants and ruminants. The absorption of HMB across ovine omasal and ruminal epithelia was evaluated in this study. Ruminal and omasal epithelia were collected from eight lambs (BW = 67.6 kg +/- 9.1) and mounted in parabiotic chambers that were repeatedly sampled throughout a 60-rain incubation. The appearance of HMB (using DL-[5-(super 14)C]-HMB as a radiolabeled marker) in serosal buffers increased quadratically (P < .004) with time in both tissues. More (P < .001) HMB appeared in the serosal buffers with omasal than with ruminal epithelia. Both tissues responded similarly, and, after 60 min of incubation, the accumulation of HMB within the tissues increased linearly (P < .001) as substrate concentration (.375, .75, 1.5, 3.0, 6.0, and 12.0 mM) increased in mucosal buffers. As the concentration of HMB in the mucosal buffers increased, there was a quadratic (P < .001) increase in the appearance of HMB in the serosal buffer of the omasal epithelium, indicating some saturation of the system. The increase in serosal appearance of HMB was linear (P < .001) with ruminal tissue. The results indicate that there are probably multiple mechanisms involved in the absorption of HMB. Because saturation was observed in the omasum, it is likely that mediated transport accounts for at least a portion of the absorption of HMB in the omasum. Other mechanisms (e.g., diffusion and(or) paracellular absorption) are responsible for the balance of the absorption. Omasal epithelium appears to have a greater capacity for HMB absorption than ruminal epithelium. The enzymes involved in the conversion of HMB to 2-keto-4-(methylthio)butanoic acid were found in ruminal and omasal epithelia, liver and kidney. These results indicate that HMB can be absorbed across ruminal and omasal epithelium and that HMB can be used as a source of L-methionine. Key Words: Absorption, Methionine, Methionine Hydroxy Analogue, Omasum, Rumen

The uptake of L-ascorbate (vitamin C) and its oxidized form, dehydro-L-ascorbic acid (DHAA), was evaluated in brush border membrane vesicles isolated from adult human duodenum, jejunum and ileum. Ascorbate was taken up along the entire length of the small intestine with a threefold higher initial uptake rate in distal than proximal segments. Ascorbate uptake was Na(super +)-dependent, potential-sensitive and saturable (K(sub m), 200 (mu)mol/L), whereas DHAA transport involved facilitated diffusion (K(sub m), 800 (mu)mol/L). Pharmacologic experiments were conducted to characterize further these transport mechanisms. DHAA uptake was not mediated by the fructose carrier GLUT5, the uridine transporter or the 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS)-sensitive anion exchanger of the apical membrane. DIDS and sulfinpyrazone , an inhibitor of the urate/lactate exchanger, both significantly reduced the initial rate of ascorbate uptake. Acidic pH inhibited ascorbate uptake, and this effect was not due to a transmembrane proton gradient. Increasing concentrations of glucose in the transport media also significantly inhibited ascorbate uptake, but no effect of glucose was seen when glucose internalization was blocked by phlorizin. Preloading the vesicles with glucose inhibited ascorbate uptake similarly, indicating that glucose interferes with the ascorbate transporter from the internal side of the membrane. The results of this study suggest that DHAA crosses the apical membrane by facilitated diffusion, whereas ascorbate transport is a Na(super +)-dependent, electrogenic process modulated by glucose.

A study was conducted to investigate Na+-dependent alanine uptake as representative of Na+-amino acid cotransport in a rabbit model of chronic ileal inflammation. In particular, the study aimed to test the theory that chronic ileitis uniquely changes Na+-alanine cotransport and to determine the cellular mechanisms of this alteration. Results indicate that Na+-alanine cotransport is inhibited during chronic ileal inflammation.

The regulation of dietary cholesterol absorption was examined in C57BL/6 and transgenic mice with liver overexpression of the scavenger receptor BI (SR-BI Tg). In C57BL/6 animals, feeding 0.02 to 1% (wt/wt) dietary cholesterol resulted in a dose-dependent decrease in the percentage of dietary cholesterol absorbed. A plot of total daily mass of dietary cholesterol absorbed versus the percentage by weight of cholesterol in the diet yielded a curve suggesting a saturable process with a Km of 0.4% (wt/wt) and a [V.sub.max] of 0.65 mg cholesterol/g body weight per day. Dietary cholesterol suppressed hepatic 3-hydroxy-3-methylglutaryl CoA reductase activity, stimulated cholesterol 7[Alpha]-hydroxylase activity, and enhanced fecal excretion of bile acids, but none of these changes correlated with the percentage of dietary cholesterol absorption. Dietary cholesterol also caused an increase in biliary cholesterol concentration, and in this case the concentration of biliary cholesterol was strongly and inversely correlated with the percentage dietary cholesterol absorption (r = -0.63, P < 0.0001). Biliary cholesterol concentration was also directly correlated with daily cholesterol intake, dietary cholesterol mass absorption, and liver cholesterol ester content. Transgene-induced overexpression of SR-BI resulted in a stimulation of excretion of cholesterol into the bile and suppressed percentage dietary cholesterol absorption. Furthermore, biliary cholesterol levels in SR-BI Tg mice were strongly and inversely correlated with the percentage of dietary cholesterol absorbed (r = -0.99, P < 0.0008). In summary, these results suggest that the excretion of cholesterol into the bile plays an important role in regulating the percentage absorption of dietary cholesterol.

The role of the folate transporter protein in colonic folate uptake was analyzed in apical membrane vesicles that were isolated from the mucosal scarppings of the human colon. Analysis of folate uptake in the isolated human colonic apical membrane vesicles indicated the presence of a hydrogen-ion concentration-dependent electroneutral carrier that mediated folate absorption. Furthermore, colonic folate absorption was stimulated by the functional plasma membrane folate transporter.

The kinetic properties of basolateral transport of D-glucose and D-fructose were analyzed in membrane vesicles isolated from chick jejunum. Basolateral transport of D-glucose and D-fructose in chicken jejunal basolateral membranes was mediated by a single type II glucose transporter isoform that promoted membrane transport with low affinity and high affinity. Furthermore, the transport of the hexoses across the jejunal basolateral membrane was not affected by Na+ or cytochalasin.

Brush-border membrane vesicles isolated from the euryhaline Anguilla anguilla were analyzed to determine the mechanisms of electroneutral anion exchange across the luminal membrane. Analysis of luminal bicarbonate translocation in isolated eel brush-border membranes indicated the presence of a Cl-/bicarbonate exchange that operates at the apical level of the eel kidney absorbing cells. The antiporter also worked in conjunction with an Na+/H+ exchanger during fluid homeostasis in euryhaline eels.

The kinetics of intestinal apolipoprotein (apo) A-IV synthesis and secretion was analyzed after single gastric loads of fat in rats to determine the role of apo A-IV in the short-term control of food intake. Analysis of Apo A-IV synthesis after the intragastric delivery of radioactive lipid indicated the role of lipid gastric loading in inducing the synthesis of the protein in the distal ileum, proximal and distal jejunum of rats. Furthermore, increases in the secretion of Apo A-IV was associated with the short-term satiety signal that was released by dietary fat.

The unidirectional flux of bipolar and cationic amino acids across the brush-border membrane of intact rat jejunal and rabbit ileal epithelia was analyzed to determine the role of Na+ in intestinal transport. Analysis of cationic and bipolar amino acid transport in rabbit ileal epithelia and rat jejunal epithelia indicated the presence of an Na+-independent flux. Furthermore, sodium was not needed in the inhibition of lysine transport by cationic and bipolar amino acids.

The role of the gastrointestinal capsaicin-sensitive primary afferent (CSPA) fibers in the regulation of amino acid absorption was analyzed in rats that were neonatally treated with capsaicin. Jejunal alanine absorption was inhibited by acute capsaicin treatment by altering the Na+-dependent component of alanine uptake across the mucosal membrane. However, neonatal treatment of rats with capsaicin destroyed the gastrointestinal CSPA fibers and abolished the effects of acute capsaicin treatment on alanine absorption.

The activity of Na+/H+ and Cl-/hydrogen bicarbonate exchange in the brush-border membrane (BBM) of vilus cells during inflammation was analyzed in rabbit models of chronic ileal inflammation. Recovery from alkaline loading in the villus cells of rabbits with chronic ileal inflammation was impaired due to the inhibition of Cl-/hydrogen bicarbonate exchange in the BBM. On the other hand, ileal crypt cells exhibited accelerated acid loading due to the stimulation of Na+/H+ exchange by chronic inflammation.

The magnitude and duration of the digestive responses of pythons during the consumption of meals equivalent to 25% or 65% of their body mass were analyzed to determine the characteristics of snake postprandial response. Increasing meal size from 5%, 25% to 65% of the python's body mass increased the magnitude of postprandial response involving metabolic oxygen consumption rate, kidney hypertrophy and upregulation of nutrient uptakes. Furthermore, pythons exhibited rapid intestinal upregulation and downregulation involving increases in intestinal mass.

The intracellular alterations and regulatory events involved in the stimulation of electroneural Na+ absorption were analyzed in isolated rabbit proximal colon. The cell interior hydrogen-ion concentration (pHi) was acidified by Na+ removal and administration of amiloride in rabbit proximal colon indicating the presence of functional Na+/H+ exchanger in proximal colonocytes. Furthermore, serosal alkalinization was induced by epinephrine without altering intracellular electrical potential difference in rabbit proximal colon.

The mechanisms that mediate the jejunal absorption of dodecyl sulfate (DS) were analyzed in perfused segment of jejunum isolated from anesthetized rats. Analysis of the steady-state absorption of DS in perfused rodent jejunum indicated the complementary permeation rates of DS across unperturbed and perturbed monolayers. Jejunal absorption of DS also involved a paracellular absorption mechanism in the presence of jejunal net water secretion.

The effects of various dietary sugars on glucose and fructose transport in the intestinal brush borders were analyzed to determine the biochemical function of dietary fructose and GLUT5 fructose transporters. Analysis of intestinal transport in normally weaned rodent pups indicated the role of high-fructose and high-sucrose diets in enhancing messenger RNA (mRNA) levels of GLUT5. However, dietary sugars did not alter SGLT1 Na+-dependent glucose transporter mRNA in the intestinal brush borders.

Mature confluent IEC-6 monolayers derived from rodent proximal small intestines were analyzed to determine the mechanisms that regulate folic acid uptake. Analysis of intestinal folate uptake in IEC-6 cells indicated the presence of a carrier-mediated system that is similar to native small intestine tissue. Furthermore, folic acid uptake by IEC-6 cells was inhibited by the administration of genistein and tyrphostin A25 indicating the role of protein tyrosine kinase in regulating folic acid uptake.

The molecular mechanisms by which dietary potassium depletion and aldosterone increases active absorption were analyzed by rat distal colon and renal tissue. Analysis of rat distal colon and renal tissue during enhanced potassium absorption indicated the role of dietary sodium depletion in stimulating messenger ribonucleic acid production and protein synthesis. Furthermore, the expression of colonic H-K-adenosine triphosphatase in renal tissue was also enhanced by dietary potassium depletion.

The mechanisms of intestinal peptide transport in European yellow eels were analyzed to determine the role of hydrogen-ion concentration (pH) and membrane potential on the kinetic properties of intestinal transport. Analysis of intestinal brush border membrane vesicles (BBMV) from European yellow eels indicated the presence of increased H+-glycyl-L-proline uptake after the application of negative membrane potential. However, the H+-glycyl-L-proline cotransport was inhibited by cephalexin in the BBMV of European yellow eels.

Intestinal transection was conducted in mice with varied dietary nutrient load in the small intestine to determine the relationship between intestinal load and capacity. Sham-operated mice exhibited similar levels of food intake, body mass and glucose uptake capacity compared to normal mice. A fatal deficit in glucose uptake was detected after 70% intestinal resection in mice. However, intestinal resection did not alter the normal mass of the stomach, liver, kidney, heart or spleen of the sham-operated mice.

The intestinal tract of adult chickens was analyzed to determine the kinetics of hexose uptake by utilizing everted sleeves to facilitate diffusion and transport analysis. The absorption of hexose was detected in the duodenum and jejunum of chicken intestinal tract which exhibited high passive permeability. The duodenum contains 38% of the passive components of hexose influx while 9% is found in jejunum and 12% is found in the ileum. Furthermore, the carrier mechanism in the ileum exhibited a higher affinity for sugar uptake.

The effects of hypoxia were analyzed in vivo in rat small intestines to determine alterations in glutathione (GSH) transport and GSH-dependent detoxication. Exposure of rat small intestines to normoxia for eight to 10 days did not alter the GSH-dependent detoxication systems. Furthermore, the synthesis rate of GSH was not affected by hypoxia. However, the GSH transport and uptake activities of rat small intestines decreased causing impaired GSH uptake and peroxidized lipid transepithelial transport.

Sodium/hydrogen (Na+/H+) exchangers (NHE) have been shown to participate in many physiological processes. Several mammalian isoforms of NHE have been identified but their regional distribution in the human intestine has not been characterized. Using ribonuclease protection assays and in situ hybridization, three NHE isoforms were detected in three regions of the intestine. The NHE-1 isoform was present throughout the intestine, NHE-2 was present in the distal colon, proximal colon and throughout the small intestine in decreasing amounts, while NHE-3 was present in high concentration on surface colonocytes in the proximal colon.

Among the components of dietary fiber, the soluble fibers have been found to impair glucose absorption. Little is known, however, about the mechanism of this effect. The direct action of soluble fibers (chicory water-soluble extract and inulin) on the intestinal absorption of glucose was investigated in gut-perfused rats. After equilibrium, both jejunal and ileal segments were simultaneously perfused with an isotonic electrolyte solution (pH 7.4) containing glucose (10 mmol/L) and chicory water-soluble extract (chicory extract) or inulin (10 g/L). Each test or control solution was perfused in random sequence, with perfusion times of 30 min. Chicory extract or inulin in the perfusate (10 g/L) inhibited the absorption of glucose from jejunum (P < 0.05). The observed changes in glucose and water absorption caused by chicory extract or inulin were reversible after switching to a fiber-free perfusate. Additionally, net water absorption changed to secretion upon addition of chicory extract or inulin. These results suggest that the reduction in intestinal absorption of glucose observed after perfusion of chicory extract or inulin may be caused by viscosity-related increases in mucosal unstirred layer thickness. J. Nutr. 126: 2236-2242, 1996. INDEXING KEY WORDS: * glucose uptake * dietary fibers * chicory * inulin * small intestine * rats

Chromium, copper, iron, manganese and zinc levels are highest in children's milk and products packed in glazed ceramic containers. Selenium, copper and iron are also easily absorbable during gastric and intestinal digestion. The presence of high concentrations of zinc, ascorbic acid and some carbohydrates decreases the bioavailability of copper, whereas, the lower levels of these minerals increase its absorption during gastric and intestinal digestion. The absorption level of chromium and manganese after gastric and intestinal digestion is very low.

The effect of dietary iron levels on the hypoxic response of iron absorption was investigated by feeding mice diets of different iron composition and determining iron absorption. Eight groups of mice were fed a purified diet consisting of casein, corn oil and sucrose with vitamins and iron-free mineral supplements. Groups A-D were fed a nonpurified diet until 6 wk old and then switched to purified diet for 4 d. Groups E-H were fed purified diet for 4 wk from weaning. Groups C, D, G and H were exposed to hypoxia (53.3 kPa) for the last 3 d of the study. Groups A, C, E and G received the low iron purified diet ( INDEXING KEY WORDS: mice; iron deficiency; iron; intestinal absorption; dietary iron

Luminal stirring is important in the delivery of solute to the brush border during digestion. Unstirred layers of luminal fluid build up over the mucosa and reduce absorption of the compounds. Herein, luminal stirring in the normal jejunum in patients with celiac disease was investigated. The results showed poor stirring of the luminal fluid in the jejunum. It was concluded that malabsorption associated with celiac disease is due to inefficient luminal stirring which slows down the transport of the absorbed compounds.