Rat Ileal Mucosa Research Articles

Ultrastructural and phenotypical diversity of macrophages in the rat ileal mucosa.

Several types of macrophages have been reported in the intestinal mucosa, but their histological localization remains ambiguous. Here, we obtained detailed information about ultrastructural and phenotypical diversity of macrophage-like cells (MLCs) in the rat ileal mucosa using immunofluorescent analysis and serial block-face scanning electron microscopy (SBF-SEM). The results revealed that the cells immunopositive for CD68, the pan-macrophage marker, included CD163-CD4+, CD163+CD4+, and CD163-CD4- cells in the lamina propria (LP) of the intestinal villus and around the crypt. CD68+CD4+CD163- cells seemed to be preferentially localized in the intestinal villus, whereas CD68+CD163+CD4+ cells were frequently localized around the crypt. SBF-SEM analysis identified three types of MLCs in the ileal mucosa, which were tentatively named types I-III MLC based on aspects of the 3D-ultrastructure, such as the localization, quantity of lysosomes, endoplasmic reticulum, and exoplasm. Type I and II MLCs were localized in the villous LP, while type III MLCs were localized around the crypt, although type II MLCs were a minor population. All three MLC types extended their cellular processes into the epithelium, with type I MLCs showing the greatest abundance of extended processes. Type I MLCs in the upper portion of the intestinal villus showed a higher level of attachment to intraepithelial lymphocytes (IELs) compared to type III MLCs around the crypt. These findings suggest that macrophages of the rat ileal mucosa differed by region along the longitudinal axis of the villous tip-crypt from the perspective of ultrastructure, cellular composition, localization, and interactions with IELs.

Morphological and phenotypical diversity of eosinophils in the rat ileum

Eosinophils are abundantly present in intestinal mucosa. However, the morphological characteristics of their cellular population are still largely unknown. In this study, we examine their characteristics in the rat ileal mucosa using histological and ultrastructural methods. The results indicated that ileal eosinophils could be distinguished into two main groups based on their nuclear shapes and distribution: eosinophils with spheric or reniform nuclei mainly localized in the villous region and eosinophils with annular or bacilliform nuclei as the major population around crypts. Immunohistochemical analysis revealed that all eosinophils in the lamina propria (LP) were immunopositive for CD11b, whereas eosinophils in LP of the intestinal villus but not those in LP around the crypt, were immunopositive for CD11c. Three-dimensional ultrastructural analysis using serial block-face scanning electron microscopy showed that the eosinophils with spheric or reniform nuclei were abundant in the upper portions of the intestinal villus, whereas those with annular nuclei were abundant in the lower portions of the intestinal villus and around crypts. The eosinophils with spheric or reniform nuclei possessed broader cellular bodies with greater abundance of surface projections compared with those with annular nuclei. Eosinophils in the upper portions of intestinal villus frequently extended their cellular bodies into the intraepithelial space. The number of total and eosinophil-specific granules was positively correlated with the minor axis of the nuclear holes in the annular nuclei. These data suggest that ileal eosinophils exhibit not homogenous but rather diverse characteristics, possible due to the mixture of eosinophils at different maturation and/or activation stages.

Three-dimensional analysis of neural connectivity with cells in rat ileal mucosa by serial block-face scanning electron microscopy.

The comprehensive targets of innervation in the intestinal mucosa are unknown, partly because of the diversity of cell types and the complexity of the neural circuits. Herein, we investigated the comprehensive targets of neural connectivity and analyzed the precise characteristics of their contact structures in the mucosa of rat ileum. We examined target cells of neural connections and the characteristics of their contact structures by serial block-face scanning electron microscopy at four portions of the rat ileal mucosa: the apical and basal portions in the villi, and the lateral and basal portions around/in the crypts. Nerve fibers were in contact with several types of fibroblast-like cells (FBLCs), macrophage-like cells, eosinophils, lymphocyte-like cells, and other types of cells. The nerve fibers almost always ran more inside of lamina propria than subepithelial FBLC, and thus contacts with epithelial cells were very scarce. The contact structures of the nerve fibers were usually contained synaptic vesicle-like structures, and we classified them into patterns based on the number of nerve fiber contacting the target cells at one site, the maximum diameter of the contact structures, and the relationship between nerve fibers and nerve bundles. The contact structures for each type of cells occasionally dug into the cellular bodies of the target cells. We revealed the comprehensive targets of neural connectivity based on the characteristics of contact structures, and identified FBLCs, immunocompetent cells, and eosinophils as the candidate targets for innervation in the rat ileal mucosa.

An Assessment of the Permeation Enhancer, 1-phenyl-piperazine (PPZ), on Paracellular Flux Across Rat Intestinal Mucosae in Ussing Chambers.

1-phenyl piperazine (PPZ) emerged from a Caco-2 monolayer screen as having high enhancement potential due to a capacity to increase permeation without significant toxicity. Our aim was to further explore the efficacy and toxicity of PPZ in rat ileal and colonic mucosae in order to assess its true translation potential. Intestinal mucosae were mounted in Ussing chambers and apparent permeability coefficient (Papp) values of [(14)C]-mannitol and FITC-dextran 4kDa (FD-4) and transepithelial electrical resistance (TEER) values were obtained following apical addition of PPZ (0.6-60mM). Exposed issues were assessed for toxicity by histopathology and lactate dehydrogenase (LDH) release. Mucosal recovery after exposure was also assessed using TEER readings. PPZ reversibly increased the Papp of both agents across rat ileal and distal colonic mucosae in concentration-dependent fashion, accompanied by TEER reduction, with acceptable levels of tissue damage. The complex mechanism of tight junction opening was part mediated by myosin light chain kinase, stimulation of transepithelial electrogenic chloride secretion, and involved activation of 5-HT4 receptors. PPZ is an efficacious and benign intestinal permeation enhancer in tissue mucosae. However, its active pharmacology suggest that potential for further development in an oral formulation for poorly permeable molecules will be difficult.

P040 Protein tyrosine phosphate non receptor type 22 regulates muramyl-dipeptide induced effects in human monocytes

microscopy. Rat ileal and colonic mucosae were mounted to Ussing chambers and exposed basolaterally to IL-22. The effect of IL-22 on mobility on intestinal epithelial cells was determined in cell culture-based models for wound-healing as well as epithelial invasion. Epithelial polarity was examined in 3-dimensional Caco-2 cysts, grown in matrigel. Results: IL-22 induced a significant and dose-dependent (1, 10, 100 ng/ml) reduction in Rt in both, Caco-2 and HT-29 cells, which was abolished by inhibition of PI-3 kinase and MAP kinase, but not by STAT inhibitors. Paracellular passage of biotin was elevated accordingly. In IL-22 treated rat ileum and colon complex changes including the subepithelial layer were found, indicating either protective or pro-inflammatory changes according to the concentration used. Preliminary data revealed a dose dependent reduction of the mucosal surface area in ileal and colonic specimen. IL-22-mediated epithelial wound healing was confirmed in the HT-29 model. Furthermore, epithelial invasion was dramatically increased in IL-22-treated intestinal epithelial cells. On the other hand, epithelial apoptosis was also modestly increased. The TJ proteins ZO-1 and JAM-A localized to intracellular pools and not to TJs. Caco-2 matrigel cysts displayed an increase in multiple lumen, atypical mitoses and basal actin protrusions. Conclusions: By reducing epithelial polarity, IL-22 reprograms intestinal epithelia to gain migratory/invasive properties and at the same time to lose barrier properties. This has implications not only for wound healing but also for inflammation-associated carcinogenesis.

Increased prokineticin 2 expression in gut inflammation: role in visceral pain and intestinal ion transport

Prokineticin 2 (PROK2) is an inflammatory cytokine-like molecule expressed predominantly by macrophages and neutrophils infiltrating sites of tissue damage. Given the established role of prokineticin signaling on gastrointestinal function, we have explored Prok2 gene expression in inflammatory conditions of the gastrointestinal tract and assessed the possible consequences on gut physiology. Prokineticin expression was examined in normal and colitic tissues using qPCR and immunohistochemistry. Functional responses to PROK2 were studied using calcium imaging and a novel antagonist, Compound 3, used to determine the role of PROK2 and prokineticin receptors in inflammatory visceral pain and ion transport. Prok2 gene expression was up-regulated in biopsy samples from ulcerative colitis patients, and similar elevations were observed in rodent models of inflammatory colitis. Prokineticin receptor 1 (PKR1) was localized to the enteric neurons and extrinsic sensory neurons, whereas Pkr2 expression was restricted to sensory ganglia. In rats, PROK2-increased intracellular calcium levels in cultured enteric and dorsal root ganglia neurons, which was blocked by Compound 3. Moreover, PROK2 acting at prokineticin receptors stimulated intrinsic neuronally mediated ion transport in rat ileal mucosa. In vivo, Compound 3 reversed intracolonic mustard oil-induced referred allodynia and TNBS-induced visceral hypersensitivity, but not non-inflammatory, stress-induced visceral pain. Elevated Prok2 levels, as a consequence of gastrointestinal tract inflammation, induce visceral pain via prokineticin receptors. This observation, together with the finding that PROK2 can modulate intestinal ion transport, raises the possibility that inhibitors of PROK2 signaling may have clinical utility in gastrointestinal disorders, such as irritable bowel syndrome and inflammatory bowel disease.

High content analysis of cytotoxic effects of pDMAEMA on human intestinal epithelial and monocyte cultures

Poly(2-(dimethylamino ethyl)methacrylate) (pDMAEMA) is a cationic polymer with potential as an antimicrobial agent and as a non-viral gene delivery vector. The aim was to further elucidate the cytotoxicity of a selected pDMAEMA low molecular weight (MW) polymer against human U937 monocytes and Caco-2 intestinal epithelial cells using a novel multi-parameter high content analysis (HCA) assay and to investigate histological effects on isolated rat intestinal mucosae. Seven parameters of cytotoxicity were measured: nuclear intensity (NI), nuclear area (NA), intracellular calcium ([Ca 2+]i), mitochondrial membrane potential (MMP), plasma membrane permeability (PMP), cell number (CN) and phospholipidosis. Histological effects of pDMAEMA on excised rat ileal and colonic mucosae were investigated in Ussing chambers. Following 24–72 h exposure, 25–50 µg/ml pDMAEMA induced necrosis in U937 cells, while 100–250 µg/ml induced apoptosis in Caco-2. pDMAEMA increased NA and NI and decreased [Ca 2+]i, PMP, MMP and CN in U937 cells. In Caco-2, it increased NI and [Ca 2+]i, but decreased NA, PMP, MMP and CN. Phospholipidosis was not observed in either cell line. pDMAEMA (10 mg/ml) did not induce any histological damage on rat colonic tissue and only mild damage to ileal tissue following exposure for 60 min. In conclusion, HCA reveals that pDMAEMA induces cytotoxicity in different ways on different cell types at different concentrations. HCA has potential for high throughput toxicity screening in drug formulation programmes.

Role of P-Glycoprotein and the Intestine in the Excretion of DPC 333 [(2R)-2-{(3R)-3-Amino-3-[4-(2-methylquinolin-4-ylmethoxy)phenyl]-2-oxopyrrolidin-1-yl}-N-hydroxy-4-methylpentanamide] in Rodents

The role of the intestine in the elimination of (2R)-2-{(3R)-3-amino-3-[4-(2-methylquinolin-4-ylmethoxy)phenyl]-2-oxopyrrolidin-1-yl}-N-hydroxy-4-methylpentanamide (DPC 333), a potent inhibitor of tissue necrosis factor alpha-converting enzyme, was investigated in mice and rats in vivo and in vitro. In Madine-Darby canine kidney cells stably transfected with P-glycoprotein (P-gp) and DPC 333, the transport from B-->A reservoirs exceeded the transport from A-->B by approximately 7-fold. In Caco-2 monolayers and isolated rat ileal mucosa, DPC 333 was transported from basolateral to apical reservoirs in a concentration-dependent, saturable manner, and transport was blocked by N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide (GF120918), confirming the contribution of P-gp/breast cancer resistance protein in B-->A efflux of DPC 333. In quantitative whole body autoradiography studies with [(14)C]DPC 333 in mice and rats, radioactivity was distributed throughout the small intestine in both species. In GF120918-pretreated bile duct-cannulated rats, radioactivity in feces was reduced 60%. Using the in situ perfused rat intestine model, approximately 20% of an i.v. dose of [(14)C]DPC 333 was measured in the intestinal lumen within 3 h postdose, 12% as parent. Kinetic analysis of data suggested that excreted DPC 333 may be further metabolized in the gut. Intestinal clearance was 0.2 to 0.35 l/h/kg. The above data suggest that in the rodent the intestine serves as an organ of DPC 333 excretion, mediated in part by the transporter P-gp.

In vitro Interactions Between the Oral Absorption Promoter, Sodium Caprate (C10) and S. typhimurium in Rat Intestinal Ileal Mucosae

The medium chain fatty acid, sodium caprate (C(10)), is a promising oral drug delivery agent that may promote permeability of peptides through increasing paracellular permeability of the intestinal epithelium. One safety concern is that it may permit co-absorption of by-stander agents including pathogens. The purpose of this in vitro study was to examine the effects of C(10) on rat intestinal ileal mucosae in the presence of co-administered Salmonella typhimurium in a low volume vertical Ussing chamber. C(10) or S. typhimurium was added to rat ileal mucosae mounted in chambers and the flux of the paracellular flux of [(14)C]-mannitol examined. S. typhimurium adherence and uptake by ileal mucosae was also examined by counting. Bacterial growth curves were assessed in the presence of C(10). Minimum inhibitory- and bacteriocidal concentrations of C(10) were determined against a range of bacteria. Apical addition of either C(10) or S. typhimurium to rat ileal mucosae mounted in modified diffusion chambers significantly increased the flux of [(14)C]-mannitol in a concentration-dependent fashion. Co-exposure with increasing concentrations of C(10) attenuated the Salmonella-induced increase in mannitol flux. Histological evaluation revealed that C(10) inhibited both adhesion and invasion of S. typhimurium to intestinal mucosae. Short term bacterial growth studies in the presence of C(10) showed evidence of concentration-dependent inhibition. C(10) was bacteriocidal in mM concentrations against S. typhimurium and selected gram positive and negative bacteria. C(10) does not promote the permeation of a common bacterium across isolated intestinal tissue upon acute co-exposure. It prevents S. typhimurium attachment to epithelia and impedes growth of a range of different bacterial strains.

High‐Resolution Intravital NADH Fluorescence Microscopy Allows Measurements of Tissue Bioenergetics in Rat Ileal Mucosa

NADH fluorescence microscopy has been used as an index of the metabolic state of tissue but is associated with various obstacles such as low spatial resolution and quenching effects of blood pigments that prevent reliable monitoring of tissue bioenergetics. The objective of this study was to develop a system to monitor tissue bioenergetics in vivo using NADH fluorescence microscopy in the rat ileal mucosa. Using an inverted microscope with an epifluorescence unit and an intensified charge-coupled device camera, NADH fluorescence images were visualized. Fluorescence intensity was measured of beta-NADH solutions at varying concentration (n = 6) and pH (n = 3) and in ex vivo (n = 6) and in vivo (n = 6) preparations of ileal mucosa of Sprague-Dawley rats anesthetized with isoflurane. Intravital fluorescence microscopy reveals a map of the microcirculation that permits visualization of NADH fluorescence and intercapillary areas. The system was adjusted so a linear relationship between physiological concentrations of beta-NADH and fluorescence was achieved (r(2) = 0.98, p < .0001). Decreasing the pH of the solution had no effect on fluorescence intensity and fluorescence intensity in an anoxic ex vivo ileal segment was similar to that of the in vivo ileum after ischemia. Ischemia also resulted in spatial heterogeneity that was abolished by the addition of a 550-nm LP filter. With this system, intravital NADH fluorescence microscopy provides the high resolution necessary to reliably monitor tissue bioenergetics in the rat ileal mucosa.

Tissue Bioenergetics and Microvascular Perfusion Are Impaired in Rat Ileal Mucosa in Normotensive Sepsis

Sepsis is a systemic inflammatory response to a bacterial infection. Inflammation may result in injury to the small bowel and an increase in translocation of bacteria and toxins across the mucosal barrier, which may contribute to the progression of sepsis. Microcirculatory perfusion or cytopathic hypoxia may cause impairment of tissue bioenergetics and injury in sepsis. The objective of this study was to determine if sepsis is associated with microcirculatory hypoperfusion and impaired tissue bioenergetics in the ileal mucosa. Sprague-Dawley rats were randomized to cecal ligation and perforation (sepsis group, n = 12) or control group (n = 14) and received arterial and venous catheters and fluid resuscitation. Following 24 h, rats were anesthetized with isoflurane and the ileum was prepared for intravital microscopy. Images of NADH fluorescence, which is an index of tissue bioenergetics, central arterial diameter, red cell velocity, red cell flux, and average intercapillary area, were recorded in 6-9 villi in each rat. Central arterial red cell flux (control 277 +/- 30 cell/s, sepsis 108 +/- 13 cells/s, p < .05), diameter (control 10.4 +/- 0.4 microm, sepsis 8.2 +/- 0.3 microm, p < .05) and red cell velocity (control 590 +/- 47 microm/s, sepsis 449 +/- 63 microm/s, p < .05) were decreased while average intercapillary area (control 815 +/- 171 microm(2), sepsis 1412 +/- 364 microm(2), p < .05) and NADH fluorescence (control 116 +/- 6 AIU, sepsis 154 +/- 9 AIU, p < .05) were increased at the villus tip in the sepsis group. Sepsis is associated with bioenergetic impairment and capillary hypoperfusion at the villus tip and a decrease in red cell flux in the central arteriole.

Luminal Regulation of Na +/H + Exchanger Gene Expression in Rat Ileal Mucosa

It is well recognized that ileostomy patients suffer from chronic depletion of Na + through the stoma effluent. In this study we evaluated the effects of ileostomy on messenger RNA levels that encode different Na +/H + exchanger isoforms (NHE-2 and NHE-3). Loop ileostomies were created in Sprague-Dawley rats. Segments of diverted ileum were harvested for quantitation of mRNA levels encoding these isoforms and the Na +/K + ATPase in mucosal scrapings and for immunofluorescence microscopy, specifically of the NHE-3 protein. Our studies indicate that as early as 8 days after diversion, NHE-3 gene expression is selectively attenuated in poststomal ileal mucosa. Mucosal morphology remains undisturbed, and the distribution of protein expression along the crypt/villus axis is not altered. Infusion of Na + or the enterocyte nutrient, glutamine, into the lumen of the diverted segment restores or even augments mRNA levels for NHE-3, again without altering the histologic appearance or distribution of the protein along the crypt/villus axis. These effects are specific because nonpolar osmolytes (mannitol) and related organic nutrients not specific for the enterocyte (i.e., butyrate) have no effect on mRNA levels of NHE-3. Further work is required to understand how the early changes in mRNA contribute to mucosal function and response to luminal diversion. ( J Gastrointest Surg 2002;6:387–395.)

Luminal regulation of Na+/H+ exchanger (NHE) gene expression in rat ileal mucosa

Luminal regulation of Na+/H+ exchanger (NHE) gene expression in rat ileal mucosa

Luminal regulation of Na+/H+ exchanger (NHE) gene expression in rat ileal mucosa

Luminal regulation of Na+/H+ exchanger (NHE) gene expression in rat ileal mucosa

Paracellular drug transport across intestinal epithelia: influence of charge and induced water flux

The influence of drug charge and transepithelial water flux on passive paracellular drug transport was investigated in Caco-2 cell monolayers and rat ileal mucosa in vitro. Three small hydrophilic compounds with different net charges (creatinine, erythritol and foscarnet) were used as model drugs. A hypotonic glucose-rich solution was applied apically to induce epithelial absorption of water. In the Caco-2 monolayers, permeability to creatinine (positively charged) was 25-fold greater than to foscarnet (negatively charged), indicating a pronounced cation selective paracellular permeability. During apical exposure to the hypotonic glucose-rich solution, transport of all model drugs increased in both the absorptive and secretory directions. This enhanced transport coincided with a decrease in transepithelial resistance. Further, fluorescence and transmission electron microscopy indicated dilatations of the paracellular spaces but no damage to the cell membranes. These findings suggested that the enhancement in drug transport was attributable to increased paracellular tight junction permeability rather than to “solvent drag”. In the ileal segments, mucosal exposure to the hypotonic glucose-rich solution had no effect on transepithelial resistance and only a marginal increase in drug transport was observed. Taken together, the modest absorption enhancement demonstrated in the in vitro models agrees with results obtained in vivo, supporting the conclusion that a more pronounced disruption of the tight junction barrier than that obtained through stimulation of epithelial absorption of water is required for efficient enhancement of paracellular intestinal drug absorption.

Pure endotoxin does not pass across the intestinal epithelium in vitro.

Numerous reports suggest that endotoxin (LPS) may play a central role in triggering the inflammatory cascade that leads to the systemic inflammatory response syndrome. Although conditions that promote bacterial translocation in vivo may also facilitate direct translocation of LPS, the exact mechanisms by which LPS crosses the intestinal barrier to reach the systemic circulation are unknown. This study was designed to determine whether pure endotoxin could pass across injured rat ileal mucosa in the Ussing chamber. Sprague-Dawley rats were subjected to mild or severe hemorrhagic shock following carotid artery cannulation, and then resuscitated. Control animals underwent carotid artery cannulation only (sham-shock). Bacterial translocation to the mesenteric lymph nodes, liver, or spleen was measured after 24 h. Transmucosal passage of fluorescein isothiocyanate (FITC)-labeled E. coli C-25, or FITC-conjugated LPS was measured in the Ussing chamber. Intestinal membranes were examined by light and confocal laser microscopy. Severe hemorrhagic shock resulted in a 60% mortality rate and a 100% incidence of bacterial translocation in surviving animals. Sham-shock rats had a 100% survival rate and a 33% incidence of bacterial translocation. Transmucosal passage of FITC-E. coli C-25 was similar in both groups; however, passage of FITC-LPS was never detected. Histologic analysis confirmed mucosal injury to the intestinal epithelium of rats subjected to severe hemorrhagic shock, and confocal laser microscopy demonstrated passage of FITC-E. coil C-25, but not of FITC-LPS across the ileal membranes. Disruption of the intestinal epithelium with a potent mucolytic agent did not result in significant increase in transmucosal passage of FITC-LPS. We conclude that pure LPS does not pass across the intestinal mucosa in vitro. Transmucosal passage of LPS in vivo may be due, at least in part, to the release of bacterial cell wall fragments containing LPS from killed bacteria that had previously translocated.

Keratinocyte growth factor (KGF) and nutritional status regulate glutathione redox state in rat jejunal and ileal mucosa

Keratinocyte growth factor (KGF) and nutritional status regulate glutathione redox state in rat jejunal and ileal mucosa

Characterization of adenosine receptors on rat ileum, ileal longitudinal muscle and muscularis mucosae

Adenosine receptors were studied in isolated rat ileum, ileal longitudinal muscle and muscularis mucosae, using a range of agonists and an antagonist. In the rat ileal longitudinal muscle adenosine receptor agonists relaxed the tissues. N 6-cyclopentyladenosine (CPA) was more potent than 5′- N-ethylcarboxamidoadenosine (NECA) or adenosine and 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) (1 nM) gave a 5-fold parallel shift to the right of the concentration–response curves to both CPA and NECA corresponding to an apparent p A 2 value of 9.6 suggesting that the agonists relax via adenosine A 1 receptors. In the intact ileum adenosine receptor agonists also relaxed the tissue but NECA and CPA were equipotent. DPCPX (3 nM) however inhibited responses to both CPA and NECA with dose-ratios of 8 and 15.6, corresponding to p A 2 values of 9.3 and 9.7, respectively. DPCPX (300 nM) gave a much greater shift to the right of the concentration–response curve to NECA with a dose-ratio of 769, corresponding to an apparent p A 2 of 9.4. This suggests that the agonists are acting at adenosine A 1 receptors to cause relaxation of the whole tissue. Adenosine receptor agonists contracted rat ileal muscularis mucosae with a potency order indicative of an A 1 adenosine receptor. DPCPX (3–100 nM) antagonized responses to CPA giving a linear Schild plot with a slope close to unity and a p A 2 of 8.4 suggesting an action on adenosine A 1 receptors.

Measurement of ileal permeability with different-sized polyethylene glycols (PEG 400, 600, and 1000)

Polyethylene glycols (PEGs; 400, 600, and 1000) were used to study the molecular weight (MW) permeability dependence in the rat ileal mucosa. Absorption of the PEGs was measured by following their recirculation perfusion over a 3 hr collection period. HPLC methods were used to separate and quantitate the individual oligomers present in the solution of PEGs mixtures (MW range 330 to 1122 D). In the range studied, a distinct molecular weight cutoff was not identified. Corrected for the length of ileum used in the study, over the molecular weight range 330 to 1122 D, the apparent permeability (Papp) of PEG ranged from 3.2±0.06×10−5 cm/sec (mean±SEM, n=7) to 0.1±0.02×10−5 cm/sec. Also, it was observed that the apparent permeability was inversely proportional to approximately MW2.4.

In vivo and in vitro effects of human growth hormone on rat intestinal ion transport.

It has been reported that: 1) ovine growth hormone stimulates intestinal water, sodium, and chloride absorption and 2) specific growth hormone receptors are present in the rat intestine. Aims of this work were to investigate the effects of acute administration of hGH on water and ion transport in the rat ileum in vivo and in vitro. In vivo, the absorption rates of water, sodium, chloride, and potassium were determined in the rat perfused ileum, during a basal period and after i.v. administration of 6 micrograms/kg recombinant DNA-derived hGH. In vitro, electrical parameters were measured before and after the hormone addition to the mucosal or the serosal side of rat ileal mucosa mounted in Ussing chambers. In vivo, growth hormone induced a rapid increase in the absorption rates of water, sodium, chloride, and potassium. In vitro, the serosal, but not the mucosal, addition of growth hormone induced a rapid decrease of transepithelial potential difference and of short-circuit current. The effect was time- and dose-dependent, saturable, but not reversible in the short time. The electrical effect was abolished in the absence of chloride, indicating that it was related, at least in part, to inhibition of basal active chloride secretion. Growth hormone also reduced the short-circuit current increase induced by the secretagogues Escherichia coli heat-stable enterotoxin, theophylline, and calcium ionophore A23187. These results indicate that hGH has a rapid absorptive effect that is related, at least in part, to a direct intestinal antisecretory mechanism. It also reduces active intestinal secretion induced by various secretagogues.