bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical properties and sensitivity to CCK of vagal gastric slowly adapting mechanoreceptors
Authors: Davison J. S. , Clarke G. D.
Published: December 2017

Sixty single afferent fibers with endings in the stomach wall were isolated from the cervical vagus of urethan-anesthetized Sprague-Dawley rats. All the fibers, most of which were spontaneously active, increased their discharge after gastric distension or during spontaneous contractions of the stomach. Because of this and the characteristic dynamic and static features of their response to inflation and deflation, they were identified as in-series tension receptors. Certain features of their responses, previously suspected from studies on reflex modulation of vagal efferent fibers or brain stem neurons, were directly confirmed. These included a broad range of mechanical thresholds and spontaneous firing frequencies that were correlated and a sensitivity only to dynamic stretch and active contraction in the highest threshold endings. The tension receptors could also be activated by circulating cholecystokinin, an effect unrelated to changes in intraluminal pressure and hence gastric wall tension, suggesting that there may be humoral modulation of visceral sensory signals that might be relevant to several behavioral situations, such as food intake regulation.
Agonist-sensitive calcium pool in the pancreatic acinar cell. II. Characterization of reloading
Authors: Muallem S. , Schoeffield M. S. , Fimmel C. J. , Pandol S. J.
Published: December 2017

45Ca2+ fluxes and free cytosolic Ca2+ measurements in guinea pig pancreatic acini indicated that after agonist stimulation and the release of Ca2+ from the agonist-sensitive pool at least part of the Ca2+ is extruded from the cell, resulting in 45Ca2+ efflux. In the continued presence of agonist, the pool remains permeable to Ca2+ but partially refills with Ca2+. This reloading is dependent on the concentration of extracellular Ca2+. In the absence of extracellular Ca2+, the pool is completely depleted of Ca2+. However, with increasing concentrations of CaCl2 in the incubation solution (from 0.5 to 2.0 mM) there is increasing repletion of the pool with Ca2+ during agonist stimulation. With termination of agonist stimulation, the Ca2+ permeability of the agonist-sensitive pool is rapidly reduced to that measured in the unstimulated cell. As a result, the Ca2+ incorporated into the pool during the stimulation period is rapidly trapped within the pool and exchanges poorly with medium Ca2+. Subsequently, the pool completely refills with Ca2+. The rate of Ca2+ reloading at the termination of agonist stimulation is slower than the conversion of the pool to the impermeable state. In incubation media containing 1.3 mM CaCl2, the half-time for reloading at the termination of stimulation is 5 min. These observations demonstrate the characteristics of Ca2+ reloading of the agonist-sensitive pool both during stimulation and at the termination of stimulation.
Cholecystokinin inhibits gastric motility and emptying via a capsaicin-sensitive vagal pathway in rats
Authors: Raybould H. E. , Tache Y.
Published: December 2017

The pathway by which cholecystokinin octapeptide (CCK-8) inhibits motility of the proximal stomach and the role of this pathway in the CCK-induced delay in gastric emptying of a liquid meal has been studied in rats by selective destruction of vagal afferent C-fibers using bilateral perineural application of the sensory neurotoxin, capsaicin, 3 or 4 days prior to the experiment. The capsaicin treatment significantly attenuated the decrease in intragastric pressure in urethan-anesthetized rats in response to CCK-8 (0.1-100 pmol iv) compared with vehicle-treated controls. Removal of the celiac-superior mesenteric ganglion completely abolished the inhibitory action of CCK-8 on gastric motility in these rats. In contrast, only celiac ganglionectomy in combination with vagotomy abolished the CCK-8 effect in vehicle-treated controls. Intravenous injection of CCK-8 (300 pmol) 5 min before intragastric administration of a methylcellulose solution decreased gastric emptying by 55% in conscious control or vehicle-treated rats. Perivagal capsaicin treatment abolished the delay in gastric emptying induced by CCK-8. In addition, capsaicin treatment alone significantly increased gastric emptying. These results demonstrate that CCK-8 decreases gastric motility in the gastric corpus and delays gastric emptying by a capsaicin-sensitive vagal afferent pathway. These same afferent fibers may also play a physiological role in the gastric emptying of liquids.
Electrolyte transport in distal colon of sodium-depleted rats: effect of sodium repletion
Authors: Turnamian S. G. , Binder H. J.
Published: December 2017

Dietary sodium depletion increases plasma aldosterone level and, as a result, induces amiloride-sensitive electrogenic sodium absorption and electrogenic potassium secretion and stimulates Na+-K+-ATPase activity in rat distal colon, while inhibiting electroneutral sodium chloride absorption. To assess the events that occur as the aldosterone-stimulated colon reverts to normal, unidirectional 22Na and 36Cl fluxes were measured under voltage-clamp conditions across isolated distal colonic mucosa of rats that were initially dietary sodium depleted for 7 days and then sodium repleted for varying periods of time before the study. Within 8 h of dietary sodium repletion, plasma aldosterone level and Na+-K+-ATPase activity declined to normal, amiloride-sensitive electrogenic sodium absorption decreased by greater than 90%, and active electrogenic potassium secretion also decreased markedly. In contrast, electroneutral sodium chloride absorption did not completely return to levels seen in normal animals until approximately 64-88 h. These results demonstrate that maintenance of electrogenic sodium absorption and potassium secretion are directly dependent on elevated plasma aldosterone levels. The inhibition of electroneutral sodium absorption, although initiated by excess aldosterone, persists after normalization of the plasma aldosterone level, thereby implying that the inhibition is dependent on additional factor(s).
Effect of bile acid hydroxylation on biliary protoporphyrin excretion in rat liver
Authors: Berenson M. M. , Garcia Marin J. J. , Gunther C.
Published: December 2017

The relationships between bile acid structure, protoporphyrin load, and biliary protoporphyrin excretion were studied in rat livers perfused with 0 or 0.7 mumol/min taurocholate and protoporphyrin loads between 350 and 35,525 nmol. Bile acid treatment increased the excretion of extracted protoporphyrin from 0.4 to 28%, the maximal biliary protoporphyrin concentration 32-fold, the protoporphyrin excretion rate approximately 150-fold, and the coupling of excreted protoporphyrin to bile acid. Infusions (0.7 mumol/min) of bile acids differing in structure with 1,500 nmol protoporphyrin all significantly increased protoporphyrin excretion but ursodeoxycholate and tauroursodeoxycholate did so less than others. Infusions (0.175-1.4 mumol/min) of taurocholate, deoxycholate, ursodeoxycholate, and chenodeoxycholate confirmed that protoporphyrin excretion increased significantly more with taurocholate or deoxycholate than chenodeoxycholate and chenodeoxycholate more than ursodeoxycholate. The relative ineffectiveness of dihydroxylated bile acids with a hydroxy group at the seven position (alpha- or beta-configuration) was not correlated with physicochemical parameters of the bile acids and remains unexplained. The findings suggest that ursodeoxycholate is the least acceptable bile acid to consider as a potential treatment for protoporphyria.
Topography and measurement of pyloric pressure waves and tone in humans
Authors: Heddle R. , Dent J. , Toouli J. , Read N. W.
Published: December 2017

The topography of human pyloric pressure is ill defined, and previous studies of pyloric motility in humans have given conflicting results. A detailed profile of pyloric pressure has been recorded in seven healthy volunteers using a manometric assembly with 13 side holes spaced at 3-mm intervals on reverse aspect of a 3.5-cm long sleeve sensor. After a fasting control period of 40 min, recordings were made for 40 min during intraduodenal infusion of a lipid emulsion. Two major patterns of pressure waves were seen during the fasting control period, namely pressure waves confined to a narrow pyloric zone (isolated pyloric pressure waves) and pressure waves that were less localized and involved the antrum and/or duodenum. During lipid infusion the motility pattern was dominated by isolated pyloric pressure waves and localized pyloric tone. Ninety-two percent of the isolated pyloric pressure waves recorded by the sleeve were recorded by only one or two side holes, consistent with a phasically active zone less than 9 mm in length. Pyloric tone was confined to an even narrower zone and was most often recorded by only one side hole. When both tone and isolated pyloric pressure waves occurred together, they were recorded by the same side holes. By comparison with the side holes, the sleeve recorded 89% of isolated pyloric pressure waves and 98% of nonlocalized waves and recorded pyloric tone with a moderate sensitivity but high specificity. The technical challenge of recording localized pyloric contraction is considerable, and much of the conflict between previous studies of the human pylorus is explicable on methodological grounds.(ABSTRACT TRUNCATED AT 250 WORDS)
Functional gradients in muscle cells isolated from gallbladder, cystic duct, and common bile duct
Authors: Severi C. , Grider J. R. , Makhlouf G. M.
Published: December 2017

The existence of a gradient inherent to muscle cells of the biliary tract was examined in muscle cells isolated separately from the fundus of the gallbladder, cystic duct, and common bile duct of the dog. Muscle cells, measured in suspension or as single perfused cells, exhibited a proximal-to-distal gradient expressed by the magnitude of response and the sensitivity to hormonal cholecystokinin octapeptide and neural (acetylcholine and methionine-enkephalin) contractile agonists. Measurements in suspensions showed that cells from the fundus 1) were 7-40 times more sensitive to contractile agonists than cells from the cystic duct and 13-200 times more sensitive than cells from the common bile duct and 2) generated greater maximal contraction. The latter was expressed by the ratio of maximal responses (fundus: cystic duct cells, 1.90 +/- 0.12, P less than 0.001; fundus: common bile duct cells, 1.50 +/- 0.07 P less than 0.001), which was independent of sensitivity to agonists. Similar results were obtained in measurements on single cells with respect to relative sensitivity and to ratio of maximal responses (fundus: cystic duct cells, 1.80 +/- 0.08, P less than 0.001; fundus: common bile duct cells, 1.49 +/- 0.06, P less than 0.001). The ratio of responses to low concentrations of agonists was even higher (three- to fourfold), reflecting both the greater sensitivity and the greater contraction of muscle cells of the fundus. We conclude that a proximal-to-distal biliary gradient exists that is an inherent property of muscle cells from various regions of the biliary tract; the gradient would act to facilitate gallbladder emptying in response to hormonal and neural stimulation.
Antigen-induced contraction of jejunal smooth muscle in the sensitized rat
Authors: Vermillion D. L. , Ernst P. B. , Scicchitano R. , Collins S. M.
Published: December 2017

We examined contractility of longitudinal muscle strips of jejunum from control rats and rats infected 34-85 days previously with Trichinella spiralis. Antigen prepared from T. spiralis larvae contracted muscle from previously infected but not control rats. Contraction was specific for the sensitizing agent because antigen from Nippostrongylus brasiliensis did not induce contraction. Contraction was resistant to atropine or tetrodotoxin but was inhibited by the 5-hydroxytryptamine (5-HT) antagonist cyproheptadine and by 5-HT desensitization. Neither histamine antagonists, diphenhydramine (H1-receptor antagonist) or ranitidine (H2-receptor antagonist), nor indomethacin, a prostaglandin synthase inhibitor, influenced the antigen response. In Trichinella-infected rats there was a significant increase in mast cell number in the muscle layers, and the contraction induced by T. spiralis antigen was inhibited by the mast cell stabilizer doxantrazole. In addition, anti-rat immunoglobulin E serum, compound 48/80, and concanavalin A each contracted muscles from rats previously infected with T. spiralis. These results are consistent with the hypothesis that T. spiralis infection leads to mast cell proliferation in the muscle layers and that subsequent exposure to antigen results in mast cell degranulation, 5-HT release, and contraction of smooth muscle.
Effect of immunization with prostaglandin metabolites on gastrointestinal ulceration
Authors: Redfern J. S. , Lee E. , Feldman M.
Published: December 2017

Active immunization of rabbits with a 6-ketoprostaglandin F1 alpha-thyroglobulin conjugate induced gastrointestinal ulceration, whereas active immunization of rabbits with 13,14-dihydro-15-keto prostaglandin E2-thyroglobulin conjugate or with thyroglobulin alone did not result in ulceration. Passive immunization of a separate group of rabbits with 6-ketoprostaglandin F1 alpha-hyperimmune plasma, obtained from actively 6-ketoprostaglandin F1 alpha-immunized donor rabbits that had ulcers, induced gastric ulceration within 9 days, whereas passive immunization of rabbits with control plasma, obtained from donor rabbits actively immunized with thyroglobulin alone, did not induce ulceration. Ulcerogenic donor plasma containing antibody to 6-ketoprostaglandin F1 alpha neutralized the inhibitory actions of prostacyclin on adenosine diphosphate-induced platelet aggregation, indicating that this antibody cross-reacted with prostacyclin. In contrast, plasma containing antibodies to 13,14-dihydro-15-ketoprostaglandin E2 cross-reacted only slightly with prostaglandin E2. Thus antibodies to inactive metabolites of prostaglandins induce ulceration only if these antibodies cross-react with an endogenous, "cytoprotective" prostaglandin.
Effect of prostaglandin E2 on rabbit colonic smooth muscle cell contraction
Authors: Kao H. W. , Hyman P. E. , Finn S. E. , Snape W. J.
Published: December 2017

Isolated circular smooth muscle cells from the rabbit distal colon were used to study the effect of prostaglandin E2 (PGE2) on bethanechol-stimulated smooth muscle cell contraction. Contraction was expressed as the percentage decrease in mean cell length compared with unstimulated cells. Incubation with different concentrations of PGE2 (10(-10)-10(-6) M) did not cause contraction or relaxation of unstimulated smooth muscle cells. Bethanechol stimulated a dose-dependent contraction that was maximal at 30 s. The threshold for bethanechol-stimulated contraction was 10(-11) M; the ED50 was 10(-10) M; and the maximum contraction (23.0 +/- 1.8%) occurred at 10(-8) M. Preincubation with PGE2 reduced both the efficacy and potency of bethanechol-stimulated contraction. Preincubation with 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP) or dibutyryl-cAMP reduced the efficacy of bethanechol-stimulated contraction without affecting potency. Increasing concentrations of PGE2 stimulated a dose-dependent increase in the production of intracellular cAMP (P less than 0.05). These studies show that PGE2 inhibits bethanechol-stimulated contraction of isolated colonic circular myocytes and is associated with increased production of intracellular cAMP. There is also a cAMP-independent effect of PGE2 on the potency of bethanechol stimulation.
Zinc absorption in human small intestine
Authors: Lee H. H. , Prasad A. S. , Brewer G. J. , Owyang C.
Published: December 2017

We determined the intestinal site of zinc absorption in humans and investigated the interaction between intestinal absorption of zinc and other solutes using the triple-lumen steady-state perfusion technique. Twenty-one healthy subjects participated in the study. During intestinal perfusion of a balanced electrolyte solution containing 0.1 mM zinc acetate, zinc absorption occurred throughout the entire small intestine. However, the jejunum had the highest rate of absorption (357 +/- 14 nM.min-1.40 cm-1) compared with the duodenum (230 +/- 33 nM.min-1.40 cm-1) and ileum (84 +/- 10 nM.min-1.40 cm-1). Over a range of zinc concentrations infused into the jejunum (0.1, 0.9, and 1.8 mM) there were linear increases in the rate of zinc absorption (P less than 0.05). Intestinal absorption of zinc was significantly stimulated by the addition of glucose (20 mM). Zinc absorption increased from 459 +/- 39 to 582 +/- 45 nM.min-1.40 cm-1 (P less than 0.05). Conversely, zinc (0.9 mM) also enhanced the absorption of glucose, which was increased from 293 +/- 43 to 447 +/- 27 microM.min-1.40 cm-1 (P less than 0.05). The enhanced absorption of zinc or glucose was not accompanied by any increase in absorption of water and sodium. In contrast, increasing the concentration of zinc in the perfusate resulted in decreased absorption of sodium and water in a dose-related manner. In conclusion, our study demonstrated that zinc absorption is concentration dependent and occurs throughout the small intestine. The jejunum has the highest rate of absorption of zinc. The interactions between absorption of zinc and other solutes suggest that the transport process of zinc is carrier mediated.
Polyamine-dependent growth and calmodulin-regulated induction of ornithine decarboxylase
Authors: Ginty D. D. , Seidel E. R.
Published: December 2017

The proliferation of cultured gastrointestinal crypt epithelial cells (IEC-6) and the role of calcium in polyamine biosynthesis were examined after serum stimulation of quiescent cells. Ornithine decarboxylase (ODC) activity was high when cells grew in 5% fetal calf serum (FCS) and dropped to nearly nondetectable levels when cells reached contact inhibition of growth. Polyamines appeared to be necessary for the proliferation of these cells, as growth was completely inhibited by the addition of 5 mM difluoromethylornithine, a specific inhibitor of ODC, to the media. This effect was reversed by 10 microM putrescine. Serum deprivation of preconfluent cells resulted in a fall in ODC activity. Readdition of serum led to an increase in ODC activity, which peaked at 4 h after addition and preceded both putrescine accumulation and [3H]thymidine incorporation into acid-precipitable material. Furthermore, readdition of serum to serum-deprived cells resulted in an approximately twofold increase in the level of free, ionized, intracellular Ca2+ as measured spectrophotometrically by monitoring fura-2 fluorescence. Inhibition of calmodulin-mediated processes with N-(6-aminohexyl)-5-chloro-1-naphthalelesulfonamide (W-7), a calmodulin antagonist, inhibited the serum-stimulated induction of ODC in a dose-dependent manner, with an IC50 of approximately 10 microM. Similar results were obtained with trifluoperazine. Lastly, 30 microM W-7 completely inhibited serum-stimulated [3H]thymidine incorporation into acid-precipitable material. These data demonstrate that polyamine biosynthesis and subsequent DNA synthesis after serum refeeding of cells is regulated by a Ca2+ activated, calmodulin-dependent process. Furthermore, the production of polyamines is essential for normal proliferation of these epithelial cells in culture.
Calcitonin gene-related peptide action on intestinal circular muscle
Authors: Holzer P. , Bartho L. , Matusak O. , Bauer V.
Published: December 2017

Isolated segments of the guinea pig small intestine were used to examine the effect of calcitonin gene-related peptide (CGRP) on the motor activity of the circular muscle. CGRP (0.3-30 nM) initiated phasic contractions of the circular muscle due to stimulation of cholinergic neurons. Peristalsis, however, was inhibited by CGRP. A further analysis of this effect showed that CGRP had no inhibitory influence on the main, cholinergic, pathway of the ascending enteric reflex (AER) contraction, whereas the hexamethonium- and atropine-resistant pathways of the AER were blocked. The inhibition of the atropine-resistant AER resulted from an action of CGRP on nerves and, since it was antagonized by apamin, might be explained by a CGRP-induced activation of enteric inhibitory neurons. The direct relaxant action of CGRP on the longitudinal muscle was not affected by apamin. These findings indicate a heterogeneity and topical selectivity in the motor actions of CGRP on the gut and suggest that this peptide, when released from nerve endings within the intestine, plays a specific role in the regulation of intestinal motility.
Different mechanisms of contraction generation in circular muscle of canine colon
Authors: Barajas-Lopez C. , Huizinga J. D.
Published: December 2017

Smooth muscle cells from the circular muscle layer of the dog colon showed a mechanical threshold of -44 mV. No gradient in mechanical threshold was measured between the cells from the submucosal and myenteric plexus surface. The threshold was passed during the upstroke and the plateau phase of the spontaneous slow-wave activity from cells at the submucosal surface and by spike potentials occurring mainly in cells at the myenteric plexus surface and sporadically in cells at the submucosal surface. Carbachol-induced specific changes in electrical and mechanical activities that were inhibited by calcium influx blockade are as follows: 1) increase in slow-wave duration; 2) decrease in plateau potential; 3) enhancement of spiking activity; and 4) increase in contractility. This indicates that calcium influx is significantly increased in the presence of carbachol in cells at both surfaces of the circular muscle layer. The increase in calcium influx could be the result of a direct action by carbachol on the calcium conductance and/or could be mediated by a decrease in outward current. The latter is suggested by the carbachol-induced membrane depolarization associated with an increase in the input resistance, which were both methoxyverapamil insensitive. The results show that an excitatory stimulus can generate contraction of the circular muscle through different electrophysiological activities. In addition, the patterns of spontaneous electrical activity and the different responses to carbachol stimulation provide further information about the heterogeneous nature of the electrical activities within the colonic circular muscle layer.
Effect of chelators on copper metabolism and copper pools in mouse hepatocytes
Authors: McArdle H. J. , Gross S. M. , Creaser I. , Sargeson A. M. , Danks D. M.
Published: December 2017

Disorders of copper storage are usually treated by chelation therapy. It is generally thought that the chelators act by mobilizing copper from the liver, hence allowing excretion in the urine. This paper has examined the effect of chelators on copper uptake and storage in mouse hepatocytes. Penicillamine, a clinically important chelator, does not block the uptake of copper or remove copper from hepatocytes. Two other copper chelators, sar and diamsar, which form very stable and kinetically inert Cu2+ complexes by encapsulating the metal ion in an organic cage, were shown to block copper accumulation by the cells and to remove up to 80% of cell-associated copper. They also removed most (approximately 80%) of the 64Cu accumulated by the cells in 30 min, but released only a small percentage (less than 20%) of that accumulated over 18 h. The results show that copper in the hepatocyte can be divided into at least two pools, an easily accessible one, and another, not removable even after long-term incubation with any of the chelators. Most of the copper normally found in the cell appeared to be associated with the former pool.
Microflora-derived polyamines modulate obstruction-induced colonic mucosal hypertrophy
Authors: Osborne D. L. , Seidel E. R.
Published: December 2017

Experiments were designed to determine the role of microflora-derived intraluminal polyamines in the colonic mucosal response to obstruction. Sprague-Dawley rats were treated per os with 0.9% NaCl or a combination of nonabsorbable antibiotics prior to the placement of either a sham or complete colonic obstruction. Sixty-six hours after surgery, wet tissue weight, DNA, RNA, and protein content were all increased in the mucosa proximal to the obstruction in NaCl-treated animals; however, DNA content was the only parameter increased after antibiotics. This induction was a purely local effect as neither hyperplasia nor hypertrophy was observed in the ileum or colon distal to the obstruction. In the NaCl-treated animals, mucosal ornithine decarboxylase activity was not induced until 48 h postsurgery, yet mucosal spermidine concentrations were significantly higher as early as 24 h. Intraluminal bacterial lysine, ornithine, and arginine decarboxylase activities were induced by obstruction but were reduced by antibiotic treatment. [14C]putrescine uptake by intestinal epithelial cells (IEC-6) in culture was blocked by the antibiotics employed in this study, but [14C]-lysine transport was relatively unaffected. These data demonstrate that intraluminal polyamines modulate the trophic response of the colonic mucosa after colonic obstruction.
Biochemical studies on opioid and alpha 2-adrenergic receptors in canine submucosal neurons
Authors: Ahmad S. , Allescher H. D. , Manaka H. , Manaka Y. , Daniel E. E.
Published: December 2017

Biochemical information about receptors for adrenergic and opioid neurotransmission in submucosal plexus (SMP) is unavailable. We have purified a fraction P2 enriched in synaptosomes and neuronal membranes (high [3H]saxitoxin binding and high vasoactive intestinal polypeptide immunoreactivity, low activity of 5'-nucleotidase) from the canine small intestine SMP. The synaptosomal fraction (fraction P2) also contained a high density of opioid diprenorphine binding sites of high affinity. [3H]rauwolscine binding was enriched both in fraction P2 and in a microsomal fraction. Competition experiments using several adrenergic and opioid receptor ligands revealed that opioid receptors were approximately 64% mu-, 24% delta-, and 12% kappa-subtypes and that adrenoceptors on fraction P2 were alpha 2-subtype but that there was a heterogeneous population of alpha 2-adrenoceptors. These studies show that a fraction enriched in synaptosomes and neural membranes from the canine intestine SMP contains opioid as well as alpha 2-adrenoceptors, that all three subtypes of opioid receptors seem to be present with mu-receptors predominant, and that subtypes of alpha 2-adrenoceptors appear to be present.
Intestinal alkaline phosphatase is secreted bidirectionally from villous enterocytes
Authors: Sussman N. L. , Eliakim R. , Rubin D. , Perlmutter D. H. , DeSchryver-Kecskemeti K. , Alpers D. H.
Published: December 2017

A fraction of intestinal alkaline phosphatase (IAP) is secreted into blood. To study this process, enzyme secretion was examined in a fetal (IRD-98) and a differentiated (Caco-2) intestinal cell line. Tissue-unspecific alkaline phosphatase (AP) activity in the IRD-98 cells increased 20-fold after addition of 1.5 mM sodium butyrate and 40 mM NaCl, but no AP activity was secreted into the medium. In contrast, newly synthesized IAP in Caco-2 cells was secreted into the medium. AP secretion increased with time and was inhibited by monensin. Medium AP was still partially bound to membranes as assessed by Triton X-114 phase separation and could be released by the addition of serum. Analysis by sodium dodecyl sulfate polyacrylamide gels and by isoelectric focussing showed that secreted AP gave a pattern similar to that of the AP released from membranes by phospholipase D treatment. When Caco-2 cells were grown on filters, AP activity was found in both basolateral (75%) and luminal (25%) media. These data demonstrate that the secretion of a particulate AP with extracellular release from the membrane can account for the appearance of the intestinal isozyme in both the serum and the lumen.
Intestinal lymphatic flow during portal venous hypertension
Authors: Dunbar B. S. , Elk J. R. , Drake R. E. , Laine G. A.
Published: December 2017

We used a circuit-model technique to analyze the flow from intestinal lymphatics. Postnodal lymph vessels from the small intestine were cannulated in five halothane-anesthetized dogs. We measured the flow rate from the cannula (QL) as we held the outflow end of the cannula at several heights above the site of cannulation. At each cannula height we calculated the pressure at the outflow end of the lymphatic (Po) as Po = QL X cannula resistance + height of the outflow end of the cannula above the cannulation site. Then we determined a best-fit regression line for QL vs. Po. The effective lymphatic resistance (RL) was estimated from the regression line as -delta Po/delta RL and the effective pressure driving lymph flow (PL) was taken as the Po at which QL = 0. At base line, RL = 0.039 +/- 0.018 (SD) cmH2O.min.microliters-1 and PL = 5.2 +/- 2.4 cmH2O. When we raised the portal venous pressure from 11.4 +/- 4.0 cmH2O (base line) to 34.4 +/- 9.0 cmH2O, RL decreased by only 26 +/- 11%, but PL rose by 160% to 13.6 +/- 8.7 cmH2O (P less than 0.05). Thus our data indicate that increases in portal venous pressure to 34.4 +/- 9.0 cmH2O cause intestinal lymph flow to increase primarily because of increases in the effective PL.
Characterization of cholinergic receptors mediating pepsinogen secretion from chief cells
Authors: Sutliff V. E. , Rattan S. , Gardner J. D. , Jensen R. T.
Published: December 2017

By use of a highly enriched preparation of chief cells (greater than 90% pure) prepared from guinea pig stomach, the cholinergic receptors regulating pepsinogen secretion were studied. Each of five different muscarinic cholinergic agonists, but not the nicotinic cholinergic agonist nicotine, stimulated pepsinogen release. Carbamylcholine-stimulated pepsinogen release was inhibited by each of seven different cholinergic receptor antagonists with relative potencies of N-methylscopolamine greater than scopolamine = 4-diphenylacetoxy-N-methylpiperidine methiodide = atropine much greater than pirenzepine greater than AF-DX-116 much greater than tetraethylammonium. Binding of [N-methyl-3H]scopolamine ([3H]NMS) was time and temperature dependent, reversible, saturable, and specific. Analysis of [3H]NMS binding demonstrated a Kd of 1.3 nM for NMS with a binding capacity of 61 fmol/mg protein or 5,920 sites/chief cell. With the agonists carbamylcholine, acetylcholine, or muscarine, the receptor population could be divided into two classes of receptor sites: a class with high affinity (Kd, 12-53 microM) representing 73% of the binding sites and a class with low affinity (Kd, 2-5 mM) representing 27% of the binding sites. Each of the antagonists had equal affinity for both receptor populations. There was a close correlation between the ability of antagonists to inhibit [3H]NMS binding and carbamylcholine-stimulated pepsinogen release. Each agonist was 29- to 63-fold more potent at stimulating pepsinogen release than interacting with high-affinity receptors and 2,000- to 11,000-fold more potent than interacting with low-affinity receptors, suggesting spare receptors. Studies with the alkylating agent, propylbenzilylcholine mustard, demonstrated that there was a receptor reserve of 50-80%.(ABSTRACT TRUNCATED AT 250 WORDS)
Human gastric emptying and colonic filling of solids characterized by a new method
Authors: Camilleri M. , Colemont L. J. , Phillips S. F. , Brown M. L. , Thomforde G. M. , Chapman N. , Zinsmeister A. R.
Published: December 2017

Our first aim was to compare 111In-labeled Amberlite IR-12OP resin pellets and 131I-labeled fiber in the assessment of gastric and small bowel transit and colonic filling in healthy humans. Both radiolabels were highly stable for 3 h in an in vitro stomach model and remained predominantly bound to solid phase of stools collected over 5 days [90.5 +/- 2.1 (SE)% for 131I and 87.4 +/- 1.4% for 111In). The lag phase of gastric emptying was shorter for 111In-pellets (30 +/- 11 min compared with 58 +/- 12 min for 131I-fiber, P less than 0.05). However, the slope of the postlag phase of gastric emptying and the half time of small bowel transit were not significantly different for 111In-pellets and 131I-fiber. Filling of the colon was characterized by bolus movements of the radiolabel (10-80% range, 26% mean) followed by plateaus (periods of no movement of isotope into colon lasting 15-120 min, range; 51 min, mean). Half of the bolus movements occurred within 1 h of the intake of a second meal. Thus 111In-labeled Amberlite pellets provide an excellent marker for the study of gastric and small bowel transit and colonic filling in humans. The ileum acts as a reservoir and transfers boluses of variable sizes into the colon, often soon after the intake of a subsequent meal.
Angiotensin receptors and angiotensin I-converting enzyme in rat intestine
Authors: Duggan K. A. , Mendelsohn F. A. , Levens N. R.
Published: December 2017

The purpose of this study was to map the distribution of angiotensin II (ANG II) receptors and ANG I-converting enzyme (ACE) in rat intestine. ANG II binding sites were visualized by in vitro autoradiography using iodinated [Sar1, Ile8]ANG II. The distribution of ACE was mapped using an iodinated derivative of lisinopril. Male Sprague-Dawley rats were killed and the interior of the whole intestine washed with ice-cold saline. Segments of duodenum, jejunum, ileum, and colon were quickly frozen in a mixture of isopentane and dry ice. Twenty-micron frozen sections were thaw-mounted onto gelatin-coated slides, incubated with either ligand, and exposed to X-ray film. After exposure and subsequent development, the films were quantitated by computerized densitometry. ANG II receptors were most dense in the colon, followed by the ileum, duodenum, and jejunum. Within each segment of intestine, specific ANG II binding sites were localized exclusively to the muscularis. In contrast, ACE was present in both the mucosa and the muscularis. The colocalization of ANG II receptors and ACE may suggest a role for locally generated ANG II in the control of intestinal function. The luminal orientation of ACE in the mucosa of the small intestine may suggest that at this site ACE serves primarily to hydrolyze dietary peptides.
Leukocyte adherence to venular endothelium during ischemia-reperfusion
Authors: Granger D. N. , Benoit J. N. , Suzuki M. , Grisham M. B.
Published: December 2017

Xanthine oxidase-derived oxidants and leukocytes have been implicated in the microvascular injury associated with reperfusion of ischemic intestine. The objective of this study was to determine whether xanthine oxidase-derived oxidants play a role in the leukocyte-microvascular interactions initiated by ischemia-reperfusion. Adherence and extravasation of leukocytes were monitored in cat mesenteric venules subjected to 1 h of ischemia (blood flow reduced to 20% of control) and reperfusion. Leukocyte rolling velocity, vessel diameter, and red cell velocity were also measured in control (untreated) animals and in animals pretreated with either allopurinol or superoxide dismutase. The responses of venular blood flow, wall shear rate, and leukocyte rolling velocity to ischemia and reperfusion did not differ between the three experimental groups. In control animals, 1 h of ischemia was associated with significant adherence and extravasation of leukocytes with reperfusion greatly enhancing these responses. Allopurinol treatment did not alter the responses to ischemia per se, yet it largely prevented the further increment in adherence and extravasation associated with reperfusion. Superoxide dismutase treatment attenuated the leukocyte responses elicited by both ischemia and reperfusion. Our observations that both allopurinol and superoxide dismutase attenuate reperfusion-induced leukocyte adherence and extravasation are consistent with the hypothesis that xanthine oxidase-derived oxidants initiate the leukocyte infiltration induced by reperfusion of ischemic intestine.
Origin of regional and species differences in intestinal glucose uptake
Authors: Ferraris R. P. , Lee P. P. , Diamond J. M.
Published: December 2017

Differences in intestinal absorption among physiological states, intestinal regions, and animal species could arise from many anatomical factors (e.g., intestinal length and diameter, or area amplification by villi and microvilli) and biochemical factors (e.g., transporter density and turnover number). In no comparison had all these factors been measured. Hence we made the necessary new measurements to identify the origin of differences in glucose absorption among three species (mouse, desert wood rat, and desert iguana) and among three intestinal regions in two of these species. Turnover numbers range from 6,900 to 32,300 glucose molecules per minute per site. Microvilli amplify intestinal area by a larger factor (36-96 times) than do villi (2-14 times), so that the intestine's actual area is at least 110-1,280 times the nominal area of the equivalent smooth-bore cylinder. Species comparisons among mammals yield the striking result that the area of the whole length of the small intestine at the microvillus level varies nearly linearly as the mammal's metabolic live mass. For the species studied, all the anatomical and biochemical factors studied proved to make significant contributions to species and regional difference in glucose uptake.
Tissue origin of peptide-responsive eicosanoid production in rabbit intestine
Authors: Leduc L. E. , Zipser R. D.
Published: December 2017

Different layers of rabbit large and small intestine display different peptide sensitivity and different profiles of eicosanoid release. Isolated perfused mesenteric pedicle alone, with muscularis/submucosa or with muscularis and mucosa from normal small bowel, normal colon, or inflamed colon were stimulated with bradykinin (BK) or n-formyl-methionyl-leucyl-phenylalanine (fMLP). Released prostaglandin (PG)E2, thromboxane (Tx)B2, and leukotriene (LT)B4 were assayed using extensively validated radioimmunoassays. In rabbit colon, PGE2 arises primarily from the mesentery, while in small intestine the muscularis/mucosa releases 70-80% of the total PGE2. BK releases no significant thromboxane from healthy colon, although both muscularis/submucosa and mucosa respond in inflamed colon. In contrast, fMLP stimulates thromboxane from muscularis/submucosa and mucosa of even healthy colon, while release is greatly potentiated in inflammation. Lipoxygenase in the colon is regulated differently than cyclooxygenase; it is not stimulated by BK in either healthy or inflamed colon. fMLP releases equal amounts of LTB4 from healthy and inflamed colon, but release was primarily from healthy colonic mucosa, whereas it was distributed throughout mesenteric pedicle, muscularis, and mucosa in inflamed colon. The ability of normal colonic mucosa to release proinflammatory LTB4 in response to a chemotactic factor (fMLP) produced by enteric bacteria suggests a possible role for these compounds as a stimulus for inflammation in some patients with inflammatory bowel disease.
Fe-saturation and proteolysis of human lactoferrin: effect on brush-border receptor-mediated uptake of Fe and Mn
Authors: Davidson L. A. , Lonnerdal B.
Published: December 2017

We have previously characterized a brush-border membrane receptor that facilitates iron uptake from human lactoferrin. The receptor is specific for human and monkey lactoferrin and does not recognize human transferrin or bovine lactoferrin. In this study, iron uptake from lactoferrin fragments was studied, as well as from lactoferrin partially saturated with iron. Brush-border membrane vesicles (BBMV) prepared from infant rhesus monkey small intestine efficiently accumulated iron from lactoferrin half-molecules, although competition experiments showed that intact lactoferrin has a higher affinity toward the receptor. Lactoferrin partially saturated with iron also effectively delivered iron to the receptor, whereas the affinity was lower than for lactoferrin saturated with iron. Lactoferrin also carries a large proportion of human milk manganese, and receptor-mediated uptake of lactoferrin-bound manganese into BBMV was demonstrated, although this complex had lower affinity than that found for iron-lactoferrin. Thus, although the receptor has a preference for intact iron-saturated lactoferrin, partially digested lactoferrin and partially iron-saturated lactoferrin can also deliver iron to the receptor. Therefore, these molecular species, which are likely to occur in the gastrointestinal tract of the infant, may contribute to the high degree of iron absorption from human milk lactoferrin.
Neurokinin inhibition of cholinergic myenteric neurons in canine antrum
Authors: Mayer E. A. , Koelbel C. B. , Snape W. J. , Vandeventer G. , Leduc L.
Published: December 2017

Neurokinins regulate gastrointestinal motility by interacting with receptors on both muscle layers and on myenteric plexus neurons. To determine if specific neurokinin (NK) receptor agonists can mediate inhibitory effects on myenteric neurons, we studied the effect of the NK-1 agonist substance P methylester (SPME) and the putative endogenous NK-2 receptor ligand neurokinin A (NKA) on [3H]acetylcholine [( 3H]ACh) release induced by electrical field stimulation from muscle strips cut from the canine gastric antrum. SPME but not NKA caused a dose-dependent inhibition of stimulated [3H]ACh release in tissues containing the myenteric plexus. The inhibition was not seen in longitudinal muscle without myenteric plexus. Pretreatment of tissues with indomethacin or antiserum to vasoactive intestinal polypeptide (VIP) but not naloxone or adrenergic or cholingergic blockade abolished the SPME-induced inhibition. Exogenous VIP stimulated the release of prostaglandin E2 (PGE2) from full thickness strips, and both VIP and PGE2 inhibited [3H]ACh release induced by electrical depolarization. These findings suggest that NK-1 receptor agonists can selectively inhibit stimulated [3H]ACh release and that this inhibition may involve the release of VIP and PGE2 from neurons within the myenteric plexus.
Effects of morphine on colonic myoelectric and motor activity in subhuman primates
Authors: Frantzides C. T. , Condon R. E. , Schulte W. J. , Cowles V.
Published: December 2017

We investigated the effects of numerous doses of morphine on colonic myoelectric and motor activity in monkeys. In each of four monkeys (Macaca arctoides), combined strain gauge transducers and bipolar electrodes were chronically implanted at four defined sites in the colon and recordings were made for 3 h in fasted, unanesthetized animals before and after intravenous administration of morphine sulfate (10-1,000 micrograms/kg). The basal fasting pattern of colonic motility was characterized by random contractions, nonmigrating clusters of contractions, and migrating individual contractions. Morphine at very low doses (10-25 micrograms/kg) had no effect on colonic motility at any site. At doses of 50-200 micrograms/kg, clusters and migrating contractions were eliminated, but there was an overall increase in the frequency of random contractions without an alteration in contraction amplitude or duration. At morphine doses of 500 and 1,000 micrograms/kg, contraction clusters and migrating contractions also were not seen, but there was a decrease in the colonic motility index caused entirely by a decreased frequency of random contractions. Both stimulation and inhibition were most marked in the sigmoid colon. Morphine has a dose-dependent biphasic effect on colonic myoelectric and contractile activity and alters colonic motility patterns by inhibiting migrating contractions and clusters of contractions.
Cold-restraint stress increases rat fecal pellet output and colonic transit
Authors: Barone F. C. , Deegan J. F. , Price W. J. , Fowler P. J. , Fondacaro J. D. , Ormsbee H. S.
Published: December 2017

Increased fecal pellet output that occurs during cold-restraint stress (CRS) was evaluated systematically. Free-feeding rats, which exhibit a reduced occurrence of gastric ulcers under these conditions, were studied. CRS significantly increased fecal pellet production and fluid content. However, the fecal output produced during CRS was not associated with increased gut secretory activity or somatic motor activity associated with cold restraint and did not occur in anesthetized animals. Cold and restraint stress were additive in producing increased fecal output. Significant dose-related decreases in fecal output were produced by drugs that decrease gut transit (i.e., B-HT 920, clonidine, Lomotil, loperamide, and lidamidine). Anticholinergic-antisecretory drugs, antidepressants, and tranquilizers had little effect on fecal output or fluid content. Changes in gastrointestinal transit did not contribute to the increased fecal output during CRS. Transit in the lower small intestine was not altered, but the cecum tended to empty more contents into the large intestine during CRS. Colonic transit was dramatically affected by CRS, which eliminated retrograde transit and produced the evacuation of the majority of colonic contents. The increased colonic transit produced by CRS was decreased in a dose-related fashion by hexamethonium, nifedipine, loperamide, and B-HT 920. In several time-response and drug-inhibition studies during CRS, both fecal pellet output and colonic transit were affected similarly. These data indicate that CRS appears to change central nervous system output to the colon and that it alters colonic smooth muscle motility in a manner that facilitates colonic transit and evacuation. Small intestinal transit is not involved in this phenomenon and is regulated differently during CRS.
Jejunal adenosine increases during food-induced jejunal hyperemia
Authors: Sawmiller D. R. , Chou C. C.
Published: December 2017

If adenosine mediates postprandial intestinal hyperemia, increases in local adenosine release must accompany the hyperemia. We tested this by determining jejunal venous and arterial plasma adenosine concentrations, jejunal blood flow, and oxygen consumption before and during placement of normal saline or predigested food plus bile into the jejunal lumen of anesthetized dogs. Adenosine concentrations were measured by high-pressure liquid chromatography. Luminal placement of food significantly increased blood flow (+46%), oxygen consumption (+40%), venous adenosine concentration (+56 nM), and adenosine release (+1.7 nmol.min-1.100 g tissue-1) during the initial 3 min of placement. Whereas blood flow and oxygen consumption remained elevated for the entire 15-min placement period, venous adenosine concentration and release returned to control levels at 7 and 11 min after placement, respectively. Placement of the same volume of normal saline did not significantly alter any variables measured, indicating that the food-induced changes were because of constituents of food. In conclusion, introduction of predigested food into the jejunal lumen significantly increases adenosine releases into the local venous blood during the initial several minutes of food placement. The increased adenosine production and release may play a role in postprandial jejunal hyperemia.