bluuebunny/crossref_metadata_2025 huggingface dataset:
Decreased secretion due to a Ca2+ influx defect in frog peptic cells isolated with EGTA
Authors: Uemura Naomi , Dickinson Kenneth E. J. , Horiguchi Yuji , Matsumoto Haruki , Hirschowitz Basil I.
Published: December 2017

Cells prepared from frog esophageal peptic glands by dispersal in low-Ca2+ medium (peptic acini) or 1 mM ethylene glycol-bis(-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA)-containing medium ("EGTA cells") were compared. EGTA cells were characterized by decreased secretory responses to agonists [bombesin (BB), acetylcholine, and isoproterenol] and intracellular messenger activators (forskolin, 12-O-tetradecanoyl-phorbol-13-acetate), decreased relative intrinsic efficacies of muscarinic agonists, and somatostatin insensitivity. Decreased BB and muscarinic receptor responses were not associated with changes in receptor number or characteristics. The time course of BB- and acetylcholine-stimulated pepsinogen secretion indicated that the marked reduction was confined largely to the late secretory phase (2–30 min), dependent on extracellular Ca2+, rather than early phase (2 min) secretion, which is related to release of intracellular Ca2+. The defect could be reversed by the Ca2+ ionophore A23187. BB-stimulated intracellular Ca2+ mobilization measured with fura-2/AM was similar in the two cell preparations, whereas BB-stimulated 45Ca2+ uptake was reduced threefold in EGTA cells, and this defect was also reversed by A23187. Somatostatin inhibited both BB-stimulated secretion and 45Ca uptake by peptic acini, but it had no significant effect on these parameters in EGTA cells. Cytochalasin B inhibited BB stimulation in peptic acini but not EGTA cells. These findings suggest that peptic cells isolated with EGTA exhibit decreased secretory responses that are due at least in part to impairment of a mechanism for uptake of extracellular Ca2+.
Gastrointestinal luminal polyamines: cellular accumulation and enterohepatic circulation
Authors: Osborne D. L. , Seidel E. R.
Published: December 2017

The concentration of polyamines contained in the lumen of the gut was quantified. The duodenum and jejunum of the rat contained 2-3 mM putrescine and 1-2 mM cadaverine, whereas in the ileum and colon the concentration of these polyamines was significantly less. In addition, the concentrations of spermine and spermidine in the intestinal lumen were low to undetectable. Putrescine in the lumen of the gut was over 90% free with only 10% or less bound to protein. The activity of the enzymes responsible for the synthesis of polyamines was also measured. In contrast to concentration, enzyme activity was found to be high in the ileum, cecum, and colon and nonexistent in the duodenal and jejunal lumen. This suggested the potential for enterohepatic circulation of polyamines that were synthesized by the colonic microflora and transported to the proximal gut via the portal circulation and biliary tree. Indeed, when [14C]putrescine was instilled into the lumen of the gut, it was secreted in pancreaticobiliary secretions. Upper and lower jejunum and colon all supported enterohepatic circulation of polyamines, whereas it was absent in the ileum. Polyamine accumulation in IEC-6 cells grown under in vitro conditions was also measured. Putrescine was transported under time- and temperature-dependent but sodium-independent conditions. The transporter displayed little selectivity for the various polyamines and compounds with related structures but did not recognize amino acids. The Michaelis constant for putrescine accumulation was 1.26 x 10(-6) M with a maximal velocity of the enzyme reaction of 5,184 pmol putrescine.mg protein-1.h-1.(ABSTRACT TRUNCATED AT 250 WORDS)
The use of intraluminal strain gauges for recording ambulant small bowel motility
Authors: Gill R. C. , Kellow J. E. , Browning C. , Wingate D. L.
Published: December 2017

Perfused-tube manometry has hitherto been the standard technique for recording intraluminal intestinal pressure in humans, but it is unsuitable for ambulant use. The aim of our study was to evaluate the ability of resistive strain gauge transducers attached to a fine catheter to detect pressure change. Simultaneous strain gauge and perfused-tube manometry was performed on six fasting subjects; in four, strain gauge activation was continuous and in two, the transducers were activated in a pulsed mode with data encoded as a pulse train with an approximate frequency of 20 Hz. Eight thousand eight hundred eighty-eight pressure waves were recorded by strain gauge, of which 96% were detected by perfused-tube manometry. There was good agreement in both phases II and III of the migrating motor complex. The amplitude of pressure waves recorded by strain gauge was slightly but significantly greater. A proportion (14-17%) of pressure waves recorded by strain gauge were bifid; this was not seen with the perfused tube. These differences are best explained by the greater sensitivity and more rapid rise time of the strain gauges. There was no loss of fidelity in the pulse-interval recording mode. A seventh subject underwent a continuous 72-h recording with the strain gauge catheter attached to a battery-operated encoder and magnetic tape cassette recorder and was freely ambulant during this period. The procedure was well tolerated and motility patterns could be clearly identified. We conclude that intraluminal strain gauge catheters are suitable for prolonged use in ambulant subjects and produce data that are closely comparable to the data acquired from perfused-tube manometry under laboratory conditions.
Evaluation of patterns of human antral and pyloric motility with an antral wall motion detector
Authors: Fone D. R. , Akkermans L. M. , Dent J. , Horowitz M. , van der Schee E. J.
Published: December 2017

We have examined the hypothesis that isolated pyloric pressure waves occur in the absence of even low-amplitude antral contractions. Antropyloroduodenal motility was recorded in seven healthy adult volunteers. A sleeve/side-hole manometric assembly was positioned across the pylorus with the aid of measurements of transmucosal potential difference. A new sensor consisting of an elliptical wire transducer 2.5 cm long and 1.5 cm in transverse diameter was incorporated into the assembly above the sleeve. This sensor was designed to detect nonlumen-occluding antral contractions. Motility was studied for 45 min under each of three conditions: 1) fasting, 2) after ingestion of a 100-g beef burger, and 3) during and after a 15-min intraduodenal infusion of 25% dextrose at a rate of 4 ml/min. Overall, only 51% of antral transducer deflections were associated with a change in antral side-hole pressures. Eighty-nine percent of antral side-hole pressure waves were associated with an indication of antral wall motion. Of the pressure waves recorded by the sleeve classified as isolated pyloric pressure waves, none was associated with antral transducer deflection during fasting, 1.1% after intraduodenal dextrose, and 18% after the solid meal. Antral contractions were detected by the wall motion detector with greater sensitivity than antral side holes, possibly reflecting the occurrence of nonlumen-occluding antral contractions. With some exceptions during solid gastric emptying, manometrically defined isolated pyloric pressure waves appear to represent truly localized contraction.
ATP-dependent efflux of GSSG and GS-conjugate from isolated rat hepatocytes
Authors: Oude Elferink R. P. , Ottenhoff R. , Liefting W. G. , Schoemaker B. , Groen A. K. , Jansen P. L.
Published: December 2017

The driving force for efflux of dinitrophenyl-glutathione (GS-DNP) and oxidized glutathione (GSSG) from freshly isolated rat hepatocytes was studied. Incubation of hepatocytes in Krebs with increasing K+ concentrations (equivalently replaced for Na+) or in Krebs with 3 mM ouabain led to a partial or complete dissipation of the plasma membrane potential, as measured by the equilibrium distribution of 36Cl-. This had no effect on the initial efflux rate of GSSG and GS-DNP. On the other hand, partial depletion of the cellular ATP content via different independent mechanisms significantly reduced the initial efflux rate of these compounds. Titration of the cellular ATP content by incubation of the cells with different concentrations of atractyloside revealed a linear relation between the cellular ATP content and the initial efflux rate of GS-DNP. The efflux of GS-DNP was also studied in hepatocytes from mutant rats with hepatobiliary transport defect (TR- rats). These rats have a hereditary canalicular secretion defect for a number of organic anions including GS-DNP. As we have shown previously, the efflux of GS-DNP from TR- rat hepatocytes is significantly slower than from normal hepatocytes (J. Clin. Invest. 84: 476-483, 1989). Depletion of the cellular ATP content in these cells had no significant effect on the residual efflux of GS-DNP. From these studies, we conclude that an ATP-dependent transport system for oxidized glutathione and glutathione conjugates is involved in the biliary transport of these compounds. The possible relation of this transport system with that described in other cell types and tissues, like erythrocytes and heart sarcolemma, is discussed.
Regulation of pancreatic duct epithelial growth in vitro
Authors: Verme T. B. , Hootman S. R.
Published: December 2017

Effects of a number of possible trophic factors on growth of guinea pig pancreatic duct epithelial monolayers were investigated. Isolated fragments of main and interlobular ducts were prepared and explanted onto both tissue culture plastic and thick gels of type I collagen. Monolayers growing out from explants were first cultured in a basal medium for 3 or 4 days. Next, the medium was supplemented individually with bombesin, carbachol, caerulein, epidermal growth factor (EGF), secretin, 12-O-tetradecanoylphorbol 13-acetate (TPA), or vasoactive intestinal peptide (VIP). Cells were cultured in the absence or presence of these possible trophic factors, and monolayer areas were determined morphometrically at 0, 2, and 4 days. Rate of growth was determined from increase in area over each 2-day period. Monolayers grown in basal medium alone on plastic increased to 479% of initial area over the 4-day test period; those grown on collagen increased to 523%. Explants cultured in presence of bombesin, carbachol, caerulein, secretin, TPA, and VIP on either substrate grew at rates not significantly different from those cultured in basal medium. By contrast, duct monolayers grown on plastic or collagen in presence of 10 nM EGF expanded in area to 722 and 1,070%, respectively, of their initial areas. The EC50 for this trophic effect was approximately 1 nM. These results show that EGF exerts a potent trophic effect on guinea pig pancreatic duct cells in vitro but also indicate that cell division in the pancreatic main and interlobular ducts is not regulated by caerulein and related peptide hormones that have been reported to have growth-promoting effects on exocrine pancreas in vivo.
H2 receptors mediate cyclical chloride secretion in guinea pig distal colon
Authors: Wang Y. Z. , Cooke H. J.
Published: December 2017

We tested the hypothesis that histamine mediates ion secretion in the guinea pig distal colon by stimulating H2 receptors on submucosal neurons. Serosal addition of histamine evoked a transient increase in short-circuit current (Isc) followed by recurrent cyclical increases in Isc. The transient phase of the response was examined previously and was not investigated in these studies. Histamine (1.5-2.5 x 10(-5) M) evoked a peak increase in Isc of 177 +/- 25 microA/cm2 at intervals of 5 min for 1-2 h. The duration of each recurrent cycle averaged 2.1 +/- 0.3 min. The H2 agonist dimaprit evoked recurrent cycles that had larger amplitudes than those caused by histamine. In the presence of histamine or dimaprit, the amplitude of the first cycle of the response was always less than subsequent cycles, regardless of the initial concentration. The cyclical responses to histamine, 2-methylhistamine, or dimaprit were unaltered by the H1 blocker pyrilamine, were reduced by the H2 antagonist cimetidine, and were abolished by the neuronal blocker tetrodotoxin. Blockade of prostaglandin formation with piroxicam did not prevent the recurrent cycles. The recurrent cycles were inhibited by the chloride transport blocker bumetanide and by removal of chloride ions. Our results demonstrate that histamine mediates prolonged cyclical chloride secretion in the guinea pig distal colon by activating H2 receptors on submucosal neurons involved in regulation of epithelial chloride transport.
Gastrointestinal peptides activate Na(+)-H+ exchanger in AR42J cells by increasing its affinity for intracellular H+
Authors: Bastie M. J. , Williams J. A.
Published: December 2017

Regulation of intracellular pH (pHi) was studied by dual wavelength fluorometry in monolayers of pancreatic AR42J cells loaded with the fluorescent probe 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. In cells superfused with N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered solution at pH 7.40, basal pHi was determined to be 7.15 +/- 0.13. Na(+)-H+ exchange could be demonstrated in both resting cells and cells subjected to acid loading by use of transient exposure to NH4Cl. Na(+)-H+ exchange was completely blocked by 300 microM amiloride and was dependent on extracellular Na+ (apparent Km = 25 mM). When the concentration of the NH4Cl pulse was varied (0.5-25 mM), the rate of pHi recovery increased as pHi became acidic, reaching a maximum of 0.007 pH units/s at pHi of 6.4. Gastrointestinal hormones, including pentagastrin, cholecystokinin, and bombesin, increased the rate of Na(+)-H+ exchange without affecting cellular buffer capacity (21.5 +/- 1.8 mM/pH unit), thereby leading to an intracellular alkalinization. This was accompanied by a shift in the curve of Na(+)-H+ exchange as a function of pHi to more alkaline values, although the maximum rate of pH recovery was unchanged. Neither protein kinase C nor Ca2+ could be conclusively linked to activation of Na(+)-H+ exchange, raising the possibility of a more direct, receptor-controlled mechanism.
Mediation of food protein-induced jejunal smooth muscle contraction in sensitized rats
Authors: Scott R. B. , Gall D. G. , Maric M.
Published: December 2017

Alterations in myoelectric and motor activity are important features of food protein-induced intestinal anaphylaxis. To determine the mediator(s) involved, rats were sensitized by injection of egg albumin (10 micrograms ip), and controls were sham sensitized with saline. Fourteen days later the contractility of longitudinally oriented jejunal segments (mucosa intact) was examined in standard tissue baths in response to antigen (Ag) or other agents. Although control and sensitized tissues similarly contracted to stretch, bethanechol, histamine, or 5-hydroxytryptamine (5-HT), Ag contracted only sensitized segments. Contractile response 1) was specific to the sensitizing Ag, as bovine serum albumin did not induce contraction, and 2) could be passively transferred with serum containing specific IgE antibody. Mast cell degranulation after Ag challenge was suggested by a significant loss of granulated mast cells in sensitized compared with control rats challenged with Ag. Concanavalin A, which degranulates mucosal and connective tissue-type mast cells, and compound 48/80, which degranulates only connective tissue-type mast cells, produced a contractile response. Ag-induced contraction was significantly inhibited by the mucosal and connective tissue-type mast cell stabilizer doxantrazole (P less than 0.001) and the connective tissue mast cell stabilizer disodium cromoglycate (P less than 0.05). Diphenhydramine and cimetidine together blocked histamine-induced contraction but failed to affect Ag-induced contraction in sensitized tissues.(ABSTRACT TRUNCATED AT 250 WORDS)
Reduced cholecystokinin mediates the inhibition of pancreatic growth induced by bile salts
Authors: Gomez G. , Townsend C. M. , Green D. W. , Rajaraman S. , Greeley G. H. , Thompson J. C.
Published: December 2017

The effects of luminal bile salts on plasma levels of cholecystokinin (CCK) and growth of the pancreas in mice were studied. Nonfasting levels of plasma CCK in control mice were 8.1 +/- 1.5 pM. Feeding mice a 0.5% (wt/wt) sodium taurocholate-supplemented diet for 1 wk significantly lowered nonfasting levels of plasma CCK to 4.1 +/- 0.5 pM and decreased the total contents of pancreatic DNA by 22%, RNA by 25%, and protein by 24%. All of the inhibitory effects of taurocholate on pancreatic growth were completely reversed by the simultaneous administration of CCK-8 (3 micrograms/kg, 3 times daily). In contrast, intraluminal neutralization of endogenous bile salts by feeding a 4% (wt/wt) cholestyramine-supplemented diet for 1 wk significantly elevated nonfasting levels of plasma CCK to 14.7 +/- 1.5 pM and increased the total contents of pancreatic DNA by 34%, RNA by 40%, and protein by 35%. All of the stimulatory actions of cholestyramine on pancreatic growth were completely abolished by the administration of the highly potent and specific CCK-receptor antagonist L364,718 (1 mg/kg, twice daily). These findings, therefore, indicate that bile salts appear to play a physiological role in pancreatic growth by regulation of plasma levels of CCK.
Effects of enteric neural defunctioning on small bowel motility
Authors: Frantzides C. T. , Condon R. E. , Doumas B. T. , Garancis J. C.
Published: December 2017

In this study, we investigated the role of intrinsic nerves of the small intestine on phase III migration of the migrating myoelectric complex. Fasting myoelectric activity was recorded from the small bowel in chronically instrumented dogs. Once control experiments were completed, the animals were divided into two groups and were reoperated. In the first group of five dogs, a 1.5-g/dl aqueous solution of cobaltous chloride (shown to induce degeneration of intestinal intrinsic nerves) was infused close intra-arterially to perfuse a 15-cm segment of jejunum. In the second group of dogs, a catheter was implanted in a branch of the superior mesenteric artery supplying a 15-cm segment of intestine. Tetrodotoxin (0.3-1 micrograms/kg) was infused through the catheter just before the arrival of phase III activity in the perfused segment. Subsequent to the fifth postcobalt perfusion day, phase III traversed but did not occur in the cobalt-treated segment. When tetrodotoxin was injected through the catheter, spontaneous phasic myoelectric and contractile activities in the perfused jejunal segment were inhibited, but phase III migration was not blocked. These findings suggest 1) acute or chronic defunctioning of enteric nerves does not interrupt phase III migration, but 2) phase III expression is dependent on the integrity of intrinsic nerves.
Paracellular intestinal absorption of glucose, creatinine, and mannitol in normal animals: relation to body size
Authors: Pappenheimer J. R.
Published: December 2017

Mice, rats, or rabbits were provided with a liquid diet of 10-12% glucose (Glc), 0.5-1% creatinine, 1-2% mannitol, and mannitol labeled with 3H on a terminal carbon. Average rates of ingestion of Glc were greater than maximum rates of active, carrier-mediated Glc transport reported for the intestines of these species. The discrepancy was small in mice but increased exponentially with body weight (BW). Ingestion-absorption of Glc increased exponentially with the 0.73 power of BW as expected from metabolic rate, whereas active transport, estimated from the literature, varied exponentially with the 0.50 power of BW. It is estimated that in humans the ingestion-absorption rate of Glc may be 10-20 times greater than active transport. In the presence of Glc, 50-65% of the ingested creatinine was recovered in urine compared with 75-85% recovered after intraperitoneal or subcutaneous injections. The amount of creatinine recovered in urine depended on the amount of ingested Glc, as predicted from the effects of Glc on width and permeability of absorptive cell junctions. Eighty percent or more of the 3H label on mannitol was recovered in urine or other body fluids, although most of the [3H]mannitol was oxidized to [3H]water after being absorbed intact from the intestine. It is concluded that in the presence of Glc, creatinine and mannitol (together with Glc, amino acids, and other small nutrients) are absorbed passively by solvent drag between absorptive cells, as found previously in anesthetized rats (J. R. Pappenheimer and K. Z. Reiss. J. Membr. Biol. 100: 123-136, 1987). The ratio of solvent drag to carrier-mediated transport increases exponentially with BW and may account for the capacity of human intestines to absorb large amounts of Glc during prolonged exercise, Glc tolerance tests, or oral Glc-saline therapy for dehydration.
Altered smooth muscle function in worm-free gut regions of Trichinella-infected rats
Authors: Marzio L. , Blennerhassett P. , Chiverton S. , Vermillion D. L. , Langer J. , Collins S. M.
Published: December 2017

We have extended a recent study demonstrating increased contractility of jejunal smooth muscle of rats infected with the nematode parasite Trichinella spiralis, the primary habitat of which is the jejunum. In this study, muscle from the worm-free ileum of infected rats showed decreased contractility compared with control, illustrating regional differences in muscle responses to the infection. However, in jejunal muscle from worm-free segments that had been excluded from the rest of the gut before the infection, we observed increased tension generation, suggesting a systemic mechanism. To evaluate whether the changes in jejunal muscle were due to the host's inflammatory reaction, the effect of beta-methasone was examined. In a dose of 3.0 mg/kg sc daily, the steroid abolished the increase in myeloperoxidase activity associated with the infection and attenuated the increased tension generation in jejunal muscle from Trichinella-infected rats. These results support the hypothesis that alterations in intestinal smooth muscle function in this model do not require the presence of the parasite in the lumen and are mediated by the host's inflammatory reaction.
Gastric effects of TRH analogue and bicuculline injected into dorsal motor vagal nucleus in cats
Authors: Feng H. S. , Lynn R. B. , Han J. , Brooks F. P.
Published: December 2017

We investigated the gastric acid secretory and motility responses to microinjection into the dorsal motor nucleus of the vagus (DMV) of RX 77368, a stable thyrotropin-releasing hormone (TRH) analogue, and bicuculline, a gamma-aminobutyric acid (GABAA) receptor antagonist in ketamine-chloralose-anesthetized cats. Gastric acid output was collected every 15 min through a gastric cannula after saline flush and titrated to pH 7.0. Antral contractions were continuously recorded by an extraluminal strain gauge force transducer. The chemicals were dissolved in saline and unilaterally microinjected in volumes of 200 nl. RX 77368 or bicuculline microinjected into the DMV induced significant dose-dependent (50-500 ng) increases in gastric acid secretion and significant dose-dependent (50-200 ng) increases in the force of antral contractions. In response to both chemicals the gastric acid output increased in the first 15 min and peaked in the second and third collections. RX 77368 (500 ng) had a second greater peak 90 min after microinjection. The motility responses were rapid in onset and lasted 60 min for RX 77368 and 30 min for bicuculline. The minimal effective dose for eliciting increased motility was consistently lower than inducing acid secretion. Electrical stimulation of the DMV with 100 microA, 50-Hz, and 0.2-ms pulse duration increased the force of antral contractions but had no effect on gastric acid secretion. Our results demonstrate that the DMV exerts important control over both gastric acid secretion and motility in cats. TRH exerts a stimulatory influence, while GABAA receptors mediate an inhibitory influence on this vagal control.
Uphill transport of beta-alanine in intestinal brush-border membrane vesicles
Authors: Miyamoto Y. , Nakamura H. , Hoshi T. , Ganapathy V. , Leibach F. H.
Published: December 2017

The characteristics of beta-alaline uptake were studied in brush-border membrane vesicles isolated from the proximal small intestine of rabbits and were compared with those of L-alpha-alanine uptake. The uptake of beta-alanine as well as L-alpha-alanine was significantly stimulated by imposing an inwardly directed Na+ gradient. Studies on transstimulation and substrate specificity provide evidence that the transport system serving beta-alanine is distinct from the system serving alpha-alanine. The beta-system also accepts taurine as a substrate. The Na(+)-dependent uptakes of beta-alanine and L-alpha-alanine were differentially influenced by anions. The order in which anions supported uptake was Cl- = SCN- greater than F- greater than NO3- = SO2(-4) for beta-alanine, whereas it was SCN- greater than F- = Cl- = NO3- greater than SO2(-4) for L-alpha-alanine. Cl- appeared to be the preferred anion to support the uptake of beta-alanine. beta-Alanine uptake was greater in the presence of an inwardly directed Cl- gradient than in the presence of Cl- at equal concentrations on both sides of the membrane. The uptake was maximal when a Na+ gradient and a Cl- gradient were present simultaneously. The NaCl gradient-driven beta-alanine uptake was stimulated by an inside-negative K(+)-diffusion potential induced by valinomycin, showing that the uptake process is electrogenic. Stoichiometric analyses suggest that multiple Na+ and one Cl- are associated with the uptake of one beta-alanine molecule. The kinetic study shows that the transporter for beta-alanine is a high-affinity, low-capacity system (Kt = 46 +/- 1 microM; Vmax = 30 +/- 1 pmol.mg protein-1.15 s-1).
Cl- channel blockers inhibit acid secretion in rabbit parietal cells
Authors: Malinowska D. H.
Published: December 2017

Mechanisms of gastric parietal cell secretory membrane Cl- transport and the role of this Cl- transport in acid secretion were investigated by examining the effects of two Cl- channel blockers, diphenylamine-2-carboxylate (DPC) and 9-anthracene carboxylate (9-AC) on acid secretion using isolated, enriched rabbit parietal cells. Resting and stimulated acid secretion in intact cells (measured as [14C]aminopyrine accumulation) was inhibited by DPC and 9-AC, irrespective of agonist used. Apparent inhibition constants (Ki) were 2.4 x 10(-4) M for DPC and 1.2 x 10(-3) M for 9-AC for all responses. Digitonin-permeabilized parietal cells were used to bypass possible inhibitory effects of these compounds on basolateral membrane transport processes and to investigate effects only on the secretory membrane. Both blockers inhibited ATP-driven acid secretion in resting and stimulated permeable cells with apparent Ki values in the same range as measured in intact cells, suggesting that the site of action of these blockers is at the secretory membrane. H(+)-K(+)-ATPase activity in situ in permeable parietal cells, measured as 2-methyl-8-(phenylmethoxy)imidazo(1,2) pyridine-3-acetonitrile (SCH28080)-inhibitable ATP hydrolysis, was higher in stimulated compared with resting cells. Addition of 10 mM NH4Cl abolished this difference, and maximal H(+)-K(+)-ATPase activity was measured. SCH28080 and NH4Cl each abolished both resting and stimulated acid accumulation. DPC and 9-AC inhibited resting and stimulated H(+)-K(+)-ATPase activities, without exerting inhibitory effects on the enzyme itself, since the blockers had no effect on maximal NH4(+)-stimulated H(+)-K(+)-ATPase activity.(ABSTRACT TRUNCATED AT 250 WORDS)
Role of microfilaments in asialoglycoprotein processing in adult and developing liver
Authors: Kaufman S. S. , Blain P. L. , Park J. H. , Tuma D. J.
Published: December 2017

To assess the role of microfilaments in receptor-mediated endocytosis of asialoglycoproteins, hepatocytes isolated from adult and 6-day-old rats were treated with the antimicrofilamentous agent cytochalasin D and then incubated with 125I-asialoorosomucoid (ASOR). Cytochalasin D (50 microM) reduced degradation of continuously endocytosed ASOR (7.5 micrograms/ml) equally in adult and neonate to approximately 20% of control. Internalization of surface-bound ASOR suggested at least two discrete sites at which ligand translocation was inhibited by drug at both ages: 1) initial movement of receptor-ligand complex from cell surface to interior and 2) postinternalization ligand transit to lysosomes. Inhibition of plasma membrane translocation was confirmed by calculation of endocytotic rate constant (Ke) values, which were decreased to approximately 20-30% of control after cytochalasin D treatment. In contrast, the antimicrotubular drug colchicine did not reduce Ke values significantly nor did colchicine in combination with cytochalasin D impede lysosome-directed transport more than cytochalasin D alone. These results indicate that internalization of occupied asialoglycoprotein surface receptor is microfilament dependent irrespective of postnatal age and that subsequent participation of microfilaments in asialoglycoprotein trafficking is closely related to that of microtubules.
Effect of substance P and neurokinin A on rat parietal cell function
Authors: Schepp W. , Schmidtler J. , Tatge C. , Schusdziarra V. , Classen M.
Published: December 2017

In enzymatically dispersed enriched (76%) rat parietal cells we studied the effect of substance P on acid sequestration as indirectly measured by [14C]aminopyrine accumulation. Substance P (10(-8)-10(-5) M) had no effect on basal [14C]aminopyrine accumulation. Yet, the peptide reduced the response to histamine and to the postreceptor agonists forskolin and dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP). Inhibition by substance P followed noncompetitive kinetics and reduced stimulated parietal cell function by up to 45% at 10(-5) M. The antagonist [D-Pro2, D-Trp7,9]-substance P at 10(-5) M partly reversed the inhibitory effect of substance P. Cholinergic stimulation of [14C]aminopyrine accumulation was not reduced by substance P. Neurokinin A, another tachykinin that is structurally related to substance P, was of comparable potency and efficacy in reducing [14C]aminopyrine accumulation in response to histamine, forskolin, and DBcAMP. Inhibition of forskolin- or DBcAMP-induced [14C]aminopyrine accumulation persisted in the presence of 10(-5) M ranitidine. Inhibition by substance P and neurokinin A of the response to histamine was not sensitive to pertussis toxin. Both tachykinins failed to reduce histamine- and forskolin-stimulated cAMP production. Our data suggest that substance P and neurokinin A exert a direct effect on rat parietal cells. They attenuate histamine-stimulated acid sequestration at an intracellular step that is distal to the adenylate cyclase and that does not involve pertussis toxin-sensitive GTP-binding proteins.
Fasting and postprandial hepatic bile flow in unanesthetized opossums
Authors: Takahashi I. , Kern M. K. , Dodds W. J. , Hogan W. J. , Layman R. D. , Ammon H. V.
Published: December 2017

In conscious opossums, we evaluated the relationship between hepatic bile flow and the intestinal motor function during fasting as well as after feeding. In six opossums, bipolar electrodes were implanted from the gastric antrum to the terminal ileum. After cholecystectomy, the common duct was ligated, and a catheter was tied into the proximal common duct for collecting hepatic bile. During subsequent studies, hepatic bile flow was measured, and bile was returned to the duodenum through an externalized duodenal catheter. Cyclic increases in bile flow during fasting did not show a close correlate with the duodenal migratory motor complex (MMC) cycle. Rather, bile flow showed peak values [0.11 +/- 0.02 (SE) ml/min] when phase III MMC activity reached the midileum. Hepatic bile flow correlated closely with the amount of bile acid secreted by the liver. When the bile acid pool was depleted by diverting bile from the intestine, hepatic secretion of bile fell to uniformly low values of approximately 0.04 ml/min that did not show cyclic variation. Hepatic bile flow after feeding increased to a maximal value of 0.12 +/- 0.01 ml/min at 90 min. We conclude that increases in hepatic bile flow during fasting and after meals are determined mainly by variations in intestinal motor activity that alter small bowel transit and thereby affect the enterohepatic circulation of bile acids.
Regulation of postprandial motility in the canine ileum
Authors: Fich A. , Phillips S. F. , Neri M. , Hanson R. B. , Zinsmeister A. R.
Published: December 2017

We describe here further observations on a novel motor phenomenon that can be recorded regularly from the canine ileum in the late postprandial period, i.e., when residue of a meal reaches the distal small bowel. We reported before that this unique pattern of motility consisted of intraluminal pressure waves at a frequency (20-24/min) much greater than that of the ileal slow wave. In the current experiments, we document that these intraluminal pressure waves coincide with contraction of the circular muscle layer, as recorded from serosal strain gauges. However, the cellular origin and propagation of these contractile events are still unclear. By studying dogs with ileal loops and those with an intact bowel, we conclude that this is a local response of the ileum to the arrival of nutrients in its lumen and that it is under cholinergic control. This report supports the concept that the ileum may be particularly sensitive to its local intraluminal environment.
Amiloride and analogues inhibit Na(+)-H+ exchange and cell proliferation in AR42J pancreatic cell line
Authors: Delvaux M. , Bastie M. J. , Chentoufi J. , Cragoe E. J. , Vaysse N. , Ribet A.
Published: December 2017

To study the relation between activation of the Na(+)-H+ antiporter and gastrointestinal cell proliferation, we characterized this antiporter in a pancreatic cell line (AR42J) and studied the effects of mitogenic and nonmitogenic agents as well as those of Na(+)-H+ exchange blocking agents on DNA synthesis. Characteristics of amiloride-sensitive Na+ uptake were those of the Na(+)-H+ exchanger: 1) Na+ uptake was increased by intracellular acidification and depended on external [Na+] and pH; 2) concentrations for half-maximal inhibition (IC50) of Na+ uptake (3 mM [Na+] in medium) were 40 nM 5-(N,N-hexamethylene)amiloride (HA) less than 0.1 microM 5-(N-ethyl-N-isopropyl)amiloride (EIPA) less than 1 microM 5-(N,N-dimethyl)-amiloride (DMA) less than 40 microM amiloride; 3) IC50 for amiloride and analogues to inhibit Na+ uptake depended on [Na+] in medium (in 25 mM Na+ medium, the IC50 values were higher than in 3 mM and were 1 microM EIPA less than 10 microM DMA less than 0.3 mM amiloride). Growth factors for AR42J cells (dialyzed fetal calf serum and epidermal growth factor) activated Na+ uptake in a dose-dependent manner. Bombesin, which is nonmitogenic for AR42J cells, also increased Na+ uptake, indicating that activation of the antiporter is not sufficient to initiate cell proliferation in the AR42J cell line. The effects of Na(+)-H+ exchange blocking agents were tested on serum-stimulated cell proliferation. Decreasing external Na+ dramatically decreased AR42J cell proliferation. Amiloride and analogues inhibited [3H]thymidine incorporation in the same range of concentrations as that with which they inhibited Na(+)-H+ exchange.(ABSTRACT TRUNCATED AT 250 WORDS)
Cytoskeleton of intestinal goblet cells: role of actin filaments in baseline secretion
Authors: Oliver M. G. , Specian R. D.
Published: December 2017

Although microtubules appear necessary to maintain mucin granule transport in intestinal goblet cells, the role of microfilaments in mucus secretion is unknown. To determine the functional significance of microfilaments in goblet cell secretion, fluorescent cytochemistry of microfilaments and autoradiographic studies on granule movement were performed on rabbit intestinal goblet cells, with and without the actin depolymerizing agents, cytochalasin D (cyto D), and dihydro-cytochalasin B (dihydro B). In normal goblet cells, cytochemical localization of F-actin with NBD-phallacidin demonstrated their restriction to the apical surface of the goblet cell. Visualization of the goblet cell apical surface by electron microscopy revealed the presence of a thin layer of cytoplasm overlying the granule mass. Treatment with cyto D and dihydro B eliminated NBD-phallacidin staining of the apical cell surface. Quantitative analysis of baseline granule translocation demonstrated that treatment with cyto D and dihydro B resulted in dramatic acceleration of granule movement through goblet cells. This cellular response results from an increase in baseline secretion and facilitation of secretion of newly synthesized mucins, not stimulation of an accelerated secretory event. These data imply that actin filaments fulfill a barrier function in baseline secretion by hindering granule access to the plasma membrane; once the granule contacts the plasma membrane, exocytosis occurs. Secretion is balanced by the translocation of subjacent granules. In contrast, an accelerated secretory event is not triggered by plasma membrane access alone; this event requires a regulatory signal. We hypothesize that, unlike accelerated secretion, baseline secretion is constitutive, with exocytosis limited solely by the physical constraint of secretory granule access to the apical plasma membrane.
Variations in muscle tone of the human rectum: recordings with an electromechanical barostat
Authors: Bell A. M. , Pemberton J. H. , Hanson R. B. , Zinsmeister A. R.
Published: December 2017

Rectal wall tone (the contractile state of the rectal tunica muscularis) should mediate accommodation and influence rectal emptying. Such changes in tone however can be only inferred from changes in baseline pressure recorded with conventional manometry. We used an isobaric volumetric device, the rectal electromechanical barostat, to quantify variations in tone of the rectal wall in response to feeding and to perturbations in response to the pharmacological agents neostigmine and glucagon. The barostat quantitates muscular wall tone indirectly by measuring its reciprocal, e.g., the volume of air within a flaccid intraluminal bag that is maintained at a constant and preselected pressure, by an electronic feedback mechanism. The barostat as well as a three-channel perfused manometric catheter were positioned in the rectum of 14 healthy volunteers. Three patterns of changes were observed: 1) respiratory fluctuations, 2) rapid volume waves, and 3) slow volume changes. Rectal tone varied little during fasting; rapid or slow changes in intrabag volume were infrequent. Ingestion of a standard meal was followed by a significant decrease in barostat bag volume (85 +/- 6 ml fasting vs. 50 +/- 8 ml fed, P less than 0.05). Pharmacological agents also induced predictable responses; neostigmine decreased bag volume and induced phasic pressure activity, whereas glucagon abolished phasic pressure activity and increased barostat bag volume. Perfused manometric catheters showed no concomitant changes in baseline pressure. We concluded that a rectal barostat measured variations in human rectal tone, which were not recorded by conventional manometric techniques. These changes in rectal tone might have important functional significance.
Effect of sustained mesenteric nerve stimulation on intestinal oxygenation in developing swine
Authors: Nowicki P. T. , Miller C. E. , Hayes J. R.
Published: December 2017

The effects of sustained mesenteric nerve stimulation on intestinal oxygenation were determined in 3- and 35-day-old swine. Studies were conducted in pentobarbital-anesthetized animals during free-flow or constant-flow perfusion. Square-wave stimuli sufficient to induce maximal resistance vessel constriction were applied to postganglionic periarterial mesenteric nerves and each stimulation was sustained until measured variables reached steady state. When vascular resistance data were analyzed without data transformation, autoregulatory escape of intestinal vascular resistance was more complete in 3- than in 35-day-old animals when the escape process was complete; however, expression of these data as escape indexes revealed a similar degree of escape in both age groups. In 35-day-old animals, (a-v)O2 increased during sustained nerve stimulation under free-flow conditions; under constant-flow conditions, (a-v)O2, 86Rb extraction, and capillary permeability-surface area product were lower at completion of the escape process compared with baseline. In 3-day-old swine, these variables remained unchanged from baseline. Intestinal O2 uptake was compromised by sustained nerve stimulation, and this effect was similar in both age groups. We conclude that sustained nerve stimulation reduces intestinal oxygenation to a similar degree in 3- and 35-day-old swine. It is important to note, however, that the response of 3-day-old swine may be dissimilar from that which occurs during immediate postnatal life; indeed, the intestinal hemodynamic response of swine less than or equal to 1 day old should not be extrapolated from the response of 3-day-old animals.
Pharmacological evidence for histamine H3 receptor in the control of gastric acid secretion in cats
Authors: Bado A. , Hervatin F. , Lewin M. J.
Published: December 2017

We investigated the possible involvement of H3 receptor in the control of gastric acid secretion in the conscious cat provided with a gastric fistula [main stomach (MS)] and a denervated Heidenhain pouch (HP). Intravenous infusion of the selective H3 agonist (R)-alpha-methylhistamine at 3, 10, and 30 nmol.kg-1.h-1 induced a dose-related inhibition of pentagastrin-stimulated gastric acid output. Maximal inhibition in MS (48 +/- 3%, P less than 0.01) and HP (36 +/- 5%, P less than 0.01) was obtained with 30 nmol.kg-1.h-1. This dose also significantly inhibited peptone meal-induced gastric acid output by 38 +/- 4 and 46 +/- 8% (P less than 0.01) in MS and HP, respectively. These inhibitions were completely prevented by 10 nmol.kg-1.h-1 iv of the selective H3 receptor antagonist thioperamide. On the other hand, (R)-alpha-methylhistamine was without any effect on histamine-stimulated gastric acid output, whereas thioperamide produced a slight but not significant increase of this output in contrast to the H2 receptor antagonist ranitidine, which showed a strong inhibitory effect. These findings suggest that pentagastrin- or meal-induced gastric acid secretion involves an H3 receptor pharmacologically distinct from the H2 receptor.
Improved high-pressure liquid chromatographic-fluorometric assay for measurement of adenosine in plasma
Authors: Zhang Y. , Geiger J. D. , Lautt W. W.
Published: December 2017

A high-pressure liquid chromatographic system using fluorescence detection was characterized for the determination of adenosine levels in plasma from anesthetized cat, rat, dog, mouse, rabbit, and guinea pig. The optimal concentration of chloroacetaldehyde necessary to convert physiological levels of adenosine to its fluorescent derivative 1,N6-ethenoadenosine (ethenoadenosine) was in excess of 220 mM. As little as 0.2 pmol of ethenoadenosine could be measured, and detection was linear up to 200 pmol. Derivatization of adenosine into ethenoadenosine was highly dependent on temperature and time. However, ethenoadenosine showed thermal instability in that levels dropped sharply after 30 min at 100 degrees C, 2 h at 80 degrees C, and 24 h at 55 degrees C. Adenosine nucleotides were extracted from plasma samples with an efficiency of greater than 91% to prevent adenosine formation from ATP and AMP that would have otherwise occurred during the derivatization procedure. Plasma levels (microM) of adenosine in venous blood were 0.31 in dog, 0.54 in cat, 0.71 in guinea pig, 1.03 in mouse, 1.04 in rat, and 1.68 in rabbit. Plasma levels of adenosine in arterial blood were not significantly different from levels in venous blood. This method can be used to measure even very low levels of adenosine without interference from nucleotide breakdown.
Absorption and metabolic effects of enterally administered glutamine in humans
Authors: Dechelotte P. , Darmaun D. , Rongier M. , Hecketsweiler B. , Rigal O. , Desjeux J. F.
Published: December 2017

To assess absorption and metabolic effects of enterally delivered glutamine, a total of 10 healthy subjects received perfusions of natural L-glutamine at graded infusion rates (ranging from 0 to 126 mmol/h; n = 2-8 subjects at each rate) along with a nonabsorbable marker (polyethylene glycol) through a double-lumen nasojejunal tube. Perfusions were administered after an overnight fast during three consecutive 1- or 2.5-h periods and in a randomized order. In eight subjects, continuous intravenous infusion of D-[6,6-2H2]glucose, L-[1-13C]leucine, and L-[15N]alanine was simultaneously performed. Glutamine was nearly quantitatively absorbed over the 30-cm study segment; estimated Km and Vmax of glutamine absorption were 2.48 and 2.32 mmol/min over the 30-cm study segment. Enteral glutamine administration induced 1) a dose-dependent increase in plasma glutamine level; 2) a rise in the plasma level and appearance rate (Ra) of alanine (from 191 +/- 42 to 213 +/- 51 mumols.kg-1.h-1, P less than 0.05, for 0 and 46.8-mmol/h glutamine infusion rates, respectively) and in plasma levels of glutamate, citrulline, aspartate, and urea; 3) a decline in plasma free fatty acid and glycerol levels; and 4) no change in leucine or glucose Ra. We conclude that glutamine is efficiently absorbed by human jejunum in vivo and may directly inhibit lipolysis, whereas it neither affects proteolysis nor glucose production in healthy postabsorptive humans.
Glycosylation is not required for ligand or receptor binding by expressed rat intrinsic factor
Authors: Gordon M. M. , Hu C. , Chokshi H. , Hewitt J. E. , Alpers D. H.
Published: December 2017

A cDNA clone encoding rat intrinsic factor (IF), pIFQ, has been inserted into the eukaryotic expression vector pSVL and used to transfect COS-1 cells. The IF produced by the transfected cells was secreted nearly exclusively into the medium at concentrations of 0.1-0.2 micrograms/ml. Tunicamycin treatment (1-10 micrograms/ml) completely blocked N-linked glycosylation but had no effect on IF secretion. The secreted glycosylated IF retained all the properties of native IF, i.e., high affinity for cobalamin (Cbl) and for the IF-Cbl receptor and relative resistance to low pH and to proteolysis. The nonglycosylated IF also retained these properties except that it was more protease sensitive. The protease degradation was prevented by the presence of the ligand Cbl. The presence of carbohydrate may play a role in protecting IF from digestion by pancreatic proteases in the intestinal lumen.