bluuebunny/crossref_metadata_2025 huggingface dataset:
Rat liver metabolism of dicarboxylic acids
Authors: Vamecq J. , Draye J. P. , Brison J.
Published: December 2017

Recently, we demonstrated in rat liver that dicarboxylic acids containing more than five carbons can be activated by a microsomal dicarboxylyl-CoA synthetase (J. Vamecq, E. de Hoffmann, and F. Van Hoof. Biochem. J. 230: 683-693, 1985). The products of this reaction, dicarboxylyl-CoA esters, were found to be substrates for an H2O2-generating dicarboxylyl-CoA oxidase. In the present work we report that 1) the catalytic center or the essential domains of dicarboxylyl-CoA synthetase are located at the cytosolic aspect of the endoplasmic reticulum membrane; 2) dicarboxylyl-CoA oxidase is optimally active on dodecanedioyl-CoA and is a peroxisomal enzyme; 3) cyanide-insensitive dodecanedioyl-CoA oxidation (NADH production) is catalyzed by rat liver homogenates. Cell fractionation studies disclose that, similar to dodecanedioyl-CoA oxidase (H2O2 production), the cyanide-insensitive dodecanedioyl-CoA oxidizing activity also belongs to peroxisomes; 4) a dodecanedioyl-CoA oxidoreductase reaction can be assayed by the dichlorphenolindophenol procedure in rat liver homogenates, and the activity is abundant in peroxisomal, mitochondrial, and soluble fractions; 5) by contrast with monocarboxylyl-CoA esters, the dicarboxylyl-CoAs are apparently not substrates for mitochondrial fatty acid oxidation; however, the use of dicarboxylylcarnitine esters as direct substrate for mitochondria suggests the existence of an active beta-oxidation of dicarboxylates in these organelles, which is further confirmed by experiments in which mitochondria are permeabilized with digitonin; 6) the in vivo oxidation of infused dodecanedioic acid results in a rapid appearance in urine of medium-chain dicarboxylic acids, with only 30-50% of the infused dose recovered in urine.
Inhibitory regulation of rat exocrine pancreas by peptide YY and pancreatic polypeptide
Authors: Putnam W. S. , Liddle R. A. , Williams J. A.
Published: December 2017

Peptide YY (PYY) and pancreatic polypeptide (PP) have been shown to inhibit exocrine pancreatic secretion in vivo in a variety of species. This study evaluates the type of stimulation inhibited by PYY and PP by examining, in urethan-anesthetized rats, the inhibition of pancreatic secretion when stimulated to a comparable extent by cholecystokinin (CCK), 2-deoxy-D-glucose (2DG), bethanecol, and electrical vagal nerve stimulation. PYY at maximal infusion rates inhibited stimulation by CCK by 83%, bethanecol by 55%, and electrical nerve stimulation by 40%. The inhibition of CCK stimulation was half maximal at 250 pmol.kg-1.h-1. By contrast, PYY totally inhibited 2DG-stimulated secretion with half-maximal inhibition at 10 pmol. kg-1.h-1. PP acted similarly to PYY in inhibiting CCK and 2DG-stimulated pancreatic protein secretion but was fivefold weaker in each case. These findings indicate that PYY and PP have multiple actions but preferentially inhibit neurally mediated pancreatic secretion at a preacinar cell locus, possibly at a central site of action.
Inhibitory function of VIP-PHI and galanin in canine pylorus
Authors: Allescher H. D. , Daniel E. E. , Dent J. , Fox J. E.
Published: December 2017

Contractions of canine pylorus and adjacent muscles were recorded with antral and duodenal strain gauges and a Dent sleeve manometric assembly with additional side holes in the pylorus. In vivo, vasoactive intestinal polypeptide (VIP) and peptide histamine isoleucine (PHI) given through the gastroepiploic artery inhibited both spontaneous and acetylcholine-induced pyloric contractions, before and after neural blockade with tetrodotoxin. Galanin inhibited only nerve-stimulated contractions. VIP greater than PHI much greater than galanin inhibited pyloric motor activity initiated by field stimulation of duodenal intramural nerves or intraduodenal infusion of 0.1 N HCl. In vitro, forskolin or field stimulation of nerves inhibited contractions of the pyloric muscle induced by various agonists but VIP-PHI failed to inhibit these contractions on two-thirds of the strips. The in vivo results suggest that VIP (or PHI) may be an inhibitory mediator in the pylorus acting directly on smooth muscle. Galanin may inhibit neural excitatory pathways in the pylorus. However, the structures on which VIP and PHI act in vivo may have become nonfunctional in vitro and other mediators account for the neural inhibition observed in isolated strips.
Heterogeneity of the exocrine pancreas
Authors: Adelson J. W. , Miller P. E.
Published: December 2017

The exocrine pancreas is generally considered to be a homogeneous organ at the morphological and functional levels. Recent work, reviewed here, has provided multiple reasons to question this. Morphologically, differences have been found in cell size and digestive enzyme content in "peri-" vs. "teleinsular" acini by methods including acinar separation, enzyme assay, and both light and electron microscopic immunocytochemistry. Detection of several blood group antigens in human acinar tissue showed striking cellular heterogeneity in a mosaic pattern. Stimulation of pancreatic lobules by specific secretagogues and separation of individual zymogen granules with microfluorometric assay of enzyme content also confirmed heterogeneity at the lobular and organellar level. Functionally, evidence that nonparallel digestive enzyme secretion can be taken as direct support for acinar heterogeneity is reviewed, as is the work leading to direct demonstration of secretagogue-specific heterogeneous sequestration and storage of nascent digestive enzyme protein. A general overview of pancreatic acinar cell specificity is presented; the model incorporates temporal changes in secretion from eligible acini, with secretagogue specificity of whole acini containing specific preset mixtures of digestive enzymes.
Effect of VIP antagonist on VIP-, PGE2-, and acid-stimulated duodenal bicarbonate secretion
Authors: Algazi M. C. , Chen H. S. , Koss M. A. , Hogan D. L. , Steinbach J. , Pandol S. J. , Isenberg J. I.
Published: December 2017

Vasoactive intestinal peptide (VIP), prostaglandin E2 (PGE2), and luminal acidification are each potent stimulants of duodenal mucosal bicarbonate secretion. The present experiments were performed to determine whether the recently described VIP antagonist, [4Cl-D-Phe6,Leu17]VIP, suppresses VIP-stimulated duodenal mucosal bicarbonate secretion and to determine whether VIP serves as a mediator of bicarbonate secretion stimulated by acid or PGE2. In anesthetized rats, the effects of intravenous VIP, intraluminal PGE2, and intraluminal HCl on duodenal mucosal bicarbonate secretion both in the presence and absence of [4Cl-D-Phe6,Leu17]VIP were measured. The VIP antagonist inhibited duodenal bicarbonate secretion stimulated by both intravenous VIP and luminal acidification but not luminal PGE2. These findings suggest that VIP could be one mediator of acid-induced duodenal bicarbonate secretion and that the mechanism of PGE2-stimulated bicarbonate secretion is independent of VIP.
Effects of islet hormones on amylase secretion and localization of somatostatin binding sites
Authors: Garry D. J. , Garry M. G. , Williams J. A. , Mahoney W. C. , Sorenson R. L.
Published: December 2017

The interaction of insulin and somatostatin on amylase secretion was examined in the isolated perfused rat pancreas. Exogenous insulin (10 mU/ml) significantly potentiated cholecystokinin- (CCK; 0.5 mU/ml) stimulated amylase secretion (12.47 +/- 2.9 micrograms/ml, n = 7). Glucose (16.7 mM) stimulated endogenous insulin secretion (523 +/- 66 microU/ml) and also significantly enhanced CCK-stimulated amylase secretion (13.41 +/- 2.8 micrograms/ml, n = 11). When somatostatin was included in the perfusion media, containing insulin and CCK, amylase secretion was reduced to 3.17 +/- 0.83 micrograms/ml (n = 7), a level comparable to that of CCK-stimulated amylase secretion alone. Similarly, addition of exogenous somatostatin to perfusion media, containing 16.7 mM glucose and CCK, reduced amylase secretion to 4.29 +/- 1.09 micrograms/ml (n = 9). The effect of somatostatin and insulin on carbamylcholine-stimulated amylase secretion was also examined. Exogenous insulin (50 mU/ml) potentiated carbamylcholine- (10(-8) M) stimulated amylase secretion, and addition of exogenous somatostatin to the media containing both insulin and carbamylcholine suppressed the insulin potentiation. Uptake of 125I-[Tyr11]somatostatin in the perfused pancreas was saturable as it decreased significantly with the addition of excess unlabeled somatostatin. Autoradiograms revealed uptake of the ligand by both the endocrine islets and the exocrine pancreas with the highest density of grains observed over the acini. These results support the hypothesis that islet peptides modulate the exocrine pancreas, that somatostatin inhibits amylase secretion by inhibiting the action of insulin, and that somatostatin may act directly on the exocrine pancreas via specific receptors on acinar cells.
Characteristics of spermidine uptake by isolated rat enterocytes
Authors: Kumagai J. , Jain R. , Johnson L. R.
Published: December 2017

Eukaryotic cells require polyamines for growth. The supply of polyamines to growing cells may be increased either by new synthesis or increased uptake. We have recently shown that putrescine uptake by isolated rat enterocytes is energy dependent, saturable, and ouabain insensitive. Although putrescine uptake was inhibited by putrescine and cadaverine, it was not inhibited by equal concentrations of spermine and spermidine. These data indicated that a carrier mechanism separate from that putrescine existed for spermidine and spermine. In the current study spermidine uptake by isolated enterocytes was saturable, temperature dependent, and inhibited by 1 mM KCN. Kinetic analysis resulted in a Km = 2.51 x 10(-6) M and a Vmax = 3.57 x 10(-12) mol.10(6) cells-1.15 min-1. Spermidine uptake was 70% inhibited by 1 mM ouabain. Replacement of sodium by choline, lithium, tetramethylammonium, or N-methyl-D-glucamine also inhibited spermidine uptake. Replacement of Na+ by mannitol or sucrose, however, depressed uptake but not significantly. Spermidine uptake was inhibited by 1 mM ouabain. Spermidine uptake was inhibited by relatively low concentrations of spermine and high concentrations of putrescine; while putrescine uptake was inhibited by relatively high concentrations of both spermine and spermidine. Kinetic data indicated that spermidine and spermine share a carrier that is distinct from the one mediating the uptake of putrescine. While spermidine uptake does not appear to depend on Na+ cotransport, it may be dependent on the electrical gradient established by the Na+-K+-ATPase.
Noradrenergic influence on epithelial responses of rabbit ileum to secretagogues
Authors: Hubel K. A. , Renquist K. S. , Varley G.
Published: December 2017

Norepinephrine is one of three neurotransmitters that may act directly on enterocytes to enhance absorption; its interaction with secretagogues is of physiological importance. We have studied the influence of norepinephrine on the short-circuit current (Isc) responses to acetylcholine (ACh; 10 microM), vasoactive intestinal polypeptide (VIP; 100 pM-10 nM), peptide histidine isoleucine (PHI; 100 pM-10 nM), histamine (0.1 mM), and to electrical field stimulation (EFS) of rabbit ileum mounted in flux chambers. Tetrodotoxin reduced the response to norepinephrine (10 microM) by 40% and to histamine by 32% but did not affect responses to VIP or PHI. Norepinephrine decreased the ACh response (EC50, 70 nM) and reduced the responses to PHI (less than or equal to 87%), to EFS (less than or equal to 75%), and to histamine (less than or equal to 42%). Norepinephrine decreased the response to VIP (500 pM) but not to higher or lower VIP concentrations. It enhanced the response to VIP (10 nM) and to theophylline (5 mM). We conclude that 1) norepinephrine increases absorption by acting on nerves and enterocytes; 2) the failure of norepinephrine to reduce the Isc response to VIP when the VIP-induced increment in Isc is comparable to that caused by EFS is evidence that VIP does not mediate the EFS response; 3) PHI might mediate the EFS response; and 4) VIP, PHI, and histamine affect enterocytes directly; histamine also affects intrinsic nerves.
Ion transport and electrophysiology in rabbit cecum
Authors: Clauss W. , Hoffmann B. , Schafer H. , Hornicke H.
Published: December 2017

We investigated the basic bioelectrical properties and the transport of Na+, Rb+, and Cl- in the isolated cecal epithelium of the rabbit. Intracellular microelectrode recordings provided first estimates of the individual membrane potentials and resistances. The cecal epithelium was found to be a moderately tight epithelium with a high transepithelial potential and a relative high paracellular resistance. It has, however, a low transepithelial resistance caused by a high rate of transcellular ion transport and a high transcellular conductance. Under short-circuit conditions Na+ and Cl- are absorbed, whereas Rb+ is secreted. Na+ absorption seems to be mediated via an electrogenic mechanism with low amiloride sensitivity and is partially linked to Cl- transport. Cl- absorption is not influenced by secretagogues, and Rb+ secretion occurs via a transcellular route. A basolateral K+ conductance was also found. The results show rabbit cecum as an epithelium with a high electrolyte transport capacity, distinctly different from the neighboring proximal colon, and suited to absorb the large quantities of electrolytes that are present in the luminal liquid.
Distribution of opioid receptors in canine small intestine: implications for function
Authors: Allescher H. D. , Ahmad S. , Kostka P. , Kwan C. Y. , Daniel E. E.
Published: December 2017

Distribution of the binding sites for [3H]diprenorphine, a non-selective opiate ligand, was studied in membrane fractions from longitudinal muscle/myenteric plexus and circular muscle containing deep muscular plexus. [3H]saxitoxin was used as a marker for neuronal plasma membranes and 5'-nucleotidase as a marker for smooth muscle plasma membranes. Saxitoxin binding correlated strongly with diprenorphine binding, but 5'-nucleotidase correlated poorly with diprenorphine or saxitoxin binding in these fractions. Opiate binding sites in membranes of myenteric and deep muscular plexus were of high affinity (Kd = 0.12 and 0.18 nM, respectively) with maximum binding capacity of 400 and 500 fmol/mg protein, respectively. Competition experiments using subtype-selective opiate ligands indicated that all three subtypes of opiate receptors were present in the same ratio of 40-45% mu-subtypes, 40-45% delta-subtypes, and 10-15% kappa-subtypes on both plexuses. Opiate receptors of canine small intestine, therefore, are located primarily or exclusively on nerves with similar distributions in nerve membranes containing only axonal varicosities (deep muscular plexus) as in those containing neurons, dendrites, and varicosities (myenteric plexus).
Local effect of substance P on colonic motor activity in different experimental states
Authors: Hou J. Y. , Otterson M. F. , Sarna S. K.
Published: December 2017

We studied the effects of close intra-arterial injections of substance P on colonic motor activity in the conscious state, during anesthesia, and during acute laparotomy. In the conscious state, with enteric nerves intact, substance P stimulated postsynaptic cholinergic neurons to induce a large amplitude and long duration contraction. This response was blocked by prior close intra-arterial injection of atropine and tetrodotoxin (TTX) but not hexamethonium. Hexamethonium and TTX given alone, close intra-arterially, induced a series of short-duration contractions. Prior close intra-arterial administration of hexamethonium significantly enhanced the colonic motor response to substance P. After blockade of nerve conduction by TTX, substance P induced a series of short-duration contractions with characteristics different from those when the nerves were functioning. Anesthesia alone had little effect on the colonic motor response to substance P, but laparotomy inhibited it significantly. Laparotomy similarly inhibited the contractile response to bethanechol. Gut handling had no further effect on this inhibition. We conclude that in the conscious state substance P acts preferentially on postsynaptic cholinergic neurons to contract colonic circular muscle. When the intrinsic nerves are blocked, substance P may act directly on the smooth muscle to induce circular muscle contractions with characteristics different from those induced when nerves are intact. Substance P also has a weak inhibitory motor effect by its action on presynaptic neurons that synapse on postganglionic intrinsic inhibitory neurons. Anesthetic doses of barbiturates have no major effects on the neuromuscular response to substance P, but laparotomy significantly inhibits the smooth muscle response and selectively blocks some neurons.
Receptor occupation, calcium mobilization, and amylase release in pancreatic acini: effect of CCK-JMV-180
Authors: Sato S. , Stark H. A. , Martinez J. , Beaven M. A. , Jensen R. T. , Gardner J. D.
Published: December 2017

We examined the relationships between receptor occupation, calcium mobilization, and stimulated amylase release for cholecystokinin octapeptide (CCK-8) and for CCK-JMV-180, an analogue of the COOH-terminal heptapeptide of CCK having the structure Boc-Tyr(SO3)-Nle-Gly-Trp-Nle-Asp-2-phenylethyl ester using dispersed acini from rat pancreas. CCK-8 and CCK-JMV-180 each bind to two classes of CCK receptors: one class has a high affinity for CCK-8 and CCK-JMV-180 and the other class has a low affinity for CCK-8 and CCK-JMV-180. Mobilization of cellular calcium was assessed by measuring cytosolic calcium with a fluorescent indicator and by measuring outflux of radioactive calcium from preloaded cells. In terms of causing an increase in cytosolic calcium or an increase in calcium outflux, CCK-JMV-180 was 50-60% as efficacious as CCK-8. Analysis of the relationship between receptor occupation and calcium mobilization caused by CCK-8 and CCK-JMV-180 in combination indicates that calcium mobilization is caused by occupation of low-affinity CCK receptors. Comparison of the dose-response curve for calcium mobilization and amylase release stimulated by CCK-8 or CCK-JMV-180 indicates that very low concentrations of each peptide stimulate amylase release without causing detectable calcium mobilization. At these very low concentrations, CCK-8 or CCK-JMV-180 do not cause potentiation of amylase release when combined with vasoactive intestinal peptide.
Compartmental modeling of the hepatic transport of taurocholate in the rat in vivo
Authors: Deroubaix X. , Coche T. , Depiereux E. , Feytmans E.
Published: December 2017

Compartmental analysis was used to study the hepatobiliary transport of taurocholate (TC) in the rat in vivo. The available data are the following: [14C]TC kinetics in blood and bile, weighting factors associated with these data and computed from a theoretical variability model, and TC excretion rate in bile. The lumped model that best fits the data contains five compartments: three compartments for TC distribution in blood and two compartments for the liver. It includes a compartmental representation of the laminar flow of bile in the collecting catheter. This model overestimates TC concentration in blood. A perfusion model that includes a compartment representing explicitly the sinusoidal TC concentration gradient was developed. TC concentration in blood estimated by this model is in good agreement with direct measurements, showing that the perfused model has a better descriptive capacity than the lumped model. The amounts of TC estimated in the two hepatic compartments are similar to values previously published.
Villus contraction aids repair of intestinal epithelium after injury
Authors: Moore R. , Carlson S. , Madara J. L.
Published: December 2017

A highly reproducible in vitro model of intestinal epithelial injury in guinea pig ileum was used to study the structural and functional events that accompany rapid epithelial repair. This model is characterized by denudation of the villus tip followed by rapid restitution of the epithelial barrier. Using standard electrophysiological and quantitative morphometric techniques, we found that immediately after injury the number of cells lost exceeded the number of empty cell positions on the denuded basement membrane by 100%. Concurrently, cytoplasmic processes of subepithelial myofibroblasts contained condensations of microfilaments that were not apparent in controls. Additionally, villus height was diminished immediately after injury, and progressively decreased during the restitution period. In tissues that were depleted of ATP using the uncoupler dinitrophenol and in tissues functionally denervated by tetrodotoxin, villus shortening after injury was significantly reduced. Denervation also retarded functionally and structurally defined reestablishment of epithelial barrier function. These data suggest that intestinal epithelial repair is aided by energy-dependent, neurally mediated villus contraction. We speculate that the subepithelial network of myofibroblasts is responsible for this process, which effectively minimizes the denuded surface area to be reepithelialized.
Carbachol inhibits stimulant-induced increases in fundic D-cell cytosolic Ca2+ concentration
Authors: Chiba T. , Fujita T. , Yamada T.
Published: December 2017

We undertook these studies to examine the mechanisms by which carbachol inhibits somatostatin release. For these studies, we utilized cultured D-cells isolated from the canine gastric fundus. Carbachol inhibited somatostatin release induced by both pentagastrin and 12-O-tetradecanoyl-phorbol-13-acetate but did not alter the redistribution of protein kinase C induced by these agents. In contrast, carbachol diminished the increase in D-cell cytosolic free calcium levels ([Ca2+]i) induced by pentagastrin, and this effect was no longer evident after pretreatment of D-cells with pertussis toxin. Although carbachol by itself had no effect on [Ca2+]i, after pretreatment of D-cells with pertussis toxin, carbachol both enhanced [Ca2+]i and stimulated somatostatin release. These data indicate that carbachol activates signals in D-cells that result in both increase and decrease in [Ca2+]i. The latter effect, which appears to be mediated via a pertussis toxin-sensitive guanine nucleotide binding protein, may be one mechanism responsible for cholinergic inhibition of somatostatin release.
Carbachol-induced down-regulation of high-affinity receptors for vasoactive intestinal peptide
Authors: Murakami M. , Vinayek R. , Jensen R. T. , Gardner J. D.
Published: December 2017

When dispersed acini from guinea pig pancreas are first incubated with carbachol, the subsequent binding of 125I-vasoactive intestinal peptide (VIP) is inhibited during a second incubation. This inhibitory action of carbachol on binding of 125I-VIP depends on time, temperature, and the concentration of carbachol in the first incubation and can be blocked by atropine. First incubating acini with A23187, ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA), cholecystokinin octapeptide, bombesin, or 12-O-tetradecanoylphorbol-13-acetate does not alter binding of 125I-VIP. Adding EGTA to the first incubation medium abolishes the effect of carbachol on binding of 125I-VIP. In control acini or acini first incubated with carbachol, approximately half of the bound 125I-VIP can be stripped by acetic acid. 125I-VIP interacts with two distinct classes of receptors on pancreatic acini. One has a high affinity for VIP (Kd, 1 nM); the other has a low affinity for VIP (Kd, 2 microM). First incubating acini with carbachol decreases the number but not the affinity of high-affinity VIP receptors with no change in the number or affinity of low-affinity VIP receptors. Pancreatic acini possess two classes of muscarinic cholinergic receptors: one has a high affinity (Kd, 4 microM) and the other has a low affinity (Kd, 698 microM) for carbachol. The dose-response curve for carbachol-induced inhibition of binding of 125I-VIP and that for occupation of low-affinity muscarinic cholinergic receptors by carbachol are similar.(ABSTRACT TRUNCATED AT 250 WORDS)
Radical production during in vivo intestinal ischemia and reperfusion in the cat
Authors: Nilsson U. A. , Lundgren O. , Haglind E. , Bylund-Fellenius A. C.
Published: December 2017

Free radical formation was studied with electron spin resonance during 2 h of intestinal ischemia in the cat, at a blood flow less than 5 ml.min-1.100 g-1, followed by 30-min reperfusion. A modification of the spin trapping technique was used to stabilize highly reactive free radicals. The rate of secondary radical formation was 0.32 +/- 0.06 mumol.min-1.100 g intestine-1 before ischemia and increased to a maximum of 0.66 +/- 0.09 mumol.min-1.100 g-1 during the first minutes of reperfusion (mean +/- SE, n = 5). This could be prevented either by maintaining intestinal blood flow at 8-15 ml.min-1.100 g-1, by administering allopurinol before and during ischemia, or by perfusing the intestinal lumen with an O2-saturated buffer solution during ischemia, resulting in maximum rates of radical production during reperfusion of 0.37 +/- 0.04 (n = 6), 0.33 +/- 0.04 (n = 5), and 0.39 +/- 0.13 mumol.min-1.100 g-1 (n = 5), respectively. The results demonstrate that free radicals are produced in the intestine during reperfusion after a period of reduced blood flow below a certain critical level, and that inhibition of xanthine oxidase and prevention of hypoxia will eliminate this radical production.
Vasoactive intestinal peptide and its receptors in fetuses with cystic fibrosis
Authors: Chastre E. , Bawab W. , Faure C. , Emami S. , Muller F. , Boue A. , Gespach C.
Published: December 2017

Fetuses were investigated to establish whether vasoactive intestinal peptide (VIP) and its receptors are involved in the basic biochemical defect causing cystic fibrosis (CF). The intestine was used as a target for the disease and the liver as control. The immunoreactive and biologically active VIP contents of the colon and lower part of the small intestine were 1.5-2.5 times higher in CF fetuses than in controls. In control and CF intestinal mucosa, there was no change in the Scatchard parameters of the 125I-labeled VIP binding sites (Kd = 4.7-6.1 X 10(-11) M; Bmax = 268-280 fmol/mg protein for the high-affinity sites), in the two molecular components constituting the cross-linked 125I-VIP binding (Mr = 66,000 and 30,000), or in the pharmacological properties and functional characteristics of the VIP receptors activating the G proteins-adenylate cyclase system (Ka = 0.7 X 10(-9) M VIP). Similar results were obtained in liver. These findings suggest that neither VIP nor its receptors are involved in CF intestine. The possible involvement of other effectors related to the VIP pathway in CF intestine, including the release of VIP and adenosine 3',5'-cyclic monophosphate signal-transduction cascade, are presented.
Altered smooth muscle contraction and sodium pump activity in the inflamed rat intestine
Authors: Muller M. J. , Huizinga J. D. , Collins S. M.
Published: December 2017

We examined changes in membrane function underlying the increased contractility of jejunal longitudinal muscle to carbachol in rats infected 6 days previously with Trichinella spiralis. Muscarinic receptor characteristics were examined in particulate fractions using [N-methyl-3H]scopolamine (NMS). There was a significant reduction in the total number of binding sites on muscle from infected rats, but the affinity for NMS was unchanged. Similarly, in competition studies, the binding of carbachol to high or low affinity sites was not significantly different in tissue from control or infected rats. However, we observed an 89% suppression of the activity of K+ -stimulated ouabain-sensitive p-nitrophenylphosphatase (pNPPase), an enzyme marker for the Na+ -K+ pump, in plasma membranes from infected compared with control rats. Similar results were obtained in 86Rb uptake studies. In contractility studies, evidence for the electrogenicity of the Na+ -K+ pump was obtained by demonstrating that pump activation by K+, Rb+, or Cs+ was associated with tissue relaxation with a rank order of potency that was identical to that for stimulation of pNPPase activity by these ions. Conversely, pump inhibition by vanadate increased tone and abolished phasic contractions in muscle from control or infected rats. This was accompanied by an increased response to carbachol in muscle from control but not infected rats. In addition, pump inhibition by removing extracellular K increased tone in control tissue but decreased tone in muscle from T. spiralis-infected rats, presumably because of preexisting pump suppression. These results are consistent with the hypothesis that suppression of electrogenic Na-pump activity contributes to the increased contractility of jejunal muscle in rats infected with T. spiralis.
Effect of cold temperature on membrane potential responses in opossum esophageal circular muscle
Authors: Kauvar D. , Crist J. , Goyal R. K.
Published: December 2017

The effects of cold temperature on resting membrane potential (RMP) and membrane potential responses to depolarizing electrical current and intramural nerve stimulation were examined in opossum esophageal circular smooth muscle. Intracellular recordings were made in smooth muscle strips obtained from 7 to 8 cm (proximal site) and 1 to 2 cm (distal site) above the lower esophageal sphincter. RMP was not affected by changes in temperature between 34 and 22 degrees C. Cooling caused progressive inhibition of the amplitude and a slight increase in the duration of the spike potential produced by depolarizing current. Cooling did not modify the threshold for spike potential generation but decreased the spike amplitude from 34.0 +/- 0.5 mV at 34 degrees C to 14.1 +/- 2.2 mV at 22 degrees C (P less than 0.01). Electrical field stimulation with single electrical pulses (1.0 ms) produced tetrodotoxin-sensitive biphasic membrane responses consisting of initial hyperpolarization, or an inhibitory junction potential followed by depolarization that increased in amplitude as temperature was decreased from 34 to 26 degrees C and then decreased in amplitude as temperature was further decreased. At both proximal and distal sites cooling from 34 to 22 degrees C caused more than a twofold increase in the duration of hyperpolarization and time to peak depolarization. However, the increase in the absolute time of the duration of hyperpolarization and the time to peak depolarization was significantly greater at the distal than proximal esophageal site. Cooling to 16 degrees C decreased RMP and nearly abolished the biphasic membrane potential response.(ABSTRACT TRUNCATED AT 250 WORDS)
Tachykinins as transmitters of ascending contractile component of the peristaltic reflex
Authors: Grider J. R.
Published: December 2017

The role of tachykinin neurons of the myenteric plexus in the regulation of the intestinal peristaltic reflex was examined in rat colonic segments that enable separate measurement of ascending contraction and descending relaxation. Release of immunoreactive substance P (SP) and substance K (SK) increased (68% for SP; 70% for SK) during ascending contraction and decreased (37% for SP; 13% for SK) during descending relaxation. Exogenous SP and SK augmented ascending contraction and inhibited descending relaxation. Neither SP antiserum nor SK antiserum had any effect on descending relaxation. The antisera had no effect also on ascending contraction induced by low grades of stretch (2 g), but they inhibited significantly contraction induced by high grades (6-10 g) of stretch (52 +/- 8% inhibition with SP antiserum and 48 +/- 8% with SK antiserum). A combination of both antisera abolished ascending contraction induced by high grades of stretch. Atropine inhibited only partially ascending contraction at high grades of stretch. The pattern of inhibition by both antisera and by atropine implied that ascending contraction induced by high grades of stretch was mediated by tachykinin neurons acting directly on smooth muscle cells as well as indirectly via release of acetylcholine from cholinergic motor neurons.
Altered intestinal motility precedes diarrhea during Escherichia coli enteric infection
Authors: Sjogren R. W. , Sherman P. M. , Boedeker E. C.
Published: December 2017

Changes in ileal and colonic myoelectric activity during the course of enteric infection of rabbits with the enteropathogenic Escherichia coli strain RDEC-1 were determined and related to microbiological, histological, and clinical parameters of disease. Rabbits were grouped into early, peak, and late stages of infection based on fecal shedding of bacteria. Weight loss and an increase in prolonged spike bursts (both action potential complexes and ileal migrating action potential complexes) developed early in infection, before the onset of diarrhea. Loose stools subsequently developed coincident with maximal numbers of action potential complexes. The myoelectric responses correlated better with mucosal enteroadherence of bacteria than with luminal colonization. These data demonstrate that, in this animal model of enteroadherent bacterial infection of the intestine, changes in intestinal myoelectric activity precede the onset of clinical diarrhea. In addition, bacterial adherence to the intestinal mucosa appears to be important in eliciting the abnormal myoelectric responses.
Intracellular pH regulation in IEC-6 cells, a cryptlike intestinal cell line
Authors: Wenzl E. , Sjaastad M. D. , Weintraub W. H. , Machen T. E.
Published: December 2017

Regulation of intracellular pH, pHi, was studied using microspectrofluorimetry of the pH-sensitive, fluorescent dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein in the rat intestinal crypt cell line, IEC-6. In N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES)-buffered solutions with pHi 7.25, treatment with a pulse of NH4Cl caused cells to acidify and then recover to control level. Because recovery was Na dependent, blocked by 1 mM amiloride, and unaffected by the presence and absence of Cl, it was likely because of a Na+-H+ exchanger. Cells were also acid loaded by changing from HEPES to HCO3-CO2-buffered solutions. pHi again recovered, but 1 mM amiloride reduced the rate of H+ efflux by only 47%. This HCO3-dependent, amiloride-insensitive H efflux required Na+ but not Cl- and was completely blocked by 200 microM [H2] 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). We conclude that a Na+-HCO3- cotransporter was operative. Cl-free solutions caused pHi to increase from 7.19 to 7.41; this effect required the presence of exogenous HCO3-CO2 but not Na and was blocked by 200 microM [H2]DIDS. A Cl- -HCO3- exchanger is the most likely explanation for these data. All the pHi regulatory mechanisms are operative in NaCl-HCO3-CO2-buffered solutions. The Na+-H+ and Na+-HCO3- mechanisms are acid extruders, whereas the Cl- -HCO3- exchanger is an acid loader. These transporters may be important for generating HCO3 secretion by intestinal crypt cells.
Vitamin D3 and glucose-6-phosphate dehydrogenase in rat duodenal epithelial cells
Authors: Nasr L. B. , Monet J. D. , Lucas P. , Bader C. A.
Published: December 2017

A microdensitometric method was employed to determine enzyme activities in situ in undisrupted tissue rat duodenum. The effect of 1 alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3] on glucose-6-phosphate dehydrogenase (G6PD) activity and on the two utilization pathways of synthesized NADPH, H1 (mixed function oxidation) and H2 (biosynthesis), was studied. In normal animals, a crypt-to-villus gradient of G6PD activity and of both NADPH utilization pathways was observed. A high level of NADPH utilization occurred predominantly via the H2 pathway. In vitamin D-deficient rat animals, G6PD activity in the middle part of the villus was approximately 60% lower than in normal animals [10.05 +/- 0.35 vs. 3.95 +/- 0.26 (means +/- SE) A585.min-1.micron-3 X 10(5), P less than 0.001] with reduced NADPH utilization via the H2 pathway (8.39 +/- 0.49 vs. 2.73 +/- 0.43 A585.min-1.micron-3 X 10(5), P less than 0.001) but not the H1 pathway (1.65 +/- 0.17 vs. 1.22 +/- 0.19 A585.min-1.micron-3 X 10(5), P = NS). Intraperitoneal administration of 1,25(OH)2D3 (500 pmol) to vitamin D-deficient animals resulted in increased G6PD activity within 30 min (4.09 +/- 0.38 vs. 5.51 +/- 0.39 A585.min-1.micron-3 X 10(5), P less than 0.05), attaining normal levels within 2 h. The H2 but not the H1 pathway of NADPH utilization increased significantly in response to 1,25(OH)2D3. This increase is essentially located in the basal and middle parts of the villus. Thus 1,25(OH)2D3 may influence biosynthesis in the duodenum via stimulation of G6PD activity and the H2 pathway of NADPH utilization.
Effect of pH on membrane potential and K+ conductance in cultured rat hepatocytes
Authors: Fitz J. G. , Trouillot T. E. , Scharschmidt B. F.
Published: December 2017

We have investigated the effects of extracellular (pHo) and intracellular (pHi) pH on membrane potential difference (PD) and cell conductance (gcell) in rat hepatocytes in primary culture. PD and pHi were measured continuously by using intracellular microelectrodes and the pH-sensitive fluorochrome 2',7'-bis(2-carboxyethyl)-5(6)-carboxy fluorescein (BCECF), respectively, during abrupt changes in the pHo or ionic composition of extracellular perfusate. In the presence of 25 mM HCO3-, PD, gcell, and pHi averaged (+/- SE) -32 +/- 1 mV, 16.4 +/- 1.0 nS, and 7.32 +/- 0.01, respectively. The transference number for K+ (tk+), which reflects the fractional contribution of K+ conductance to gcell, averaged 0.36 +/- 0.03. Exposure to 1 mM Ba2+ produced membrane depolarization and decreased tK+ by approximately 90%. Lowering pHo by a variety of maneuvers in the presence and absence of HCO3- consistently decreased pHi, decreased gcell (approximately 30 nS per unit change in pHi), and depolarized PD. Increasing pHo had opposite effects, but the changes in gcell were generally greater with intracellular acidification than alkalinization. The decrease in PD produced by lowering pHo was associated with a decrease in tK+ of 73 +/- 2% and was inhibited by Ba2+. Exposure to butyrate or withdrawal of NH+4, which lowered pHi without changing pHo, also caused depolarization of PD and a decrease in gcell that was inhibited by Ba2+. These observations indicate that the PD of hepatocytes is strongly influenced by pHi, with or without changes in pHo, and they further suggest that the effects of pH on PD are mediated through changes in plasma membrane K+ conductance.
Effects of acetylcholine and substance P on electrical activity of intact toad gastric muscles
Authors: Shonnard P. Y. , Sanders K. M.
Published: December 2017

By using isolated gastric muscle cells of Bufo marinus, others have studied the mechanism of action of muscarinic agonists and substance P (SP). To compare responses of isolated cells with those of intact muscles, we have studied the effects of acetylcholine (ACh) and SP on membrane potentials of circular muscle cells in strips of intact muscle from the toad gastric corpus region. These cells had average resting potentials of -69 +/- 0.7 mV. Membrane potential rhythmically depolarized, producing slow waves at an average frequency of 1/min and average amplitude of 25 +/- 2.2 mV. The major effect of ACh (10(-7) to 10(-4) M) was chronotropic; the frequency of slow waves was increased by 88 +/- 11% by 10(-6) M ACh. The amplitudes and rates of rise of slow waves were decreased by ACh. SP had effects similar to ACh; its major effect was chronotropic. The data suggest that ACh and SP primarily affect the pacemaker mechanism in gastric muscles. Since rhythmicity is apparently not expressed in isolated gastric myocytes, it is possible that this effect of these agonists may have been missed in studies of dispersed cells. Our data suggest that the excitatory effects of ACh and SP on contractions may be due to summation of Ca2+ signals, a partial tetanus-like effect.
The propulsive behavior of the opossum sphincter of Oddi
Authors: Calabuig R. , Ulrich-Baker M. G. , Moody F. G. , Weems W. A.
Published: December 2017

This study investigates whether the phasic contractions of the opossum sphincter of Oddi (SO) delay bile flow by acting as a resistor or facilitate bile flow by acting as a pump. The common bile duct (CBD) and an adjacent segment of duodenum from eight opossums were studied in a propulsion evaluation system in vitro. This system required the production of hydrostatic work by the SO to transfer fluid from the CBD to the duodenum when the pressure in the duodenum was equal or greater than the pressure in the CBD. Fluid movement from the CBD to duodenum and duodenum to CBD was studied at pressure gradients up to 50 cmH2O before and after sodium nitroprusside (10(-7) M) inhibition of smooth muscle contractile activity. All preparations propelled fluid from the CBD to the duodenum against a pressure gradient ranging from 10 to 50 cmH2O. The SO emptied the CBD in a monoexponential fashion, with a time constant of 1.52 +/- 0.7 min, until CBD pressure was reduced to 8.5 +/- 3.2 cmH2O, when propulsion ceased. Superimposed on the CBD pressure waveform were pressure pulses of 1-2 cmH2O in amplitude that resulted from the contractions of the SO. CBD pressure was higher at the start than at the end of a periodic pressure pulse, whereas CBD pressure was stable between pulses. The frequency of the pressure pulses was greatest at the maximal CBD pressure (9.4/min) and decreased significantly when the basal pressure was reached (1.5/min, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)
Absence of synchrony between human small intestinal migrating motor complex and rectal motor complex
Authors: Kumar D. , Thompson P. D. , Wingate D. L.
Published: December 2017

Both the human small intestine and rectum exhibit motor activity in which relatively brief bursts of powerful regular contractions recur with a similar periodicity. We used prolonged ambulant manometry to test the hypothesis that these activities are synchronous. Pressure activity from the duodenojejunum and the rectum was recorded continuously for 24 h in eight freely ambulant healthy adults. A total of 61 migrating motor complexes and 61 rectal motor complexes occurred in the group; the median periodicities of the two rhythms differed significantly (P = 0.025). There was no evidence of synchrony between the two biorhythms. We conclude that they are independent oscillations.
Hormonal stimulation of Ca2+ release from the perfused liver: effects of uncoupler
Authors: Kraus-Friedmann N. , Higham S. , Fleschner C. R.
Published: December 2017

Administration of vasopressin and glucagon evokes a transient release of Ca2+ from perfused livers. The Ca2+ is released from a pool that is depletable by the mitochondrial uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP). Therefore, the mechanism of the FCCP-stimulated Ca2+ release was examined. The FCCP-stimulated Ca2+ release was associated with a decrease in ATP levels. In the presence of oligomycin, which blocked the FCCP-induced rapid ATP breakdown, FCCP did not release Ca2+ though it still stimulated respiration. The possibility that FCCP might indirectly cause a release of Ca2+ by lowering hepatic ATP was examined at two levels of organization: 1) in the whole organ, by perfusing livers with fructose, a compound that was shown previously to drastically lower ATP in the liver, and 2) in isolated microsomal vesicles by depleting ATP with glucose and hexokinase. Fructose evoked Ca2+ release from the perfused liver. Similarly, depletion of ATP by the addition of glucose and hexokinase evoked a rapid release of the accumulated Ca2+ from microsomal vesicles probably by the inhibition of the Ca2(+)-ATPase. These results demonstrate that the major mechanism by which FCCP releases Ca2+ in intact cells is by lowering ATP levels.
Human intestinal water absorption: direct vs. indirect measurements
Authors: Gisolfi C. V. , Summers R. W. , Schedl H. P. , Bleiler T. L. , Oppliger R. A.
Published: December 2017

Distilled water, a carbohydrate-electrolyte (CE; 4% sucrose, 2% glucose, 17.2 meq/l NaCl, and 2.8 meq/l KCl) solution, or a 10% glucose solution, all containing the nonabsorbed indicator polyethylene glycol (PEG) and deuterium oxide (D2O, 30 ppm), were infused (15 ml/min) into the duodenojejunum of seven men by using the triple lumen technique. Net water absorption was determined directly from the change in PEG concentration and was calculated from plasma D2O derived from D2O in the perfusion solutions. The protocol included a 45-min equilibration period followed by a 90-min test period. Intestinal samples were drawn at 10-min intervals from 15 to 45 min and at 15-min intervals thereafter. Blood was drawn at 45, 50, 55, 60, 75, 90, 105, 120, and 135 min. Intestinal samples were analyzed for D2O, Na+, K+, osmolality, PEG, and glucose; blood was analyzed for D2O. Results (+/- SE; positive values secretion, negative values absorption) showed net fluid absorption from distilled water (-9.40 +/- 1.28 ml.h-1.cm-1) and the CE (-13.30 +/- 1.22 ml.h-1.cm-1) solution, but net secretion (4.40 +/- 1.25 ml.h-1.cm-1) from the 10% glucose solution. All values were significantly (P less than 0.05) different from each other. Perfusing the CE solution caused net Na+ and K+ absorption, whereas perfusing the 10% dextrose solution caused net electrolyte secretion. Rates of D2O accumulation in the plasma were independent of the solutions perfused.(ABSTRACT TRUNCATED AT 250 WORDS)
Villous motility and unstirred water layers in canine intestine
Authors: Mailman D. , Womack W. A. , Kvietys P. R. , Granger D. N.
Published: December 2017

The possibility that villous motility reduces the mucosal unstirred water layer by mechanical stirring was examined. The frequency of contraction of villi was measured by using videomicroscopic techniques while a segment of anesthetized canine jejunum or ileum with its nerve and blood supply intact was maintained in a sealed chamber through which Tyrode solution was perfused. Radioisotopically labeled inulin, H2O, and butyric and lauric acid were used to measure net and/or unidirectional fluxes from the chamber. The unidirectional absorptive transport of H2O and butyric acid but not lauric acid by jejunal segments was significantly correlated with flow through the chamber. Plasma volume expansion increased villous motility but decreased the absorption of H2O and lauric acid. Absorption of butyric acid from the ileum was little different than from the jejunum although the degree of villous motility was less and net water absorption was greater from the ileum. Absorption of butyric acid into dead tissue indicated that passive diffusion into the tissue accounted for between 7 and 25%, depending on flow rate, of the absorption in intact tissue and that nonspecific binding was low. It was concluded that villous motility did not stir the unstirred water layers and was not directly associated with altered transport.