bluuebunny/crossref_metadata_2025 huggingface dataset:
Site and mechanisms of action of kinins in rat ileal mucosa
Authors: Warhurst G. , Lees M. , Higgs N. B. , Turnberg L. A.
Published: December 2017

Kinin-induced secretion in the intestine is accompanied by marked increases in mucosal adenosine 3', 5'-cyclic monophosphate (cAMP) and prostanoids that undoubtedly contribute to the overall secretory response. The cellular site at which these effects are initiated is unclear although a recent hypothesis has suggested the epithelial cell as the target for kinin action (6). We have investigated the effects of kallidin on the phospholipase-prostanoid-cAMP pathway in whole ileal mucosa and in epithelial cells isolated from the same tissue in the rat. Kallidin (1 microM) stimulated a marked rise (24 to 30-fold) in PG (prostaglandin) E2 release from the serosal surface of stripped ileal mucosa within 1-2 min, which correlated closely with the rise in mucosal short-circuit current. Mucosal cAMP levels were also increased two to threefold by kallidin. However, kinins were unable to elicit effects under the same conditions in suspensions of viable epithelial cells. PGE2 release was unaffected by kallidin or bradykinin at concentrations up to 100 microM, whereas cAMP levels could be stimulated by forskolin and PGE2 but not by kinin. Studies of intestinal phospholipase A2 (PLA2) activity also suggest a nonepithelial site for kinin action. This enzyme is responsible for liberating arachidonic acid from cellular phospholipids and has been shown to be activated by kinins in several tissues. In the intestine, PLA2 activity was found to be concentrated within the subepithelium with significantly lower levels in the epithelium itself. In addition, kallidin was unable to influence phospholipid labeling (an indirect measure of PLA2 activity) in cells incubated with [14C]arachidonic acid.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of morphine on electrophysiological properties of circular and longitudinal muscles
Authors: Gilbert R. J. , Sarna S. K. , Harder D. R.
Published: December 2017

We have measured the effects of morphine on the intracellular electrophysiological properties of smooth muscle cells from the circular and longitudinal muscle layers of the canine jejunum. Morphine hyperpolarized the circular muscle membrane by approximately 12 mV and increased the electrical control activity (ECA) amplitude and dV/dt. Morphine had no significant effect on the electrical properties of the longitudinal muscle cells. The morphine-induced hyperpolarization of the circular muscle membrane was blocked by tetrodotoxin (TTX) and naloxone, but not by atropine and hexamethonium, propranolol, or phentolamine. Morphine significantly increased the slope of the resting membrane potential vs. the log of the potassium concentration in bathing medium from 38 to 50 mV/decade. The sodium permeability to potassium permeability ratio, calculated from the Goldman constant field equation, was reduced by morphine from 0.13 to 0.07 at mM of K+. The above results suggest that when measured by intracellular techniques, morphine hyperpolarizes the circular muscle membrane by release of a nonadrenergic, noncholinergic neurotransmitter. The mechanism of this hyperpolarization is consistent with an increase in potassium conductance.
Simultaneous measurements of 22Na and 36Cl in aqueous samples: a comparison of three different methods
Authors: Rangachari P. K. , McWade D.
Published: December 2017

We have critically analyzed three methods that measure the combined presence of 36Cl and 22Na in aqueous samples. These were a sequential method, a dual-label spectral analysis method (Beckman 1983), and a AgNO3 precipitation method (Thompson 1983). The former requires the use of both a gamma counter and a beta liquid scintillation counter, whereas the latter two require access to a beta counter only. Our analysis suggests that investigators who have access to both a liquid scintillation counter and a gamma spectrometer would find the sequential method relatively simple to use and reasonably reliable. Those with access to only a liquid scintillation counter would be best advised to use the AgNO3 method described by Thompson.
Paracrine regulation of gastric acid secretion by fundic somatostatin
Authors: Schubert M. L. , Edwards N. F. , Arimura A. , Makhlouf G. M.
Published: December 2017

The isolated, luminally perfused mouse stomach was used to determine whether somatostatin cells located in proximity to parietal cells exert a paracrine influence on acid secretion. Acid secretion in response to histamine and pentagastrin was accompanied by a dose-dependent increase in somatostatin secretion. Incubation of the stomach with somatostatin antiserum (final dilution 1:100), but not with normal serum, augmented significantly basal and secretagogue-stimulated acid secretion. The augmentation was most evident with submaximal stimuli (92 +/- 18%, P less than 0.01, with 15 microM pentagastrin and 160 +/- 6%, P less than 0.001, with 5 microM histamine) and least evident with maximal stimuli (30 +/- 12%, P less than 0.05, with 200 microM histamine). The acid response to submaximal field stimulation (10 V, 20 Hz, 0.5 ms), which was accompanied by an increase in somatostatin secretion, was also augmented by somatostatin antiserum (115 +/- 12%, P less than 0.01), whereas the response to maximal field stimulation (20 V, 20 Hz, 0.5 ms), which was accompanied by a decrease in somatostatin secretion, a typically cholinergic effect, was not augmented further. It is concluded that fundic somatostatin modulates the acid secretory response to paracrine (histamine), hormonal (gastrin), and neural (acetylcholine) stimuli and that cholinergic stimulation of acid secretion reflects both the direct effect of acetylcholine on the parietal cell and its ability to eliminate the paracrine restraint exerted by somatostatin.
Vagal influence on gastroduodenal HCO3- secretion in the cat in vivo
Authors: Nylander O. , Flemstrom G. , Delbro D. , Fandriks L.
Published: December 2017

Gastric and duodenal secretions of HCO3- were studied simultaneously in chloralose-anesthetized cats. The adrenals were ligated, and the cervical vagal as well as the abdominal splanchnic nerves were cut. Gastric secretions of H+ and HCO3- were calculated from measurements of the pH and PCO2 in the luminal perfusate. A duodenal segment devoid of Brunner's glands and pancreaticobilary secretions was cannulated in situ and the alkaline secretion determined by continuous titration at luminal pH 7.4. Electrical stimulation in the distal direction for 10–15 min of the cervical vagal nerves resulted in a 6- to 10-fold increase in gastric H+ and in a 20–60% rise in gastric HCO-3 secretion. Duodenal HCO3- secretion increased by 65–155%. Gastric basal secretions of H+ and HCO3- were not affected by atropine or hexamethonium, but both agents inhibited basal duodenal HCO3- secretion. Hexamethonium abolished and atropine reduced the rise in all secretions in response to vagal nerve stimulation. Thus gastroduodenal mucosal HCO3- secretion is stimulated by vagal mechanisms involving action on nicotinic as well as on muscarinic receptors and possibly also noncholinergic neurotransmission.
Reflex gastric relaxation in response to distention of the duodenum
Authors: De Ponti F. , Azpiroz F. , Malagelada J. R.
Published: December 2017

Using a newly developed gastric barostat, we studied the effect of duodenal distention on gastric tone in a chronic canine model. In the conscious, fasted dogs, duodenal distention for 15 s consistently induced a marked gastric relaxation (delta intragastric volume = 226 +/- 23 ml). This response could be induced repeatedly without evidence of fatigue. Neither bethanechol nor combined phentolamine and propranolol infused intravenously had any significant effect on gastric relaxation in response to duodenal distention. To investigate the pathway of this duodenogastric mechanism, in four dogs we isolated the vagal nerves at the supradiaphragmatic level within an implanted cooling jacket. During intravenous infusion of bethanechol (used as a cholinergic background to maintain base-line gastric tone), supradiaphragmatic vagal blockade by cooling abolished the gastric relaxatory response to duodenal distention (delta intragastric volume = 11 +/- 5 ml during vagal blockade vs. 194 +/- 36 after vagal rewarming; P less than 0.05). This effect of acute and reversible vagal blockade by cooling was also mimicked by bilateral surgical vagotomy. We conclude that a nonadrenergic, noncholinergic mechanism participates in gastric relaxation induced by duodenal distention. This mechanism is mediated by the vagus nerve.
Splanchnic blood flow during stimulation of gastrointestinal growth
Authors: Ulrich-Baker M. G. , Smidt W. R. , Gaginella T. S. , Granger D. N.
Published: December 2017

The primary objective of this study is to determine whether a relationship exists between the rate of blood flow and the gastrointestinal response to a trophic stimulus. A new prostaglandin E2 (PGE2) derivative, Ro 22-1327, was employed as a growth stimulus. Rats were treated by gavage for 14 days with Ro 22-1327 (0.5 and 5 mg/kg). The vascular and trophic effects of Ro 22-1327 were studied in the gastric antrum and oxyntic gland area, duodenum, jejunum, ileum, colon, liver, and pancreas. Generally, the trophic effects were 1) similar to those reported with other PGE2 analogues, 2) more pronounced in the antrum than in the oxyntic gland area, 3) greatest in the stomach, diminishing toward the colon, and 4) dose dependent. Organ blood flows were largely unaffected by the low-dose treatment, while the high-dose treatment tended to increase blood flow. The changes in blood flow were most pronounced proximally where the trophic responses were maximal. We speculate that the greater trophic response to the high dose of Ro 22-1327 may reduce the vasoconstriction produced by this agent.
Freeze-thaw and high-voltage discharge allow macromolecule uptake into ileal brush-border vesicles
Authors: Donowitz M. , Emmer E. , McCullen J. , Reinlib L. , Cohen M. E. , Rood R. P. , Madara J. , Sharp G. W. , Murer H. , Malmstrom K.
Published: December 2017

High-voltage discharge or one cycle of freeze-thawing are shown to transiently permeabilize rabbit ileal brush-border membrane vesicles to macromolecules. Uptake of the radiolabeled macromolecule dextran, mol wt 70,000, used as a marker for vesicle permeability, was determined by a rapid filtration technique, with uptake defined as substrate associated with the vesicle and releasable after incubation of vesicles with 0.1% saponin. Dextran added immediately after electric shock (2,000 V) or at the beginning of one cycle of freeze-thawing was taken up approximately eightfold compared with control; with both techniques, the concentration of dextran after being taken up into the vesicles was similar to that in the incubation medium, suggesting attainment of equilibrium. ATP also was taken up into freeze-thawed vesicles, whereas there was no significant uptake into control vesicles. The increase in vesicle permeability was reversible, based on Na-dependent D-glucose uptake being decreased when studied 5 but not 15 min after electric shock, and was not significantly decreased after completion of one cycle of freeze-thawing. In addition, adenosine 3',5'-cyclic monophosphate and Ca2+-calmodulin-dependent protein kinase activity were similar in control vesicles and vesicles exposed to high-voltage discharge or freeze-thawing. Also, vesicles freeze-thawed with [32P]ATP demonstrated increased phosphorylation compared with nonfrozen vesicles, while freeze-thawing did not alter vesicle protein as judged by Coomassie blue staining. These techniques should allow intestinal membrane vesicles to be used for studies of intracellular control of transport processes, for instance, studies of protein kinase regulation of transport.
Effect of tetraethylammonium on an evoked spike potential in feline colonic muscle
Authors: Snape W. J. , Tan S. T.
Published: December 2017

The purpose of these studies is to examine the contribution of calcium influx and potassium efflux to the amplitude and maximum rate of rise of an evoked spike potential in colonic circular smooth muscle. The double sucrose gap was used to record changes in the membrane potential after passing a constant depolarizing current. Tetraethylammonium (TEA) (5 mM) increased the amplitude of the evoked potential to 58 +/- 5 mV (P less than 0.001) from 32 +/- 4 mV in regular Krebs solution. The duration of the potential increased from 121 +/- 3 to 216 +/- 5 ms when a solution of 5 mM [TEA+]o bathed the tissue. The addition of [TEA+]o did not alter the dV/dtmax of the evoked spike. Other K+ channel blockers, cesium and 4-aminopyridine, did not alter the spike potential. Verapamil (10(-6) M) decreased the dV/dtmax of the evoked potential recorded from tissue bathed in 4.5 and 40 mM [K+]o. Verapamil also decreased the amplitude of the spike potential in tissue pretreated with 5 mM TEA. These studies suggest that the amplitude of an electrically evoked spike potential is dependent on Ca2+ influx in circular colonic muscle and an increase in K+ efflux, which occurs early after the current pulse, limits the amplitude of the evoked potential.
Intestinal capillary filtration in experimental diabetes mellitus
Authors: Korthuis R. J. , Pitts V. H. , Granger D. N.
Published: December 2017

There is indirect evidence that indicates that intestinal transcapillary fluid and solute exchange is significantly altered in diabetes mellitus. To directly assess the dynamics of microvascular fluid and solute exchange in the small intestine (jejunum-ileum), we measured lymph flow, capillary pressure, capillary filtration coefficient, plasma and lymph oncotic pressures, and the osmotic reflection coefficient in anesthetized, fasted control rats and in rats in which diabetes was induced by a single injection of streptozotocin (65 mg/kg ip) 4 wk before the experiments. Diabetes was associated with an increase in lymph flow (by 120%), capillary pressure (by 34%), and capillary filtration coefficient (by 75%) when compared with values from control rats. The transcapillary oncotic pressure gradient was not altered by diabetes. Interstitial fluid pressure, calculated from the measured parameters in the Starling equation, was increased from -1.6 mmHg in control rats to +2.5 mmHg in diabetic animals. Analysis of lymph-to-plasma protein concentration ratios at various lymph flows suggests that the osmotic reflection coefficient in the diabetic intestine is comparable to that obtained in control animals. The results of this study indicate that experimental diabetes mellitus is associated with increases in intestinal capillary pressure and capillary filtration rate but that intestinal capillary permeability is not altered in this disorder.
Degradation of endogenous heptadecapeptide gastrin by endopeptidase 24.11 in the pig
Authors: Power D. M. , Bunnett N. , Turner A. J. , Dimaline R.
Published: December 2017

Hydrolysis of heptadecapeptide gastrin (G-17) by endopeptidase 24.11 (EC 3.4.24.11) was studied in vivo and in vitro in the pig. Ion exchange chromatography and radioimmunoassay with three region-specific antisera were used to identify the products of porcine G-17 degradation. Incubation of antral extracts with pure endopeptidase 24.11 resulted in a substantial loss of intact G-17: 80% C-terminal immunoreactivity was lost in 60 min. This hydrolysis was completelyinhibited by phosphoramidon, which is a specific inhibitor of endopeptidase 24.11. In antral extracts G-17 accounted forgreater than 95% of total C-terminal immunoreactivity, compared with less than 60% C-terminal immunoreactivity in the gastric venous outflow; shorter C-terminal forms comprised the major part of the remaining immunoreactivity. After infusion of phosphoramidon, the concentration of intact G-17 was increased, and there was a corresponding reduction in the concentration of other C-terminal immunoreactive fragments. We conclude that endopeptidase 24.11 degrades G-17 in vitro and in vivo and may be responsible for the generation of C-terminal fragments from G-17 after secretion from the porcine antral mucosa.
Pyloric contribution to antroduodenal resistance to flow in the conscious dog
Authors: Mearin F. , Azpiroz F. , Malagelada J. R.
Published: December 2017

We have developed a pneumatic resistometer to monitor antroduodenal resistance to flow for prolonged periods of time in conscious dogs. To investigate the specific contribution of the pylorus to antroduodenal resistance we compared resistance during fasting in four control dogs and in four dogs with extramucosal pyloric myotomy (1.5 cm long). After pyloric myotomy, as in controls, resistance to flow changed cyclically, being lowest during phase I and highest during phase III of the interdigestive motor cycle. Pyloric myotomy decreased resistance during phase III. Atropine (0.1 mg X kg-1 X h-1) administered during motor quiescence (phase I) reduced resistance in the control group (P less than 0.05) but not in myotomized animals. Bethanechol(0.2 mg X kg-1 X h-1) significantly increased resistance in both groups (P less than 0.05). We conclude that antroduodenal resistance to flow is related to cyclic interdigestive motility. The pylorus is the predominant determinant of antroduodenal resistance during motor quiescence, but its contribution diminishes markedly during motor activity.
Comparative influences of acoustic and cold stress on gastrointestinal transit in mice
Authors: Gue M. , Fioramonti J. , Bueno L.
Published: December 2017

The effects of acoustic and cold stress on gastric emptying and intestinal transit were evaluated in mice treated with saline, diazepam, muscimol, propranolol, and naloxone using a radiolabeled chromium test meal. Acoustic stress (AS) was produced by playing music from a magnetic tape through loudspeakers (less than 86 dB) in a confined box at room temperature; and cold stress (CS) was produced by cold (10 degrees C) exposure. AS and CS sessions lasted 20 min. Both AS and CS were accompanied by a significant (P less than 0.05) increase in gastric emptying during at least 1 h. When measured 30 min after the meal, AS and CS increased gastric emptying from 43% of the test meal to 63 and 73%, respectively. Only CS affected intestinal transit, causing a 12.1% increase of the geometric center when measured 30 min after the test meal. Diazepam (0.5 mg/kg) muscimol (0.5 mg/kg), or propranolol (1 mg/kg) administered intraperitoneally reduced or abolished the effects of AS and CS on both gastric emptying and intestinal transit. In contrast naloxone (0.2 mg/kg im), which increased gastric emptying when injected alone, was unable to affect the AS-induced alterations of gastric emptying but partially reduced those of CS. Intracerebroventricular administration of corticotropin-releasing factor (250 ng/kg) also increased by 52.1% the gastric emptying, whereas the geometric center was not affected. It is concluded that both AS and CS accelerate gastric emptying in mice.(ABSTRACT TRUNCATED AT 250 WORDS)
Central nervous system action of corticotropin-releasing factor to inhibit gastric emptying in rats
Authors: Tache Y. , Maeda-Hagiwara M. , Turkelson C. M.
Published: December 2017

The present study evaluates the central nervous system action of rat corticotropin-releasing factor (CRF) on gastric emptying of a liquid meal in conscious rats using the phenol red method. Intracisternal injection of CRF (63-210 pmol) dose-dependently inhibited gastric emptying of a liquid meal by 37-80%. Peptide action was rapid in onset, long acting, and not mimicked by intracisternal injection of growth hormone-releasing factor. Intracisternal CRF-induced inhibition of gastric emptying was reversed by subdiaphragmatic vagotomy but not by naloxone pretreatment or adrenalectomy. Intravenous injection of CRF (21-630 pmol) also dose-dependently inhibited gastric emptying. CRF antiserum blocked the effect of intravenous but not of intracisternal injection of CRF (63 pmol). These results demonstrated that CRF injected in a picomole amount into the cerebrospinal fluid acts within the brain to inhibit gastric emptying of a liquid meal through vagal-dependent pathways.
Stimulation of ornithine decarboxylase activity in digestive tract mucosa
Authors: Jain R. , Eikenburg B. E. , Johnson L. R.
Published: December 2017

Refeeding fasted rats with normal rat food and with a variety of amino acids increases ornithine decarboxylase (ODC) activity considerably. The time course of that increase, the areas of the digestive tract directly affected, and the effective concentrations of stimulants are unknown. By use of isolated 5-cm segments of rat jejunum, we determined that maximal activation of ODC occurred after a 2-h exposure to 0.6 M glycine. Increased activity was first apparent after a 1-h exposure to glycine and was significant after a 2-h exposure to 0.05 M glycine. ODC activity increased the most in segments of jejunum, followed by segments of ileum and then duodenum. Glycine (0.4 M) failed to increase ODC activity in gastric and colonic mucosa. Interestingly, D-alanine was more effective than L-alanine in stimulating ODC activity in the jejunum. Enzyme activity was not dependent on osmotic activity of the test substances. Glucose increased enzyme activity, but mannitol and fructose were without effect. The effects of glycine were significantly greater than those of glucose. In summary, ODC of the small intestinal mucosa is increased by direct contact with amino acids and glucose within 2 h after exposure. Increased enzyme activity depends on the nature of the stimulant rather than the osmotic activity of the solution in contact with the mucosa.
Intestinal transport and metabolism of oxidized ascorbic acid (dehydroascorbic acid)
Authors: Rose R. C. , Choi J. L. , Koch M. J.
Published: December 2017

The transport and metabolic properties of dehydroascorbic acid have been evaluated in the small intestine of one ascorbic acid-dependent animal species (guinea pig) and one ascorbic acid-synthesizing animal species (rat). Loops of guinea pig jejunum in vitro brought about net transepithelial absorption of L-[14C]dehydroascorbic acid with most of the absorbed substrate appearing in the reduced form (ascorbic acid). Saturation of brush-border transport occurs at a lower concentration than saturation of the enzymatic reduction. Rat intestine did not bring about net transepithelial transport. The intestines of both guinea pigs and rats took up substantial dehydroascorbic acid from the serosal bathing solution, with the majority appearing in the mucosa as ascorbic acid. It is proposed that in guinea pig intestinal mucosa, dehydroascorbic acid reductase has a nutritional role in extracting the vitamin from chyme and reducing it for subsequent use in the body. The intestines of both guinea pig and rat appear to take up dehydroascorbic acid across the basolateral surface and reduce it, thus maintaining a substantial endogenous level of ascorbic acid in the mucosa. The transport and metabolic properties described might play an important role as a protective antioxidant mechanism in intestinal mucosa.
Role of glucagon in cholecystokinin-stimulated bile flow in dogs
Authors: Kaminski D. L. , Deshpande Y. G. , Beinfeld M. C.
Published: December 2017

Although many choleretic agents are known, their physiological roles and interrelationships in increasing bile flow remain largely undetermined. Exogenous cholecystokinin (CCK), glucagon, and insulin are stimulants of hepatic bile flow in animals and humans. Of possible importance in the choleresis produced by CCK is the stimulation by exogenous CCK of glucagon and insulin release from the pancreas. This research evaluates the role of glucagon and insulin in the choleresis produced by CCK. Dogs with chronic biliary and gastric fistulas were used. The synthetic octapeptide of CCK (CCK-8) administered in increasing doses produced progressive increases in bile volume, bile bicarbonate secretion, and bile chloride concentration and output. The choleresis produced by CCK-8 was qualitatively similar to that produced by intravenous glucagon. CCK-8 administration in increasing doses produced progressive increases in plasma glucagon. When bile flow changes during CCK-8 administration were correlated with changes in plasma glucagon, significant correlation existed. CCK-8 significantly increased serum insulin concentration only at the highest dose of CCK-8 administered. Somatostatin is an inhibitor of hormone release. Administration of somatostatin, along with CCK-8, inhibited the choleresis and the increased plasma glucagon produced by CCK-8 administration alone. During acute experiments in anesthetized dogs, the pancreas and stomach were removed to eliminate endogenous glucagon and insulin release. (ABSTRACT TRUNCATED AT 250 WORDS)
Abnormal gallbladder motility in irritable bowel syndrome: evidence for target-organ defect
Authors: Kamath P. S. , Gaisano H. Y. , Phillips S. F. , Miller L. J. , Charboneau J. W. , Brown M. L. , Zinsmeister A. R.
Published: December 2017

We have described previously that the gallbladder responds abnormally to infusions of cholecystokinin octapeptide (CCK-8) in patients with irritable bowel syndrome (IBS). To confirm these results and to examine the possible mechanisms, patients with IBS and predominant symptoms of diarrhea or constipation were compared with matched controls. During infusions of CCK-8 at one of three doses, the response of the gallbladder was measured ultrasonographically. The levels of CCK-8 reached in the peripheral circulation and degradation of the peptide in vitro and in vivo were used to evaluate metabolism of cholecystokinin. We confirmed that the gallbladders of patients with IBS responded abnormally to CCK-8; however, the differences were not due to any prereceptor event. Instead, this abnormality in IBS must be explained by an atypical response at the level of the target tissues.
Enhanced responsiveness to CNS-induced natriuresis in anesthetized nonascitic cirrhotic rats
Authors: Colina I. , Quiroga J. , Guarner F. , Purroy A. , Prieto J.
Published: December 2017

Central nervous system (CNS)-induced natriuresis was investigated in nonascitic rats with CCl4-induced cirrhosis (CTC rats) under pentobarbital anesthesia. At baseline, urine sodium output (UNa+V, in mumol.min-1.100 g body wt-1) (-30%, P less than 0.01) and mean arterial pressure (MAP, in mmHg) (-12%, P less than 0.001) were significantly reduced in CTC rats (n = 32) compared with matched controls (n = 34). In response to intracerebroventricular infusion of sodium-rich (349 mM) artificial cerebrospinal fluid (Na(+)-CSF infusion), UNa+V was significantly higher in CTC rats (2.8 +/- 0.3; n = 15) than in controls (1.7 +/- 0.2; n = 17; P less than 0.01); no differences were found in pressor changes (24 +/- 3 vs. 19 +/- 2). A similar but normal sodium CSF (150 mM) infusion did not influence UNa+V or MAP in any group (n = 12, both). In contrast, CTC rats (n = 5) showed, compared with controls (n = 5), significantly reduced natriuretic (UNa+V, 6.9 +/- 0.5 vs. 12.4 +/- 0.9; P less than 0.001) and pressor (+16 +/- 3 vs. +31 +/- 2; P less than 0.01) responses to an intravenous hypertonic sodium overload. Natriuresis induced by Na(+)-CSF infusion was related to increases in creatinine clearance (similar in both groups) and in fractional sodium excretion, which was significantly higher in CTC rats (5.90 +/- 0.15%) than in controls (3.65 +/- 0.14%; P less than 0.01). In summary, CNS-dependent efferent natriuretic mechanisms were preserved in CTC rats and were able to reverse renal tubular sodium retention in these animals. It is proposed that Na(+)-CSF infusion may be a useful tool for the study of renal sodium retention in experimental liver cirrhosis.
Mechanism of secretagogue-induced HCO3- and Cl- loss from rat parotid acini
Authors: Lee S. I. , Turner R. J.
Published: December 2017

The Cl(-)- and HCO3(-)-dependent components of muscarinic agonist (carbachol)-induced K+ loss from a rat parotid mince were studied using 86Rb+ as a K+ marker. Both components of 86Rb+ loss were blunted by K+ and Cl- channel blockers and by removal of extracellular Ca2+, consistent with the hypothesis that 86Rb+ loss occurs via a Ca(2+)-activated K+ channel and that this cation loss serves to electrically balance a concomitant loss of the corresponding anion via one or more conductive pathways (channels). Two tissue "pools" of 86Rb+ were observed, a carbachol-sensitive pool and a carbachol-insensitive pool (approximately 70 and approximately 30% of the total 86Rb+ content, respectively). There was no evidence for a time-dependent desensitization of the muscarinic response of the carbachol-sensitive pool. Cl(-)-dependent 86Rb+ loss was not affected by HCO3- addition, suggesting that both Cl- and HCO3- secretion are accompanied by 86Rb+ loss from the same pool and thus occur from the same cells. HCO3(-)-dependent 86Rb+ loss was not enhanced by lowering the extracellular Na+ concentration, indicating that the HCO3- exit pathway is not a Na(+)-HCO3- symport. The data are consistent with the postulate that Cl- and HCO3- are secreted by rat parotid acinar cells via the same or very similar conductive transport pathways in response to muscarinic stimulation.
Mechanism of agonist-induced downregulation of muscarinic receptors in rat pancreatic acini
Authors: Hootman S. R. , Valles S. M. , Kovalcik S. A.
Published: December 2017

Exposure of pancreatic acini to cholinergic agonists reduces their muscarinic acetylcholine receptor content. To investigate the mechanism of this reduction, rat pancreatic acini were cultured in the presence of carbachol and its effects on binding of [N-methyl-3H] scopolamine (NMS), which labels only cell surface receptors, and [3H]scopolamine, which also accesses intracellular receptors, were determined. Carbachol (0.1 mM) caused disappearance of 90% of binding sites for [3H]NMS and [3H]-scopolamine with half-time values of 3.9 +/- 0.4 and 5.7 +/- 0.7 h, respectively. Nocodazole and cytochalasin D, ouabain, ionophore A23187, 12-O-tetradecanoylphorbol 13-acetate (TPA), bombesin, cholecystokinin octapeptide (CCK-8), secretin, and vasoactive intestinal peptide (VIP) had no effect on the carbachol-induced decrease in binding sites for either antagonist, although staurosporine and the calmodulin inhibitor W-7 each caused slight inhibition. By contrast, the lysosomotropic agents methylamine and ammonium chloride caused 80% inhibition of disappearance of binding sites for [3H]scopolamine, although they only slightly inhibited disappearance of [3H]NMS binding sites. These results implicate the endosomal/lysosomal pathway in cholinergic agonist-evoked downregulation of muscarinic receptors in the pancreatic acinar cell.
Use of a modified Ussing chamber to monitor intestinal epithelial and smooth muscle functions
Authors: Li Y. F. , Weisbrodt N. W. , Harari Y. , Moody F. G.
Published: December 2017

A technique that allows the simultaneous monitoring of epithelial and smooth muscle function was developed and used to study rat small intestine in vitro. A Ussing chamber was modified so that a strain gauge force transducer could be sewn to the serosal surface of an intestinal segment clamped in the chamber. The apparatus was used to monitor short-circuit current, potential difference, and resistance across the segment, and contractions of the longitudinal layer of the muscularis externa. Both spontaneous activity and responses to the application of carbachol were recorded. Carbachol applied to the serosal side induced dose-dependent increases in both short-circuit current and contractile force. The median effective doses of the two responses differed, with contractions being more sensitive to the drug. Carbachol applied to the mucosal side induced no changes in either epithelial or contractile activities. The ability of the serosal strain gauge transducer to monitor contractions faithfully was tested in an organ bath in which the gut segment was attached to an external force-displacement transducer. There was a close correlation between the dose-dependent increase in force in response to carbachol measured by the serosal transducer and that measured by the force-displacement transducer (r = 0.988). Thus our technique can be used to study simultaneously epithelial and smooth muscle functions of the intestine.
Adenosine is a vasodilator in the intestinal mucosa
Authors: Sawmiller D. R. , Chou C. C.
Published: December 2017

The vasoactivity of adenosine in the intestinal mucosa of anesthetized dogs was determined using two experimental techniques. By use of the microsphere technique, infusion of adenosine (1 mumol/min ia) was found to increase significantly venous outflow and mucosal and muscularis blood flows in both jejunum (+77, +72, and +78%) and ileum (+111, +146, and +71%). In constant flow jejunal preparations, intra-arterial adenosine significantly decreased perfusion pressure (-32%), an index of vascular resistance, but did not significantly alter the blood flow distribution between the mucosa and muscularis as determined by microspheres. Thus adenosine equally dilated the mucosal and muscularis vasculatures. Using the second experimental technique, we found that local mucosal application of adenosine or non-metabolizable adenosine analogues [N6-cyclohexyladenosine or 5'-(N-ethylcarboxamido)-adenosine] dose dependently increased jejunal venous outflow. Almost all of the adenosine absorbed from the lumen was localized in the mucosal tissue, suggesting that the above hyperemia resulted from exposure of the mucosal vasculature to these compounds. The hyperemia produced by the luminal placement was not mediated by stimulation of the mucosal nerves, because the hyperemia was unaltered after treating the mucosal surface with a local anesthetic. The present results demonstrate therefore that adenosine is a vasodilator in the canine intestinal mucosa.
Glutamine and fatty acid oxidation are the main sources of energy for Kupffer and endothelial cells
Authors: Spolarics Z. , Lang C. H. , Bagby G. J. , Spitzer J. J.
Published: December 2017

This study assessed and compared the rate of glucose utilization, activity of the hexose-monophosphate shunt (HMS), and the oxidation of glutamine, lactate, and palmitate in Kupffer (KC), endothelial (EC), and parenchymal liver cells (PC). Cells were isolated by collagenase and pronase digestion followed by centrifugal elutriation. The freshly isolated cells were incubated in the presence of 5 mM glucose, 0.5 mM glutamine, 1 mM lactate, and 0.4 mM palmitate, and the oxidation rate of individual substrates was determined by the measurement of 14CO2 production. Glucose utilization was assessed by detritiation of [2-3H]glucose. Glucose flux through HMS was 2.6, 1.6, and 0.72 nmol.h-1.mg protein-1 in KC, EC and PC, respectively. The oxidation rate of palmitate in PC (3.5 nmol.h-1.mg protein-1) was about twofold greater than in nonparenchymal cells. Glutamine oxidation was 6.1, 4.2, and 2.1 nmol.h-1.mg protein-1 in KC, EC, and PC, respectively. In contrast, oxidation of exogenous lactate by PC (32.1 nmol.h-1.mg protein-1) was about seven- to eightfold greater than by KC or EC. Presence of prevailing lactate concentrations did not inhibit glucose oxidation in these cells, while it attenuated glucose utilization by PC. Our data show that in the presence of a physiological substrate mixture, less than 20% of the ATP generated from exogenous substrates is derived from glycolysis in KC or EC. Oxidation of glutamine and palmitate are the main sources for energy in these cells. In PC, however, lactate and palmitate oxidation is responsible for approximately 90% for the ATP production derived form the oxidation of exogenous substrates.(ABSTRACT TRUNCATED AT 250 WORDS)
Electrical characteristics of inward-rectifying K+ channels in isolated bullfrog oxyntic cells
Authors: Mieno H. , Kajiyama G.
Published: December 2017

The properties of K+ channels in the isolated oxyntic cells of the bullfrog (Rana catesbeiana) were investigated using the patch-clamp method. Two types of K+ channels on the basolateral membrane were identified on the basis of their electrophysiological and pharmacological properties. The K+ channel most frequently observed has a single-channel conductance of 61.0 +/- 2.9 pS (n = 10) and is activated by an increase in intracellular Ca2+. The other K+ channel has a single-channel conductance of 30.3 +/- 2.7 pS (n = 7), which is activated by adenosine 3',5'-cyclic monophosphate (cAMP). The physiological and pharmacological characteristics common to the two K+ channels are inward-going rectification with a high selectivity for K+ and indirect inhibition by omeprazole. The inward rectification is controlled by intracellular Mg2+ in such a way that the more Mg2+ is applied intracellularly, the more their inward-rectifying property is enhanced. The finding that bethanechol and cAMP increase the open probability of these K+ channels as well as activating the acid secretion indicates that there may be a relationship between these two processes in the oxyntic cells.
Endothelin causes prolonged inhibition of nicotinic transmission in feline colonic parasympathetic ganglia
Authors: Nishimura T. , Krier J. , Akasu T.
Published: December 2017

The action of endothelin (0.03-1 microM) on neurons in colonic parasympathetic ganglia of cats was studied in vitro, using intracellular microelectrode recording techniques. Electrical stimulation of the pelvic nerve evoked excitatory postsynaptic potentials (EPSPs) and orthodromic action potentials that were reversibly blocked by (+)-tubocurarine, hexamethonium, or external solutions containing nominal zero calcium and elevated magnesium. Endothelin blocked orthodromic action potentials and caused a concentration-dependent prolonged reversible depression of fast EPSPs. Endothelin had minimal effects on nicotinic depolarizations evoked by pressure application of acetylcholine. Endothelin also caused membrane depolarization (2-12 mV) followed by membrane hyperpolarization (1-8 mV). The depolarization and hyperpolarization were associated with a decrease and increase in membrane input resistance, respectively. The actions of endothelin were not altered by superfusion of the ganglia with external solutions containing atropine (300 nM), yohimbine (300 nM), naloxone (1 microM), or substance P (3 microM). We conclude that endothelin modulates synaptic transmission by slow membrane depolarization, membrane hyperpolarization, and prolonged depression of fast EPSPs. We suggest that the blockade of orthodromic action potentials and the depression of fast EPSPs is primarily due to inhibition of release of acetylcholine from presynaptic terminals.
Characterization of the antigen-induced contraction of colonic smooth muscle from sensitized guinea pigs
Authors: Barnette M. S. , Grous M.
Published: December 2017

To study the potential of inflammatory mediators to alter colonic motility, we characterized the response of distal colonic smooth muscle to antigen challenge. Addition of ovalbumin to isolated segments of circular smooth muscle obtained from sensitized guinea pigs produced a biphasic contraction. The initial response consisted of a rapid contraction followed by a late response, which was a more sustained but smaller increase in tone and phasic activity. Interestingly, these two responses could be antagonized differentially. Pretreatment with mepyramine (10 microM) inhibited the initial response, whereas the leukotriene antagonist WY 48252 (10 microM) inhibited the late response. The mast cell stabilizer doxantrazole (0.1 microM) reduced only the late response. Inhibition of cyclooxygenase with meclofenamic acid (1 microM) potentiated both responses, whereas blocking neuronal activity with tetrodotoxin (1 microM) only enhanced the initial response. These data indicate clear differences between the inflammatory mediators important in the initial vs. the late response. The initial response is probably mediated by the release of histamine, with enteric neuronal interactions important in attenuating the magnitude of this response. In contrast, the late response appears to be mediated by the release of peptidyl leukotrienes. In this system, cyclooxygenase products apparently function to decrease the response of the smooth muscle to these mediators. These results suggest that release of mediators during an inflammatory response could profoundly alter colonic motility and that these alterations may be important in the pathophysiological manifestations associated with colonic inflammation.(ABSTRACT TRUNCATED AT 250 WORDS)
Leuprolide acetate affects intestinal motility in female rats before and after ovariectomy
Authors: Khanna R. , Browne R. M. , Heiner A. D. , Clench M. H. , Mathias J. R.
Published: December 2017

Leuprolide acetate, a gonadotropin-releasing hormone (GnRH) analogue, is currently being proposed to control debilitating symptoms in women with functional bowel disease. Whether leuprolide alters gastrointestinal motility as part of its actions is unknown. This study was designed to assess, using myoelectric techniques in an animal model, the effects of leuprolide on potential mechanisms of neuromuscular function of small intestine. Female rats with (n = 6) or without (n = 8) bilateral ovariectomy were used to study jejunal motility before and after leuprolide therapy. Throughout the study, daily leuprolide dosages of 0.02, 0.2, or 0.4 micrograms/kg were injected into intact rats and 0.02, 0.2, 0.4, 1.0, or 2.5 micrograms/kg into ovariectomized rats. Recordings were made while the rats were fasted and postprandial and before and after leuprolide administration. Under control conditions, migrating myoelectric complexes (MMCs) were found in intact female rats, whether fasted or postprandial. After ovariectomy, postprandial controls and those treated with low-dose leuprolide (0.02, 0.2, and 0.4 micrograms) had typical fed-state patterns and no MMCs, but at 1.0 and 2.5 micrograms the fed state was inhibited and cycling MMCs occurred at a frequency similar to that of fasted controls. Reproductive hormones thus have a significant effect on gastrointestinal motility.
Influence of acid secretory state on Cl(-)-base and Na(+)-H+ exchange and pHi in isolated rabbit parietal cells
Authors: Seidler U. , Roithmaier S. , Classen M. , Silen W.
Published: December 2017

Parietal cell apical proton secretion is accompanied by apical Cl- secretion, K+ cycling, and the generation of intracellular base. We examined the ability of the parietal cell to maintain intracellular pH (pHi) during its transformation from the resting to the stimulated state and evaluated the ion transport mechanisms involved in the maintenance of ionic equilibrium. Isolated rabbit parietal cells were loaded with the pH-sensitive fluorescent dye BCECF, and pHi was monitored in maximally stimulated, resting (absence of a secretagogue), and omeprazole-inhibited cells. Although [14C]aminopyrine (AP) accumulation increased up to 30-fold above basal during stimulation, the mean pHi of maximally stimulated cells was not different from that of inhibited cells both immediately and late after stimulation in an extracellular pH range from 6.2 to 7.8 in either HEPES or CO2/HCO3- buffer. When the stilbene DIDS was added 2 min after stimulation of acid formation, pHi rapidly increased (0.09 +/- 0.02 vs. 0.04 +/- 0.02 pH units in unstimulated cells in 6 min), indicating an increased base efflux through a DIDS-sensitive transporter (most likely the Cl(-)-base exchanger). Stimulation of acid secretion did not change the transport capacity, apparent affinity for extracellular Cl-, or dependency of the anion flux rate on pHi of the DIDS-sensitive base exporter. For a given pHi, amiloride-inhibitable proton efflux rates during pHi recovery from an acid load were identical in resting and stimulated cells, suggesting that neither the transport capacity not the pHi set point of the parietal cell Na(+)-H+ exchanger is altered by cAMP-dependent stimulation of acid formation. We conclude that, during the cAMP-mediated stimulation of acid formation in isolated rabbit parietal cells, the pHi remains constant, but an increased base efflux occurs without a change in the transport capacity of the involved base extrusion mechanisms or an inhibition of the parietal cell base loading mechanisms. Whether changes in the intracellular Cl- concentration on stimulation of acid formation initiate the increased base efflux and whether additional ion transporters are involved in the maintenance of ion homeostasis during acid secretion remain to be determined.
Nitric oxide as a mediator of nonadrenergic noncholinergic neurotransmission
Authors: Sanders K. M. , Ward S. M.
Published: December 2017

Part of the regulation of gastrointestinal (GI) smooth muscles is provided by nonadrenergic noncholinergic (NANC) nerves. Stimulation of these nerves, either by field stimulation or via neural reflex pathways, elicits hyperpolarization of postjunctional smooth muscle membranes referred to as inhibitory junction potentials and relaxation. The transmitter(s) that mediate NANC inhibitory neural transmission have been a controversial topic for nearly 30 years. Recent evidence suggests that nitric oxide (NO) may serve as a NANC inhibitory transmitter in the GI tract. This hypothesis is supported by the following. 1) Immunohistochemical studies have shown that the enzyme necessary for NO synthesis is expressed in enteric neurons. In vitro studies of muscles from nearly all levels of GI tract have also shown that arginine analogues, which inhibit NO synthesis, reduce inhibitory effects of NANC neurotransmission. Effects of arginine analogues can be restored by addition of excess L-arginine, the substrate for NO synthesis. These data suggest that NO can be synthesized by enteric nerves. 2) Bioassays have demonstrated nerve-evoked release of a substance that has been identified as NO during NANC nerve stimulation. Oxyhemoglobin, known to bind to and sequester NO, also blocks NANC responses. These data suggest that NO is released into extracellular fluid during nerve stimulation. 3) Addition of NO causes rapid hyperpolarization of GI smooth muscle cells and relaxes muscles strips. These effects are similar to NANC nerve responses. NO and electrical field stimulation also increase tissue guanosine 3',5'-cyclic monophosphate, which may be the second messenger involved in NANC responses. 4) Removal of NO is easily accomplished by its rapid spontaneous breakdown in physiological solutions. 5) The pharmacology of NO and the NANC neurotransmitter in many preparations is similar, e.g., oxyhemoglobin blocks responses to NANC nerve stimulation and to exogenous NO. In summary, it would appear that many of the criteria necessary for NO to be considered a neurotransmitter have been satisfied.
Role of vagus nerve in increased DNA synthesis after hypothalamic ventromedial lesions in rat liver
Authors: Kiba T. , Tanaka K. , Endo O. , Inoue S.
Published: December 2017

We recently reported that ventromedial hypothalamic (VMH) lesions produced an increase in DNA content in rat liver. In the present study, we examined the mechanism of increased hepatic DNA content produced by VMH lesions. Hepatic DNA content began to increase 3 days after VMH lesioning and continued to increase until 7 days after the lesioning. Hepatic DNA synthesis increased and reached maximum 3 days after the lesioning and then decreased to the initial level 7 days after lesioning. The increased DNA content and synthesis after VMH lesioning were completely inhibited by vagotomy (hepatic vagotomy or bilateral subdiaphragmatic vagotomy) and largely inhibited by the administration of atropine but not by administration of anti-insulin antibody. These results suggest that vagus firing produced by VMH lesions stimulates DNA synthesis in rat liver mainly through cholinergic receptor mechanisms.