bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural and functional maturation of rat gastrointestinal barrier with thyroxine
Authors: Israel E. J. , Pang K. Y. , Harmatz P. R. , Walker W. A.
Published: December 2017

It has been noted that the closure of the intestinal barrier to immunoglobulins is a normal maturational process in the rat. It has also been noted that the microvillus membrane (MVM) of newborn animals differs from adult MVM. The purpose of this study is to document whether thyroid hormone can induce closure in vivo in the rat and to relate this effect of thyroxine to the structural and functional maturation of the intestinal MVM. To assess closure, 2-wk-old rats were fed a rat immunoglobulin G (IgG), and serum antibody binding activity was measured 4 h later. The antibody binding activity of treated animals (T) was 1.5-2 times less than that of controls (C) (P less than 0.001), indicating that thyroxine stimulates closure. The MVM similarly showed signs of maturation. Structural maturation was demonstrated by the lower fluidity of the thyroid-treated animals' membranes. Under the influence of thyroxine, the number of receptors on the MVM for IgG had decreased [2.8 X 10(-7) M (C) vs. 1.7 X 10(-7) M (T)], while the Ka remained the same, demonstrating the functional maturation of the MVM. In conclusion, thyroid hormone can induce both structural and functional maturation of the intestinal MVM and can enhance the intestinal mucosal barrier by decreasing the penetration of antibodies.
Reflectance spectrophotometry for the assessment of gastroduodenal mucosal perfusion
Authors: Leung F. W. , Morishita T. , Livingston E. H. , Reedy T. , Guth P. H.
Published: December 2017

Reflectance spectrophotometry in assessing gastroduodenal mucosal perfusion was evaluated. Ischemia without congestion, e.g., during hemorrhagic hypotension or celiac artery occlusion, was associated with a reduction in the indexes of mucosal hemoglobin concentration and of oxygen saturation. Ischemia with congestion, e.g., during portal vein occlusion, or in absolute ethanol or suction-induced mucosal lesions, was associated with an increase in the index of mucosal hemoglobin concentration but a reduction in the index of oxygen saturation. An increase in the index of mucosal hemoglobin concentration associated with a normal index of oxygen saturation was found in the postischemic hyperemia after release of celiac artery occlusion and during the sustained increase in corpus mucosal blood flow induced by vagus nerve stimulation. Thus reflectance spectrophotometric measurements reflected ischemia, without or with congestion, and hyperemia. Additionally, although regional differences in reflectance spectrophotometric measurements were demonstrated in the duodenal, antral, and corpus mucosa, such differences bore no consistent relationship to regional differences in blood flow demonstrated in previous studies.
Influence of apolipoprotein E on soluble and heparin-immobilized hepatic lipase
Authors: Landis B. A. , Rotolo F. S. , Meyers W. C. , Clark A. B. , Quarfordt S. H.
Published: December 2017

The effect of human apolipoprotein E (apoE), either alone or in combination with apoC, on the lipolysis of a radiolabeled triglyceride emulsion was studied with hepatic lipase in solution and immobilized on heparin-Sepharose. The soluble hepatic lipase was inhibited, whereas the heparin-immobilized lipase was stimulated by apoE. This stimulation was attenuated by combining apoE with either apoC-II or C-III. The heparin-immobilized lipase demonstrated much less lipolysis of the zwitterionic phosphatidylcholine-stabilized triglyceride emulsion than did the soluble enzyme. This difference was less when the emulsion was stabilized by a nonionic detergent. apoE inhibited lipase activity when assayed under conditions (0.4 M NaCl) of bound enzyme and unbound substrate. Increasing the emulsion apoE content beyond optimum inhibited lipolysis by the immobilized enzyme. Kinetic analysis of phosphatidylcholine-stabilized triglyceride emulsions revealed a significant decrease in immobilized enzyme Km and an increase in Vmax when the emulsion was supplemented with apoE. Distributing the immobilized lipase in clustered aggregates produced more lipolysis than when the same enzyme content was uniformly bound.
Role of lipid peroxidation in gastric mucosal lesions induced by HCl, NaOH, or ischemia
Authors: Kusterer K. , Pihan G. , Szabo S.
Published: December 2017

We investigated whether lipid peroxidation is an important biochemical mechanism in acute gastric mucosal injury induced by acid, base, or postischemic reperfusion. Lipid peroxidation products, i.e., the concentration of conjugated dienes (absorbance at 242 nm), products absorbing at 270 nm, and malondialdehyde were measured in the gastric mucosa of rats killed 30 s or 1, 3, or 6 min after intragastric (ig) administration of 0.6 N HCl or 0.2 N NaOH. No increase in any of the lipid peroxidation products was detected at any of the time intervals. Mucosal lesions, however, were already visible at 30 s. Cumene hydroperoxide (1 ml, 100 mM ig) induced neither mucosal lesions nor lipid peroxidation. In vitro incubation of mucosal homogenates with cumene hydroperoxide (1 or 10 mM) however, rapidly induced elevation of the three parameters of lipid peroxidation. Ischemia induced by clamping the blood vessels of the stomach for 20, 30, and 40 min followed by reperfusion for 10, 30, and 40 min did not induce lipid peroxidation, despite the development of hemorrhagic mucosal lesions. Similarly, in gastric mucosal lesions induced by hemorrhagic shock no lipid peroxidation products were detected. In the small intestine, however, prolonged ischemia (2 h) followed by reperfusion (30 min) resulted in mucosal necrosis and elevation of malondialdehyde levels. These results suggest that lipid peroxidation is not a major pathogenetic mechanism in rapidly developing acute gastric mucosal injury caused by 0.6 N HCl or 0.2 N NaOH, or in the more slowly developing mucosal injury caused by postischemic reperfusion.
Relationship between ornithine decarboxylase activity and gastric damage
Authors: Thirumalai C. H. , Tseng C. C. , Tabata K. , Fitzpatrick L. R. , Johnson L. R.
Published: December 2017

Hypertonic NaCl increases the activity of gastric mucosal ornithine decarboxylase (ODC). Intragastric administration of concentrated NaCl solution also induces ulcers in the glandular gastric mucosa. The relationship between ODC activity and gastric mucosal damage and the significance of ODC increases in hypertonic NaCl-treated rats are unknown. Rats were fasted 24 h before being given 1.0 ml of 3.4 M NaCl, 120 mM aspirin in 100 mM HCl or 50% ethanol intragastrically. The oxyntic gland mucosa was removed and assayed for ODC and in some experiments DNA, RNA, and protein content. DNA, RNA, and protein content were decreased by 3.4 M NaCl, and these decreases were much greater if ODC was inhibited by pretreatment with alpha-difluoromethylornithine (DFMO). Both aspirin and 3.4 M NaCl induced ODC activity 6 h later. However, DFMO increased the lesion index only in NaCl-treated rats. Although ethanol produced damage, it had no effect on ODC levels, and DFMO did not alter the severity of ethanol lesions. When different concentrations (0.4, 0.8, 1.6, 2.5, and 3.4 M) of NaCl were administered, ODC activities were increased 6 h later in rats receiving 1.6, 2.5, and 3.4 M NaCl but not lower concentrations. Gross lesions appeared in response to the 2.5 M dose and increased with increasing NaCl concentration. However, microscopic damage of the gastric mucosa occurred at all the concentrations tested. These data show that 1) ODC activation is not necessarily produced by damage, 2) in the case of NaCl, increasing damage increases ODC, and 3) ODC appears to have a role in the prevention of a recovery to damage caused by NaCl.
Potential mediation of somatostatin secretion from canine fundic D-cells by protein kinase c
Authors: Chiba T. , Sugano K. , Park J. , Yamada T.
Published: December 2017

We examined the possible importance of protein kinase c-dependent mechanisms in mediating the stimulatory effects of gastrin and cholecystokinin (CCK) on the release of somatostatin-like immunoreactivity (SLI) from isolated canine fundic D-cells. Diacylglycerides, presumably the products of phosphoinositide breakdown that activate protein kinasec, and phospholipase C, which catalyzes the production of endogenous diacylglycerides from membrane phospholipids, both stimulated SLI secretion in a dose-dependent fashion. Both classes of agents potentiated the actions of adenosine 3',5'-cyclic monophosphate-dependent agonists but not those of gastrin and CCK. The stimulatory effects of gastrin and CCK correlated with their abilities to enhance the incorporation of 32P into membrane phosphatidyl inositol and phosphatidic acid and promote the release of [3H]inositol trisphosphate from prelabeled D-cells, two parameters of phosphoinositide turnover. These data suggest that protein kinase c may serve to transduce the signals activated by gastrin and CCK in D-cells.
Three-dimensional imaging of the stomach: role of pylorus in the emptying of liquids
Authors: Kumar D. , Ritman E. L. , Malagelada J. R.
Published: December 2017

Using the dynamic spatial reconstructor and manometry, we measured gastric emptying, pyloric size, and antral contractile activity in three anesthetized dogs in the prone position. Our objective is to evaluate the effect of intestinal perfusion of equicaloric, neutral, and isosmolar nutrients (Maltose 32.5 mg/ml, casein hydrolysate 32.5 mg/ml, and oleic acid 15.5 mg/ml) at a constant rate of 10 ml/min in the proximal jejunum on the dynamics of the antropyloric region. Isotonic saline perfusion was used as a control solution. Test meal in the stomach was 600 ml of isotonic Gastrograffin. Antral phasic pressure activity was recorded using an antroduodenal six-channel (ports 5 mm apart) perfused probe(2 mm OD). Gastric emptying in response to intestinal perfusion of fat was significantly slower (P less than 0.02) in comparison to other nutrients or isotonic saline. There was no significant difference in the maximum or minimum pyloric diameter in response to the four intestinal perfusates. However, the pylorus was closed for a significantly longer duration (P less than 0.05) during the perfusion of fat in the upper intestine. Antral contractions were related to pyloric opening in an “antral contraction followed by pyloric opening” sequence. This study suggests that the presence of fat in the upper intestine delays gastric emptying and that this effect is regulated in part by increased resistance to flow offered by the pylorus.
Kinetics of transepithelial movement of heavy metals in rat jejunum
Authors: Foulkes E. C. , McMullen D. M.
Published: December 2017

The kinetics of the transepithelial movement of heavy metals were studied in the perfused rat jejunum in situ. The peak appearance time (TET) of Zn, Ni, and Cd in portal venous blood was determined after their transient (10 s) introduction into the intestinal lumen. Observed TET values for these metals were positively correlated with their affinities for metallothionein and agreed with those predicted on the basis of a linear three-compartment model that does not allow for paracellular pathways. Further evidence was provided to support the hypothesis that Cd absorption consists first of Cd binding to negative membrane charges followed by a temperature-dependent internalization step.
Splanchnic circulatory changes during development of renal hypertension
Authors: Meininger G. A. , Benoit J. N. , Ostrowska E. Z. , Muckleroy S. K.
Published: December 2017

Total and regional splanchnic blood flows were measured with radiolabeled microspheres (15 micron) in one-kidney, one-clip renal hypertensive rats at 2, 4, and 6 wk after induction of hypertension. Arterial pressures (mean +/- SE, mmHg) for the normotensive rats (N) and age-matched hypertensive rats (H) were 110 +/- 5 and 114 +/- 6 at 2 wk, 104 +/- 4 and 148 +/- 13 at 4 wk, and 117 +/- 6 and 164 +/- 11 at 6 wk, respectively. Total splanchnic blood flow was increased in H compared with N at 4 wk but not at 2 or 6 wk. The blood flow changes among individual splanchnic organs varied in N and H. For example, at 2 and 4 wk, stomach, small intestine, large intestine, pancreas, hepatic artery, and portal venous blood flows in H were unchanged compared with N. At 6 wk, small intestinal and hepatic arterial blood flows were increased in H compared with N, and pancreatic blood flow was decreased. Vascular resistance was not different for any splanchnic organs between N and H at 2 wk, but it was elevated in H for all organs at 4 and 6 wk except for the hepatic artery. In another group of rats, the renal and superior mesenteric arteries (SMA) were instrumented with ultrasonic Doppler flow probes. Acute one-kidney, one-clip hypertension was produced by removing one kidney and mechanically reducing flow to the remaining kidney with a pneumatic occluder. After 2 h of stenosis, mean arterial pressure and SMA flow velocity was decreased by 6%.(ABSTRACT TRUNCATED AT 250 WORDS)
Reflex decreases in intragastric pressure in response to cholecystokinin in rats
Authors: Raybould H. E. , Roberts M. E. , Dockray G. J.
Published: December 2017

The actions of intravenous sulfated cholecystokinin octapeptide (CCK-8) on intraluminal pressure in the body of the stomach were studied in urethan-anesthetized rats. There was a dose-related decrease in pressure in response to CCK-8 over the range 0.3-33 pmol. Bilateral cervical vagotomy alone reduced the response to CCK-8 and together with splanchnic section abolished it. Hexamethonium also reduced the response. Vagotomy did not change the response to CCK-8 in hexamethonium-treated rats, but celiac ganglionectomy abolished it. Guanethidine and phentolamine, but not propranolol, significantly decreased the response to CCK-8; subsequent vagotomy abolished the response. Similarly, depletion of tissue catecholamines by pretreatment with 6-OH dopamine, reserpine, or celiac ganglionectomy together with vagal section abolished the effect of CCK-8. It concluded that CCK-8 decreases mean intragastric pressure in the rat by pathways involving both vagal and splanchnic nerves. The splanchnic pathway involves an alpha-adrenergic mechanism but is hexamethonium resistant. The vagal pathway is hexamethonium sensitive and nonadrenergic. Similar pathways may mediate the effect of CCK on gastric emptying.
Influence of sacral nerves on the internal anal sphincter of the opossum
Authors: Rattan S. , Shah R.
Published: December 2017

The purpose of the present studies is to 1) compare the effects of stimulation of different sacral nerves (S1-S5) on internal anal sphincter (IAS) pressures and 2) examine the nature of synaptic transmission in the sacral inhibitory pathway to the IAS. Pressures from the IAS of alpha-chloralose-anesthetized opossums were recorded using a low-compliance continuously perfused catheter assembly. Electrical stimulation of the third and fourth sacral nerves (S3 and S4) caused frequency-dependent IAS relaxation, whereas stimulation of other sacral nerves was without significant effect on the IAS. Relaxation of the IAS in response to S4 stimulation was not significantly modified by atropine, pirenzepine dihydrochloride, hexamethonium chloride, or adrenergic antagonists. However, a combination of either atropine and hexamethonium or pirenzepine and hexamethonium caused a significant antagonism of sacral nerve-stimulated relaxation without modifying the inhibitory responses of local transmural nerve stimulation and isoproterenol. From these studies we conclude that 1) in the opossum the sacral nerves primarily exert inhibitory influences on the IAS and 2) the sacral inhibitory pathway involves the release of acetylcholine from preganglionic fibers, which in turn causes the activation of both muscarinic (M1) and nicotinic receptors on postganglionic, noncholinergic, nonadrenergic inhibitory neurons.
Amylase secretion by parotid glands and pancreas of diabetic rats during feeding
Authors: Kurahashi M. , Inomata K.
Published: December 2017

Parotid and pancreatic amylase secretion into the gastrointestinal tract during feeding was investigated in diabetic rats. In control rats, both parotid and pancreatic amylase activity decreased after feeding, while the amylase activity present in the gastric and small intestinal contents increased. In diabetic rats, parotid amylase activity, although reduced from control levels, decreased after feeding, and amylase activity of the parotid type appeared in the gastric content. Amylase activities in the diabetic pancreas and small intestinal contents at fasting were markedly reduced and did not show appreciable change with feeding. The total amylase activity in the small intestinal contents after feeding was markedly reduced in the diabetic rats, whereas the ratio of parotid to pancreatic amylase was markedly increased. These results suggest that the amylase secreted from the parotid glands into the gastrointestinal tract during feeding acts not only in the mouth and stomach but also in the small intestine of diabetic rats.
Aldosterone and PCO2 enhance rubidium absorption in rat distal colon
Authors: Perrone R. D. , McBride D. E.
Published: December 2017

Recent studies of rabbit colon have indicated the presence of a vanadate-sensitive K+-dependent proton pump, suggesting the existence of an H+-K+-ATPase. The participation of such a mechanism for colonic K+ absorption in the rat has not been determined. To this purpose, we attempted to detect the presence of pH-linked mechanisms for K+ absorption in rat distal colon using 86Rb as a marker for K+. We found that Rb+ absorption in Na-Ringer directly correlated with the in vitro partial pressure of CO2 (PCO2) in aldosterone-stimulated but not in control rats. Similar studies performed using Na-free Ringer demonstrated that PCO2 markedly augmented Rb+ absorption in both control and aldosterone-stimulated rat colon. Rb+ absorption was inhibited by orthovanadate, SCH28080, and mucosal ouabain in Na-free Ringer, but there was no effect of omeprazole, furosemide, or bumetanide. Barium applied to the serosa was also effective in inhibiting Rb+ absorption, suggesting that Rb+ exit from the cell was conductive. These findings are consistent with the presence of an active K+ pump that is activated by pretreatment with aldosterone and increased in vitro PCO2 and that is inhibited by orthovanadate, SCH28080, and mucosal ouabain. The constellation of findings suggests that participation of an ATPase that is not typical of either Na+-K+-ATPase or H+-K+-ATPase.
Calcitonin and CGRP inhibit gastrointestinal transit via distinct neuronal pathways
Authors: Jurgen Lenz H.
Published: December 2017

This study compares the central nervous system effects of rat calcitonin and rat calcitonin gene-related peptide (CGRP) on gastrointestinal transit in freely moving rats. Calcitonin and CGRP (0.01-1.0 nmol) injected into the lateral cerebral ventricle significantly inhibited gastric emptying and small bowel transit but did not affect large bowel transit. These biological actions were abolished by ganglionic blockade with chlorisondamine but not by noradrenergic blockade with bretylium. Truncal vagotomy abolished the inhibitory effects of CGRP but not those of calcitonin. Neither adrenalectomy nor hypophysectomy prevented the inhibitory actions of calcitonin and CGRP on gastric emptying and small bowel transit. Intraperitoneal administration of calcitonin and CGRP (1 nmol) produced inhibition of gastric emptying only, and this was not abolished by ganglionic blockade. These results indicate that calcitonin and CGRP exhibit similar central nervous system effects, producing inhibition of gastric emptying and small bowel transit but not altering large bowel transit. Calcitonin inhibits gastrointestinal transit via nonvagal, nonnoradrenergic autonomic efferents, yet CGRP inhibits gastrointestinal transit via vagal efferent fibers.
Postnatal expression of the canalicular bile acid transport system of rat liver
Authors: Novak D. A. , Sippel C. J. , Ananthanarayanan M. , Suchy F. J.
Published: December 2017

Canalicular plasma membrane (CPM) vesicles prepared by a Ca2+ precipitation method from developing (7 and 14 days old) and adult rat liver were used to directly examine the postnatal ontogenesis of taurocholate (TC) transport. The initial rate of 50 microM TC uptake by vesicles derived from 14-day-old and adult but not 7-day-old animals was markedly inhibited by the anion transport inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). DIDS-sensitive TC uptake was 21.6 +/- 5.6 (SE) at 14 days compared with 58.1 +/- 8.1 pmol.mg protein-1.5 s-1 in adults (P less than or equal to 0.01). Kinetic studies were performed by preloading these predominantly "right-side out" vesicles with TC (25-800 microM) and measuring the initial rate (5 s) of efflux into bile salt-free medium. Computer analysis of the DIDS-sensitive portion of efflux revealed saturable kinetics with a similar Vmax (2.72 +/- 0.36 vs. 1.97 +/- 0.17 nmol.mg protein-1.min-1; P = NS) but a threefold higher Km (0.35 +/- 0.09 vs. 0.11 +/- 0.02 mM; P less than or equal to 0.05) in 14 day vs. adult CPM vesicles. In contrast, efflux from 7 day CPM vesicles increased linearly with increasing concentrations of TC and was not inhibited by DIDS. Immunoblots of canalicular membranes, probed with an antibody against the 100-kDa bile acid transport protein, showed that the amount of immunoreactive carrier protein in the membranes of 14-day-old and adult rats was similar but was only 37% of the adult level at 7 days of age.(ABSTRACT TRUNCATED AT 250 WORDS)
Transport of propionate by human ileal brush-border membrane vesicles
Authors: Harig J. M. , Soergel K. H. , Barry J. A. , Ramaswamy K.
Published: December 2017

Human ileal brush-border membrane vesicles were employed to study the mechanisms of short-chain fatty acid (propionate) absorption especially to determine the effects of intravesicular HCO3- and the component of nonionic diffusion. Preloading the vesicles with HCO3- resulted in up to 20-fold "overshoots" of transport, and this effect was not seen with other intravesicular anions. This transport process was very fast (peak uptake 6 s) and was not due to intravesicular buffering by HCO3-. Radiolabeled propionate transport demonstrated transstimulation when the vesicles were preloaded with unlabeled propionate. An inward H+ gradient led to stimulation of propionate transport much smaller than in the presence of trans-HCO3-, whereas an inward Na+ gradient had no effect. Propionate transport was attenuated by the anion exchange inhibitors SITS and DIDS. Under HCO3- gradient conditions, propionate transport exhibited saturation kinetics with an apparent Km of 21 +/- 3 mM and a Vmax of 50 +/- 3 nmol.mg protein-1.3 s-1. Propionate transport was inhibited up to 40% by 2-5 carbon short-chain fatty acids (10 mM) but not by other organic anions. Short-chain fatty acid transport in the human ileum is Na+ independent and occurs mostly via a specific anion exchange mechanism with HCO3-. Our results also demonstrate a small component of nonionic diffusion of the protonated fatty acid (or anion exchange for OH-).
Cytoskeleton of intestinal goblet cells: role of microtubules in baseline secretion
Authors: Oliver M. G. , Specian R. D.
Published: December 2017

To determine the involvement of microtubules (MTs) in granule translocation, autoradiographic analysis of maximal granule movement in the absence or presence of MT inhibitors was performed. Rabbit colonic mucosal explants were pulse-labeled with [3H]glucosamine for 30 min in organ culture, then maintained on nonradioactive medium for 1-6 h. Radio-labeled mucin granules appear in the apical granule mass in 1-2 h, then they migrate to the apical plasma membrane, with a total transit time of 4-6 h. Mucosal explants were treated with either nocodazole or taxol for 30 min, pulse-labeled for 30 min, then maintained in organ culture with the same drug for up to 6 h. Nocodazole binds tubulin, preventing polymerization. In response, granule movement out of the supranuclear region and along the apical granule mass is significantly impeded. Taxol stabilizes MTs, preventing depolymerization. In response, supranuclear MTs are misoriented, but thecal MTs maintain normal orientation. Taxol treatment impedes granule migration out of the supranuclear region of the cell but not migration along the theca. These data suggest that the organization of MTs dictate the spatial organization of the baseline secretory pathway. Microtubules are necessary for granule translocation by providing directed tracks for granule movement, but microtubule dynamics are not the motile mechanism transporting mucin granules to the apical plasma membrane for secretion.
Antisecretory effect of prostaglandin D2 in rat colon in vitro: action sites
Authors: Goerg K. J. , Diener C. , Diener M. , Rummel W.
Published: December 2017

The effect of prostaglandin D2 (PGD2) on colonic ion transport was studied in the Ussing chamber. PGD2 (10(-6) M) decreased baseline short-circuit current (Isc) in two preparations of rat colon descendens, a mucosa-submucosa preparation with and a mucosa preparation without the submucosal plexus. In both preparations, PGD2 inhibited the neuronally mediated secretory responses to electric field stimulation, the sea anemone toxin ATX II, and different cholinergic agents. Unidirectional flux measurements revealed that PGD2 diminished the secretagogue-induced increase in the serosal-to-mucosal flux of Cl- and thereby inhibited net Cl- secretion. PGD2, however, had no effect on the adenosine 3',5'-cyclic monophosphate-mediated response to forskolin or vasoactive intestinal peptide or on guanosine 3',5'-cyclic monophosphate-mediated secretion induced by the heat-stable enterotoxin of Escherichia coli. The PGD2 also blocked the increase in Isc evoked by two neuronally acting inflammatory mediators, i.e., bradykinin and PGI2 in the mucosa-submucosa preparation, but had no effect on the response to PGE2. Consequently, PGD2 exerts an indirect antisecretory effect caused by an inhibition of enteric secretomotor neurons of both the submucosal and the mucosal plexus.
CCK-B (gastrin) receptor regulates gastric histamine release and acid secretion
Authors: Sandvik A. K. , Waldum H. L.
Published: December 2017

To study the interdependence between gastric histamine release and acid secretion, we examined the effects of gastrin-(1-17) [G-(1-17)] or cholecystokinin-(1-33) [CCK-(1-33)] alone or combined with the gastrin (CCK-B) antagonist L365,260 or the CCK-A antagonist L364,718 in the isolated vascularly perfused rat stomach. G-(1-17) and CCK-(1-33) gave concentration-dependent increases in acid secretion and histamine release. Gastrin or CCK-A antagonist alone did not stimulate histamine release or acid secretion. Maximally G-(1-17) or CCK-(1-33) stimulated histamine release and acid secretion was unchanged by the CCK-A antagonist, while the gastrin antagonist induced a parallel and concentration-dependent decrease in stimulated histamine and acid secretion. We conclude that G-(1-17) and CCK-(1-33) stimulate histamine and acid secretion by a CCK-B (gastrin) receptor. The present results indicate that gastrin, at least in this species, stimulates acid secretion by releasing histamine.
GLP-1-(7-36) amide, -(1-37), and -(1-36) amide: potent cAMP-dependent stimuli of rat parietal cell function
Authors: Schmidtler J. , Schepp W. , Janczewska I. , Weigert N. , Furlinger C. , Schusdziarra V. , Classen M.
Published: December 2017

We investigated the effect of glucagon-like peptide 1 (GLP-1)-(7-36) amide and its molecular variants GLP-1-(1-37) and GLP-1-(1-36) amide on enzymatically dispersed enriched rat parietal cells using [14C]aminopyrine accumulation as a measure of H+ production. GLP-1-(7-36) amide was 100 times more potent than GLP-1-(1–37) and GLP-1-(1–36) amide in stimulating [14C]aminopyrine accumulation. At their maximally effective concentrations, GLP-1–(7–36) amide (10(-8) M), GLP-1–(1–37) (10(-6) M), and GLP-1–(1–36) amide (10(-6) M) reached 80-90% of the response to 10(-4) M histamine. However, the peptides were 100-10,000 times more potent than histamine, which induced maximal [14C]aminopyrine accumulation at 10(-4) M. Stimulation by GLP-1 was dependent on the presence of a phosphodiesterase inhibitor and was not altered by pertussis toxin. Ranitidine failed to affect the response to the GLP-1 variants. Stimulation of H+ production by GLP-1 was accompanied by an increase in the formation of adenosine 3',5'-cyclic monophosphate (cAMP) but not by changes in phosphoinositol breakdown. In stimulating [14C]aminopyrine accumulation, the GLP-1 variants acted additively to threshold but not to maximal concentrations of histamine, suggesting that histamine and GLP-1 activate the same cAMP pool. In contrast, in anesthetized rats GLP-1-(7–36) amide (10–500 ng.kg-1.h-1) had no effect on basal and pentagastrin-stimulated acid secretion in vivo. We conclude that GLP-1 exerts a direct stimulatory effect on rat parietal cells. This potent effect is mediated by cAMP and is independent of H2 receptors. In vivo direct stimulation by GLP-1 of the parietal cells might be counterbalanced by indirect inhibitory mechanisms that are excluded in the in vitro cell system.
Postprandial hemodynamics and oxygenation in developing piglet intestine
Authors: Crissinger K. D. , Burney D. L.
Published: December 2017

Age-related differences in the intestinal hemodynamic and oxygenation responses to feeding were studied in 1-day- (never-nursed and nursed-fasted), 3-day-, 2-wk-, and 1-mo-old piglets. A distal branch of the superior mesenteric vein draining an isolated loop of jejunoileum was used to measure intestinal blood flow, arteriovenous oxygen content difference, venous pressure, and capillary pressure. Calculations of oxygen uptake and vascular resistance were performed from the measured variables. Radioactive microspheres were used to measure fractionated flow. After luminal instillation of a cow milk-based formula, postprandial oxygen uptake increased to a similar extent in all age groups. In never-nursed newborns the increase was achieved by a dramatic rise in oxygen extraction with no change in total flow, while all other groups demonstrated a combined increase in blood flow and oxygen extraction. Mucosal blood flow increased to a similar extent in all age groups, but in never-nursed newborns it was at the expense of muscularis-serosa flow. Thus, because oxygen extraction and mucosal blood flow appear to be near maximal during feeding alone, newborn intestine may be at risk for tissue hypoxia and subsequent mucosal injury in the presence of a superimposed cardiovascular stress.
Gastric contractions produce phasic changes in perfusion pressure
Authors: Wood J. G. , Cheung L. Y.
Published: December 2017

This study examined the relationship between motility and perfusion pressure of an ex vivo segment of the canine stomach perfused at constant flow. Changes in luminal pressure were used to quantitate contractile force. Under control conditions, spontaneous contractions increased luminal pressure by 18.8 +/- 1.1 mmHg and gastric perfusion pressure by 14.2 +/- 0.8 mmHg. Changes in luminal and perfusion pressures during contractions were highly correlated (r2 = 0.963, P less than 0.0001, 109 observations in 5 dogs). In separate studies, we assessed the effects of atropine, neostigmine (an acetylcholinesterase inhibitor), and bethanechol (a muscarinic cholinergic agonist). Atropine attenuated the peristaltic-induced changes in perfusion pressure in a concentration-dependent manner (10(-9) to 10(-6)M) with nearly total inhibition at the highest dose. Neostigmine (10(-9) to 10(-6) M) and bethanechol (10(-8) to 10(-5) M) stimulated contractions, resulting in dose-related increases in luminal and perfusion pressures. Our results demonstrate that cholinergic-dependent contractions produce marked, phasic changes in gastric perfusion pressure.
Link between cell apical morphology and H+ secretion in salamander small intestine
Authors: Yu Q. C. , White J. F.
Published: December 2017

To determine the morphological basis for the cellular secretion of H+ by in vitro salamander jejunum the transepithelial proton flux (JH) was measured under different conditions and compared with the ultrastructure of the villus absorptive cells using transmission electron microscopy in conjunction with morphometric analysis. Norepinephrine (NE) stimulated JH and significantly increased the density of small cytoplasmic vesicular and tubular profiles in the region immediately below the apical plasma membrane of the absorptive cells. Cytoplasmic tubular elements were often observed in direct contact with the plasma membrane at the base of the microvilli, suggesting that expansion of the plasma membrane had occurred. The alpha 2-antagonist, yohimbine, blocked NE-stimulated H+ secretion and reduced the number of tubulovesicles. Theophylline reduced the rate of spontaneous acid secretion and the density of apical tubules and vesicles. Exposure to horseradish peroxidase revealed a physical connection between the extracellular space and the apical tubulovesicular compartment. The direct relationship between the number of apical vesicular and tubular profiles and JH suggests that the luminal membrane plays a fundamental role in the cellular events in H+ secretion. The membranes of the tubules and vesicles may be elements of a dynamic pool of transporting membranes under the control of exogenous effectors such as catecholamines.
Gastric HCO3- secretion: relationship with Na+ secretion and effect of acetazolamide in humans
Authors: Feldman M. , Goldschmiedt M.
Published: December 2017

We examined the relationship between gastric HCO3- and Na+ secretion under fasting and sham-fed conditions in nine healthy men and also evaluated the effect of the carbonic anhydrase inhibitor acetazolamide on gastric secretion of HCO3- and Na+. Secretion of H+, K+, and Cl- were also measured. Gastric HCO3- secretion rates under fasting and sham-fed conditions closely paralleled Na+ secretion rates. A maximally tolerated intravenous dose (10 mg/kg) of acetazolamide significantly inhibited H+, Cl- and K+ secretion but did not significantly affect Na+ or HCO3- secretion. Thus the gastric mucosa secretes HCO3- and Na+ in parallel in humans both under fasting and sham-fed conditions. Relative to parietal secretion of HCl, nonparietal secretion of HCO3- and Na+ is resistant to carbonic anhydrase inhibition.
Serotonin receptors on submucous neurons in guinea pig colon
Authors: Frieling T. , Cooke H. J. , Wood J. D.
Published: December 2017

Intracellular microelectrodes were used to investigate the neuropharmacology of 5-hydroxytryptamine (5-HT) in the submucous plexus of the distal colon of the guinea pig. Three effects resulted from application of 5-HT to submucous neurons. Two of the effects were components of a biphasic depolarization mediated by receptors on the neuronal cell body. The third was suppression of acetylcholine release at nicotinic synapses on the cell bodies and was mediated by presynaptic 5-HT receptors. The initial component of the biphasic depolarization was a rapidly activating response characterized by increased ionic conductance and a tendency for rapid desensitization. Pharmacological analysis with selective agonists and antagonists suggested mediation of this response by the 5-HT3 receptor subtype. The second component of the depolarizing response was a slowly activating and long-lasting depolarization associated with decreased ionic conductance. Analysis of this response suggested it was mediated by the 5-HT1P receptor subtype. Identification of the presynaptic receptors for 5-HT was equivocal. These receptors did not behave like 5-HT3 or 5-HT1P receptor subtypes. The putative 5-HT4 agonist 5-methoxytryptamine was equipotent with 5-HT in producing presynaptic inhibition at the fast nicotinic synapses.
Role of nitric oxide as a mediator of internal anal sphincter relaxation
Authors: Rattan S. , Chakder S.
Published: December 2017

The studies were performed in in vitro to examine the role of nitric oxide (NO) in nonadrenergic noncholinergic (NANC) nerve-mediated relaxation of the internal anal sphincter (IAS) smooth muscle strips of opossums. NO caused a concentration-dependent fall in the resting tension of the IAS. The inhibitory action of NO may be exerted directly on the IAS smooth muscle since it was not modified by the neurotoxin tetrodotoxin (1 x 10(-6) M), which abolished the neurally mediated fall in the IAS tension. The inhibitor of NO synthesis NG-nitro-L-arginine (L-NNA) produced concentration-dependent suppression of the neurally mediated fall in the IAS tension. The suppression of the neurally mediated IAS relaxation was stereoselective because D-NNA had no effect on the control responses. The suppressant action of L-NNA was selectively reversed by L-arginine in a concentration-dependent manner. The reversal was complete with 3 x 10(-4) M L-arginine. D-Arginine on the other hand, at the same concentration had no effect on L-NNA-suppressed IAS relaxation. Interestingly, the fall in the IAS tension caused by vasoactive intestinal polypeptide (VIP) (an inhibitory neurotransmitter in the IAS) was also inhibited by L-NNA (3 x 10(-5) M). From these data we conclude that NO or NO-like substances serve as important inhibitory mediators for the NANC nerve-mediated IAS relaxation. A part of the inhibitory action of VIP on the IAS involves NO-synthase pathway. The exact site of formation and release of NO or NO-like substances in response to NANC nerve stimulation remain to be investigated.
Prostaglandin stimulates Cl(-)-HCO3- exchange in amphibian oxynticopeptic cells
Authors: Yanaka A. , Carter K. J. , Goddard P. J. , Silen W.
Published: December 2017

Prostaglandins, shown to stimulate Cl- transport in epithelial cells of several different tissues, protect gastric mucosa against physiological injury induced by luminal acid. To clarify the relationship between the stimulation of Cl(-)-transport and the protection of gastric mucosa, the effect of prostaglandin on Cl(-)-HCO3- exchange in oxynticopeptic cells (OPC) was examined in intact sheets of in vitro frog gastric mucosa, in which OPC were selectively loaded with the pH-sensitive fluorescent dye 2',7'-bis(carboxyethyl)-5(6')-carboxyfluorescein (BCECF). In omeprazole (0.3 mM)-pretreated frog fundic mucosae, in which H+ secretion was totally inhibited, 16,16-dimethyl prostaglandin E2 (dmPGE2) induced a significant decrease in intracellular pH (pHi) in OPC simultaneously with a significant increase in pHi in adjacent muscularis mucosae, an effect abolished by removal of ambient Cl- or addition of 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) (0.5 mM). dmPGE2 accentuated the rates of alkalinization of OPC after either removal of ambient Cl- or addition of serosal H2DIDS. During exposure to luminal or serosal acid, dmPGE2 significantly attenuated acidification of OPC induced by the exogenous H+, effects abolished either by removal of ambient Cl- or by addition of H2DIDS (0.5 mM). These results suggest that 1) dmPGE2 stimulates extrusion of HCO3- through the basolateral Cl(-)-HCO3- exchanger in resting OPC (H+ secretion inhibited) and that 2) relatively high extracellular [HCO3-] on the basolateral surface afforded by dmPGE2 protects OPC from acidification during exposure to luminal or serosal acid.
Effect of somatostatin on mesenteric vascular resistance in normal and portal hypertensive rats
Authors: Sieber C. C. , Mosca P. G. , Groszmann R. J.
Published: December 2017

Vasoactive effects of natural somatostatin (SRIF-14) and its analogue octreotide were studied in in vitro perfused superior mesenteric arterial beds of normal (Sham) and portal hypertensive (PVL) rats. Tested concentrations covered the whole range used in clinical settings (10(-10) to 10(-5) M for SRIF-14 and 10(-11) to 10(-6) M for octreotide, respectively). Vessel resistances only minimally changed to infusions of SRIF-14 (from 3.5 +/- 0.4 to 3.7 +/- 0.5 mmHg.ml-1.min and 3.8 +/- 0.3 to 3.9 +/- 0.4 mmHg.ml-1.min for PVL and Sham) and octreotide (from 3.3 +/- 0.2 to 3.4 +/- 0.4 mmHg.ml-1.min and 3.8 +/- 0.4 to 4.0 42- 0.4 mmHg.ml-1.min for PVL and Sham). The same was true for bolus injections. In contrast, norepinephrine induced significant increases in vessel resistance (up to 110.6 +/- 20.1 mmHg.ml-1.min). In conclusion, SRIF-14 and octreotide exert no direct effect on vascular smooth muscle tone in splanchnic resistance vessels of Sham and PVL rats. The vasoconstriction reported in vivo seems therefore probably mediated by the ability of these peptides to inhibit the secretion of vasodilatatory substances.
Effects of hypoxia on function and morphology of in vitro frog gastric mucosa
Authors: Yanaka A. , Ito S. , Carter K. J. , Goddard P. J. , Silen W.
Published: December 2017

The effects of gaseous hypoxia and reoxygenation on oxynticopeptic (OPC) and surface mucous cells (SMC) were examined in in vitro bullfrog gastric fundic mucosae mounted in Ussing chambers. Forskolin-stimulated H+ secretion, transmucosal potential difference (PD), and electrical resistance (R) were monitored in tissues incubated in HCO3(-)-free or HCO3(-)-containing buffer. At serosal pH (pHs) 7.2, 1 h of hypoxia with 100% N2 resulted in a decrease in PD, increase in R, and complete inhibition of H+ secretion. After 30 min of hypoxia, the morphology of OPC changed from the secretory to the nonsecretory state without recognizable cytopathology. Destructive changes in OPC increased progressively at pHs 7.2 as the hypoxic period was prolonged from 4 to 24 h. After 4 h of reoxygenation following 12-24 h of hypoxia, OPC remained necrotic and H+ secretion showed no recovery, whereas in some areas where SMC were exfoliated adjacent SMC showed epithelial restitution. The recovery of H+ secretion and PD during 2 h of reoxygenation after 4 h of hypoxia at pHs 6.0 and 6.8 was less than that at 7.2 and 8.0 and was greater in the presence of serosal HCO3- than its absence at pHs 7.2. These results suggest that, in in vitro frog gastric mucosa, 1) OPC are more vulnerable to hypoxia than SMC, 2) basolateral acidosis exaggerates hypoxic injury of OPC, and 3) serosal HCO3- protects OPC from hypoxic injury.
Morphology of electrophysiologically identified myenteric neurons in the guinea pig rectum
Authors: Tamura K.
Published: December 2017

Dye-filled microelectrodes were used to investigate relations between morphology and electrophysiological behavior of neurons in the myenteric plexus of the guinea pig rectum. The neurons were divided into two general classes on the basis of morphology. The first class had smooth ovoid somas with multiple long processes that exited the ganglion in several different fiber tracts and fit the description of Dogiel type II neurons. Neurons of the second class had a single long process that exited the ganglion in a fiber tract and sometimes projected to the circular muscle. Neurons of the second class were subdivided into three groups. One of these had short club-shaped dendrites like Dogiel type I neurons. Another had short tapering filamentous processes. Neurons with a single long neurite that could not be classified made up the third group. AH/type 2 electrophysiological behavior was found in both general classes of neurons. S/type 1 electrophysiological behavior occurred only in neurons of the general class with a single long neurite. Type 3 electrical behavior, characterized by robust fast synaptic input in inexcitable neurons, was found only in the cells defined by a single long neurite. Single-spike neurons behaved electrophysiologically like AH/type 2 neurons without long-lasting hyperpolarizing afterpotentials. This behavior was limited to the class of neurons characterized morphologically by a single long neurite.
Identification and localization of 5-HT1P receptors in the guinea pig pancreas
Authors: Kirchgessner A. L. , Liu M. T. , Tamir H. , Gershon M. D.
Published: December 2017

Enteropancreatic 5-hydroxytryptamine (5-HT)-immunoreactive nerve fibers have recently been described. To test the hypothesis that pancreas contains 5-HT receptors similar to those that characterize the enteric nervous system, binding of 5-[3H]HT to pancreatic membranes was investigated. Membranes were prepared by differential centrifugation from guinea pig pancreas, and binding of 5-[3H]HT was measured by use of a rapid filtration assay. Alternatively, 5-[3H]HT-binding sites were analyzed and located by radioautography on frozen sections of unfixed pancreas. The 5-HT1P receptor-specific antagonist, N-acetyl-5-hydroxytryptophyl-5-hydroxytryptophan amide (5-HTP-DP), was used to define nonspecific binding in all assays. High-affinity reversible binding of 5-[3H]HT to pancreatic membranes was found. Good agreement was observed when Kd was determined from saturation isotherms (Kd = 2.1 +/- 0.4 nM; Bmax = 0.6 +/- 0.07 pmol/mg protein) or from the ratio of association and dissociation constants (2.7 +/- 0.04 nM). As is true of 5-[3H]HT binding to enteric 5-HT1P receptors, binding of 5-[3H]HT to pancreatic membranes was inhibited by 5-HTP-DP, 5- and 6-hydroxyindalpine (agonists at 5-HT1P receptors), and guanine nucleotides. In contrast, binding of 5-[3H]HT to pancreatic membranes was not inhibited by a variety of compounds known to bind to other types of 5-HT receptor, to the neuronal 5-HT transporter, to alpha- or beta-adrenoceptors, or to dopamine receptors. We concluded that pancreas contains 5-HT1P receptors with properties similar to those of bowel. Radioautography and immunocytochemistry with an anti-idiotypic antibody that recognizes 5-HT receptors revealed that pancreatic 5-HT1P receptors (identified with appropriate inhibitors of 5-[3H]HT or antibody binding) were concentrated in ganglia, nerves, and unidentified cells in both exocrine and endocrine pancreas. These observations suggest that future studies of 5-HT's role in pancreatic physiology should concentrate on enteropancreatic innervation and 5-HT1P receptors.
Calcitonin gene-related peptide: mechanisms of modulation of antral endocrine cells and cholinergic neurons
Authors: Ren J. , Young R. L. , Lassiter D. C. , Rings M. C. , Harty R. F.
Published: December 2017

Actions of human calcitonin-gene related peptide (hCGRP) on acetylcholine (ACh) discharge and gastrin and somatostatin release from rat antral mucosal-submucosal fragments were examined in both dynamic perifusion experiments and short-term static incubation studies. The principal findings of the dynamic perifusion experiments were that hCGRP exerted a dual or biphasic effect on ACh discharge and gastrin release. Initial exposure of antral tissues to hCGRP (1 x 10(-8) M) resulted in stimulation of both ACh and gastrin release that was of brief duration. Continued hCGRP perifusion caused subsequent inhibition of ACh and gastrin release that was substantially greater in duration and magnitude than the initial stimulatory responses. Static incubation studies indicated that hCGRP (10(-10) to 10(-7) M) stimulated somatostatin and inhibited gastrin release in a dose-dependent manner. Inhibition of gastrin and ACh release by hCGRP appeared to be an indirect effect that was mediated by somatostatin as suggested by studies with pertussis toxin (200 ng/ml). Furthermore, studies with atropine (1 x 10(-6) M) and tetrodotoxin (1 x 10(-6) M) indicated that CGRP-induced stimulation of somatostatin release and inhibition of ACh discharge occurred independent of muscarinic receptor activation and nerve excitation. In conclusion, results of these studies indicate that CGRP is capable of exerting both stimulatory and inhibitory effects on ACh release from mucosal-submucosal neurons and gastrin release from antral mucosal G cells in in vitro studies. These data suggest that the inhibitory effects of CGRP on cholinergic discharge and gastrin release are due to the paracrine effects of somatostatin released from antral D cells by direct action of CGRP.