bluuebunny/crossref_metadata_2025 huggingface dataset:
Erythromycin is a motilin receptor agonist
Authors: Peeters T. , Matthijs G. , Depoortere I. , Cachet T. , Hoogmartens J. , Vantrappen G.
Published: December 2017

Erythromycin A (EMA) is a potent stimulator of gastrointestinal motor activity. In vitro studies suggest that it mimics motilin, a peptide that stimulates motor activity in human and in rabbit via smooth muscle receptors. We have compared the in vitro contractile effect of EMA and two derivatives, 8,9-anhydro-EMA-6,9-hemiketal (EM201) and EMA N-oxide, on rabbit duodenal smooth-muscle strips with their ability to displace iodinated motilin bound to crude smooth-muscle membrane fractions. The concentrations required to induce 50% of the maximum contractile response to a supramaximal dose of acetylcholine were 5.0 x 10(-8), 2.0 x 10(-6), and 1.0 x 10(-4) M for, respectively, EM201, EMA, and EMA N-oxide. The concentrations required to displace 50% of the labeled motilin were, in the same order, 1.0 x 10(-8), 1.3 x 10(-7), and 4.0 x 10(-6) M. Both parameters were well correlated. The dose-response curve of the EMA was parallel to that of motilin and the effects of motilin and EMA were additive. Contractions induced by EMA were insensitive to pretreatment with tetrodotoxin or atropine. EMA had no effect on muscle strips of rat or dog duodenum but did induce contractions in human strips. EMA was totally ineffective on ileal preparations, which are also unresponsive to motilin and in which motilin binding is absent. EMA has therefore the same regional and species specificity as motilin. We conclude that EMA is a motilin receptor agonist.
Putative mechanisms involved in excitatory and inhibitory effects of somatostatin on intestinal motility
Authors: Takeda T. , Taniyama K. , Baba S. , Tanaka C.
Published: December 2017

The mechanism of action of somatostatin on the motility of intestine was examined in the entire preparation and the longitudinal muscle attached with Auerbach's plexus (LA) preparation of guinea pig ileum, in relation to the cholinergic neuron and gamma-aminobutyric acid (GABA)ergic neuron. Somatostatin produced a transient potentiation of electrical stimulation-induced twitch contractions followed by an inhibition. The excitatory effect of somatostatin was associated with an increase in the release of [3H]acetylcholine (ACh) from the preparations preloaded with [3H]choline. Bicuculline, a GABAA antagonist, inhibited the somatostatin-induced excitatory effect. Somatostatin inhibited the electrical stimulation-induced twitch contraction and release of [3H]ACh, and the inhibition was greater in the entire preparation than in the LA. Phaclofen, a GABAB antagonist, prevented the inhibitory effects of somatostatin. Somatostatin induced a Ca2+ -dependent, tetrodotoxin-sensitive release of [3H]GABA from the preparations preloaded with [3H]GABA. Therefore somatostatin exerts excitatory and inhibitory effects on the cholinergic neuron due to the stimulation of the GABAergic neuron, and the motility of the intestine is regulated.
Effects of staurosporine on protein kinase C and amylase secretion from pancreatic acini
Authors: Verme T. B. , Velarde R. T. , Cunningham R. M. , Hootman S. R.
Published: December 2017

The effects of staurosporine, a recently isolated microbial alkaloid, on amylase secretion and protein kinase C activity of guinea pig pancreatic acini were investigated. Staurosporine at a concentration of 1 microM completely inhibited both acinar protein kinase C activity (IC50 = 5.5 +/- 1.4 nM) and amylase secretion induced by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) (IC50 = 4.1 +/- 0.4 nM). At this concentration, staurosporine reduced amylase secretion elicited by maximally effective concentrations of carbachol and cholecystokinin by approximately 50% but did not appreciably alter the potencies of the two secretagogues. In the presence of staurosporine, amylase secretion induced by carbachol was linear for at least 60 min. Staurosporine had no effect on amylase release elicited by the Ca2+ ionophore A23187. It did, however, inhibit secretion induced by vasoactive intestinal peptide, although with a reduced potency relative to its effects on amylase release stimulated by TPA, carbachol, and cholecystokinin (IC50 = 34 +/- 17 nM). These results indicate that staurosporine is a potent inhibitor of protein kinase C activity in pancreatic acini and that protein kinase C has an important role as an intracellular mediator of digestive enzyme secretion induced by cholecystokinin and carbachol in the acinar cell. In addition, a separate staurosporine-insensitive coupling pathway, most likely involving Ca2+, appears to be equally important and can maintain long-term secretion in the absence of functional protein kinase C activity.
Protein-lipid interactions in human small intestinal brush-border membranes
Authors: Dudeja P. K. , Harig J. M. , Ramaswamy K. , Brasitus T. A.
Published: December 2017

Brush-border membranes prepared from proximal and distal human small intestine were characterized with respect to lipid fluidity, lipid composition, and protein-lipid interactions. Steady-state fluorescence polarization and differential polarized phase fluorometry revealed that the "static" and "dynamic" rotational components of fluidity (assessed by r infinity values of 1,6-diphenyl-1,3,5-hexatriene and r values of 12-anthroylstearate, respectively) were greater in the distal membranes compared with their proximal counterparts. The lipid fluidity of distal brush-border membranes was also greater as measured by excimer/monomer fluorescence ratio intensities of pyrene decanoate. A lower molar ratio of cholesterol/phospholipid in the distal membranes was responsible for these regional fluidity differences. Lipid thermotropic transitions were detected at 26-28 degrees C using 1,6-diphenyl-1,3,5-hexatriene in proximal and distal membranes. Arrhenius plots of p-nitrophenylphosphatase and gamma-glutamyl transpeptidase activities demonstrated breakpoints in the vicinity of the lipid thermotropic transition temperatures (28-30 degrees C), whereas maltase and sucrase yielded a single activity slope over the range of 10-40 degrees C. Moreover, 50 mM benzyl alcohol fluidized proximal brush-border membranes and increased p-nitrophenylphosphatase activity in this membrane. This agent also shifted the phase transition temperature of the membrane and breakpoint temperature of this enzymatic activity from approximately 28 degrees C to 19 degrees C. These findings demonstrate that differences in human small intestinal brush-border membrane lipid fluidity and lipid composition exist between proximal and distal regions of this organ. Furthermore, alterations in fluidity and/or lipid composition modulate p-nitrophenylphosphatase and gamma-glutamyl transpeptidase but not sucrase or maltase activities in these membranes.
Analysis and comparison of sigmoidal curves: application to dose-response data
Authors: Meddings J. B. , Scott R. B. , Fick G. H.
Published: December 2017

A number of physiological or pharmacological studies generate sigmoidal dose-response curves. Ideally, data analysis should provide numerical solutions for curve parameters. In addition, for curves obtained under different experimental conditions, testing for significant differences should be easily performed. We have reviewed the literature over the past 3 years in six journals publishing papers in the field of gastrointestinal physiology and established the curve analysis technique used in each. Using simulated experimental data of known error structure, we have compared these techniques with nonlinear regression analysis. In terms of their ability to provide accurate estimates of ED50 and maximal response, none approached the accuracy and precision of nonlinear regression. This technique is as easily performed as the classic methods and additionally provides an opportunity for rigorous statistical analysis of data. We present a method of determining the significance of differences found in the ED50 and maximal response under different experimental conditions. The method is versatile and applicable to a variety of different physiological and pharmacological dose-response curves.
Human pancreatic secretion and intestinal motility: effects of ileal nutrient perfusion
Authors: Layer P. , Peschel S. , Schlesinger T. , Goebell H.
Published: December 2017

To study the effects of intraileal nutrients on human pancreatic secretion and gastrointestinal motility, nine healthy subjects were intubated with an oroileal multilumen tube for ileal perfusion, duodenal juice aspiration, and intestinal motility recording. The duodenum was perfused continuously with essential amino acids to induce submaximal stimulation of pancreatic enzyme secretion and fed motility pattern. Additional ileal perfusion with carbohydrate at quantities similar to those observed under physiological late postprandial conditions or fat at isocaloric loads significantly decreased pancreatic enzyme outputs by greater than 80% (P less than 0.001) compared with saline. Ileal carbohydrate or fat induced a duodenal motor activity front that migrated distally and was followed by reduced motility. In summary, ileal delivery of small quantities of nutrient markedly decreased endogenously stimulated pancreatic enzyme secretion in humans. This was associated with specific changes in fed intestinal motility that converted to patterns characteristic of the interdigestive state. Our findings suggest that the distal small intestine may participate in the late postprandial regulation of gastrointestinal function in humans.
Effects of tetrodotoxin on chloride secretion in rabbit distal colon: tissue and cellular studies
Authors: Biagi B. , Wang Y. Z. , Cooke H. J.
Published: December 2017

The effects of tetrodotoxin (TTX) were examined in muscle-stripped segments of rabbit distal colon and in cells of isolated colonic crypts. Electrical field stimulation (EFS) of the submucosa/mucosa evoked an increase in short-circuit current (ISC) that was due to an increase in chloride secretion. The EFS-evoked response was reduced 81% by 10(-7) M TTX and 30% by 5 X 10(-6) M atropine. Vasoactive intestinal peptide (VIP), carbachol, aminophylline, and 1,1-dimethyl-4-phenylpiperazinium increased ISC. Bumeta nide reduced the responses to neural stimulation, aminophylline, and VIP. To determine whether TTX had direct effects on crypt epithelial cells, crypts were isolated and cells were impaled with microelectrodes. Mean resting potential (Vbl) was -67 +/- 1.1 mV (n = 63). VIP and aminophylline depolarized Vbl by 34 +/- 4.6 (n = 13) and 34 +/- 3.5 mV (n = 18), respectively. TTX had no significant effect on resting Vbl or on the responses to VIP or aminophylline. We conclude that stimulation of submucosal neurons in the rabbit distal colon evokes a TTX- and bumetanide-sensitive increase in net chloride secretion that is dependent on the release of acetylcholine and other secretory neurotransmitters. Electrophysiological studies rule out a direct effect of TTX on colonic crypt cells.
Effects of PGF2 alpha and of indomethacin on rabbit small and large intestinal motility in vivo
Authors: Burakoff R. , Nastos E. , Won S.
Published: December 2017

Prostaglandin F2 alpha (PGF2 alpha) has been shown to increase contractility in the small intestine and colon in vitro, and increased mucosal prostaglandin synthesis has been reported in ulcerative colitis. The purpose of this study was to determine the effects of PGF2 alpha and of indomethacin on myoelectric and contractile activity in the rabbit ileum and colon in vivo. PGF2 alpha caused an increase in spike potential frequency and contractile activity in the terminal ileum and proximal and distal colon. Indomethacin alone increased spike potential frequency and contractile activity in the terminal ileum and proximal colon but decreased myoelectric activity in the distal colon. It is concluded that PGF2 alpha may play an important role in modulating intestinal motility, especially in the distal colon but to a lesser extent in the terminal ileum and proximal colon.
Acute and chronic ethanol on hepatic oxygen ethanol and lactate metabolism in cats
Authors: Greenway C. V. , Lautt W. W.
Published: December 2017

The effects of increasing blood ethanol levels on hepatic hemodynamics and O2, ethanol, and lactate metabolism were studied in two groups of anesthetized cats: a control group and a group whose prior fluid intake contained 2, 4, then 8% ethanol for 24 days. Within each group, responses were compared in cats with acutely denervated and innervated livers. A hepatic venous long-circuit technique with an extracorporeal reservoir was used to allow hemodynamic measurements and repeated sampling of arterial, portal, and hepatic venous blood without depletion of the cats' blood volume. Vmax for ethanol was 105 +/- 9 and 91 +/- 6 mumol.min-1 g liver-1 and Km was 136 +/- 18 and 168 +/- 24 microM for control and chronic alcohol groups, respectively. There was no stimulation of ethanol metabolism after chronic administration. O2 uptake by the liver was not altered during acute ethanol administration in any group and base-line O2 uptakes before acute administration of ethanol were not different between normal and chronic ethanol groups. No evidence for a hypermetabolic state induced by chronic ethanol administration was seen in innervated or acutely denervated livers. Oxidation of ethanol required 40-45% of normal O2 uptake; thus other oxidative processes must have been suppressed during ethanol metabolism. Hepatic lactate uptake remained unaltered when ethanol metabolism was less than 0.5 Vmax, but was suppressed on an equimolar basis with ethanol metabolism when ethanol metabolism rose to greater than 0.5 Vmax. Thus lactate metabolism is one process that can be suppressed to allow ethanol metabolism without additional O2 uptake by the liver.
Transfer of enalaprilat across rat liver cell membranes is barrier limited
Authors: Schwab A. J. , Barker F. , Goresky C. A. , Pang K. S.
Published: December 2017

The liver cell entry of enalaprilat, the polar, pharmacologically active dicarboxylic acid metabolite arising from esterolysis of enalapril, a new angiotensin-converting enzyme inhibitor, was examined in the perfused rat liver by use of the multiple-indicator dilution technique. [Phenylpropyl-2,3-3H]enalaprilat was injected into the portal vein in a bolus of blood containing 51Cr-labeled red blood cells (a vascular reference) and 125I-labeled albumin and [14C]sucrose (interstitial references that do not enter cells), with observation of the time courses of their outflow into the hepatic venous blood. A quantitative evaluation of the data was carried out by use of the barrier-limited, space-distributed variable transit time model (C.A. Goresky, G.G. Bach, and B. E. Nadeau, J. Clin. Invest. 52:991-1009, 1973). For data up to 60 s after injection, the transfer coefficients for influx, efflux, and sequestration were 0.018 +/- 0.004 (means +/- SD), 0.044 +/- 0.017, and 0.033 +/- 0.007 s-1, respectively. The influx permeability surface area product (influx clearance) per gram was 0.0057 +/- 0.0013 ml.min-1.g-1, and the rapidly accessible cellular equilibrium distribution space for enalaprilat was 0.137 +/- 0.022 ml water/g wet wt. At times beyond 60 s, the fitted data deviated systematically from the experimental data, suggesting the presence of an additional intracellular pool. With this addition, the coefficients for transfer between the intracellular pools were 0.0150 +/- 0.0045 s-1 for the direction cytoplasmic pool (pool 1)----additional pool (pool 2) and 0.0234 +/- 0.0069 s-1 for the opposite direction, and the fitted volumes of pools 1 and 2 became 0.126 +/- 0.021 and 0.082 +/- 0.018 ml/g, the total accessible cellular distribution space became 0.208 +/- 0.036 ml/g wet wt, and the sequestration transfer coefficient became 0.027 +/- 0.007 s-1. The data indicate that, as previously postulated (I. A. M. de Lannoy and K. S. Pang, Drug Metab. Dispos. 14: 513-520, 1986), the enalaprilat flux across liver cell membranes is retarded by a diffusional barrier. The results also indicate that enalaprilat is excluded from part of the volume of hepatocytes, as expected for an anionic compound crossing the membrane in charged rather than protonated form, given the negative electrical potential of the cytosol vs. the extracellular space.
Aldosterone and glucocorticoid receptor-specific agonists regulate ion transport in rat proximal colon
Authors: Turnamian S. G. , Binder H. J.
Published: December 2017

Dietary sodium depletion increases electroneutral Na-Cl absorption and potassium secretion in the proximal colon of the rat. Although sodium depletion results in secondary hyperaldosteronism, the stimulation of electroneutral Na-Cl absorption is not a typical mineralocorticoid-mediated event. These studies were performed to determine whether the aldosterone or glucocorticoid receptor mediates these changes in electrolyte transport. Continuous infusion of aldosterone at 70 micrograms.100 g body wt-1.day-1 for 7 days resulted in a significant increase in net Na+ and Cl- absorption (5.5 +/- 0.8 and 5.9 +/- 1.0 mueq.h-1.cm-2, respectively). A 7-day infusion of RU 28362, a glucocorticoid receptor-specific agonist, at 70 micrograms.100 g body wt-1.day-1 similarly increased net Na+ and Cl- absorption (5.4 +/- 1.3 and 4.1 +/- 0.5 mueq.h-1.cm-2, respectively). Both aldosterone and RU 28362 produced a minimal increase in Isc (0.4 +/- 0.2 and 0.8 +/- 0.2, respectively). Administration of spironolactone prevented the stimulation of Na+ absorption induced by aldosterone but not that by RU 28362, and aldosterone but not RU 28362 stimulated active potassium secretion. These studies indicate that aldosterone mediates the stimulation of both electroneutral Na-Cl absorption and K+ secretion produced by dietary sodium depletion and that both aldosterone and glucocorticoid agonists each stimulate electroneutral Na-Cl absorption as a result of interacting with the mineralocorticoid and glucocorticoid receptors, respectively.
Comparative analysis of protein content in rat mesenteric tissue, peritoneal fluid, and plasma
Authors: Barber B. J. , Schultz T. J. , Randlett D. L.
Published: December 2017

Albumin, transferrin, and total protein concentrations were measured in the mesenteric tissue, peritoneal fluid, and plasma of 12 ketamine-Nembutal-anesthetized Sprague-Dawley rats. Tissue samples were obtained with an 8-mm trephine; tissue water content was determined by a microgravimetric method to be 5.2 +/- 0.3 microgram water/microgram dry wt. Peritoneal fluid was collected by capillary action in hematocrit tubes, and blood samples were taken from a femoral artery catheter. Total protein concentrations of plasma (5.8 +/- 0.3 g/dl) and peritoneal fluid (2.6 +/- 0.1 g/dl) were determined by Lowry assay. Ratios of peritoneal fluid and tissue densitogram areas to plasma area were used to calculate total protein content of peritoneal fluid (2.5 +/- 0.1 g/dl) and tissue (1.8 +/- 0.2 g/dl). Albumin concentrations were 1.1 +/- 0.1 g/dl for tissue, 1.4 +/- 0.1 g/dl for peritoneal fluid, and 2.8 +/- 0.1 g/dl for plasma. Transferrin concentrations were 0.09 +/- 0.01 g/dl for tissue, 0.13 +/- 0.01 g/dl for peritoneal fluid, and 0.28 +/- 0.01 g/dl for plasma. Peritoneal fluid protein concentrations were similar to values found for lymph in previous studies. Protein concentration in the tissue buttons was significantly less than that of peritoneal fluid. This contradicts the widely held assumption that the protein concentration of fluid outside the matrix is representative of a well-mixed interstitial matrix fluid protein concentration.
Membrane currents and cholinergic regulation of K+ current in esophageal smooth muscle cells
Authors: Sims S. M. , Vivaudou M. B. , Hillemeier C. , Biancani P. , Walsh J. V. , Singer J. J.
Published: December 2017

The tight-seal whole cell recording technique with patch pipettes was used to study membrane currents of smooth muscle cells freshly dissociated from the esophagus of cats. Under voltage clamp with K+ in the pipette, depolarizing commands elicited an initial inward current followed by a transient outward current that peaked and then declined to reveal spontaneous outward currents (SOCs). SOCs were evident at -60 mV and more positive potentials. The reversal of SOCs at the K+ equilibrium potential and their suppression by tetraethylammonium chloride lead to the conclusion that they represent the activity of K+ channels. Acetylcholine (ACh) caused reversible contraction of these cells and had two successive effects on membrane currents, causing transient activation of K+ current followed by suppression of SOCs. Both of these effects were blocked by atropine. Consistent with these observations, in current clamp, ACh caused a transient hyperpolarization followed by depolarization. The inward current activated by depolarization was blocked by external Cd2+, consistent with the inward current being a voltage-activated calcium current. Two types of Ca2+ current could be distinguished on the basis of voltage-activation range, time course of inactivation and "run-down" during whole cell recording.
Pathways of slow-wave propagation in proximal colon of cats
Authors: Conklin J. L. , Du C.
Published: December 2017

Colonic slow waves (SWs) are generated by nonneuronal cells located at the interface of the submucosa and muscularis propria. It has been proposed that SWs arise from a complex of nerves, interstitial cells of Cajal, and smooth muscle found at this location. These experiments test the hypothesis that the propagation of colonic SWs depends on an intact interface between the submucosa and muscularis propria. The electromyogram was recorded from segments of the proximal colon of the cat. All intact tissues generated SWs that propagated in the long and circumferential axes of the colon. Tetrodotoxin did not disrupt SW propagation in either axis. Transection of tissues between recording sites interrupted the spread of SWs in both axes. Transection of the submucosa disrupted the longitudinal spread of SWs, whereas transection of the muscularis propria did not. Removing the submucosa from the midportion of tissue segments oriented in the long axis of the colon resulted in a loss of SWs from the segment devoid of submucosa. Transection of the submucosa of tissue segments oriented in the circular axis of the colon did not disrupt circumferential propagation of SWs. Dissecting a 1-cm-wide segment of submucosa from the midportion of such a circularly oriented tissue did not disrupt the circumferential spread of SWs, and SWs were recorded from the muscle segment that was devoid of submucosa. SWs were not recorded from the segment devoid of submucosa when it was isolated from adjacent intact segments. The data support the hypothesis that the regeneration of SWs during their longitudinal propagation takes place at the interface between the submucosa and muscularis propria.
Effect of a leukotriene receptor antagonist on LTC4 vasoconstriction in rat stomach
Authors: Yonei Y. , Guth P. H.
Published: December 2017

With the use of an in vivo microscopy technique in anesthetized-laparotomized rats, the effect of L660,711, a cysteinyl-leukotriene (LT) receptor antagonist, on the gastric submucosal microvascular response to leukotrienes was studied. The direct application of 50-400 nM LTC4 onto the exposed submucosal vasculature caused constriction of both arterioles (maximum constriction: 24 +/- 3%) and venules (26 +/- 3%), whereas LTD4 had no significant effect. Pretreatment with 5 mg/kg L660,711 intragastrically significantly attenuated the LTC4-induced vasoconstriction. The submucosal application of 2 x 10(-7) to 2 x 10(-2) M L660,711 dose dependently inhibited the 400 nM LTC4-induced vasoconstriction. The IC50 of L660,711, preapplied to the gastric submucosa for 15 min, was 4.4 x 10(-4) M in arterioles and 3.9 x 10(-4) M in venules, and 3.6 x 10(-5) M and 3.2 x 10(-5) M, respectively, when it was applied simultaneously with LTC4. Schild plot analysis revealed that L660,711 was not a pure competitive receptor antagonist. L660,711 had no significant effects on epinephrine- or vasopressin-induced arteriolar constriction. In conclusion, L660,711 significantly antagonizes the gastric microvascular effects of LTC4, but not those of other vasoconstrictors, and appears to be a useful new tool for studying LTC4 effects.
Amylase release from streptolysin O-permeabilized pancreatic acini
Authors: Kitagawa M. , Williams J. A. , De Lisle R. C.
Published: December 2017

Intracellular mediators of exocytosis were investigated using isolated mouse pancreatic acini permeabilized with the bacterial toxin streptolysin O (SLO). Permeabilization was demonstrated by fluorescent staining with ethidium bromide and fluorescein diacetate and release of cytoplasmic lactate dehydrogenase. When SLO-permeabilized acini were incubated at 37 degrees C in Ca2(+)-EGTA buffers containing MgATP, amylase secretion was Ca2+ dependent with an EC50 of 0.40 microM Ca2+ and a maximally effective Ca2+ concentration of 1 microM. Maximal amylase secretion was 330% of that in Ca2(+)-free buffer (basal). The nonhydrolyzable GTP analogue guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S; 30 microM) increased the maximal secretion to 451% of basal in the presence of 1 microM Ca2+ and decreased the EC50 to 0.14 microM Ca2+. Removal of ATP plus addition of antimycin A and 2-deoxy-D-glucose inhibited Ca2(+)-dependent, GTP gamma S-enhanced amylase secretion by 56%. The phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA; 1 microM) also enhanced maximal secretion to 450% of basal and decreased the EC50 to 0.18 microM Ca2+. Enhancement of amylase secretion by submaximal concentrations of GTP gamma S or TPA was inhibited by the protein kinase C inhibitor staurosporine. These results suggest that Ca2+ stimulation of amylase secretion is potentiated by activation of protein kinase C. However, the enhancement of secretion by GTP gamma S and TPA was additive at their maximally effective concentrations, suggesting that another G protein(s) maybe involved in the terminal steps of exocytosis.
Control of interdigestive and intraduodenal meal-stimulated pancreatic secretion in rats
Authors: Chariot J. , Nagain C. , Hugonet F. , Tsocas A. , Roze C.
Published: December 2017

Mechanisms of neural (vagal and cholinergic) and hormonal [cholecystokinin (CCK)] control of pancreatic exocrine secretion were studied in basal interdigestive conditions and after stimulation by an intraduodenal meal in rats equipped with a semichronic pancreatic fistula. Bile was recirculated into the duodenum, and a solution of trypsin and electrolytes was continuously infused. Pancreatic secretion was compared in control experiments, after vagotomy, and after venous infusion of cholinergic and CCK antagonists. Basal pancreatic secretion was decreased by atropine, pirenzepine, and hexamethonium and to a lesser extent by vagotomy (protein output decreased more than fluid and HCO3- outputs). The CCK antagonists L364,718 and lorglumide had no effect on basal interdigestive pancreatic secretion. Small doses of atropine (8 and 25 micrograms.kg-1.h-1) did not modify the cumulated pancreatic response to the meal, whereas larger doses (75 and 225 micrograms.kg-1.h-1) increased it by 40-85%, according to the variables. Pirenzepine and hexamethonium did not modify the pancreatic response. Vagotomy had no effect on fluid and HCO3- responses and tended to increase protein response. L364,718 and lorglumide completely inhibited the protein response and decreased the fluid and HCO3- responses by 75 and 40%, respectively. L364,718 also suppressed the increased pancreatic response induced by atropine. This work confirms the prominent role of neural cholinergic mechanisms in the control of basal interdigestive pancreatic secretion in rats. In contrast, the pancreatic protein response to an intraduodenal meal depends on CCK, whereas fluid and HCO3- responses also depend on other hormonal factors. Our results suggest that a muscarinic (probably M3) mechanism can decrease the postprandial CCK release independently of the pancreatic feedback control by trypsin.
VIP antagonist [N-Ac-Tyr1,D-Phe2]-GRF-(1-29)-NH2: an inhibitor of vasodilation in the feline colon
Authors: Blank M. A. , Kimura K. , Fuortes M. , Jaffe B. M.
Published: December 2017

The effect of the vasoactive intestinal polypeptide (VIP) antagonist [N-Ac-Tyr1,D-Phe2]-GRF-(1-29)-NH2 on pelvic nerve-induced colonic vasodilation and VIP release was investigated in chloralose-anesthetized cats. VIP antagonist (10 and 50 nmol/kg in saline) or saline alone was injected into a branch of the superior mesenteric artery immediately before bilateral pelvic nerve stimulation. The increase in conductance in the inferior mesenteric artery during pelvic nerve stimulation was reduced in an apparently dose-dependent fashion by the VIP antagonist (by 35 +/- 10 and 42 +/- 9%, respectively) compared with the pelvic nerve-induced increase in conductance after injection of saline alone. Injection of the VIP antagonist (50 nmol/kg) did not alter conductance in the absence of pelvic nerve stimulation. VIP was released into portal venous blood during pelvic nerve stimulation in the presence of the antagonist (from 103 +/- 29 to 165 +/- 45 pmol/l). This was not significantly different from release in the presence of saline. The effect of the VIP antagonist (10 nmol.kg-1.min-1) on inferior mesenteric arterial vasodilation induced by exogenous VIP was also quantitated. The increase in conductance after VIP injection (0.2 nmol/kg) was significantly reduced when accompanied by simultaneous infusion of the VIP antagonist (by 54 +/- 6%) compared with the increase in conductance during simultaneous infusion of saline. We conclude that [N-Ac-Tyr1,D-Phe2]-GRF-(1-29)-NH2 is an inhibitor of pelvic nerve-induced vasodilation in the feline colon and does not act by modulating VIP release.(ABSTRACT TRUNCATED AT 250 WORDS)
Phosphoinositide metabolism in intestinal brush borders: stimulation of IP3 formation by guanine nucleotides and Ca2+
Authors: Vaandrager A. B. , Ploemacher M. C. , De Jonge H. R.
Published: December 2017

The potential role of polyphosphoinositide (PPI) metabolism as a signal-transduction mechanism in apical membranes of polarized epithelial cells was evaluated by examining the formation and breakdown of PPI in rat intestinal brush-border membranes (BBM) prelabeled by intraluminal injection of [3H]inositol in vivo or by [gamma-32P]ATP in vitro. Freshly isolated BBM prelabeled with [3H]inositol contained higher amounts of [3H]phosphatidylinositol 4,5-diphosphate compared with a basolateral membrane (BLM) preparation (approximately 14 and 6.8% of total [3H]PPIs, respectively) and were enriched in inositol lipid kinases, diacylglycerol (DAG) kinase, and phosphomonoesterases degrading PPI, inositol bisphosphate, and inositol triphosphate (IP3). In the presence of nonhydrolysable GTP analogues and low Ca2+ (pCa 6-8) or at high Ca2+ alone (pCa 4) endogenous pools of PPI were rapidly depleted by an intrinsic PPI-specific phospholipase C apparently coupled to a GTP-binding protein (G protein). Surprisingly, despite the assignment of most G protein-coupled hormone receptors to the BLM, the capacity of isolated BBM to release [3H]IP3 in response to Ca2+ or GTP gamma S appeared comparable to that in a BLM preparation. Intestinal secretagogues acting through apical membrane receptors (adenosine, heat-stable Escherichia coli toxin), however, were unable to promote [3H]IP3 release in isolated BBM in the presence of GTP. PPI metabolism in BBM may be coupled to receptors for as yet unidentified secretagogues or may serve as an amplification mechanism for hormone-stimulated PPI breakdown in BLM. The local release of DAG and IP3 at the interior of the intestinal microvilli likely plays a role in the regulation of ion transport systems in microvillar membranes.
Effect of denervation of the myenteric plexus on gastroduodenal motility in turkeys
Authors: Chaplin S. B. , Duke G. E.
Published: December 2017

The effect of denervation of portions of the myenteric plexus on initiation and coordination of gastric and duodenal contractions was examined in domestic turkeys. Three areas of the muscular stomach (MS), the isthmus between the glandular stomach (GS) and MS, and the pylorus were denervated by application of 1% benzalkonium chloride. Motor activity of the gastroduodenal organs was monitored for 1 h every other day for 13 days using strain gauge transducers implanted at selected sites. Denervation of the isthmus reduced the frequency of MS and duodenal contractions by 50% and abolished GS contractions. Pyloric denervation did not affect the frequency of GS or MS contractions but abolished duodenal contractions. These results suggest that 1) a driving pacemaker for the gastroduodenal cycle is located in the isthmus, and 2) the myenteric plexus is essential for conduction from the pacemaker to the GS and to the duodenum. Denervation of the medial commissure of the myenteric plexus of the MS significantly impaired the function of the ventral half of the MS. It caused atrophy of the underlying medial thick muscle and significantly decreased contraction amplitude. Denervation at this site also caused an enlargement and impaction of the adjacent caudal thin muscle with food and a significant decrease in contraction amplitude. In contrast, denervation of the lateral commissure enlarged the underlying lateral thick muscle and significantly increased its contraction amplitude. Denervation of the cranial thin muscle delayed contractions of that muscle, causing an asynchronization of thin muscle pair.(ABSTRACT TRUNCATED AT 250 WORDS)
Evaluation of selective liver denervation methods
Authors: Cucchiaro G. , Yamaguchi Y. , Mills E. , Kuhn C. M. , Anthony D. C. , Branum G. D. , Epstein R. , Meyers W. C.
Published: December 2017

This study compares four methods of hepatic denervation and defines the rate and physiological significance of reinnervation. Five groups of rats were prepared: 10 underwent orthotopic liver transplantation. In nine rats a 90% aqueous phenol solution was applied circumferentially to the portal vein. Thirteen rats underwent microsurgical denervation; 28 received different doses of 6-hydroxydopamine (6-HODA) administered as a single intraportal injection [50 (n = 10), 75 (n = 6), and 100 mg/kg (n = 6)]. Twelve rats were studied as controls. Rats were killed 1, 4, and 8 wk after surgery to determine liver tissue content of norepinephrine (NE). Changes in mean arterial pressure (MAP) in response to hepatic nerve stimulation, which was supramaximum in intensity and frequency, were measured before rats were killed. NE content in controls ranged from 121 to 204 ng/g and MAP increased by 30-38 mmHg after electrical stimulation. At 1, 4, and 8 wk after treatment the liver NE content was less than 1, 2.3, and 20.2 ng/g in the transplant group; less than 1, 2.7, 4.1 ng/g in the phenol group; and 17.2, less than 1, and 3 ng/g in the surgically denervated group. In the 6-HODA group, values were 18.9, 47, and 61.5 ng/g (50 mg/kg); 5.7, 20.2, and 15 ng/g (75 mg/kg); and 7.7, 2.5, and 17.5 ng/g (100 mg/kg). When the level of NE was undetectable, MAP increase after stimulation was 0-18% that of controls. When NE content was 15-23% of normal, MAP increased 49-62% regardless of the denervation technique.(ABSTRACT TRUNCATED AT 250 WORDS)
Mode of stimulation of gallbladder contraction by substance K
Authors: Yau W. M.
Published: December 2017

Substance K (SK) contracted the guinea pig gallbladder in vitro by predominantly acting on the neurokinin (NK2) receptors localized on the smooth muscle. A comparison of the 50% effective dose among the tachykinins showed that SK is 20 and 176 times more active than neurokinin B (NKB) and substance P (SP), respectively. Senktide, a synthetic NKB agonist with presumably a specificity for only NK3 receptor subtype, was completely inactive even when tested at 6 x 10(-6) M. Studies on both atropine-treated tissues and [3H]acetylcholine release from myenteric plexus have revealed a minor action of SK by way of a stimulation on the intramural cholinergic neurons. There was still a residual 77.4% SK-evoked contraction that was not blocked by atropine. However, the SK-induced contraction was completely abolished in the presence of 1-(5-isoquinolinylsulfonyl)-2-methyl-piperazine, a direct protein kinase C (PKC) inhibitor. This latter observation suggests a link in the PKC-specific pathway of intracellular signal transduction initiated by NK2 receptor activation on the gallbladder musculature. The preponderance of NK2 receptor subtype further implies a unique functional role it may play in gallbladder contractility.
Characterization of K+ and Cl- conductances in apical membrane vesicles from stimulated rabbit oxyntic cells
Authors: Reenstra W. W. , Forte J. G.
Published: December 2017

K+ and Cl- conductance pathways in apical membrane vesicles (SA vesicles) of stimulated oxyntic cells have been characterized. SA vesicles were prepared from rabbit fundic mucosa after stimulation of acid secretion with histamine. Conductive K+ and Cl- fluxes were assayed by several methods: by their effects on pH gradient formation by endogenous H(+)-K(+)-ATPase, by the protonophore-induced dissipation of preformed pH gradients, and by the effects of channel blockers. pH gradient formation by H(+)-K(+)-ATPase required K+ and was greatly reduced when the permeant anion chloride was replaced by gluconate or sulfate. In the presence of 75 mM K+, 1 mM Cl- was sufficient for generation of near maximal pH gradients, as was 5 mM K+ in the presence of 75 mM Cl-. At all K+ and Cl- concentrations tested, the ATP-generated formation of pH gradients was inhibited and the dissipation of these pH gradients stimulated by the protonophore tetrachlorosalicylanilide (TCS). Similar effects of TCS were also seen when Cl- was replaced by impermeant anions. Both processes were blocked by the K+ channel inhibitor Ba2+. The Ki for Ba2+ inhibition of pH gradient formation was 1.5 microM at 5 mM K+ and was proportional to the 3rd power of the K+ concentration. At 75 mM K+ the Cl- channel blocker diphenylamine-2-carboxylate inhibited ATP-dependent pH gradient formation when the Cl- concentration was 1 mM; however, when the Cl- concentration was greater than 5 mM no inhibition was observed. The membrane potential-sensitive dye DISC (5) was used to measure membrane potential generated by K+ gradients.(ABSTRACT TRUNCATED AT 250 WORDS)
Differential effects of calcium ions and calcium phosphate on cytotoxicity of bile acids
Authors: Van der Meer R. , Termont D. S. , De Vries H. T.
Published: December 2017

Unconjugated secondary bile acids can promote colon cancer by damaging colonic mucosa and consequently increasing epithelial proliferation. It has been proposed that dietary calcium inactivates intestinal bile acids either by a Ca2(+)-dependent precipitation or by binding to insoluble calcium phosphate (CaPi). We studied the molecular mechanisms of these opposing hypotheses by using hemolysis of erythrocytes as a model parameter for cytotoxicity. Washed human erythrocytes were incubated for 15 min with buffered media (pH 7.4) containing increasing amounts of different bile acids. Deconjugation and 7 alpha-dehydroxylation of mixtures of glycine- or taurine-conjugated cholate and chenodeoxycholate drastically increased their cytotoxicity. Parallel measurements, using a fluorescent micellar probe, indicated that micellar aggregation is a prerequisite for this bile acid-induced lysis. Ca2+ concentrations up to 15 mM did not precipitate bile acids but stimulated cytotoxicity of both deoxycholate (DC) and its glycine conjugate (GDC). Cytotoxicity of the taurine conjugate (TDC) was stimulated to a much lesser extent. Increasing amounts of CaPi precipitated micellar DC and GDC, but not TDC, and consequently inhibited only cytotoxicity of the former two. These findings indicate that 1) hydrophobicity and micellar aggregation are important determinants of bile acid-induced cytotoxicity that explain the high cytotoxic potential of secondary bile acids in colon, and 2) cytotoxicity of bile acids is stimulated by free Ca2+ and inhibited by CaPi. This inhibition is due to binding of carboxylic (including secondary) bile acids to CaPi.
Use of stereoisomers of zacopride to analyze actions of 5-hydroxytryptamine on enteric neurons
Authors: Wade P. R. , Mawe G. M. , Branchek T. A. , Gershon M. D.
Published: December 2017

Two subtypes of excitatory 5-hydroxytryptamine (5-HT) receptor, 5-HT1P and 5-HT3, are found on type 2-AH neurons of the guinea pig myenteric plexus. The 5-HT1P receptor mediates a slow and the 5-HT3 receptor a fast depolarization of these cells, however, the role of these receptors in the physiology of the gut is unknown. Renzapride (BRL 24924), a substituted benzamide, has previously been found to antagonize responses of myenteric neurons mediated by both 5-HT1P and 5-HT3 receptors. The effects on myenteric type 2-AH neurons of a structurally similar benzamide, zacopride, which unlike renzapride has S and R stereoisomers, were investigated to gain further insight into 5-HT receptor function. In contrast to renzapride, S-, but not R-zacopride, was found to mimic the 5-HT1P receptor-mediated slow response to 5-HT. Desensitization of 5-HT1P receptors with 5-HT inhibited slow depolarizing responses to S-zacopride, and desensitization with S-zacopride antagonized slow responses to 5-HT. Responses to S-zacopride were also inhibited by renzapride and the 5-HT1P receptor antagonist N-acetyl-5-hydroxytryptophyl-5-hydroxytryptophan amide (5-HTP-DP). S-zacopride, like renzapride and 5-HT, presynaptically inhibited nicotinic fast excitatory postsynaptic potentials, an effect that can be mediated by 5-HT1P or 5-HT1A receptors. Both S and R stereoisomers of zacopride antagonized 5-HT3 receptor-mediated fast responses to 5-HT. Unlike 5-HTP-DP, neither zacopride or its stereoisomers nor renzapride inhibited the binding of 5-[3H]HT to 5-HT1P receptors. [3H]zacopride (5-10 nM) was found to bind to a site in the gut from which it could be displaced by a 1,000-fold excess of renzapride and S-zacopride (but not R-zacopride) greater than 5-HTP-DP much greater than the 5-HT3 receptor antagonist ICS 205-930. These observations suggest that, in addition to 5-HT3 receptors, there is a benzamide binding site on myenteric neurons that interacts with, but is distinct from, the 5-HT recognition site of 5-HT1P receptors. Benzamides may affect coupling of the 5-HT1P receptor to its effector.
Amino acid- and amine-induced gastrin release from isolated rat endocrine granules
Authors: Dial E. J. , Cooper L. C. , Lichtenberger L. M.
Published: December 2017

Secretory granules from rat antral tissue were isolated by differential centrifugation in sucrose and were confirmed as intact by electron microscopy. Gastrin release from the isolated granules was measured in response to stimulation with amino acids or their decarboxylated amine metabolites. Nine of 13 amino acids tested were ineffective at inducing gastrin release, whereas all 13 of the amine metabolites were potent stimulants of gastrin release. A pH gradient across the granule fraction membranes was estimated by acridine orange fluorescence and indicated an acidic interior. Changes in acridine orange fluorescence as an indicator of pH gradient dissipation showed that all of the amines, but only one of the amino acids, reversed acridine orange fluorescence. Ammonium chloride, similar to amines, both reversed acridine orange fluorescence and induced release of gastrin. It is concluded that amines 1) may directly stimulate gastrin granules to release their contents and 2) tend to alkalinize the gastrin granule interior. Some amino acids, in contrast, appear to directly stimulate gastrin release and do not affect the granule pH gradient.
Ion transport across isolated pig jejunum
Authors: Holtug K. , Skadhauge E.
Published: December 2017

Sodium, chloride, and glucose transport were studied in stripped pig jejunal epithelium mounted between halfchambers. The epithelium proved to be stable for experimental purposes for up to 2 h. Net sodium absorption was electrogenic and was dependent solely on sodium-glucose cotransport. Both sodium and glucose influx varied with mucosal glucose concentration; when fitted to the Michaelis-Menten equation the two fluxes generated glucose-dependent Michaelis constant values of 1.5 and 9.6 mM, respectively. In the absence of mucosal glucose, the flux ratios for sodium and chloride were of unity, and the unidirectional fluxes were linearly dependent on the ion concentrations. The chloride accompanying sodium in open circuit was driven by the potential generated by the sodium-glucose absorption (-5 mV) and supported an absorption of 1 mumol.cm-2.h-1 NaCl. Substituting 2-hydroxyethanesulfonate for chloride decreased total tissue conductance and reduced the sodium fluxes. This effect cannot be ascribed to sodium-chloride cotransport but reflects the different mobilities of the ion pairs in solution. Chloride secretion can be induced by theophylline.
pH regulation in ileum: Na(+)-H+ and Cl(-)-HCO3- exchange in isolated crypt and villus cells
Authors: Sundaram U. , Knickelbein R. G. , Dobbins J. W.
Published: December 2017

Current evidence suggests that intestinal crypt and villus cells have different functions in electrolyte transport. To study the regulation of transporters, we isolated and separated these two cell types. This was accomplished by sequential collection of enterocytes from rabbit ileal loops incubated with buffered solutions of calcium chelators. Alkaline phosphatase and thymidine kinase activity, sodium-glucose cotransport, and morphological criteria were used to determine cell separation. Cell viability was evaluated with trypan blue exclusion, leucine incorporation into protein, and morphological features. The role of Na(+)-H+ and Cl(-)-HCO3- exchange in the regulation of intracellular pH was analyzed using an intracellular pH sensitive dye, BCECF. Removal of external Na+ or the addition of amiloride resulted in acidification of both crypt and villus cells. Removal of Cl- or the addition of DIDS resulted in alkalinization of both cell types. The cells could be acidified with NH4Cl, and recovery from this acid load was dependent on Na+ and inhibited by amiloride. Similarly, the cells could be alkalinized with propionate and recovery was Cl- dependent and DIDS sensitive. These data are consistent with the presence of Na(+)-H+ and Cl(-)-HCO3- exchange in both crypt and villus cells. Both exchanges appear to be involved in the regulation of basal pH as well as in recovery from alterations in intracellular pH. Having demonstrated the presence of Na(+)-H+ and Cl(-)-HCO3- exchange activity in both crypt and villus cells, we can now use these cells to determine the regulation of these exchangers by intracellular second messengers.
Measurement of tone in canine colon
Authors: Neri M. , Phillips S. F. , Fich A.
Published: December 2017

We sought to determine whether the proximal colon modifies its capacity to accommodate contents by altering the tone within its wall. In dogs equipped with manometric recorders in the terminal ileum and proximal colon, a highly compliant bag was introduced into the proximal colon. With the use of an electromechanical barostat, the capacity of the colonic segment was monitored at a constant low-distending pressure; the volume of air required to maintain a preset pressure in the bag was recorded by the barostat. During fasting, rhythmic cycles of volume were recorded, with a cycle frequency of approximately 1/min. Importantly, this phenomenon was not related to the simultaneous recording of manometric pressures in the adjacent bowel or to the interdigestive cycle (phase III) in the ileum. Peristaltic-like pressure complexes (recorded manometrically) in the ileocolonic region were associated with receptive relaxation of the proximal colon. Feeding, bethanechol, and morphine reduced volumes accommodated in the bag, presumably by increasing tone in the wall of the colon. Atropine had the opposite effect. These results support the concept that tonic changes in the wall of the proximal colon, which could influence accommodation and storage in the large bowel, are not always recorded by conventional techniques.