bluuebunny/crossref_metadata_2025 huggingface dataset:
Acid secretion in fetal rat stomach in vitro
Authors: Ducroc R. , Desjeux J. F. , Garzon B. , Onolfo J. P. , Geloso J. P.
Published: December 2017

In vivo fetal rat stomach produces HCl 48 h before birth. This study examines the mechanisms of H+ secretion from days 19 to 21 before birth. Isolated fetal stomachs were mounted as flat sheets in Ussing chambers for measurement of the transepithelial H+ fluxes (JH+) and short-circuit current (Isc), as indexes of the active ionic fluxes, and for measurement of total ionic conductance (G) and unidirectional mannitol fluxes from serosa to mucosa (JMans leads to m), as indexes of passive permeability. The results indicate that JH+ was absent at day 19 but reached 0.75 +/- 0.1 and 0.75 +/- 0.09 mueq . h-1 . cm-2 at days 20 and 21, respectively. Concomitantly, Isc increased significantly (56%) between days 19 and 20 in the direction of anion secretion or cation absorption. Parallel reductions in G (45%) and in JMans leads to m (66%) were observed between days 19 and 20. In conclusion, the simultaneous appearance of active H+ secretion and decreased passive transepithelial permeability strongly suggests that both processes are involved in the mechanism of acidification of the fetal rat stomach before birth.
Inhibition of canine interdigestive proximal gastric motility by cholecystokinin octapeptide
Authors: Schang J. C. , Kelly K. A.
Published: December 2017

Feeding abolishes cyclic interdigestive motility and decreases intraluminal pressure in autotransplanted pouches of canine proximal stomach. Our aim was to determine whether cholecystokinin might be the hormonal messenger involved. In four conscious dogs with autotransplanted proximal gastric pouches and chronic duodenal electrodes, intrapouch pressure and duodenal myoelectric activity were measured during fasting, while cholecystokinin octapeptide (CCK-OP) was infused intravenously for 4 h at doses 0, 15, 31, 62, 125, and 250 mg . kg-1 . h-1. Each dose was given five times to each animal. Cholecystokinin octapeptide inhibited the interdigestive cycles in both pouch and duodenum and decreased the pressure in the pouch. The threshold for these effects was 31 ng . kg-1 . h-1, and the ED50 was 62 ng . kg-1 . h-1. The dose of 125 ng . kg-1 . h-1 suppressed the cycles nearly completely and decreased mean +/- SE intrapouch pressure from 15.3 +/- 1.1 to 6.3 +/- 2.8 cmH2O . min (P less than 0.001). After the infusions were stopped, cyclic activity and intrapouch pressure returned promptly to control values. We concluded that CCK-OP at "physiological" doses abolished interdigestive cycles and decreased intraluminal pressure in autotransplanted pouches of canine proximal stomach.
RES hyperphagocytosis by rats with streptozotocin-induced diabetes mellitus
Authors: Cornell R. P.
Published: December 2017

In contrast to previous studies of neutrophils from diabetic animals and humans in vitro and of macrophages from diabetic humans in vivo, which reported phagocytic depression, reticuloendothelial system (RES) hyperphagocytosis of colloidal carbon was observed in rats at 14 and 28 days after diabetes induction with streptozotocin (STZ). Carbon clearance half times were significantly enhanced to 6.3 +/- 0.79 and 8.1 +/- 1.04 min at 14 and 28 days post-STZ, respectively, compared with the nondiabetic value (12.7 +/- 0.98 min). The severity of uncontrolled STZ-induced diabetes in rats was confirmed by significant hypoinsulinemia, hyperglucagonemia, hyperglycemia, and hyperlipidemia. Although body weights of STZ-diabetic animals declined progressively, liver weights as a percent of body weight increased above the control value at 14 and 28 days post-STZ. In fact, expression of carbon phagocytosis as the corrected phagocytic index, which accounts for changes in liver and spleen weights relative to body weight, eliminated the significant difference between STZ-diabetic and nondiabetic animals. Antibiotic treatment of diabetic rats failed to alter the hyperphagocytosis, implying that a chronic bacterial infection was not the cause of phagocytic stimulation. Daily insulin replacements, but not a single large insulin dose to 14-day post-STZ rats, reversed the enhanced phagocytosis of colloidal carbon.
Secretin is an enterogastrone in the dog
Authors: Chey W. Y. , Kim M. S. , Lee K. Y. , Chang T. M.
Published: December 2017

To determine the physiological significance of secretin on gastric secretion, effects of normal rabbit serum (control) and rabbit antisecretin serum (anti-S) on meat meal-stimulated gastric secretion of acid and pepsin from vagally innervated fundic pouches were studied in four dogs with gastric fistulas. The intravenous administration of control serum did not affect the postprandial rise in plasma secretin concentration, whereas intravenous anti-S virtually eliminated the circulating plasma secretin. Both plasma gastrin concentration and acid output following intravenous anti-S were significantly greater than those following intravenous control serum. However, pepsin outputs in the two groups of experiments were not significantly different. In the same dogs in the fasting state, during intravenous infusion of secretin in doses of 0.06 and 0.125 U . kg-1 . h-1, the acid output stimulated by intravenous human synthetic gastrin in a dose of 0.25 micrograms . kg-1 . h-1 was significantly less than that during intravenous saline. The studies indicate that secretin in a physiological dose can inhibit postprandial release of gastrin and gastric secretion of acid, and thus secretin is an enterogastrone in the dog.
Origins of positive potential difference of frog gastric mucosa in Cl--free solutions
Authors: Schwartz M. , Chu T. C. , Carrasquer G. , Rehm W. S. , Holloman T. L.
Published: December 2017

Experiments were performed on gastric mucosae of Rana pipiens with an in vitro method. Bathing both sides of the mucosae in Cl--free solutions resulted in an inverted potential difference (PD) (i.e., nutrient negative). Cimetidine in a concentration of 10(-4) or 10(-3) M in the nutrient solution gave a positive PD when the H+ secretory rate was zero or near zero and confirmed that the PD versus H+ rate was linear. the origins of the positive PD were examined by ion replacement, e.g., choline for Na+ in both solutions. When both solutions had 25 mM HCO(-)3 (i.e., no HCO(-)3 gradient), the difference in PD between choline sulfate and Na2SO4 solutions indicated a possible small active transport of Na+ from the secretory to nutrient side. Similar experiments indicated no active K+ transport. A residual PD occurred without Na+. With H+ rate zero, 100% O2, and no HCO(-)3, a base secretion of about 0.4 mueq.h-1.cm-2 was obtained in a direction to contribute to the positive PD. Active SO2(-)4 transport may occur.
Oxygen consumption by the gastrointestinal tract and liver in conscious newborn lambs
Authors: Edelstone D. I. , Holzman I. R.
Published: December 2017

We determined blood flow to and O2 consumption (VO2) by the gastrointestinal tract (GI) and liver and also measured cardiac output and whole-body VO2 in nine chronically catheterized unanesthetized lambs (7-16 days of age). Blood flows were calculated with the radionuclide-labeled microsphere technique, and blood O2 contents were measured with an O2 content analyzer. During the fasting state, GI blood flow was 58 +/- 4 (means +/- SE) ml.min-1.kg body wt-1; GI VO2 was 1.4 +/- 0.1 ml O2.min-1.kg-1. Neonatal GI VO2 was linearly related to both GI blood flow and O2 delivery (DO2). GI O2 extraction [(VO2/DO2).100] averaged 28% and did not vary with blood flow or DO2. Liver blood flow was 73 +/- 4 ml.min-1.kg-1 (271 +/- 23 ml.min-1.100 g liver-1), and liver VO2 was 2.0 +/- 0.1 ml O2.min-1.kg-1 (7.3 +/- 0.5 ml O2.min-1.100 g-1). Hepatic O2 extraction varied from 18 to 81% . VO2 by the neonatal liver did not correlate with liver blood flow or DO2. Hepatic O2 extraction, however, was inversely related to liver DO2. Our data indicate that the gastrointestinal tract and liver of the unanesthetized newborn animal exhibit O2 demands 1.5-3 times those reported in the adult. The neonatal gastrointestinal tract meets its O2 demands with a comparatively large blood flow and O2 delivery, whereas the neonatal liver provides for its O2 requirements by varying its O2 extraction.
Neural regulation of interdigestive motor activity in canine jejunum
Authors: Itoh Z. , Aizawa I. , Takeuchi S.
Published: December 2017

The hypothesis that extrinsic innervation of the small bowel provides pathways for initiation and coordinated propagation of the interdigestive migrating contractions (IMC) was reinvestigated in dogs. Motor activity was measured by chronically implanted force transducers. After a control study, 40-cm segments of the jejunum were extrinsically denervated. All IMC migrated distally through the extrinsically denervated segments. Thiry loops were then constructed from the extrinsically denervated segments, and continuity of the intestine was restored by end-to-end anastomosis. IMC proximal to the anastomosis did not migrate through the extrinsically denervated loop but migrated to sites across the anastomosis. In the extrinsically denervated loop, bands of strong contractions, quite similar to the IMC, occurred at the orad end of the loop independent of the IMC and propagated distally to the caudad end of the loop. The duration, frequency, and migrating velocity of these bands of contraction were different from those of IMC. These results suggest that extrinsic innervation is not essential for the initiation and orad sequential propagation of periodic motor activity like IMC, even when intrinsic innervation is discontinued.
Sugar absorption and secretion by winter flounder intestine
Authors: Naftalin R. J. , Kleinzeller A.
Published: December 2017

Transport of sugars by winter flounder (Pseudopleuronectes americanus) intestine has been examined, and the following observations have been made. 1) No net absorption of D-galactose was found in controls; however, mucosally applied 0.1 mM phlorizin stimulated the mucosal-serosal flux with net sugar secretion. 2) Net absorption of methyl glycosides was inhibited by D-galactose, 0.1 mM ouabain, and phlorizin (without induction of secretion). 3) Net secretion of 2-deoxy-D-galactose was found without cellular accumulation of free sugar. The secretory process had a Km of 10 mM and was inhibited by serosally applied 0.1 mM phloretin, bilateral replacement of Ringer Na+ by choline, serosal ouabain, and D-galactose. 4) No net absorption or secretion of 2-deoxy-D-glucose was found with a variety of experimental conditions. 5) At least two active transport systems for sugars appear to be operative in the flounder intestine: a conventional Na+-dependent sugar transport system across the brush border that allows net absorption and a Na+-dependent secretory system that apparently also operates across the mucosal border. Because D-galactose is transported by both systems, there is no net flux of this sugar. Several possible models for the net secretory system are discussed.
Transcellular transport of calcium and inorganic phosphate in the small intestinal epithelium
Authors: Murer H. , Hildmann B.
Published: December 2017

Transport mechanisms involved in the small intestinal handling of inorganic phosphate and calcium have been studied by different in vitro methods during the last few years. In concordance with studies on intact epithelial preparations, studies with brush-border and basal-lateral membrane vesicles isolated from the small intestinal epithelial cell revealed that transcellular calcium and inorganic phosphate fluxes are coupled to transcellular sodium flux, i.e., secondary active via coupling to the primary active sodium flux. A sodium-coupled mechanism in the brush-border membrane leads to cellular accumulation of inorganic phosphate. A sodium-coupled mechanism leads to extrusion of calcium from the cell into the serosal interstitium. A primary active transport mediated by the Ca-ATPase and located in the basal-lateral membrane also exists for calcium. Regulation of transcellular phosphate and calcium flux proceeds via altered influx rates at the luminal cell pole.
Corticosteroid-binding studies in cytosol of colonic mucosa of the rat
Authors: Marusic E. T. , Hayslett J. P. , Binder H. J.
Published: December 2017

Cytosolic binding of [3H]dexamethasone was studied in the colon of the rat. [3H]dexamethasone binding was rapid and stable at 4 degrees C for 240 min. Scatchard analysis revealed a Kd of 6.2 +/- 0.5 X 10(-9) M and a binding capacity of 149 +/- 6.4 fmol/mg cytosolic protein (100,000-g fraction). Although dexamethasone inhibited [3H]dexamethasone binding more than that of aldosterone, [3H]aldosterone binding was inhibited equally by both aldosterone and dexamethasone. The relative order of potency of other steroids to inhibit [3H]dexamethasone binding was: dexamethasone greaterthan progesterone greater than spironolactone greater than aldosterone greater than corticosterone greater than cortexolone greater than estradiol. In other experiments, low doses of dexamethasone and aldosterone were infused into adrenalectomized animals to determine functional importance of these cytosolic steroid receptors. One-hour infusion of aldosterone at 2 micrograms/100 g body wt, which was the minimal dose of dexamethasone that increased transmural potential difference, did not alter the potential difference. These studies demonstrate the presence of a cytosolic receptor for dexamethasone and suggest that the action of dexamethasone on electrolyte transport in adrenalectomized animals is not mediated by the mineralocorticoid type of receptor and may be mediated by the specific high-affinity receptor for dexamethasone.
Synaptic activation of erratic burst-type myenteric neurons in cat small intestine
Authors: Athey G. R. , Cooke A. R. , Wood J. D.
Published: December 2017

To study further the ongoing spike discharge of burst-type myenteric neurons, extracellular recordings were made with either Teflon-insulated Pt wire electrodes (tip diam, 20 micrometers) or 3 M NaCl-filled glass micropipettes (tip diam, 1–2 micrometers). Presynaptic fibers to the erratic bursters were activated by electrical shocks delivered through Teflon-insulated Pt wire electrodes. Single electrical shocks applied to either the surface of the ganglion or an interganglionic connective elicited bursts of spikes that had parameters (interspike intervals and spikes per burst) that closely resembled the spontaneously occurring bursts in the same neuron. The latencies of the responses to electrical stimulation ranged from 5 to 30 ms. The responses were reversibly abolished when the concentration of Mg2+ in the bathing solution was elevated to 12 mM. The responses to electrical stimulation were unaffected by atropine, hexamethonium, d-tubocurarine, epinephrine, norepinephrine, methysergide, morphine, naloxone, and substance P. The ongoing burst-type discharge of cat myenteric neurons appeared to reflect a synaptic event that could be mimicked by electrical stimulation of presynaptic fibers. The identity of the neurotransmitter that elicits the burst-type discharge is unknown. The transmitter is probably not acetylcholine, serotonin, norepinephrine, an opiatelike peptide, nor substance P.
Mucosal gastrin receptor. VI. Induction by corticosterone in newborn rats
Authors: Peitsch W. , Takeuchi K. , Johnson L. R.
Published: December 2017

Serum and antral gastrin levels as well as specific binding of [125I]gastrin-17 to a 270–30,000 g oxyntic gland mucosa crude membrane preparation were measured in rats between 5 and 40 days of age. Rats were normally weaned at day 18, although weaning was prevented in some animals until day 25. The results of these studies confirmed our previous data showing that mucosal gastrin receptors and antral gastrin levels begin to increase at the time of normal weaning and reach adult levels within a few days. Although the shift from liquid to a solid diet enhances the response, it is not essential for it and does not trigger it. In addition, the current studies demonstrated that injection of corticosterone caused a premature increase in both gastrin receptor and antral gastrin levels. Once maturation had occurred, however, corticosterone had no further effect. Adrenalectomy delayed but did not prevent the maturational changes in gastrin receptors and antral gastrin levels. Normal serum gastrin concentrations were necessary for the number of gastrin receptors and the amount of antral gastrin to reach normal levels.
Cholecystokinin-induced persistent stimulation of enzyme secretion from pancreatic acini
Authors: Collins S. M. , Abdelmoumene S. , Jensen R. T. , Gardner J. D.
Published: December 2017

When pancreatic acini are first incubated with cholecystokinin, washed to remove free cholecystokinin and then reincubated in fresh incubation solution, there is significant residual stimulation of amylase secretion. This residual stimulation requires relatively high concentrations of the secretagogue, is reversible, and is specific for cholecystokinin. Induction of residual stimulation occurs more rapidly at 37 degrees C (maximal by 1 min) than at 4 degrees C (maximal by 10 min), and, once induced, residual stimulation persists for up to 75 min at 37 degrees C and for more than 90 min at 4 degrees C. The persistent effect of cholecystokinin on enzyme secretion cannot be accounted for by incomplete removal of the secretagogue by the wash procedure or by activation of some intermediate step in the mechanism of action of cholecystokinin that persists after the secretagogue dissociates from its receptors. Instead, cholecystokinin-induced residual stimulation of enzyme secretion appears to result from persistent occupation of cholecystokinin receptors by the secretagogue.
Alkaline secretion by amphibian duodenum. II. Short-circuit current and Na+ and Cl- fluxes
Authors: Simson J. N. , Merhav A. , Silen W.
Published: December 2017

The relations among alkaline secretion, short-circuit current (Isc), and fluxes of Na+ and Cl- are examined. The Isc (1.15 +/- 0.03 microeq.cm-2.h-1) was significantly greater than the rate of alkaline secretion (1.02 +/- 0.02 microeq.cm-2.h-1). Regression analysis (n = 300) showed a highly significant correlation between alkaline secretion and Isc and indicated a residual Isc of 0.26 microeq.cm-2.h-1. In the absence of HCO3-, there was a residual Isc of 0.25 +/- 0.04 microeq.cm-2.h-1. This residual Isc is accounted for by an observed net Na+ absorption of 0.28 +/- 0.04 microeq.cm-2.h-1. Fluxes of Na+ fail to fit the flux-ratio equation and were not significantly affected by 2 X 10(-6) M ouabain, 5 X 10(-5) M amiloride, or anoxia but were significantly reduced by 2,4,6-triaminopyrimidine. The net Cl- flux was not significantly different from zero. Cl- fluxes conform to the flux-ratio equation and were reduced by anoxia or 2,4,6-triaminopyrimidine but were not affected by 4-acetamido-4'-isothiocynostilbene-2,2'-disulfonic acid (SITS). Anoxia or ouabain significantly inhibited alkaline secretion and Isc without affecting net fluxes of Na+ or Cl-, whereas amiloride or SITS had no effect on any of these parameters. There is no NaCl-coupled transport nor anion exchange, but solute-coupled Na+ absorption is demonstrated. We conclude that alkaline secretion by the duodenum involves a transcellular, energy-requiring, Na+-dependent, ouabain-sensitive, electrogenic mechanism that accounts for at least 80% of the Isc. Net Na+ absorption accounts for the residual Isc. Movements of Cl- are passive, do not contribute to Isc, and are not involved in the mechanism of alkaline secretion. Two hypothetical models of transcellular alkaline secretion are proposed.
Intrinsic nervous control of migrating myoelectric complexes
Authors: Sarna S. , Stoddard C. , Belbeck L. , McWade D.
Published: December 2017

The role of intrinsic nerves in the control of migrating myoelectric complexes (MMCs) was studied in seven conscious dogs, each implanted with a set of eight bipolar Trimel wire electrodes. Local areas, 3-5 cm long, were perfused close intra-arterially via an exteriorized heparinized Silastic cannula. Experiments consisted of giving bolus injections of atropine (20-50 micrograms), hexamethonium (20 mg), and tetrodotoxin (TTX; 3-30 micrograms) via the catheter at varying periods of time with respect to the arrival of phase III at the perfused site. Atropine and hexamethonium, given close intra-arterially immediately before the arrival of phase II at the perfused site, blocked its further propagation. Tetrodotoxin given locally also blocked the propagation of phage III, as above. After the block, TTX initiated a new phase III activity at, or distal to, the perfused site in 10 out of 14 perfusions. The new phase III activity propagated distally. This study shows that the mechanisms for the initiation and propagation of MMCs are built into the enteric plexus. Once an MMC is initiated, its propagation is achieved by proximal-to-distal excitation through the intrinsic cholinergic network of neurons. This study explains the lack of any significant changes in the propagation parameters of MMCs after vagotomy or celiac and superior mesenteric ganglionectomy.
Permeability of intestinal capillaries to small molecules
Authors: Perry M. A. , Granger D. N.
Published: December 2017

The permeability of capillaries in the isolated, vascularly perfused cat ileum was studied with the double-indicator diffusion technique. The molecules studied were raffinose, inulin, and beta-lactoglobulin A. Plasma flow through the tissue was increased by local intra-arterial infusions of isoproterenol (a selective mucosal vasodilator) or adenosine (a dilator of the muscularis vasculature). The permeability-surface area product (PS) for all solutes increased with increasing plasma flow. At the highest plasma flow acquired with isoproterenol, PS values for raffinose, inulin, and beta-lactoglobulin A were approximately 40, 20, and 4 ml.min-1.100 g-1, respectively. These data suggest that capillaries in the mucosa-submucosa of the ileum are at least five to seven times more permeable to raffinose and inulin than has been reported for skeletal muscle capillaries. Selective vasodilation of the muscularis region with adenosine reduced PS values for raffinose and inulin at each flow rate studied. The data are consistent with equivalent pore radii of approximately 60 A for capillaries in the mucosa-submucosa and 40 A in the muscularis of the small intestine.
Interstitium-to-blood movement of macromolecules in the absorbing small intestine
Authors: Granger D. N. , Perry M. A. , Kvietys P. R. , Taylor A. E.
Published: December 2017

The relative roles of diffusion and convection in the transport of plasma proteins across intestinal capillaries were estimated for absorbing and nonabsorbing segments of cat ileum. Diffusive, convective, and net protein fluxes were estimated with steady-state lymph and plasma protein concentrations, lymph flow, net transmucosal volume flow, and phenomenological transport equations. The results acquired indicate that convection accounts for approximately 80-90% of total net transcapillary solute movement at normal and increased capillary filtration rates. When the intestinal capillaries are converted from filtering to absorbing vessels by enhancing transmucosal water movement, the convective and diffusive protein fluxes occur in opposite directions, i.e., significant quantities of plasma proteins move from interstitium to blood by convection. These findings suggest that the magnitude of the capillary protein leakage during absorption is far greater than predicted using lymphatic protein flux changes. The massive movement of plasma proteins into and out of the mucosal interstitium during absorption may be advantageous for the removal of protein-bound nutrients (e.g., fatty acids).
Release of somatostatin from rodent antral mucosae maintained in organ culture
Authors: Lichtenberger L. M. , Shaw L. S. , Bailey R. B.
Published: December 2017

Somatostatin secretion was investigated from rodent antral mucosal biopsies maintained in organ culture. Under control conditions, the somatostatin secretory output was fairly constant, with each biopsy releasing a mean value of 29.1 +/- 7.5 pg of hormone over a 15-min period. Incubation of the mucosa in medium containing 5% peptone directly induced a 20-fold increase in medium somatostatin levels to 622.5 +/- 15.5 pg/ml. In contrast, a peptone dialysate was a weaker stimulant of hormone release, inducing a three- to fourfold increase in medium somatostatin concentration. Additionally, it was determined that a peptic hydrolysate of bovine serum albumin was a significantly more potent in vitro stimulant of somatostatin secretion than the intact undigested molecule. These results suggest that the amino acid and peptide constituents of these proteinaceous substances are the major stimulants of somatostatin release in vitro. It is presently uncertain whether this direct peptone-induced release of somatostatin from antral mucosal explants can account for the previously reported [Am. J. Physiol. 235 (Endocrinol. Metab. Gastrointest. Physiol. 4): E410-E415, 1978] gastrin secretory "off response" to the same agent, because addition of exogenous somatostatin to the medium failed to block this peptone-induced gastrin secretory response.
Ouabain binding to isolated frog gastric mucosa
Authors: France V. M. , Durbin R. P.
Published: December 2017

Inhibition of gastric acid secretion by the cardiac glycoside, ouabain, is considerably reduced by elevating external K+ as first shown by Davenport (Proc. Soc. Exp. Biol. Med. 110: 613-615, 1962). To determine the possible role of K+ in this effect, we measured [3H]ouabain binding in isolated bullfrog gastric mucosa. Uptake of the labeled drug showed two components: one that saturated at 0.36 pmol ouabain per milligram wet weight and one that was linear with the external ouabain concentration. The former component is considered to represent specific binding to Na+-K+-ATPase; activity of this enzyme system in mucosal homogenates was 0.2 mumol per milligram protein per hour. Increase of K+ in the nutrient bathing solution from 3 to 30 mM, or replacement of Na+ by K+ in the secretory bathing solution, largely reversed inhibition of acid secretion by ouabain but did not affect maximum specific binding. The results fit a model in which Na+-K+-ATPase is normally required in oxyntic cells to maintain a high K+ level, which in turn supports exchange of K+ for H+ at the apical surface.
Human esophageal response to rapid swallowing: muscle refractory period or neural inhibition?
Authors: Meyer G. W. , Gerhardt D. C. , Castell D. O.
Published: December 2017

The peristaltic response of the normal human esophagus to 10 repeated water swallows separated by varying time intervals (5, 10, 15, 20, and 30 s) between swallows was studied. Pressures measured during the shorter time intervals were of lower amplitude than those at 30-s swallowing intervals throughout the esophagus, with the distal esophagus showing the greatest effect. Frequency of peristalsis was decreased throughout the esophagus with rapid swallowing, especially distally at the 5- and 10-s time intervals. There was no significant change in wave velocity or duration at these time intervals. These data suggest that there is a refractory period in the distal (smooth muscle) esophagus. A series of paired swallows separated by 5 s resulted in a significant decrease in amplitude of the first swallow, and this was more marked in the distal esophagus. These data indicate that there is an inhibition of the progression of peristalsis by a subsequent swallow, probably through a neural mechanism. These studies show that repeated liquid swallows may effect peristalsis by two mechanisms: refractoriness of esophageal smooth muscle and a neural inhibitory discharge.
Transmembrane and transepithelial movement of calcium during stimulus-secretion coupling
Authors: O'Doherty J. , Stark R. J.
Published: December 2017

Electrophysiological studies were undertaken to determine the transmembrane and transepithelial changes in free Ca2+ concentration that occur during serotonin-induced secretion in the salivary glands of the blowfly, Phormia regina. Ca-selective and conventional microelectrodes were used to measure intracellular and luminal Ca2+ concentrations ([Ca]L), serosal membrane and transepithelial potentials (Em, Etr), and their changes during serotonin (5-hydroxytryptamine, 5HT)-induced salivary secretion. The effect of stimulus concentration on these parameters and enzyme release was also determined. Previous studies provided evidence that serosal stimulation with 10(-8) M 5HT caused a hyperpolarization of Em and short phasic two- to threefold increases in [Ca]i. In these studies, higher concentrations of 5HT (10(-7) M) resulted in depolarization of Em by 13 +/- 1.2 mV and of ECa by 64 +/- 2.1 mV, a dramatic increase in [Ca]i, and a decrease in enzyme release. In addition, serotonin (10(-8) M) reduced the normal spontaneous Etr (+19.6 +/- 1 mV) to near zero while causing an increase in [Ca]L from 1.3 +/- 0.3 X 10(-5) mM to 2.0 +/- 0.1 X 10(-3) mM, a concentration isomolar with that of the bathing medium. These results provide direct electrochemical evidence that, during stimulus-secretion coupling of the salivary epithelial cells, the neurohormone serotonin controls the secretory response by the regulation of intracellular Ca2+ and induces transepithelial transport of Ca2+, thereby suggesting that, during secretion, the neurohormone causes the salivary gland to behave as a "leaky epithelium" by activating the paracellular shunt pathways.
Does endogenous prostaglandin affect gastric antral motility?
Authors: Sanders K. M. , Szurszewski J. H.
Published: December 2017

Intracellular electrical activity and muscle contraction were recorded simultaneously from circular muscle of the canine antrum. Treatment with indomethacin enhanced the plateau phase of the spontaneously occurring gastric action potential and the amplitude of the phasic contraction. Exogenous PGE2 reversed this effect of indomethacin. Treatment with indomethacin also enhanced the electrical and mechanical responses to pentagastrin; this enhancement was also reversed by PGE2. Considered together, these results suggest that endogenous prostaglandin, probably of the E series, tonically suppresses the spontaneous electrical and mechanical activities of antral circular muscle and the responsiveness of the muscle to excitatory stimuli.
Intestinal transport of bile acids
Authors: Wilson F. A.
Published: December 2017

The intestinal absorption of bile acids is determined by two resistances: diffusion through an unstirred water layer and penetration of the cell membrane. Passive jejunal uptake of polar bile acids is limited by the mucosal membrane, whereas the unstirred layer exerts resistance on uptake of more nonpolar species. After correction for the diffusion layer, the membrane permeability coefficients were derived to calculate the delta delta Fw leads to 1 associated with uptake of the -OH (+874 cal.mol-1), glycine (+897), and taurine (+1,498) groups. The delta delta F1 (-6,126 cal.mol-1) for the -OH group suggested that the jejunal mucosa is a relatively polar membrane. The unstirred layer is even more rate limiting for bile acid uptake from micellar solutions. Once the micelle reaches the aqueous-membrane interface, it is not absorbed intact, but rather uptake is explained in terms of monomers in the aqueous phase that are in equilibrium with the micelle. The presence of the unstirred water layer introduces artifactually high Km values for active transport. Structure-activity studies suggest that the ileal recognition site consists of a component for the steroid moiety, a positive charge, and an adjacent anionic charge. The energy for active transport arises from the Na+ gradient across the brush-border membrane that, in turn, is dependent on the activity of Na+-K+-ATPase. The Na+ stimulation of bile acid transport across the ileal brush-border membrane is due to influx coupling via a cotransport system rather than electrical coupling to satisfy overall electrical neutrality.
Effects of somatostatin on intestinal calcium transport in the rat
Authors: Favus M. J. , Berelowitz M. , Coe F. L.
Published: December 2017

The addition of somatostatin (SRIF) to rat descending colon in vitro increased the calcium secretory flux from serosa to mucosa (Js leads to m) and reduced tissue short-circuit current (Isc) but did not alter the absorptive flux from mucosa to serosa (Js leads to m). Js leads to m increased by 37% at 10(-9) M SRIF and by 48% at 10(-6) M. The response to SRIF was not altered by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], and SRIF did not interfere with stimulation of calcium Jm leads to s by 1,25(OH)2D3. Removal of sodium from the buffer abolished the stimulation of Js leads to m by SRIF without reducing basal Js leads to m. Secretory fluxes of mannitol and calcium were strongly correlated in the presence and absence of SRIF, suggesting that SRIF stimulates a paracellular transepithelial pathway for calcium. In the duodenum, SRIF altered neither calcium Js leads to m nor Isc. In the ileum, calcium Js leads to m increased and Isc decreased, as in the colon, but only by 28 and 12%, respectively. The maximal change in calcium Js leads to m caused by SRIF in these three intestinal segments was negatively correlated with the tissue concentration of immunoreactive SRIF. These results suggest that intestinal calcium secretion could, in part, be regulated by intestinal SRIF.
Adaptation of intestinal muscle in continuity after jejunoileal bypass in the rat
Authors: Nemeth P. R. , Kwee D. J. , Weisbrodt N. W.
Published: December 2017

Functional and structural adaptations of the intestine that remained in continuity after jejunoileal bypass [the in-continuity (IC) segment] were characterized in the rat. Three days after bypass, transit was rapid in fed rats, but, by 35 days, transit had slowed to mimic that seen in the intact intestine of control animals. In fasted rats, transit was as rapid as in the fed animals at 3 days after bypass; however, in fasted rats, transit did not slow when tested up to 35 days after operation. Transit in animals at 3, 14, and 35 days after sham operation was not different from control. Mucosal weights in the proximal and distal portions of the IC segment were increased at 3, 14, and 35 days after bypass. The wet weights and protein contents of the muscle and serosal layers of both portions of the IC segment were increased at 35 days. These findings support the hypothesis that the adaptation seen in the IC segment after bypass involves changes in function and structure of the intestinal smooth muscle as well as the intestinal mucosa.
Endogenous norepinephrine release induced by tyramine modulates intestinal ion transport
Authors: Tapper E. J. , Bloom A. S. , Lewand D. L.
Published: December 2017

To study the effects of endogenous norepinephrine on intestinal ion transport, we tested the actions of an indirect sympathomimetic agent, tyramine, on electrolyte fluxes in the short-circuited rabbit ileum in vitro. Tyramine (10(-5) M) alone had no effect on short-circuit current or Na transport but increased Cl absorption. Tyramine decreased the short-circuit current, stimulated both Na and Cl absorption, and increased tissue conductance when its breakdown by endogenous monoamine oxidase enzymes was inhibited by pretreatment with pargyline (10(-4) M). Pargyline alone had no effect on short-circuit current and NaCl transport. The effect of norepinephrine on NaCl transport was inhibited by the alpha-adrenergic receptor antagonist, phentolamine (10(-7) M). This response was also prevented when animals were chemically sympathectomized with 6-hydroxydopamine. Although sympathectomy decreased measurable tissue norepinephrine by 80%, it did not alter basal short-circuit current, Na and Cl absorption, and the short-circuit current response to glucose-stimulated Na transport and to exogenous norepinephrine. Thus, a pool of norepinephrine in intestinal adrenergic neurons released by tyramine affects intestinal ion transport but does not alter basal ion transport. These data suggest close neuropharmacologic similarities between the adrenergic nervous system in the intestine and other organs.
Effect of extracellular manganese on amylase release from dispersed pancreatic acini
Authors: Abdelmoumene S. , Gardner J. D.
Published: December 2017

In dispersed acini from guinea pig pancreas, adding extracellular manganese increased amylase release. A significant effect could be detected with 0.25 mM manganese, and maximal stimulation occurred with 1 mM manganese. When manganese was added, the rate of amylase release did not change during the first 20 min of incubation and then gradually increased to a new steady state by 80 min, which with 1 mM manganese represented a fourfold increase in the rate of enzyme release. Extracellular manganese inhibited the stimulation of amylase release caused by those secretagogues that mobilize cellular calcium but augmented the stimulation caused by those secretagogues whose actions are mediated by cellular cAMP. The mechanism by which manganese altered stimulated amylase secretion differed from the mechanism by which manganese stimulated basal amylase release because the change in stimulated release was maximal within 10 min, whereas the change in basal release did not occur until after 20 min. The actions of manganese on secretagogue-stimulated amylase release were not attributable to manganese-induced changes in secretagogue-stimulated calcium outflux or cAMP and, instead, appear to result from actions of manganese on one of the later steps in the mechanisms for stimulating the secretory process.
Search for resistances controlling canine gastric emptying of liquid meals
Authors: Miller J. , Kauffman G. , Elashoff J. , Ohashi H. , Carter D. , Meyer J. H.
Published: December 2017

Previous work has indicated that a chemoselective resistance controls gastric emptying. By use of meals of glucose or oleate, which were shown to empty spontaneously from dogs' stomachs half as fast as saline, we sought to locate this resistance by studying flow under controlled pressures in various regions of the gastrointestinal tract. In intact dogs, gastric outflow of glucose or oleate rose one-third as fast as outflow of saline as gastric pressure was raised, and this increased resistance to outflow of nutrients was unaffected by truncal vagotomy and pyloroplasty. In fistula dogs, gastroduodenal outflow rose linearly with gastroduodenal pressure gradients; outflow was markedly inhibited in a dose-related manner by intestinal oleate but not glucose. Inhibition by oleate was abolished by pyloroplasty. Glucose or oleate flowed into the small bowel from a barostat only slightly slower than saline. However, there was a strong inhibition of intestinal inflow of all three meals by gastric distension, an effect unaltered by truncal vagotomy. The findings suggest that gastric emptying is controlled by complex interactions among pressures and resistances, both within and beyond the stomach.
Effects of lecithin ingestion on plasma and lymph lipoproteins of normo- and hyperlipemic rats
Authors: Clark S. B. , Clark V. E. , Small D. M.
Published: December 2017

Rats were fed low- or high-cholesterol diets in which all fatty acids were derived from either polyunsaturated phosphatidylcholine (PC) or safflower oil (SO) for 15 days. In hypercholesterolemic rats, plasma high-density lipoprotein cholesterol esters were increased by dietary PC compared with SO. In normolipemic rats, PC administered either in the diet or by short-term, maximal-rate intraduodenal infusion had no effect on aortic or portal plasma lipoprotein lipids or on mesenteric lymph and plasma lipoproteins compared with SO. The phosphoryl component of PC, when absorbed by the enteral route, may influence lipoprotein profiles in hypercholesterolemic rats but has no effect in normolipemic rats.
Sodium-coupled nonelectrolyte transport across epithelia: emerging concepts and directions
Authors: Freel R. W. , Goldner A. M.
Published: December 2017

Since the proposal of the sodium-gradient hypothesis, research efforts have focused on two major areas: 1) establishing the thermodynamic efficacy of the electrochemical gradient for sodium as a driving force for uphill solute accumulation, and 2) determining the mechanism of energy coupling in cotransport systems. On the whole it is now reasonably well established that the Na+ electrochemical gradient can indeed energize the uphill accumulation of various nonelectrolytes in epithelia. This conclusion is substantiated by electrophysiological studies on intact epithelia using both conventional and Na+-selective microelectrodes and has been repeatedly verified in studies using brush-border membrane vesicles. One important additional concept that has emerged from these studies is that the overall transport process is intimately associated with, and perhaps controlled by, the electrical properties of leaky epithelia. The mechanism of energy coupling, as deduced from kinetic studies and modeling, has proven to be more elusive. Interpretations of earlier kinetic measurements on intact epithelia are complicated by unstirred layer effects and varying electrochemical Na+ gradients. Even more recent studies using brush-border membrane vesicles have failed to provide a unified mechanism, even for Na+-glucose transport, because of the various methods used to extract kinetic parameters and the variety of assumptions underlying different kinetic models. The common assumption that a translocation step rate limits the coupled entry process has been recently challenged, leading to novel proposals that are not based on mobile carriers. Future mechanistic studies will undoubtedly rely on recent advances in the isolation and purification of Na+-dependent proteins and their subsequent reconstitution into well-defined artificial membranes.
Blood sugar oscillations and duodenal migrating myoelectric complexes
Authors: Fioramonti J. , Bueno L. , Ruckebusch M.
Published: December 2017

Blood concentration of reducing sugar and electrical activity of the duodenum were simultaneously measured in four conscious pigs, each chronically fitted with a catheter in a jugular vein, a duodenal infusion catheter, and transparietal intestinal electrodes. After a meal, blood sugar concentration exhibited cyclic variations at a frequency similar to that of the migrating myoelectric complexes (MMC) observed on the duodenum (1.6 +/- 0.3 per h). During the fasting state (15 h), glucose or xylose infusions into the duodenum also induced blood sugar oscillations at the same frequency as that of duodenal MMC (0.9 +/- 0.3 per h). Injections of xylose boluses into the duodenum induced more rapid and larger increases in blood reducing sugar concentration when injected during the last two-thirds of the phase of irregular spiking activity or during the phase of regular spiking activity than when injected during quiescence or the first third of the phase of irregular spiking activity. It is concluded that intestinal motility is a prerequisite for optimal intestinal absorption of sugar that is markedly enhanced at the time of maximal digesta flow in the pig.
Relative contribution of fat, protein, carbohydrate, and ethanol to intestinal hyperemia
Authors: Siregar H. , Chou C. C.
Published: December 2017

The relative contribution of dietary fat, protein, carbohydrate, and ethanol to postprandial intestinal hyperemia was assessed by comparing the vascular and metabolic effects of luminal placement of various solutions prepared from standard high -fat, high-protein, and high-carbohydrate test diets, corn oil, and ethanol in the jejunum of anesthetized dogs. The high-fat diet (45% fat, 18% protein, 29% carbohydrate) produced the greatest hyperemia (+30.4% of control), followed by high-protein (22% fat, 64% protein, 4% carbohydrate) (+24.1%) and high-carbohydrate (8% fat, 18% protein, 68% carbohydrate) (+18.2%) diets. When the fat content of the high-carbohydrate diet was raised to equal that of the high-protein diet, the two diets produced the same degree of hyperemia. All three diets produced a significantly greater hyperemia than the solutions containing the same amount of fat. All these dietary solutions increased intestinal oxygen consumption. Ethanol, however, increased blood flow without altering oxygen consumption. Thus, on weight basis, fat produces the greatest hyperemia, but the contribution of protein and carbohydrate to postprandial intestinal hyperemia cannot be considered as insignificant. The hyperemia results from a synergistic effect of all three dietary components.
Nature of flow dependence of protein secretion by the exocrine pancreas
Authors: Ho J. J. , Rothman S. S.
Published: December 2017

It has been proposed that bidirectional and concentration-dependent fluxes of digestive enzymes across pancreatic acinar cell membranes account for secretion. One implication of such a model is that protein secretion should be a function of fluid outflow, inasmuch as flow would be required to generate the necessary concentration gradient by carrying away secreted material. In an earlier study (Science 204: 1212, 1979) when fluid flow was decreased by a backpressure applied to fluid in the pancreatic duct, proportional reductions in protein secretion occurred. The present study uses metabolic rather than mechanophysical methods to decrease flow, reduction of the sodium concentration of the medium bathing the pancreas, or addition of the Na+-K+-ATPase inhibitor ouabain. Both treatments produced similar results: decreases in protein output synchronous with and proportional to the observed decreases in flow. Essentially the same relationship was seen when flow was reduced during protein secretion augmented by the secretagogue cholecystokinin-pancreozymin. These results suggest that the reduction in flow rate (whether produced mechanically or chemically) was the variable directly responsible for the decrease in protein secretion by the acinar cell.
Elevated intraluminal pressure alters rabbit small intestinal transport in vivo
Authors: Swabb E. A. , Hynes R. A. , Donowitz M.
Published: December 2017

The effect of acutely increased intraluminal hydrostatic pressure (IHP) on rabbit jejunal, ileal, and colonic water and electrolyte transport was determined in vivo in a distended test segment and adjacent control segment using a perfusion system with [14C]polyethylene glycol as a nonabsorbable marker. Test-segment IHP was increased by raising the efflux catheter to produce 10-70 cm water IHP, while control-segment IHP was held constant at 0 cm water. Acutely increased IHP up to 40 cm water in the jejunum and up to 30 cm water in the ileum caused decreased net absorption in the jejunum and net secretion in the ileum but caused no significant change in control-segment transport. This indicated that IHP-induced changes in transport were mediated by local rather than systemic effects. The IHP-induced secretory process was dependent on the magnitude of elevation in IHP and reversible at less than or equal to 20 cm water in the ileum. An IHP of 30 cm water was associated with nonreversible transport changes in the ileum. Acutely increased IHP to 70 cm water did not significantly alter colonic transport. This experimental model is suitable for a comprehensive investigation of the mechanism of IHP-induced changes in small intestinal transport.