bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of methionine-enkephalin and morphine on myoelectric activity of small bowel
Authors: Konturek S. J. , Thor P. , Krol R. , Dembinski A. , Schally A. V.
Published: December 2017

Enkephalins, naturally occurring peptides with powerful opiatelike effects, have recently been detected throughout the tissues of the alimentary tract, but their role is unknown. This study was designed to compare the effects of methionine-enkephalin (met-enkephalin) and morphine on the myoelectrical pattern of the small bowel. Five conscious dogs were prepared with electrodes spaced 25 cm apart along the entire small intestine. Spike activity and slow waves were recorded with a Beckman Dynograph. Records were obtained in fasted conditions and following a meat meal or intravenous infusion of caerulein while animals received intravenous infusion of either met-enkephalin or morphine in various doses (range 10-160 microgram/kg . h). Met-enkephalin at a dose of 40 microgram/kg . h caused a significant decrease in spike activity and in the frequency of bursts of the interdigestive myoelectric complexes (IMC), whereas morphine almost doubled the frequency of the IMC. Met-enkephalin in dogs given food or infused with caerulein significantly decreased the fed-type spike activity of the small bowel, whereas morphine did not affect it. The effects of met-enkephalin and morphine on the intestinal myoelectrical pattern can be reversed by naloxone, an opioid antagonist, suggesting that they are mediated by separate opioid receptors.
Na+-dependent H+ and Cl- transport in in vitro frog gastric mucosa
Authors: Machen T. E. , McLennan W. L.
Published: December 2017

Na+ dependency of H+ and Cl- transport in resting and stimulated gastric mucosae was investigated. We measured transepithelial potential difference (PD), short-circuit current (Isc), conductance, H+ secretion (JH), and unidirectional fluxes of 36Cl- (muscosal (m) to serosal (s), JClm leads to s and JCLs leads to m) during Isc conditions in Ussing-type chambers. Resting tissues: Na+-free serosal solution (choline replacement), but not mucosal, Ringer solution caused PD and Isc to decrease to zero with a time course identical to that observed with Cl--free solutions. Conductance also decreased by more than 50%. Isc = JCLs leads to m--JCLm leads to 8 = JClnet during control ([Na+] = 105 mM), and Na+-free conditions. When [Na+] = 50 mM (choline replacement) Isc (=JClnet) was reduced by approximately 25%; when K+ replaced Na+, Isc (=JClnet) was reduced by approximately 65%. The dependence of Isc on [Na+] (choline replacement) was sigmoidal indicating that there may be two sites at which Na+ activates Cl- secretion. Plots of 1/Isc vs. 1/[Cl-] with different [NA+] indicated, that the affinity of the Cl- "carrier" may be affected by [Na+]. stimulated tissues: Na+-free (choline replacement) solutions caused PD, Isc, and JClnet all to decrease to zero but sometimes Na+-containing mucosal solution caused JH to increase back to 50% of control, whereas Isc increased by only 16%. Na+-free effects were not reversed by 1 mM dibutyryl cAMP plus 0.1 mM isobutyl methylxanthine in the serosal solution. As [Na+] was increased, Isc (sigmoidal) and JH (monotonic) both increased. K+ replacement of Na+ caused a larger decrease in Isc than when choline was used; JH remained constant if [Na+] greater than or equal to mM. We have proposed that the energy-dependent step for active Cl- transport occurs at the serosal membrane in a Na+-coupled process. Cl- that accompanies JH during open-circuit conditions may utilize a separate system.
Interpretation by theoretical model of dynamic and steady components in frog gustatory response
Authors: Kashiwagura T. , Kamo N. , Kurihara K. , Kobatake Y.
Published: December 2017

The behavior of dynamic component (slow component) and steady component of the frog glossopharyngeal nerve response to CaCl2, measured in number of impulses firing per second, was examined under various conditions. 1) The magnitude of the dynamic component increased with the flow rate below about 0.3 ml/s, whereas that of the steady component was independent of the flow rate. 2) The magnitude of the dynamic component increased with a rise of temperature between 2.5 and 20 degrees C, whereas that of the steady component was practically independent of temperature. Removal of Ca2+ from the receptor membrane yielded a large dynamic component even at 2.5 degrees C. 3) The treatment of the tongue with procaine led to a large reduction in the magnitude of the dynamic component, whereas the effect of procaine on the steady component was not pronounced. 4) The magnitude of the dynamic component varied with the pH of the stimulating solution, whereas that of steady component was practically independent of a pH between 4.5 and 7.5. The above results were well interpreted by the following reaction scheme: S (stimulus + A (receptor domain) in equilibrium (SA)active in equilibrium (SA) inactive where (SA) active and (SA) inactive are active and inactive complexes.
Biosynthesis, segregation, and secretion of exportable proteins by the exocrine pancreas
Authors: Scheele G. A.
Published: December 2017

Recent findings that contribute to an understanding of the secretory process in the pancreatic exocrine cell are reviewed. These include 1) the separation, identification, and characterization of secreted proteins by two-dimensional gel electrophoresis, 2) the intracellular route and timetable of movement of secretory proteins from one intracellular compartment to another, 3) the evidence that suggests that all enzymes and zymogens secreted by the pancreas are segregated and transported within a single intracellular pathway, and 4) the mechanism by which presecretory proteins are thought to be transported across the lipid bilayer of the rough endoplasmic reticulum (the transport peptide hypothesis).
Effect of time interval between swallows on esophageal peristalsis
Authors: Ask P. , Tibbling L.
Published: December 2017

Esophageal peristaltic pressure amplitude, peristaltic incidence, speed of peristalsis, and wave duration were investigated as a function of swallow interval. In the distal half of the esophagus, the amplitude decreased at swallow intervals of 8 s and shorter. At intervals of 8 and 4 s, dropouts of contractions that were obtained were most frequent in the distal esophagus and for the 4-s interval. At continuous swallows no contractions were obtained below the upper esophageal sphincter until the end of the swallow sequence, after which a peristaltic wave of high amplitude propagated along the esophagus. The peristaltic speed increased toward a level 5 cm above the lower esophageal sphincter. The peristaltic wave duration was approximately the same in different parts of the esophagus and at different swallow intervals. The findings indicate an impairment of esophageal transport function by short swallow intervals.
Topical effects of 16,16-dimethyl prostaglandin E2 on gastric blood flow in dogs
Authors: Cheung L. Y.
Published: December 2017

The effects of luminal instillation of 16,16-dimethyl prostaglandin E2 (dmPGE2) on total gastric blood flow and its fractional distribution between the layers of gastric tissue were determined in exteriorized segments of the greater curvature of dog stomach. Total gastric blood flow was measured simultaneously by venous outflow and alpha-labeled microspheres; both methods correlated well with each other (r = 0.88, P less than 0.01). In the nonstimulated stomach, dmPGE2 caused an increase in total gastric blood flow from 4.2 +/- 0.8 to 7.4 +/- 1.2 ml/min (P less than 0.05). In contrast, dmPGE2 significantly reduced gastric blood flow in histamine-stimulated stomach (from 14.6 +/- 1.2 to 9.2 +/- 1.0 ml/min; P less than 0.01). The changes in mucosal blood flow ere proportional to the alterations in total blood flow because the fractional distribution of blood flow to the mucosa remained relatively unchanged during dmPGE2 administration. These observations suggest that dmPGE2, a known vasodilator, induces an increase in gastric blood flow in the resting stomach, whereas it reduces gastric blood flow in the actively secreting stomach as a result of secretory inhibition.
External scintigraphy in measuring rate of gastric emptying in beagles
Authors: Theodorakis M. C.
Published: December 2017

The application of external scintigraphy and preparation of a new radiopharmaceutical agent for the investigation of the rate and pattern of gastric emptying in beagles and for the visualization of segments of the intestines have been described. 99mTc-labeled triethylenetetramine-polystyrene resin was mixed in a test meal and was administered to the animal. The gastric emptying rate of the beagle was evaluated by serially recording the gastric radioactivity by means of a scintillation camera, The experimental data indicate that the pattern of gastric emptying of beagles during the first 60 min was monoexponential and the gastric emptying half time was 1.3 h. The usefulness of external scintigraphy as a noninvasive method for determining the gastric emptying rates and for visualizing segments of GI tract in animals has been demonstrated.
Evidence for oscillation of prostaglandin release from spontaneously contracting guinea pig taenia coli
Authors: Coburn R. F.
Published: December 2017

Two strips of guinea pig taenia coli were mounted 1-2 mm apart in a small organ bath. One of the strips was incubated before mounting with indomethacin, which inhibited release of prostaglandin E2 for at least 4 h to levels not detectable by biological assay. Both stretch-evoked contractions or spontaneous contractions of the prostaglandin-releasing strip reduced the contraction time intervals between spontaneous contractions in the paired strip. Neither stretch-evoked nor spontaneous contractions of the nonprostaglandin-releasing strip influenced spontaneous contractions in the paired strip. With the strips widely separated, stretch-evoked contractions of the prostaglandin-releasing strips caused shortened contraction-time intervals in the paired strips, but spontaneous contractions had no such effect. Rat fundus, separated 1-2 mm from prostaglandin-releasing taenia coli, showed small contractions occurring at the same frequency as spontaneous taenia contractions. These rat fundus contractions were abolished by indomethacin. Data show that there is communication between the prostaglandin-releasing strip and the nonprogestaglandin-releasing strip, There is evidence that this communication was mediated by released prostaglandin E2 and that release of this mediated is augmented during spontaneous contractions of guinea pig taenia coli.
Gastric emptying of liquids and solids: roles of proximal and distal stomach
Authors: Kelly K. A.
Published: December 2017

The objective was to explore the hypothesis that the proximal stomach has a major role in gastric emptying of liquids and the distal stomach a major role in gastric emptying of solids. The results of experiments on the intact stomach and on the stomach after selective resections, denervations, and during hormonal infusions are, in general, consistent with the hypothesis.
Gastroenteropancreatic hormonal changes during exercise
Authors: Hilsted J. , Galbo H. , Sonne B. , Schwartz T. , Fahrenkrug J. , de Muckadell O. B. , Lauritsen K. B. , Tronier B.
Published: December 2017

Peripheral plasma concentrations of gastroenteropancreatic peptides were measured during a 3-h period of bicycle exercise at 40% of maximal oxygen uptake in six normal men. Marked increases (P < 0.02) were found in vasoactive intestinal polypeptide (VIP) [1.8 +/- 0.7 (rest) vs. 22.3 +/- 5.4 pmol x l-1 (mean +/- SE) (3 h)], secretin (0.5 +/- 0.5 vs. 11.1 +/- 2.7 pmol x l-1), pancreatic polypeptide (PP) (4.0 +/- 1.5 vs. 46.3 +/- 11.5 pmol x l-1), somatostatin (SRIF) (12.8 +/- 1.2 vs. 17.7 +/- 0.6 pmol x l-1), whereas no changes occurred in gastric inhibitory polypeptide (37.3 +/- 5.9 vs. 39.2 +/- 9.8 pmol x l-1). Immunoreactive insulin and C-peptide decreased from 0.08 +/- 0.004 and 0.39 +/- 0.03 pmol x l-1, respectively, to 0.04 +/- 0.003 (P < 0.005) and 0.13 +/- 0.02 (P < 0.001). The significant decrease in C-peptide and in the C-peptide-to-insulin molar ratio indicate decreased insulin secretion and clearance, respectively, during exercise. Plasma glucose decreased [5.0 +/- 0.1 (rest) vs. 4.2 +/- 0.3 mmol.l-1 (3 h)] (P < 0.01). During 3 h of rest, none of the measured parameters had changed. The marked exercise-induced changes in plasma concentrations of PP, secretin, VIP, and SRIF are provocative. We know in detail neither the stimuli for the release of these peptides nor their physiological role during exercise.
Metabolic dependence of the electromyogram of the cat colon
Authors: Anuras S. , Chien S. M. , Christensen J.
Published: December 2017

Strips of colon muscle (1 x 10 cm) were exposed to alterations of temperature, to 2,4-dinitrophenol, and were deprived of O2. Cooling reduced slow-wave frequency in proximal colon from 5.2 at 37 degrees C to 3.9, 2.7, 1.2 and 0.5 cycle/min at 34, 30, 25, and 20 degrees C, respectively; all changes were significant (P < 0.05). Heating also reduced slow-wave frequency in proximal colon from 5.2 at 37 degrees C to 5.1, 4.8 (P < 0.05), and 3.3 (P < 0.05) cycle/min at 39, 41, and 43 degrees C, respectively. Hypoxia reduced slow-wave frequency from 4.6 at 95% O2 to 2.8 cycle/min at 0% O2 (P < 0.05). 2,4-Dinitrophenol (10(-4) M) reduced frequency from 5.3 to 2.7 cycle/min (P < 0.05). The results of studies of distal colon were similar. In distal colon cooling reduced the time occupied by migrating spike bursts from 20.7% at 37 degrees C to 11.1% at 25 degrees C, and 7.9% at 20 degrees C (P < 0.05). Hypoxia also reduced the time occupied by migrating spike bursts from 16.7% at 95% O2 to 5.9% at 0% O2 (P < 0.05).
Effects of carbachol on extracellular Na-dependent AIB uptake in rat parotid gland
Authors: Keryer G. , Rossignol B.
Published: December 2017

In rat parotid glands the uptake of 2-[1-14C]aminoisobutyric acid (AIB), in vitro, depends on a Na concentration gradient between the intra- and extracellular medium. Ouabain (1 mM) which inhibits the Na+-K+-ATPase and a Na+ ionophore, monensin (which dissipates the Na+ gradient), both suppress this amino acid uptake. Carbachol (5 microM) (through muscarinic receptors) evokes a decrease in AIB uptake, and in the presence of 0.1 mM ouabain the cholinergic effect is enhanced. Ouabain alone (0.1 mM) very slightly depresses the [14C]AIB uptake. Neither 1 microM isoproterenol, nor 1 microM Ca2+ ionophore A23187, which affect the membrane potential in rat parotid acinar cells, modifies the AIB uptake. When the Ca is removed from the incubation medium, carbachol still evokes a small decreasing effect on AIB uptake. From these data we can suggest that the reduced AIB uptake (induced by the cholinergic agonist) appears to be related to a process dependent on variation of intracellular Na concentration that may be triggered by the cholinergic agonist.
Pancreatic enzyme stimulation of intestinal chloride secretion
Authors: Liebow C.
Published: December 2017

Mucosal addition of pancreatic enzymes (i.e., chymotrypsinogen and amylase) to a short-circuited Ussing chamber containing a section of stripped rabbit ileum greatly increases short-circuit current (SCC). SCC increases slowly, requiring several hours to reach peak response to enzyme addition. Serosal addition of enzyme or mucosal addition of albumin produces no such response. Chloride flux in the absence of enzyme conforms to behavior predicted for predominantly paracellular movement. Chymotrypsinogen in the mucosal bath augments serosal-to-mucosal chloride flux in a manner consistent with an intracellular pathway. The chloride secretion produced by enzyme addition is of similar magnitude to the additional increment in SCC.
Stimulation of HCO3- transport in isolated proximal bullfrog duodenum by prostaglandins
Authors: Flemstrom G.
Published: December 2017

An in vitro preparation of proximal duodenum from the bullfrog transported alkali into the luminal solution (approximately 1 mueq x h-1 x cm-2) and generated a transepithelial electrical potential difference (5-10 mV, lumen negative). Transport was inhibited by 2,4-dinitrophenol (10(-5) M), CN- (5 X 10(-3) M), indomethacin (5 X 10(-5) M), and acetazolamide (5 X 10(-3) M) indicating that metabolism is required. Both alkali transport and the electrical potential difference showed a dose-dependent increase on administration of the prostaglandins E2, 16,16-dimethyl E2, and F2 alpha. The minimal concentration stimulating transport was lower with the E-type prostaglandins (10(-8) M than with F2 alpha (10(-6) M), and the former also produced greater maximal responses. In addition to metabolic-dependent transport of alkali, there was passive transmucosal migration of HCO3-, amounting to approximately 40% of basal (unstimulated) transport and sensitive to variation of the transmucosal hydrostatic pressure. Morphological examination showed that the preparation is devoid of Brunner glands. Stimulation of duodenal epithelial HCO3- transport by prostaglandins may contribute to their previously demonstrated ability to prevent duodenal ulceration.
Retinol lymphatic and portal transport: influence of pH, bile, and fatty acids
Authors: Hollander D.
Published: December 2017

Absorption of [3H]retinol into lymph and bile was studied in unanesthetized rats with cannulated thoracic and common bile ducts. Retinol in a micellar solution was infused into the duodenum. Absorption of retinol into lymph increased when the infusate's taurocholate concentration was increased to 10 mM, when the hydrogen ion concentration was increased, or when octanoic acid was added to the infusate. Absorption of retinol into lymph decreased when the taurocholate concentration was decreased to 5 mM or when long-chain unsaturated fatty acids or retinoic acid were added to the duodenal infusate. Retinol absorption into bile increased following additions of linoleic and arachidonic acids to the infusate, but absorption did not change following modifications of the infusate's taurocholate concentration or pH. These experiments, which demonstrate that intraluminal factors do modify the extrusion of retinol into bile and lymph, enhance our overall understanding of the process of absorption of this lipid nutrient.
Phosphorus adaptation in rats in absence of vitamin D or parathyroid glands
Authors: Cramer C. F. , McMillan J.
Published: December 2017

Growing rats even when vitamin D deficient became adapted to inorganic phosphorus (Pi) deficiency by increasing absorption and minimizing excretion. Feeding low-Pi diet for 3 wk reduced urinary Pi by 80% (P < 0.001), and urinary 32P by 50% (P < 0.001). Low-Pi regimen increased 32p absorption from a 32P-labeled meal by 50% (P < 0.001), even when the animals were vitamin D deficient or thyroparathyroidectomized. The marked increase in retention of 32P in phosphorus-deficient rats could not be accounted for by decreased endogenous intestinal excretion plus increased kidney reabsorption; increased intestinal absorption played a part. 32P absorption was significantly reduced (P < 0.001) by vitamin D deficiency in rats fed either control diet (.6%) Pi or low-Pi diet (0.03%). Endogenous intestinal or urinary excretion of 32P was unaltered by vitamin D deficiency. The evidence supports the hypothesis that there are two mechanisms for phosphorus adaptation: kidney retention not requiring vitamin D, and inreased intestinal absorption of Pi not requiring parathyroids, thyroids, or vitamin D.
Actions of pentagastrin on smooth muscle of isolated dog intestine
Authors: Stewart J. J. , Burks T. F.
Published: December 2017

Adult dogs were anesthetized and segments of small intestine were isolated and perfused via a mesenteric artery with Krebs-bicarbonate solution. Muscle responses were monitored with extraluminal force transducers implanted along the circular and longitudinal axes of the segments or by means of an intraluminal balloon. Agonists were administered as intra-arterial bolus injections in volumes not exceeding 0.1 ml. Antagonists were dissolved in the Krebs perfusion solution. Smooth muscle responses to pentagastrin (25 microgram), dimethyl-phenylpiperazinium (DMPP, 5 microgram), and bethanechol (BeCh, 5 microgram) were reduced during perfusion with atropine sulfate (25 ng/ml). Responses to DMPP (5 microgram) and pentagastrin (25 microgram) were diminished by perfusion with tetrodotoxin (20 ng/ml) and after depolarizing doses of nicotine (500 microgram), whereas responses to BeCh (5 microgram) were unaffected in both cases. Hexamethonium (10 microgram/ml) reduced responses to DMPP (5 microgram) but did not affect responses to BeCh (5 microgram) or pentagastrin (5 microgram). Responses to DMPP (5 microgram) were not reduced in segments desensitized to pentagastrin. The results suggest that the stimulatory effect of pentagastrin on isolated dog intestine results from an interaction of the peptide with nonnicotinic cholinergic receptors on postganglionic cholinergic nerves.
Tryptophan transport by isolated newborn rabbit jejunum
Authors: Cooke H. J. , Pfankuche L. , Cooke A. R.
Published: December 2017

Segments of newborn or adult rabbit jejunum were mounted as flat sheets in flux chambers. Mucosal-to-serosal (Jm leads to s) and serosal-to-mucosal (Js leads to m) fluxes of tryptophan (Try), phenylalanine (Phe), and alanine (Ala) were measured in the absence of electrochemical gradients. In the presence of Na, J Try s leads to m increased linearly with concentration, whereas the relationship of J Try m leads to s and concentration contained both linear and saturating components. The relationship of net Try flux and concentration was in accord with Michaelis-Menten kinetics. Ouabain (10(-3) M) abolished net Na fluxes in both newborn and adult rabbit jejunum and abolished net Try flux in the adult, but did not reduce net Try flux to zero in the newborn. In the presence of Na-free solutions small net fluxes of Try, Phe, and Ala occurred in the newborn. Addition of 10(-4) M 2,4-dinitrophenol abolished net Try flux in ouabain-treated newborn rabbit jejunum that was bathed by either Na-free or Na-containing solutions. In the presence of Na, Phe and Ala reduced J Try m leads to s, and Try reduced the fluxes of Phe and Ala. Phe inhibited J Try m leads to s in Na-free solutions, and Try reduced J Phe m leads to s. These results suggest that the newborn rabbit jejunum resembles the adult in that Try is absorbed primarily by a Na-dependent system. These results show that the newborn differs from the adult in that Try is absorbed by a system that is independent of Na but requires metabolic energy.
Action of theophylline on secretagogue-stimulated amylase release from dispersed pancreatic acini
Authors: Korman L. Y. , Walker M. D. , Gardner J. D.
Published: December 2017

In dispersed acini from guinea pig pancreas, theophylline did not alter basal amylase release, but had three functionally distinct modes of action on the stimulation of amylase release caused by various secretagogues. 1) At relatively low concentrations (0.1-1.0 mM), theophylline augmented the increase in enzyme secretion caused by vasoactive intestinal peptide, secretin, or 8-bromoadenosine 3',5'-monophosphate, but did not alter the increase in amylase release caused by other secretagogues. 2) At intermediate concentrations (1-10 mM), theophylline selectively altered the increase in enzyme secretion caused by carbamylcholine, but did not alter the effects of cholecystokinin or bombesin, secretagogues whose modes of action are similar to that of cabamylcholine. 3) At high concentrations (greater than 10 mM), theophylline inhibited the increase in enzyme secretion caused by all secretagogues tested.
Effect of small intestinal bypass on hepatic lipid accumulation in rats
Authors: Kaminski D. L. , Mueller E. J. , Jellinek M.
Published: December 2017

Bypass of large segments of the small intestine to produce weight loss in morbidly obese human subjects has been associated with increased lipid accumulation in the liver. Congenital and nutritional obese rat models were employed to evaluate hepatic lipid accumulation following bypass of 90% of the small intestine. When small intestinal bypass was performed on nutritionally obese rats ingesting a high-fat diet (17%) supplemented with choline dihydrogen citrate (3,4 g/kg diet), a 59% loss of weight at 1 mo was unassociated with increased hepatic lipid accumulation when compared to sham-operated controls. When small intestinal bypass was performed on a nutritionally obese rat fed a relative choline-methionine-deficient diet following intestinal bypass, marked increases in total hepatic lipid and hepatic triglyceride content were evident when compared to the lipid content in sham-operated controls ingesting a similar choline-deficient diet. Hepatic steatosis following small intestinal bypass could be produced in a rat model only by a deficiency in a required substrate for triglyceride conversion to phospholipid and suggests that similar deficiencies may contribute to the increased hepatic lipid accumulation occurring in human subjects following intestinal bypass.
Intestinal enzyme adaptation to normal diets of different composition
Authors: McCarthy D. M. , Nicholson J. A. , Kim Y. S.
Published: December 2017

Groups of rats were fed isocaloric amounts of diets rich in starch, protein, or fat. After 7 days, activities of sucrase, maltase, lactase, alkaline phosphatase, L-phenylalanylglycine hydrolase, and L-leucyl-L-alanyl hydrolase were measured in the duodenal, jejunal, and ileal mucosa of fed rats. Peptide hydrolase and alkaline phosphatase activities were significantly higher in rats fed high-protein diets, particularly in the ileum. Disaccharidases were highest in rats fed high-starch diets, especially in jejunum; the lowest activities of peptide hydrolase were seen with this diet. The high-fat diet was generally associated with intermediate activities of most enzymes, except disaccharidases, which were lowest on this diet. The different macromolecular nutrients were associated with adaptive differences in intestinal enzyme activities, which were biologically appropriate and coordinated with similar known changes in pancreatic and other enzyme activities concerned with assimilation of the particular food. However, other less interpretable changes occurred, which may have been due to effects on pancreatic secretion or on the metabolism, growth, and differentiation of intestinal cells.
Divalent cations and vitamin B12 uptake by intestinal brush-border membrane vesicles
Authors: Beesley R. C. , Bacheller C. D.
Published: December 2017

Brush-border membrane vesicles from hamster intestine were employed to investigate uptake (binding) of vitamin B12 (B12). Ileal vesicles took up 25 times more B12 than did jejunal vesicles. Uptake of B12 by ileal vesicles was dependent on intrinsic factor (IF) and required Ca2+. Increasing the Ca2+ concentration caused an increase in uptake of B12 reaching a maximum at approximately 8 mM Ca2+. At high Ca2+ concentrations, 6–8 mM, Mg2+ had little effect on uptake of B12. At low Ca2+ concentrations, up to 2 mM, Mg2+ stimulated B12 uptake. Mg2+, Mn2+, and, to a lesser extent, Sr2+ stimulated Ca2+-dependent B12 uptake, but Zn2+, Ba2+, Na+, K+, and La3+ did not. B12 was apparently not metabolized and was bound as IF-B12 complex, which could be removed with (ethylenedinitrilo)tetraacetic acid (EDTA). Our results suggest that two types of divalent cation reactive sites are involved in binding of IF-B12. One is Ca2+ specific. The other is less specific reacting with Mg2+, Mn2+, Sr2+, and perhaps Ca2+ itself, thereby stimulating Ca2+-dependent binding of IF-B12 to its ileal receptor.
Effect of serotonin on active electrolyte transport in rabbit ileum, gallbladder, and colon
Authors: Donowitz M. , Tai Y. H. , Asarkof N.
Published: December 2017

The effect of serotonin on active electrolyte transport was evaluated in vitro in epithelial sheets of rabbit ileum, gallbladder, and colon under short-circuited conditions. Serotonin added to the serosal surface of rabbit ileum caused a dose-dependent short-lived increase in short-circuit current and a more prolonged equal effect on net Na and Cl fluxes. The latter consisted primarily of inhibition of mucosal-to-serosal fluxes of both Na and Cl. In addition serosal serotonin decreased ileal Na influx from the mucosal solution into the epithelium, suggesting an effect on Na absorption. Serotonin did not alter all aspects of ileal absorptive function and did not affect glucose-dependent Na absorption. Consistent with serotonin acting by inhibiting NaCl absorption in the ileum, serotonin induced equal inhibition of net Na and Cl absorption in rabbit gallbladder (which has a linked Na and Cl absorptive process) but had no effect on rabbit colon (which lacks a linked Na and Cl absorptive process). In addition, adenosine 3',5'-cyclic monophosphate and serotonin both appeared to alter the same ileal NaCl absorptive process, since following stimulation of ileal secretion with the maximum concentration of theophylline, addition of serotonin did not cause any further effects.
Effect of metabolic acidosis in intestinal absorption of calcium and phosphorus
Authors: Gafter U. , Kraut J. A. , Lee D. B. , Silis V. , Walling M. W. , Kurokawa K. , Haussler M. R. , Coburn J. W.
Published: December 2017

To investigate the effect of metabolic acidosis on intestinal calcium (Ca) and phosphorus (P) absorption and vitamin D metabolism, metabolic balance studies and in vitro gut sac uptake of 45Ca and [32P]phosphate were performed in rats maintained on low-Ca and moderately low-P diet and fed NH4Cl for 3 or 9 days and pair-fed controls. Plasma 1,25(OH)2D concentration was measured in the rats fed NH4Cl for 9 days and their controls. Net Ca and P absorption was 87–92% in the acidotic rats and did not differ from control. Moreover, gut sac uptakes of 45Ca and [32P]phosphate were not different from control. Plasma 1,25(OH)2D was higher in the ammonium chloride-fed rats than in controls (213 +/- 44 vs. 110 +/- 12 pg/ml), and serum P was lower in the acidotic animals (4.6 +/- 0.7 vs. 7.6 +/- 0.3 mg/dl). These data indicate that metabolic acidosis does not depress the augmented intestinal absorption of calcium and phosphorus noted during their dietary deprivation nor reduce the plasma level of 1,25(OH)2D.
Suppression of gastric acid secretion by furosemide in isolated gastric mucosa of guinea pig
Authors: Ayalon A. , Corcia A. , Klemperer G. , Caplan S. R.
Published: December 2017

The effect of furosemide on acid secretion and Cl- transport was studied in isolated fundic mucosa of the guinea pig. Furosemide (10(-3) M), applied to the serosal side produced an immediate effect on the short-circuit current (Isc), lowering it by 47 +/- 2%. Potential difference decreased by 29 +/- 3%, electrical conductance by 18 +/- 4%, acid secretion by 38 +/- 1%, and net flux of Cl- from serosal-to-mucosal side by 37%. Application of the drug to the mucosal side produced similar effects on acid secretion and on the electrical parameters. It is suggested that furosemide blocks the entrance of Cl-, by the Na+--Cl- cotransport mechanism, through the basolateral membrane of the secreting cell. The consequent reduction in electrogenic Cl- transport would cause Isc and acid secretion to decrease. A reduction of Cl- conductance of the apical membrane, upon mucosal application of the drug, would cause similar effects on acid secretion and Cl- transport.
Cholera toxin stimulates secretion of immunoreactive intestinal mucin
Authors: Forstner J. F. , Roomi N. W. , Fahim R. E. , Forstner G. G.
Published: December 2017

In vitro secretion of goblet cell mucin from rat small intestine was measured using a double-antibody radioimmunoassay for mucin. Cholera toxin (12.5-50 mg crude filtrate/ml) added to incubations of intestinal slices caused a dose-dependent increase in mucin secretion. By 90 min there was a four- to fivefold enhancement in secretion over noncholera-treated controls. Crude filtrate (dialyzed or nondialyzed) was a more effective mucin secretogogue than purified enterotoxin. Secretion was also assessed by administering [1-14C]glucosamine intraperitoneally to rats in vivo and 3 h later monitoring in vitro secretion of radioactive glycoprotein from intestinal slices. Cholera filtrate (12.5-50 mg/ml) caused a 1.5- to 2.0-fold enhancement in secretion after 90 min. The radioactivity data, however, underestimated total mucin secretion and the dependency of secretion on the dose of cholera filtrate. Cholera preparations also caused an enhancement (20-30% over controls) in the incorporation of [3H]glucosamine into tissue acid-precipitable glycoprotein, indicating a stimulation of glycoprotein synthesis. In the same experiments it was noted that the secretion of 3H-labeled (i.e., newly glycosylated) glycoprotein was increased 2.5- to 3.0-fold over untreated controls. Assuming that radioactivity partially reflects mucin synthetic and secretory events, it is possible, therefore, that cholera toxin promotes the release of both "old" mucin from storage granules as well as the synthesis and secretion of "new" mucin formed in goblet cells during incubation.
Response of rat jejunum to angiotensin II: role of norepinephrine and prostaglandins
Authors: Levens N. R. , Peach M. J. , Carey R. M. , Poat J. A. , Munday K. A.
Published: December 2017

At low doses, angiotensin II (AII) stimulates jejunal sodium and water absorption in the pentobarbital sodium-anesthetized rat. This response to the hormone can be blocked by cycloheximide and has a rapid onset and decay, indicating that any protein involved must have a short half-life and/or fast turnover. At high doses, AII inhibits jejunal absorption by a process that does not involve protein synthesis and has a rapid onset but slow decay. The AII-induced inhibition of water absorption can be abolished, and a net stimulation ensues after pretreatment of the animals with meclofenamate or indomethacin, suggesting that at high doses AII stimulates intestinal prostaglandin biosynthesis. The AII analogue, [Sar1,Leu8]AII, significantly stimulated jejunal water absorption and was devoid of any inhibitory response at any dose administered. Simultaneous infusion of low doses of [Sar1,Leu8]AII and AII resulted in a stimulation of water transport, while simultaneous infusion of high dose [Sar1,Leu8]AII and AII also stimulated water absorption. It is suggested that the AII analogue is a full agonist with regard to stimulation of jejunal transfer but antagonizes the inhibitory response to high doses of AII. A model consistent with these data is discussed.
Effect of Ca intake on saturable and nonsaturable components of duodenal Ca transport
Authors: Pansu D. , Bellaton C. , Bronner F.
Published: December 2017

Calcium absorption was studied by an in situ ligated-loop procedure in 9-wk-old male Wistar rats that had been placed from weaning on one of three semisynthetic regimens, 0.17% Ca, 0.44% Ca, or 0.44% Ca plus lactose. Lactose was added because it is known to increase intestinal calcium retention. When the amount of calcium absorbed was expressed as a function of calcium instilled in the loop, it became possible to describe absorption as the sum of a hyperbolic and a linear function, equivalent to a saturable and a nonsaturable process, respectively. The slope of the nonsaturable component was independent of prior calcium intake, while the maximum saturable flux (Jmax) decreased as calcium intake increased. Analysis of the duodenal content of the vitamin D-dependent calcium-binding protein (CaBP, Mr congruent to 10(4)) revealed a positive relation between Jmax and CaBP. Thus, vitamin D appears to be implicated in the saturable, but not in the nonsaturable, component of calcium absorption.
Calcium fluxes in isolated pancreatic acini: effects of secretagogues
Authors: Dormer R. L. , Poulsen J. H. , Licko V. , Williams J. A.
Published: December 2017

45Ca2+ exchange and total calcium content were measured in isolated mouse pancreatic acini. 45Ca2+ uptake could be described as the sum of a constant and a single exponential kinetic component; about 60% of total acinar calcium was exchangeable. Stimulation by bethanechol increased 45Ca2+ uptake, but the time course of uptake could be fit only by the addition of a more rapid kinetic component without any change in the total exchangeable Ca2+. 45Ca2+ washout after 1-h loading could be fit as the sum of two exponential components. Stimulation increased the rate of 45Ca2+ washout with the appearance of a third and more rapid kinetic component. There was not, however, a good correspondence between the exponential constants measured in uptake and washout protocols in unstimulated acini. Exponential constants were also affected by the concentration of calcium in the medium, further indicating the presence of nonlinearities in 45Ca2+ exchange. The dose-response relationships were similar for bethanechol stimulation of 45Ca2+ uptake and amylase release, whereas stimulation of 45Ca2+ washout reached a maximum at a higher concentration of bethanechol. Both 45Ca2+ uptake and analytical measurement of total Ca2+ showed a rapid drop in acinar Ca2+ content followed by a gradual reuptake on stimulation by bethanechol. It is concluded that the initial primary effect of secretagogues is to increase Ca2+ efflux, which is interpreted to be the result of release of sequestered calcium into the cytosol.
Insulin action in pancreatic acini from streptozotocin-treated rats. III. Electron microscope autoradiography of 125I-insulin
Authors: Goldfine I. D. , Kriz B. M. , Wong K. Y. , Hradek G. , Jones A. L. , Williams J. A.
Published: December 2017

Electron microscope autoradiographs were prepared from diabetic rat pancreatic acini that had been incubated with 125I-insulin. Distribution histograms of the distance of the 125I-insulin silver grains from the nearest plasma membrane were prepared and compared with a histogram of an 125I line source. After 3 min of incubation, insulin was located predominately on the plasma membrane, but even at this early time 15% of the grains had an intracellular location. After 30 min of incubation, there was a decrease in grains on the plasma membrane and an increase (to 45%) in grains localized in the cell. At both times of incubation, a comparison of the distribution of the insulin grains overlying subcellular organelles to a theoretical random grain distribution pattern indicated that the intracellular distribution of insulin grains was nonrandom. At 3 min, there was a relative concentration of grains over the plasma membrane and vesicles with an average diameter of 100 nm. At 30 min, there was a concentration of grains over the plasma membrane, 100-nm vesicle, and Golgi. These studies suggest that 125I-insulin is internalized into pancreatic acinar cells in a time-dependent manner and then is nonrandomly distributed inside the cell.
Characterization of an ATP-dependent Ca2+ uptake system in mouse pancreatic microsomes
Authors: Ponnappa B. C. , Dormer R. L. , Williams J. A.
Published: December 2017

The uptake of 45Ca2+ was studied in microsomes prepared from isolated mouse pancreatic acini. These microsomes accumulated 45Ca2+ in the presence of ATP; uptake was potentiated by addition of oxalate. Sequestered microsomal 45Ca2+ was only gradually removed by ethyleneglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA) but was readily released by the divalent cation ionophore A23187. Inhibitors of mitochondrial oxidation and mitochondrial calcium transport had little effect on microsomal 45Ca2+ uptake. A separate subcellular fraction enriched in plasma membranes took up 45Ca2+ poorly compared with the microsomal fraction. Half-maximal 45Ca2+ uptake by the microsomal fraction was observed at a free Ca2+ concentration of 1.1 microM. 45Ca2+ uptake was dependent on Mg-ATP and showed a pH optimum at 6.8-7.0. Subfractionation of the total microsomes into "heavy" and "light" microsomal fractions indicated higher 45Ca2+ uptake activity associated with the heavy fraction. A Ca2+-activated, Mg2+-dependent ATPase was demonstrated in this fraction. Stimulation of pancreatic acini with the cholecystokinin analogue caerulein prior to homogenization increased the subsequent rate of 45Ca2+ uptake by the microsomal fraction.
Mechanism of propagation of canine migrating motor complex--a reappraisal
Authors: Ormsbee H. S. , Telford G. L. , Suter C. M. , Wilson P. D. , Mason G. R.
Published: December 2017

This study quantitatively evaluated the characteristics of the aboral propagation of the canine migrating motor complex (MMC). Five conscious dogs were implanted with extraluminal force transducers along the small intestine. After constructing a 30-cm Thirty-Vella loop of jejunum, 56 of 91 activity fronts were outside the tolerance limits for propagation from the proximal intestine to the loop established in the same dogs before operation. Similarly, 44 of 109 activity fronts were outside the tolerance limits for propagation from the loop to the distal intestine. After surgery, the propagation time from the proximal jejunum to the loop was significantly increased, and activity fronts were observed to originate in the loop and in the intestine distal to the anastomosis. Our study indicates that the hypothesis that extrinsic nerves alone control the migration of the MMC is incomplete. We suggest that the extrinsic and the intrinsic innervation of the gastrointestinal tract are both required for the precise pattern of the migration of the MMC.
Fluid propulsion by cat intestinal segments under conditions requiring hydrostatic work
Authors: Weems W. A. , Seygal G. E.
Published: December 2017

The intrinsic ability of duodenal, jejunal, and ileal segments of cats to propel fluid by doing hydrostatic work was investigated in vitro. Segments of terminal ileum demonstrated two functional states. In the net propulsive state, propulsive complexes occurred at an average interval of 7.9 min. These complexes consisted of an initial phase characterized by the simultaneous ejection of equal fluid volumes from both ends of a segment at a frequency of 8/min and a second phase that ejected a net volume of fluid from the aboral end. Ileal segments not in the net propulsive state demonstrated complexes consisting only of the 8/min ejections. Segments of proximal duodenum and midjejunum failed to produce net propulsion when evaluated under similar conditions. These results indicate that 1) ileal segments can intrinsically produce net fluid transport in the aboral direction when hydrostatic work is required for propulsion, 2) propulsive activity intrinsic to ileal segments is regulated by intrinsic control mechanisms having an effective oscillatory period of 8 min, and 3) basic differences exist in the intrinsic control structures between ileal and other intestinal regions.
Linolenate transport by human jejunum: presumptive evidence for portal transport at low absorption rates
Authors: Surawicz C. M. , Saunders D. R. , Sillery J. , Rubin C. E.
Published: December 2017

Are the small quantities of linolenic acid (LA) in a meal absorbed via a different pathway than the higher concentrations of the other long-chain fatty acids (LCFA) in a mixed meal? To answer this question, varying LA concentrations were infused into the human jejunum via a quadruple-lumen hydraulic biopsy tube. After 0.01-mM LA infusion, no LA was found in triglyceride (TG) extracted from jejunal biopsies, although 58% of the phospholipid plus monoglyceride fraction (PL + MG) and 42% of the LCFA fraction were LA. In marked contrast, after 5.0-mM LA infusion, 60% of the TG, 28% of the PL + MG, and only 3% of the LCFA fractions were LA. By electron microscopy, mostly very low-density lipoprotein-sized (less than 750 A) particles were seen within jejunal fasting biopsies and in biopsies after 0.01, 0.1, or 1.0-mM LA infusions; mostly chylomicrons (greater than 750 A) were seen within jejunal biopsies after 5.0-mM LA infusion. We conclude that LA at its usual very low dietary concentrations is absorbed mostly as invisible LCFA and PL molecules; whereas at higher concentrations it is absorbed like most dietary fat via lacteals as TG and PL within visible chylomicrons.
Mucosal gastrin receptor. V. Development in newborn rats
Authors: Takeuchi K. , Peitsch W. , Johnson L. R.
Published: December 2017

We determined the development of the oxyntic gland mucosal gastrin receptor in rats killed at various times from 5 to 60 days after birth. Rats were weaned on the 18th day after birth. Newborn animals had no detectable gastrin binding, high serum gastrin levels (800-1,200 pg/ml), low antral gastrin levels (0.5-2.0 micrograms/g tissue), or high pH of gastric contents (pH greater than 5.0) and did not respond to pentagastrin. At the time of weaning, serum gastrin dropped to 600 pg/ml and reached adult levels (300 pg/ml) on day 40. Antral gastrin increased to 7.5 micrograms/g tissue on day 20 and reached adult levels (20 micrograms/g tissue) on day 22. Specific binding of gastrin was first detected on day 20 and reached the adult level of 4 fmol/mg protein on day 60. Pentagastrin significantly stimulated acid secretion on day 20 and DNA synthesis on day 25. Prevention of weaning through day 25 decreased the magnitude but did not prevent or delay the onset of the above changes. These results indicate that 1) the absence of a gastrin response in newborn rats is due to a lack of gastrin receptors, 2) development of gastrin receptor and biological sensitivity to gastrin appear at the time of weaning, and 3) the development that occurs with weaning is enhanced but not triggered by the shift to solid food.
On the mechanism of folate transport in isolated intestinal epithelial cells
Authors: Eilam Y. , Ariel M. , Jablonska M. , Grossowicz N.
Published: December 2017

The mechanism of folic acid (FA) uptake was studied in isolated intestinal epithelial cells prepared from 2- to 6-wk-old chicks. The cells accumulated FA, reaching a level of three- to fivefold that at equilibrium. In the presence of the metabolic inhibitors, NaN3 or KCN, FA was taken up only until equilibration while accumulation of FA was inhibited. Addition of these inhibitors at a steady state of FA accumulation caused a release of intracellular FA. The kinetics of FA uptake were found to be saturable (Km = 3.5 x 10(-5) M), indicating a carrier-mediated mechanism. The steady-state level of FA accumulation was higher as the concentration of NA+ in the medium increased from 0 to 120 mM. This stimulation of FA uptake by Na+ was not due to the stimulation of glucose uptake, because in experiments carried out in the presence of phlorizin, a glucose-transport inhibitor, FA accumulation was not diminished. It is suggested that FA is taken up by a Na+-coupled transport system.
Stimulus-secretion coupling in exocrine pancreas: role of protein carboxyl methylation
Authors: Povilaitis V. , Gagnon C. , Heisler S.
Published: December 2017

The role of protein carboxyl methylation in amylase secretion from incubated rat pancreatic lobules was assessed. All the components of the carboxyl methylation system, protein carboxyl methylase, methyl-acceptor protein substrates, and protein methylesterase, were found in the rat pancreas. Protein carboxyl methylation is stimulated by both pancreozymin and carbachol at concentrations that are equally effective in stimulating amylase release. The secretagogue-enhanced increase in protein carboxyl methylation was concomitant with the onset of the secretory response. These responses were blocked by the receptor antagonists, dibutyryl cGMP and atropine. Inhibitors of protein carboxyl methylase inhibited carboxyl methylation stimulated by pancreozymin but did not affect the secretory response to the hormone. Ethyleneglycol-bis-(beta-aminoethylether)-N-N'-tetraacetic acid blocked protein carboxyl methylation and amylase release, indicating that extracellular calcium was essential for both processes. The presence or absence of calcium did not alter the enzyme activity in lobule homogenates. The data suggest that only a small part of the total cellular protein carboxyl methylation activity is directly involved in pancreatic enzyme secretion. Like the calcium requirement in secretion, protein carboxyl methylation also lies distal to the stimulant-receptor interaction.