bluuebunny/crossref_metadata_2025 huggingface dataset:
How to measure first-order hepatic transfer coefficients by distributed modeling of a recirculating rat liver perfusion system
Authors: Luxon B. A. , King P. D. , Forker E. L.
Published: December 2017

A digital computer is used to simulate solute disappearance curves evolving in the reservoir of a rat liver perfusion system. The results show that it is feasible to obtain good estimates of these kinetic parameters with only approximate information about the distribution of sinusoidal flows and the transfer function of the nonexchanging vasculature. By contrast satisfactory estimates of the transfer coefficients for uptake and efflux (but not excretion) are critically dependent on accurate measurements of the system transit times. A perfusion system suitable for implementing the method is tested and found to maintain normal liver function for upward of 60 min. The means to achieve the required volume and flow measurements are discussed, and an empirical criterion is developed for recognizing disappearance curves whose information content is too low to yield reliable results.
Developmental changes in the mechanisms of duodenal calcium transport in the rat
Authors: Pansu D. , Bellaton C. , Bronner F.
Published: December 2017

Duodenal calcium transport was resolved into a saturable and a nonsaturable process by means of an in situ ligated loop procedure applied to Wistar rats at 3, 12, 19, 24, 30, 40, 60, 110, and 150 days of age. All postweaning animals were males that had been placed on a 1.5% calcium, 1.5% phosphorus semisynthetic diet. Duodenal calcium-binding protein (CaBP) levels were determined at all ages. The newborn rat had no saturable transport component and no CaBP. Its nonsaturable component was very high. With increasing age the saturable component and CaBP varied biphasically, increasing steeply until the animals were about 35 days old; thereafter, each decreased to low but detectable values. The nonsaturable component, on the other hand, decreased in near-linear fashion in the first 35 days; in animals beyond that age it remained invariant. The difference in age dependence between the saturable and nonsaturable components may be considered to constitute additional evidence for the existence of the two transport processes. CaBP and the saturable transport process were highly correlated, further proof that both are vitamin D dependent. Histological studies have revealed the presence of many vacuoles in the intestinal cells of the very young rats; these vacuoles were absent in rats older than 35 days. It is suggested that these vacuoles may be implicated in a pinocytosislike nonsaturable transport that is superimposed on the nonsaturable, non-vitamin D-dependent calcium transport found in all enterocytes.
Mechanism of Ca2+ transport by Ca2+-Mg2+-ATPase pump: analysis of major states and pathways
Authors: Haynes D. H.
Published: December 2017

Mechanistic studies of Ca2+ transport by the Ca2+-Mg2+-ATPase of skeletal sarcoplasmic reticulum are reviewed, and a unifying model is proposed. The significant steps in the transport cycle are modeled in terms of occupation and disposition of three binding sites on the enzyme: a) two translocation sites capable of binding to Ca2+ or a charge-stoichiometric amount of alkali cation (M+) or H+, b) an ATP-ADP-binding site, and c) a phosphorylation or phosphate-binding site. The normal transport cycle is characterized as the following sequence of steps: a) binding of two Ca2+ and Mg-ATP to external sites with high affinity and random order, b) enzyme phosphorylation, c) inward translocation of the Ca2+-laden sites, d) Ca2+ release to the sarcoplasmic reticulum lumen and ADP release to the external medium (random order), e) binding of Mg2+ or a charge-stoichiometric amount of K+ plus H+ to the translocators, f) dephosphorylation, g) the return of the K+- and H+-laden translocators to the outside, and h) dissociation of K+ and H+ from the translocator and completion of the cycle with step a. The enzyme is characterized as a Ca2+-K+ plus H+ countertransporter. The K+ plus H+ remove Ca2+ from the inwardly oriented translocator, thereby relieving a product inhibition and increasing the rate of enzyme dephosphorylation.
Interaction of enkephalin and caerulein on guinea pig small intestine
Authors: Yau W. M. , Lingle P. F. , Youther M. L.
Published: December 2017

This is a report on the effect of caerulein and methionine-enkephalin interaction on mechanical contraction and acetylcholine release in vitro. The ability of enkephalin to relax caerulein-induced contractions and the manner in which the caerulein dose-response curve was shifted in the presence of enkephalin strongly suggest that enkephalin and caerulein are functional antagonists in this system. The failure of enkephalin to alter the action of exogenous acetylcholine implies that such an antagonism is not mediated through a competition with postsynaptic muscarinic receptors on the muscle. Data from acetylcholine-release studies indicate that caerulein stimulation was dose related. As with the mechanical contractions, the release of acetylcholine in response to caerulein was inhibited by enkephalin. However, naloxone was capable of blocking this inhibition and restoring the release to its control level without interfering with caerulein stimulation. These data provide evidence for the modulatory roles of neuronal peptides in the cholinergic control of gut motility.
What is meant by the term "bile acid"?
Authors: Roger L. , St Pyrek J. , Little J. M. , Adcock E. W.
Published: December 2017

The bile acids are a set of acidic steroids. Many conventional bile acids share a common derivation and have functional characteristics in common. Exceptions exist, however, to virtually all of the rules that can be applied to a definition of bile acids. The term is thus best applied to those steroids with a side chain at C-17, which contains a carboxylic acid group, and to acidic derivatives of such compounds. Naturally occurring bile acids are a more numerous and diverse group than has been generally recognized. The site of origin, synthetic pathways, metabolism, and bioactivity of recently recognized unconventional bile acids are under intensive investigation.
Postprandial inhibition of canine enteric interdigestive myoelectric complex
Authors: Heppell J. , Becker J. M. , Kelly K. A. , Zinsmeister A. R.
Published: December 2017

Our aim was to determine whether the passage of postprandial duodenal chyme into the jejunum activates jejunal feedback mechanisms that inhibit the interdigestive myoelectric complex (IMC) of the canine small bowel. In five conscious dogs with 75-cm Vella loops of proximal jejunum and recording electrodes on the duodenum and the loop, intestinal myoelectric activity was recorded for approximately 4 h during fasting. The dogs were then given either a 200-g liver meal orally or they underwent perfusion of the jejunal loop with postprandial duodenal chyme collected from a donor dog given an identical liver meal. Before feeding, IMCs occurred at mean intervals of 126 +/- 16 (SE) min in the duodenum and 88 +/- 10 min in the loop. Feeding by mouth completely inhibited the IMCs in the duodenum but failed to inhibit the IMCs in the loop. However, perfusion of the jejunal loop with duodenal chyme suppressed the IMCs in both the loop and the duodenum. We concluded that postprandial inhibition of duodenal IMCs is mediated in part by neural and/or hormonal factors activated by chyme in the jejunum, whereas local factors inhibit jejunal IMCs. An enteric phase of postprandial IMC inhibition is postulated.
Copper transport kinetics by isolated rat hepatocytes
Authors: Schmitt R. C. , Darwish H. M. , Cheney J. C. , Ettinger M. J.
Published: December 2017

Uptake and efflux of 64Cu were examined to determine whether hepatic parenchymal cells exhibit the kinetic criteria of a specific transport system for copper and related trace metals. Saturation kinetics were clearly indicated by both v versus [Cu] and 1/v versus 1/[Cu] plots (Km = 11 +/- 0.6 microM and Vmax = 2.7 nmol Cu X min-1 X mg prot-1). Identical results were obtained by cold-copper analyses, and contributions from simple diffusion or nonspecific binding were not detected. Virtually all of the accumulated 64Cu was intracellular by 0.5 min (the initial velocity period), with approximately 40% in the cytosolic fraction. Several related trace metals inhibited 64Cu uptake, but Ni(II) at a 10:1 molar excess did not. Zn(II) acted as a simple competitive inhibitor of 64Cu uptake (Ki = 16 microM). Efflux from preloaded cells was biphasic, with an initial rapid phase of approximately 5 min. Approximately 35% of preloaded 64Cu was transported out of the cells by 40 min, and little efflux occurred thereafter. Thus, hepatocytes exhibit saturation kinetics, competition by related substrates, and countertransport criteria of specific facilitated transport. A wide variety of metabolic inhibitors have no effect on 64Cu uptake under the same conditions that inhibit the active transport of bile acids. Specific inhibitor tests for electrogenic coupling were also negative. Because the identical kinetic parameters were obtained for free 64Cu and the 1:1 64Cu-histidine complex, it is inferred that copper is probably transported as the free ion. Cells incubated with greater than or equal to 10 microM 64Cu showed a net loss of copper after 40- to 60-min incubation, which may involve specific hepatic mechanisms in copper homeostasis.
Measurement of cholecystokinin octapeptide-induced motility of rat antrum, pylorus, and duodenum in vitro
Authors: Scheurer U. , Varga L. , Drack E. , Burki H. R. , Halter F.
Published: December 2017

Motor effects of cholecystokinin octapeptide (CCK-OP) on rat antrum, pylorus, and duodenum have been studied in vitro under standard conditions. Intraluminal pressure changes were simultaneously measured at the three locations using a perfusion manometric system with a novel intraluminal pressure-sensor device. This device comprised an acrylic cast of the rat gastroduodenal tract containing the perfusion catheters that reached the surface of the cast with their outlets in the antrum, pylorus, and duodenum. A selective and sensitive intraluminal local pressure measurement was achieved with this pressure sensor due to its shape. CCK-OP increased base-line pressure in the antrum, pylorus, and duodenum; frequencies of phasic contractions in the antrum and pylorus; and amplitudes in the duodenum. The peptide also decreased contraction amplitudes in the antrum and pylorus and frequency of phasic contractions in the duodenum. It is concluded that the novel intraluminal pressure sensor is a useful tool for measuring local pressure changes in the gastroduodenal tract of the rat. In this experimental model, effects of CCK-OP on antral, pyloric, and duodenal base-line pressure are comparable with those observed in isolated muscle strips and in the intact organ of humans, dogs, and opossums. A different behavior, however, was observed in the force of antral and frequency of duodenal phasic contractions.
Effect of short-chain fatty acids on the secretory response of the ovine exocrine pancreas
Authors: Harada E. , Kato S.
Published: December 2017

The secretory response of the exocrine pancreas to short-chain fatty acids has been studied in anesthetized sheep and in isolated lobules. Butyrate, propionate, and acetate stimulated pancreatic juice flow and protein and amylase output in the anesthetized sheep. The secretory response to butyrate was significantly greater than that of propionate or acetate. Rapid intravenous injection of butyrate (625 mumol/kg) caused a 13-fold rise in the juice flow, 26-fold in protein output, and 37-fold in amylase output above the basal levels within 5 min and declined to basal levels over a period of 30 min. Responses to butyrate (625 mumol/kg) were comparable with those obtained with 2 U/kg pancreozymin (Boots). Detectable responses were obtained with 15 mu/kg butyrate, 125 mumol/kg propionate, and 312.5 mumol/kg acetate. The secretory response to butyrate (625 mumol/kg) was not affected by pretreatment with atropine and hexamethonium. In the isolated lobule preparation, amylase release increased in response to butyrate in a concentration-dependent manner, reaching a maximal level at 1 mM and declining at 100 mM. It is concluded that short-chain fatty acids act directly on pancreatic acinar cells to stimulate secretion. The physiological implications of these findings are considered.
A novel method for continuous monitoring of bilirubin production in unstressed rats
Authors: Reichen J. , Hoilien C. , Sheldon G. F. , Kirshenbaum G.
Published: December 2017

We describe a device for continuous infusion and monitoring of exhaled 14CO as a test of hepatic bilirubin production in rats. A Silastic catheter, implanted into a jugular vein under light ether anesthesia, was protected with a spring shield and a cannula swivel. The animals were kept in a modified Bollman cage. delta-[5-14C]aminolevulinic acid, a heme precursor yielding 14CO upon breakdown of heme to bilirubin, was infused at a constant rate. Exhaled 14CO was oxidized to 14CO2 and collected in ethanolamine. The efficiency of the system averaged 97.8%. In untreated animals 14CO production reached a plateau within 12 h; thereafter, it increased by 2.8% per day. The responsiveness of the system was tested by fasting the animals, which stimulated hepatic bilirubin production. Fasting increased 14CO production by 32.8 +/- 8% (mean +/- SD, P less than 0.005) after 72 h. This was associated with an increase in hepatic heme oxygenase activity (+48%, P less than 0.05) and a decrease in microsomal cytochrome P-450 content (-45%, P less than 0.05). Thus, our approach permits continuous monitoring of hepatic bilirubin production without subjecting the animals to the stress of handling, restraint, or anesthesia. The method can easily be applied to other breath tests involving formation of 14CO2.
Characterization of Mg-ATP-dependent Ca2+ transport in cat pancreatic microsomes
Authors: Kribben A. , Tyrakowski T. , Schulz I.
Published: December 2017

Mg-ATP-dependent 45Ca2+ uptake and Ca2+-ATPase activity have been examined in isolated microsomes obtained by differential centrifugation and in purified subcellular fractions obtained by Ficoll-sucrose density centrifugation in the presence of mitochondrial inhibitors. Mg-ATP-dependent 45Ca2+ uptake increased with increasing EGTA-buffered free [Ca2+], reaching a maximum of 2 nmol 45Ca2+ X 15 min-1 X mg prot-1 at 2 mumol/1 [Ca2+] in the incubation medium. Half-maximal 45Ca2+ uptake was at approximately 0.2 mumol/1 [Ca2+]. Maximal Ca2+ -Mg2+ -ATPase activity was 130 nmol X 15 min-1 X mg prot-1 at 2 mumol/l [Ca2+], with an apparent Km of approximately 0.3 mumol/l [Ca2+]. The Ca2+ ionophore A23187 (10(-6) mol/l), the mercurial compounds mersalyl (10(-5) mol/l) and CH3ClHg (10(-3) mol/l), as well as La3+ (10(-4) mol/l), vanadate (10(-4) mol/l), and saponin (50 micrograms/mg prot), abolished Mg-ATP-promoted 45Ca2+ uptake. In the absence of Mg2+, ATP did not provoke 45Ca2+ uptake. Using the purified smooth membrane fraction (F1) from the Ficoll-sucrose density gradient (enrichment of Na+-K+-ATPase specific activity by ninefold and of NADH-cytochrome c reductase by threefold as compared with total tissue homogenate), Mg-ATP-dependent 45Ca2+ uptake correlated better with Na+-K+-ATPase (r = 0.97) than with the smooth endoplasmic marker NADH-cytochrome c reductase (r = 0.52). No correlation was found with RNA, the marker for rough endoplasmic reticulum. We conclude that pancreatic plasma membranes contain a Ca2+-Mg2+-ATPase that represents the Ca2+ extrusion system from acinar cells. It is also possible that vesicular membrane structures associated with the plasma membrane, or endocytotic plasma membrane vesicles, take up Ca2+ and represent an intracellular Ca2+ pool.
Protection of epithelial function in human jejunum cultured with hydrocortisone
Authors: Scott J. , Peters T. J.
Published: December 2017

Over 24-h culture with hydrocortisone (400 nM), activity of brush-border alkaline phosphatase, alpha-glucosidase, and leucyl-2-naphthylamidase and cytoplasmic-mitochondrial malate dehydrogenase increased (P less than 0.05) by 80-133% compared with controls. Uptake of 3-O-methyl-D-[14C]glucose after 24-h culture was increased (P less than 0.05) by 30% compared with cultures without hydrocortisone. Labeling of protein with L-[14C]tyrosine and glycoprotein with D-[3H]glucosamine increased (P less than 0.05) by 40 and 88%, respectively, with hydrocortisone. The effects of hydrocortisone were dose dependent at normal serum concentrations (100-600 nM) and not further stimulated by larger concentrations. Cytoplasmic lactate dehydrogenase and lysosomal hexosaminidase activity, specific radioactivity of soluble precursor pools for protein and glycoprotein labeling, incorporation of [3H]thymidine into DNA, and morphology were unaffected by hydrocortisone. Inhibitors of glucocorticoid receptor binding (progesterone), mRNA transcription (alpha-amanitin), and protein synthesis (cycloheximide) prevented the effects of hydrocortisone. We suggest that hydrocortisone maintains the digestive, absorptive, and cellular function of cultured human jejunum. These protective effects were associated with increased protein synthesis and glycosylation and dependent on a classical steroid-hormone mechanism.
Functional and anatomic heterogeneity in the liver acinus: impact on transport
Authors: Gumucio J. J.
Published: December 2017

The site of solute exchange between blood and hepatocytes is the liver acinus, the structural and functional unit of hepatic parenchyma. Because the perfusion of acinar hepatocytes occurs in a sequential manner, differences in solute concentration between hepatocytes located at the inlet (zone 1) and at the outlet (zone 3) of the acinus are predictable. However, the distribution and transport of solutes by hepatocytes of each acinar zone also seem to be influenced by factors other than the sequential perfusion of blood. The concentration of receptors in hepatocytes at each zone, the presence of specific chemical groups on the incoming molecules, and the binding of the solutes to plasma protein are all factors that modify the interaction with, and the cellular concentration attained by, solutes in each acinar zone. Therefore, solute concentration in hepatocytes of each acinar zone may produce a profile of decreasing solute concentration from cells in zone 1 to those in zone 3, a reverse profile from zone 3 to zone 1, or a similar concentration in all hepatocytes.
Cholecystokinin octapeptide and gastric mechanoreceptor activity in rat brain
Authors: Ewart W. R. , Wingate D. L.
Published: December 2017

Extracellular unitary recordings were made from neurons in the rat dorsal vagal nucleus, and the response of these neurons to iontophoretically applied cholecystokinin octapeptide (CCK-OP) and proglumide (a novel CCK antagonist) was studied. The effect of CCK-OP and proglumide on the response of the neurons to gastric distension was also studied. Seventy-four percent (n = 39) of the neurons studied were excited by CCK-OP. It was not possible to antagonize the response to CCK-OP with proglumide. CCK-OP was also found to be an effective modulator of the response to gastric distension; the effects were diverse (“on” responses were augmented; ”off“ and “transient” responses were diminished) but were always the same within each characteristic pattern of response to distension. These results provide supporting evidence for CCK-OP, a peptide common to both brain and gut, acting in the role of a neural modulator in the control of the gastrointestinal tract. It is possible to speculate that the potent effect of CCK-OP on neuronal excitability and on the central representation of gastric mechanoreceptor activity may well substantiate the role of CCK-OP as a central regulator of feeding behavior.
Distribution of surfactants in the canine gastrointestinal tract and their ability to lubricate
Authors: Butler B. D. , Lichtenberger L. M. , Hills B. A.
Published: December 2017

Surface-active phospholipids, chemically similar to pulmonary surfactants, have been identified by thin-layer chromatography in gastric juice and on the mucosal lining of five tissues along the canine gastrointestinal tract. These included esophagus, oxyntic tissue, midduodenum, midjenunum, and midcolon. The mucosal phospholipid composition did not change appreciably along the length of the gastrointestinal tract, with the most prominent species being phosphatidylcholine (PC) (34–45%) and phosphatidylethanolamine (PE) (18–32%). The gastrointestinal mucosal surface also contained lesser amounts (5–10% each) of sphingomyelin (Sp), lysophosphatidylcholine, phosphatidylinositol (PI), and phosphatidylserine (PS) and small but detectable quantities of phosphatidylglycerol (PG) and phosphatidic acid. Both the lipid extracts of all six gastrointestinal sources as well as commercially available phospholipids identified in these samples (PC, Sp, PE, PI, PS, and PG) proved to be good boundary lubricants. Each reduced the coefficient of friction by greater than 75% between glass and carboxylated yarn when tested by a standard method for evaluating textile “sizes.” The results are discussed in relation to the possible role of the surface-active molecules in imparting properties conducive to lubrication and acid protection onto the gastrointestinal epithelium.
Mechanisms responsible for SCN increase in resistance of in vitro frog gastric mucosa
Authors: Rehm W. S. , Chu T. C. , Schwartz M. , Carrasquer G.
Published: December 2017

Thiocyanate (SCN) inhibits H+ secretion and increases the resistance and potential difference (PD) of the gastric mucosa. These results support our separate-site electrogenic theory of HCl secretion. Recent work shows that an ATP-driven mechanism in the gastric mucosa can produce H+ by a neutral exchange of K+ for H+. The SCN increase in resistance and PD, if due to an inhibition of a high-conductance mechanism(s) in the secretory plasma membrane, is not easily compatible with the neutral mechanism. Therefore, the possibility was examined that SCN induces the increase in resistance by other mechanisms. The HCl and NaCl concentration profiles in the pit and tubular lumina were calculated. The effects of SCN were determined with isotonic, hypotonic, hypertonic, buffered, and high [H+] secretory solutions. The results indicate that SCN produces an increase in resistance of about 130 omega. cm2 of the plasma membranes of the tubular cells. A scheme is proposed that incorporates the neutral K+-H+ mechanism into an electrogenic system.
Use of 125I-secretin to identify and characterize high-affinity secretin receptors on pancreatic acini
Authors: Jensen R. T. , Charlton C. G. , Adachi H. , Jones S. W. , O'Donohue T. L. , Gardner J. D.
Published: December 2017

We prepared 125I-secretin and studied the kinetics, stoichiometry, and chemical specificity with which the labeled peptide binds to dispersed acini prepared from guinea pig pancreas. Iodinated secretin retained intrinsic biological activity in that it was as effective but 2.5-times less potent than native secretin in its ability to bind to pancreatic acini and to increase cellular cAMP. Scatchard analysis of binding of 125I-secretin indicated that each pancreatic acinar cell has approximately 93,000 binding sites, half of which are occupied by 11 nM iodinated secretin. Binding of 125I-secretin was rapid, reversible, saturable, specific, and temperature dependent. Binding of 125I-secretin was inhibited by secretin, vasoactive intestinal peptide, PHI, and Gila monster venom but not by glucagon, gastric inhibitory polypeptide, cholecystokinin, caerulein, gastrin, bovine pancreatic polypeptide, somatostatin, neurotensin, leucine-enkephalin, methionine-enkephalin, carbachol, bombesin, litorin, eledoisin, physalaemin, or substance P. With agonists (secretin, vasoactive intestinal peptide, PHI, or Gila monster venom), as well as antagonists (C-terminal fragments of secretin), there was a close correlation between their relative potencies for inhibiting binding of 125I-secretin and their relative potencies for increasing cAMP (agonists) or inhibiting the secretin-induced increase in cAMP (antagonists). For a given agonist, however, a 40-fold higher concentration was required for half-maximal inhibition of binding of 125I-secretin than was required to produce a half-maximal increase in cellular cAMP. Thus, maximal stimulation of cellular cAMP occurs when approximately one-third of the secretin receptors are occupied by an agonist.
Effects of Met-enkephalin and naloxone on gastric emptying and secretion in rhesus monkeys
Authors: Shea-Donohue P. T. , Adams N. , Arnold J. , Dubois A.
Published: December 2017

Recent studies have demonstrated the presence of enkephalins in gastric neurons and endocrine cells; however, their role in the regulation of gastric function is unknown. The effect of Met-enkephalin (MET), the stable analogue of Met-enkephalin [D-Ala2]Met-enkephalinamide (DMET), and the opiate receptor antagonist naloxone were studied in five chair-adapted rhesus monkeys. A dye-dilution technique was used to determine simultaneously fractional emptying rate, hydrogen, sodium, potassium, and chloride ion output, and fluid output. Both MET and DMET significantly inhibited fractional emptying rate and H+ secretion following an 80-ml water meal. Only MET, however, significantly altered fluid and sodium ion output. Naloxone had no effect on gastric function following the water meal.
Antral control of canine gastric emptying of solids
Authors: Becker J. M. , Kelly K. A.
Published: December 2017

We wondered whether antral mucosal nerves sense the size of particles in gastric chyme and then activate motor mechanisms that allow only small particles to empty. Four conscious dogs with duodenal Thomas cannulas were fed 100 g of bovine liver, half of which was labeled with cyano[57Co]cobalamin. Duodenal chyme was then collected in 15-min periods for 5 h and poured through a stack of sieves of decreasing pore size, and the percentage of radioactivity recovered on each sieve was determined per hour. Five studies were carried out on each dog before and beginning 2 wk after antral mucosal neurolysis, during which the antral mucosal nerves were divided by dissecting the entire antral mucosa circumferentially free from the surrounding antral muscularis. In the control tests, nearly all liver (93%) emptied as particles less than 1.4 mm in diameter, but the percentage emptied as larger particles increased in the 3rd through 5th postprandial h. After antral mucosal neurolysis, the increase in the percentage of larger particles emptied occurred sooner and to a greater extent, but the overall rate of emptying of liver was not changed. We concluded that antral mucosal nerves have a role in regulating the size of gastric particles emptied, but a minor one.
Cholinergic stimulation of ouabain-sensitive respiration in rat submandibular gland
Authors: Stewart D. J. , Pon D. J. , Sen A. K.
Published: December 2017

Oxygen consumption of slices of rat submandibular gland was monitored with an oxygen electrode method. Carbachol stimulated an immediate increase in tissue respiration that was inhibitable by ouabain. The stimulation required the presence of calcium in the incubation medium and was blocked by atropine. The calcium ionophore A23187 also stimulated ouabain-sensitive oxygen consumption in the tissue slices. The results show that the mechanism using the extra energy during cholinergic stimulation is the sodium pump. Amiloride at a 1, 10, or 100 microM concentration had no effect on stimulation of ouabain-sensitive respiration by carbachol. Since amiloride, which is known to block the sodium reabsorption process in the ductal segment, has no effect on the stimulation, the increased sodium pump activity is probably located in the acinar region and is associated with the primary fluid secretion process.
Peripheral sympathetic pathways to gastroduodenal region of the guinea pig
Authors: Kreulen D. L. , Muir T. C. , Szurszewski J. H.
Published: December 2017

The sympathetic pathways to the stomach and duodenum of the guinea pig were studied by electrical nerve stimulation and by gastric distension in vitro and in vivo. The in vitro preparation consisted of the stomach and duodenum connected by para-arterial nerves to the celiac plexus. Gastroduodenal motility was measured with intraluminal pressure catheters. Stimulation of splanchnic nerves resulted in inhibition of propulsive contractions of both the stomach and duodenum. Stimulation of the left gastric nerve inhibited the stomach but not the duodenum, and stimulation of the gastroduodenal nerve inhibited the duodenum only. When the gastroduodenal nerve was stimulated, excitatory postsynaptic potentials were elicited in 18% of the cells from which intracellular recordings were made in the celiac ganglia. When the stomach was distended to a pressure of 5-7 cmH2O, propulsive contractions in the duodenum stopped in 86% of the distensions in the in vivo preparations and in 62% of the distensions in the in vitro preparations. Section of the gastroduodenal nerve eliminated the distension-induced inhibition of duodenal propulsion in vitro. These experiments describe the efferent sympathetic pathways to the celiac plexus of the guinea pig and demonstrate reflex pathways to the celiac plexus that can mediate a gastroduodenal inhibitory reflex.
Effects of alloxan diabetes and insulin in vivo on rat parotid gland
Authors: Anderson L. C.
Published: December 2017

Parotid gland growth and secretory enzyme levels were studied in male Sprague-Dawley rats following the induction of alloxan diabetes. Diabetes resulted in a retardation of parotid gland, as well as body growth, and in a reduction of parotid gland DNA, RNA, and total protein compared with control rats. Morphologically, parotid glands of diabetic animals were characterized by an intracellular accumulation of lipid within acinar and intercalated ductal cells. Parotid amylase was reduced 40% in diabetic rats compared with control rats. In contrast, peroxidase levels increased by 54%, and DNase was unaffected. Insulin treatment of diabetic rats led to a restoration of gland and body growth. Parotid gland DNA, RNA, total protein, and secretory enzyme levels returned to control values within 7 days. Thus, insulin in vivo may play a major role in the regulation of parotid gland growth and function.
Release of endogenous and labeled GABA from isolated guinea pig ileum
Authors: Taniyama K. , Miki Y. , Kusunoki M. , Saito N. , Tanaka C.
Published: December 2017

The release of gamma-aminobutyric acid (GABA) was studied by comparing the properties of labeled GABA released from preloaded preparations to those of endogenous GABA released from the isolated guinea pig ileum. The spontaneous release of endogenous GABA was 4.46 +/- 0.10 pmol X min-1 X g wet wt-1, and the fractional rate of endogenous GABA release was much lower. The ratio of evoked to spontaneous release of endogenous GABA was high compared with that of labeled GABA. The electrical transmural stimulation-evoked release of labeled and endogenous GABA was inhibited by superfusion with tetrodotoxin and Ca2+-free Krebs-Ringer solution containing 1 mM ethyleneglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid. Thus the nature of the stimulation-evoked release of labeled GABA was similar to that of endogenous GABA. These results indicate that the released GABA is neuronal in origin and provide additional evidence for the presence of GABA-ergic neurons in the guinea pig ileum.
Effects of neurotransmitter release on mucosal transport in guinea pig ileum
Authors: Cooke H. J. , Shonnard K. , Highison G. , Wood J. D.
Published: December 2017

Scorpion venom (Leiurus quinquestriatus), a substance that evokes neurotransmitter release by depolarizing neurons, was used to activate enteric neurons in short-circuited guinea pig ileum. Scorpion venom increased transmural potential difference and short-circuit current, and this response was similar to the increase that occurred after electrical stimulation of enteric neurons. The stimulus- or venom-evoked response in short-circuit current was abolished by tetrodotoxin. Atropine reduced by 47% the increments in short-circuit current produced by either electrical stimulation or venom. Scorpion venom increased active chloride secretion in short-circuited guinea pig ileal mucosa but had no significant effect on active sodium absorption, residual flux, or total tissue conductance. No morphological changes in transmission electron micrographs of ileal mucosa treated with scorpion venom were evident compared with controls. Alanine caused an increase in short-circuit current in venom-treated tissue that was similar to control values. These results show that scorpion venom mimics the mucosal effects of electrical activation of enteric neurons. These results suggest that a significant component of both scorpion venom action and the response to electrical field stimulation is mediated by neural release of acetylcholine, which activates epithelial muscarinic receptors.
Gastric and duodenal HCO3- transport in vivo: influence of prostaglandins
Authors: Smeaton L. A. , Hirst B. H. , Allen A. , Garner A.
Published: December 2017

Gastric and duodenal HCO3- transport was compared in the same mammalian species (cat) in vivo. The most appropriate technique for detecting HCO3- in the lumen of the stomach was measurement of pH and CO2 tension, whereas in the duodenum it was pH-stat titration. For experiments on gastric HCO3- transport, conscious cats prepared with vagally denervated fundic pouches were used; for those on duodenal transport anesthetized animals with in situ perfused segments were studied. When expressed in terms of gross surface area, basal HCO3- output was six times greater in the duodenum than in the stomach (approximately 1.5 cf. approximately 0.25 mumol X cm-2 X 15 min-1). topical application of 16,16-dimethyl prostaglandin E2 (dmPGE2) to duodenal mucosa caused a concentration-dependent increase in HCO3- output and transmucosal electrical potential difference (PD) over the range 0.01–1.0 microgram X ml-1. PGE2 was approximately 200 times less potent than dmPGE2 as a stimulant of duodenal HCO3- transport. Increases in the rate of luminal HCO3- output following application of dmPGE2 were considerably less in the stomach compared with the duodenum (approximately 50% cf. approximately 1,000% at 1 microgram X ml-1). Intravenous dmPGE2 (1 microgram X kg-1 X h-1) had no effect on either gastric or duodenal HCO3- outputs. Indomethacin (5 mg X kg-1 iv) inhibited duodenal HCO3- output by approximately 50% and reduced PD but did not influence gastric HCO3- output. We propose that in the cat duodenum in vivo local prostaglandins regulate HCO3- transport, but in the cat stomach in vivo they have a less important role.
Cl- - and K+-related fluctuations of ionic current through oxyntic cells in frog gastric mucosa
Authors: Zeiske W. , Machen T. E. , Van Driessche W.
Published: December 2017

Transport and conductance pathways for Cl- and K+ were studied in frog gastric mucosa using noise analysis techniques. The current-noise power spectra exhibited both Cl- - and K+-dependent characteristics. In Cl- -containing solutions, reductions in Cl- transport were associated with reductions of the overall noise power. Such changes appeared to reflect the movement of Cl- through the apical (mucosal) membranes of oxyntic cells. In Cl- -free solutions a K+-dependent Lorentzian component was detected in the power spectrum when applying a mucosally or serosally directed transepithelial K+ concentration gradient. This component was enhanced by 1) stimulating the oxyntic cells with histamine and 2) appropriate voltage clamping. It was reduced by mucosal Ba2+ in resting tissues and enhanced by mucosal Ba2+ in stimulated tissues. The K+ noise measured in gastric mucosae in Cl- -free solutions appeared also to be generated at the apical membranes of oxyntic cells. This is in analogy to previous findings in other gastrointestinal epithelia with fluctuating apical K+ channels. In the gastric mucosa these channels may play a key role in the mechanism of electrogenic H+ secretion.
Dihydroxy bile salt-induced alterations in NaCl transport across the rabbit colon
Authors: Freel R. W. , Hatch M. , Earnest D. L. , Goldner A. M.
Published: December 2017

The effects of increasing mucosal or serosal concentrations (1–4 mM) of taurochenodeoxycholate (TCDC) on sodium chloride transport across the isolated, short-circuited rabbit colon were examined. Mucosal TCDC produced dose-related increases in tissue conductance (Gt) and the unidirectional fluxes of Na+ and Cl- and dose-related decreases in net NaCl absorption. At 4 mM mucosal TCDC, Gt was increased fivefold, net sodium flux (JNanet) was reduced 50%, and JClnet was abolished. Serosal TCDC also produced dose-dependent changes in permeability that were quantitatively different. Four millimolar serosal TCDC produced a 2.7-fold increase in Gt, abolished JNanet, and stimulated electrogenic Cl- secretion. TCDC-induced Cl- secretion was stimulated by 10(-5) M serosal TCDC, inhibited by serosal furosemide or ouabain, did not alter theophylline-induced secretion (and vice versa), and occurred in the absence of serosal Ca2+. It is suggested that 1) TCDC inhibition of sodium absorption is indirect (i.e., not simply due to a reduction in the activity of the Na “pump,” since Cl- secretion persists during conditions that abolish JNanet) and 2) TCDC induces Cl- secretion by enhancing the activity of basolateral membrane adenylate cyclase.
Effects of dietary fiber constituents on intestinal morphology and nutrient transport
Authors: Sigleo S. , Jackson M. J. , Vahouny G. V.
Published: December 2017

Adult male rats were fed for 4 wk on diets containing no addition, 10% fiber (methoxylated pectin or cellulose), or 2% cholestyramine. Weight gain and food intake in the fiber-fed groups were significantly greater than in control or cholestyramine-fed rats. The small intestine was examined for changes in jejunal villus structure and for in vitro transport characteristics by estimation of unidirectional influxes of 3-O-methylglucose (3-O-MG), alpha-aminoisobutyric acid (AIB), and sodium (Na). Feeding of either fiber component resulted in increases in intestinal villus length and width and in a marked increase in the influxes of 3-O-MG and AIB. Influx of Na also increased but less dramatically than the organic solutes. Cholestyramine feeding resulted in shortened villi and increased separation between villi in the jejunum. With this feeding regimen, influxes of 3-O-MG and AIB were increased, but Na influx was not changed. The results show that certain dietary fiber components may modify intestinal architecture and indicate that these structural changes may be correlated with altered functional characteristics.
Copper efflux kinetics from rat hepatocytes
Authors: Darwish H. M. , Schmitt R. C. , Cheney J. C. , Ettinger M. J.
Published: December 2017

The kinetics of copper efflux from rat hepatocytes were determined to further characterize the hepatic Cu(II) transport system. Efflux was biphasic. Net efflux was rapid for 1-5 min, and 35-45% of preloaded copper was lost by 40 min. Efflux was negligible after 40 min. The retained percentage was independent of the preloading concentration, but the total amount of intracellular copper that was available for efflux gradually decreased as the duration of the preloading period increased. Unlabeled extracellular Cu(II) displaced 64Cu from intracellular pools, but exchange with intracellular Cu was not required for uptake. Zinc also displaced copper but less effectively than copper. This implies some specificity in intracellular binding components. No transstimulation of uptake or efflux was detected. Copper efflux was strictly passive. Extracellular Cu(II) decreased the rate of efflux and preloading inhibited Cu(II) uptake. Metabolic inhibitors had no effect on the rate or total amount of 64Cu efflux, and significant efflux occurred at 4 degrees C. Moreover, when a steady state was attained at the end of a preloading period, the effective intracellular concentration of free copper approximated the Cu(II) concentration in the extracellular medium. By use of this estimate for the intracellular concentration of free copper, efflux kinetic parameters were obtained from initial (1-min) rate data (Km = 5.5 +/- 0.8 microM; Vmax = 1.1 +/- 0.1 nmol X min-1 X mg prot-1). These parameters are similar to those obtained for Cu(II) uptake, and the saturation kinetics observed are consistent with specific facilitated efflux by this copper transport system.(ABSTRACT TRUNCATED AT 250 WORDS)
Microtubule modulation of biliary excretion of endogenous and exogenous hepatic lysosomal constituents
Authors: Sewell R. B. , Barham S. S. , Zinsmeister A. R. , LaRusso N. F.
Published: December 2017

We tested the hypothesis that hepatocyte microtubules modulate the biliary excretion of endogenous and exogenous constituents of hepatocyte lysosomes. We collected bile via bile fistulas from male rats before and after acute administration of colchicine and vinblastine, agents known to bind to hepatocyte microtubules; rats were then killed and livers were homogenized for biochemical analyses or processed for electron microscopy. Colchicine caused biphasic, parallel alterations in the biliary excretion of three lysosomal enzymes compared with control rats given saline or lumicolchicine; a peak rise in enzyme outputs of approximately 175% at 45-60 min after colchicine administration was followed by a sustained fall to approximately 25% of control values, which persisted for 2-4 h. When hepatocyte lysosomes were prelabeled in vivo by administration of [3H]Triton WR-1339, a nonionic detergent that is sequestered in hepatic lysosomes, the biliary excretion of radiolabel in response to colchicine paralleled the biliary excretion of the three lysosomal enzymes. Vinblastine also induced a biphasic response in biliary lysosomal enzyme output that was similar to that produced by colchicine administration. Morphometric analysis of electron micrographs of rat livers demonstrated changes in the number of lysosomelike vesicles in the vicinity of bile canaliculi after colchicine and vinblastine administration; the initial increase in lysosomal enzyme secretion was associated with a significant decrease in the number of pericanalicular lysosomes after both agents, while the subsequent decrease in enzyme secretion coincided with an increase in the number of pericanalicular lysosomes after vinblastine.(ABSTRACT TRUNCATED AT 250 WORDS)
Gastrointestinal absorption of epidermal growth factor in suckling rats
Authors: Thornburg W. , Matrisian L. , Magun B. , Koldovsky O.
Published: December 2017

Epidermal growth factor (EGF) was detected in the milk of adult lactating Sprague-Dawley female rats (38.85 ng/ml) and in the stomach (37.25 ng/g content) and plasma (32.36 ng/ml) of 13-day-old suckling offspring. Sixty-nanogram (0.12 mCi/ml) doses of 125I-EGF were administered orally to sucklings in 200 microliters of buffer for 0, 0.5, 1.0, and 3.0 h. Lung, liver kidney, brain, and blood each contained 1% or less of the administered radioactivity. Stomach wall (8%) and content (63%), intestinal wall (15%) and flushing (38%), and skin (18%) contained larger amounts reaching maxima in these three regions at 0, 0.5, and 3.0 h, respectively. Except for skin, a substantial amount of radioactivity from all tissues represented intact (6-90%) and immunoreactive (3-90%) EGF based on Sephadex G-25 chromatography and anti-EGF antibody binding, respectively. From 30 to 55% of the radioactivity from wall (gastric or small intestinal) or lumina was also capable of binding to A-431 cell surface receptors. Isoelectric points of major species found in stomach (4.2), intestine (4.1), and other tissues differed from that of administered EGF (4.5).
Intracellular recordings from vagally innervated intramural neurons in opossum stomach
Authors: King B. F. , Szurszewski J. H.
Published: December 2017

Intracellular recordings were made from intramural neurons in parafascicular ganglia in the opossum stomach. These ganglia were situated between the myenteric and subserosal plexuses and were found lying adjacent to vagal nerve fascicles. The neurons at these ganglia showed active and passive electrical properties similar only to S/type I enteric neurons. They received a complex innervation from preganglionic vagal fibers. These parasympathetic nerves elicited three distinct transmission processes in intramural neurons: fast and slow excitation (excitatory postsynaptic potentials, EPSP) and slow inhibition (inhibitory postsynaptic potential, IPSP). Fast EPSPs were cholinergically mediated via postjunctional nicotinic receptors, with convergence of numerous cholinergic fibers in several vagal fascicles to individual neurons. When seen, slow EPSPs increased neuronal excitability, whereas slow IPSPs decreased excitability.
Regulation of gastroduodenal HCO-3 transport by luminal acid in the frog in vitro
Authors: Heylings J. R. , Garner A. , Flemstrom G.
Published: December 2017

Luminal acid (10 mM HCl) is a stimulant of surface epithelial HCO-3 transport in mammalian stomach and duodenum in vivo. To determine whether a humoral mechanism is involved in mediation of this response, amphibian fundic, antral, or proximal duodenal mucosae were mounted in parallel in an in vitro chamber with their nutrient (serosal) surfaces facing a common solution. The mucosal surfaces were bathed by separate solutions and the rate of HCO-3 transport by one mucosa titrated (at pH 7.40) during exposure of the parallel tissue to luminal acid. In studies of fundic HCO-3 transport, H+ secretion was inhibited with the histamine H2-antagonist tiotidine (10(-4) M). Fundic luminal acid stimulated HCO-3 transport by a parallel fundus (27 +/- 6%) or antrum (53 +/- 27%) but had no effect on a parallel duodenum. Antral luminal acid had no effect on a parallel antrum, indicating that the gastric stimulant is of fundic origin. Duodenal luminal acid increased HCO-3 transport by both parallel duodenum (21 +/- 5%) and fundus (109 +/- 32%). Stimulation of HCO-3 transport occurred at higher luminal pH in duodenum (approximately 4.0) than in fundus (approximately 2.0). Thus, exposure to luminal acid releases humoral factor(s) capable of stimulating surface epithelial HCO-3 transport by both stomach and duodenum. The actions of these putative stimulants are in part tissue specific, and they may be important in mediation of mucosal protection against luminal acid.
Potentiating effect of secretin on cholecystokinin-stimulated pancreatic secretion in dogs
Authors: Chey W. Y. , Lee K. Y. , Chang T. M. , Chen Y. F. , Millikan L.
Published: December 2017

A possible potentiating effect of cholecystokinin octapeptide (CCK-OP) on the action of secretin on exocrine pancreatic secretion was studied in five dogs with gastric fistulas and modified Herrera pancreatic fistulas. Secretin in a dose, 2.45 pmol (0.03 clinical units) X kg-1 X h-1, that mimics the plasma secretin level in the postprandial state increased pancreatic bicarbonate secretion, but the increase was not statistically significant. CCK-OP in graded doses, 26.2, 52.5, 109, and 219 pmol (0.03, 0.06, 0.125, and 0.25 microgram) X kg-1 X h-1, given intravenously produced a significant increase in both bicarbonate and protein secretion, and the increase was dose related. The plasma concentrations of immunoreactive CCK during intravenous infusion of CCK-OP in doses of 26.2 and 52.5 pmol X kg-1 X h-1 were found to mimic the postprandial plasma concentrations of immunoreactive CCK in eight dogs. When CCK-OP in four graded doses was added to intravenous infusion of secretin, 2.45 pmol X kg-1 X h-1, the actual bicarbonate output at each dose level of CCK-OP was greater than the sum of the bicarbonate outputs produced by secretin alone and CCK-OP alone in a corresponding dose. Thus, we conclude that the action of secretin in a physiological dose that mimics the plasma level of secretin after a meal is potentiated by CCK-OP in a dose range that produces a plasma CCK-OP level comparable with that in the postprandial state and vice versa. The study indicates that, like secretin, CCK-OP is another necessary agent for pancreatic secretion of bicarbonate during digestion.(ABSTRACT TRUNCATED AT 250 WORDS)