bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical properties of primate gallbladder: description by a dynamic method
Authors: Schoetz D. J. , LaMorte W. W. , Wise W. E. , Birkett D. H. , Williams L. F.
Published: December 2017

Biomechanical theory was applied to devise a dynamic method for describing gallbladder tone in an in situ baboon model. Under pentobarbital sodium (Nembutal) anesthesia, cyclical infusion of bile into and withdrawal of bile from the gallbladder with continuous pressure monitoring allow instantaneous measurement of the pressure-volume ratio and thus of mean gallbladder compliance. This paper describes the method and details the manner of data analysis. Pharmacologic and hormonal agents with known gallbladder effects are used in order to demonstrate the sensitivity of the method. Pilocarpine, histamine, and cholecystokinin cause contraction of the primate gallbladder smooth muscle; this contraction is reflected in decreased compliance by continuous monitoring. Atropine administration results in increased ability to accommodate volume infusions; this effect has not been demonstrated by static monitoring in previous experiments. This new method allows continuous monitoring of compliance and offers both simplicity and sensitivity when compared with previous methods.
Sites of carbonic anhydrase in avian gastric mucosa identified by electron microscope autoradiography
Authors: Gay C. V. , Schraer H. , Shanabrook V. M.
Published: December 2017

Carbonic anhydrase was localized at the ultrastructural level by autoradiography of [3H]acetazolamide in quail gastric mucosa. Grains were associated predominantly with mucin granules at the apical end of surface mucosal cells. Secreted mucin was also labeled. Oxynticopeptic cells of the multilobular glands were not labeled. The pH of fluid secreted by was 7.0-7.4 compared with a pH of 1.3-1.8 of freshly secreted fluid in the gastric lumen. The results of this study suggest that surface mucosal cells, which are strikingly similar in birds, amphibians, and mammals, are the site of acid secretion in the vertebrate stomach.
Permeability of gastric capillaries to small and large molecules
Authors: Perry M. A. , Crook W. J. , Granger D. N.
Published: December 2017

The permeability of capillaries in the stomach to small and large solutes was studied with the double-indicator diffusion technique in the dog stomach and by analysis of steady-state lymph and plasma samples in the cat stomach. The effective pore radius in gastric capillaries determined by indicator diffusion was 53 A, whereas steady-state lymph samples predicted a small-pore radius of 47 A. At the highest plasma flow rates studied (achieved by intra-arterial infusion of isoproterenol), indicator diffusion estimates of the permeability-surface area product for raffinose, inulin, and beta-lactoglobulin A were 140, 70, and 8 ml . min-1 . 100 g-1, respectively. The lymph studies indicate that gastric capillaries are more permeable than capillaries in the intestine and colon to albumin and larger molecules. The calculated effective large-pore radius of gastric capillaries was 250 A. The osmotic reflection coefficients (sigma d) ranged from 0.73 +/- 0.03 for albumin to 0.91 +/- 0.02 for beta-lipoprotein (120-A radius). The sigma d for total plasma protein was 0.78 +/- 0.03, indicating a substantial transcapillary oncotic pressure gradient, despite the greater permeability of these capillaries for macromolecules.
Actions of a newly isolated intestinal peptide PHI on pancreatic acini
Authors: Jensen R. T. , Tatemoto K. , Mutt V. , Lemp G. F. , Gardner J. D.
Published: December 2017

In dispersed acini from guinea pig pancreas, PHI, a peptide recently isolated from porcine intestine and found to contain 27 amino acids, inhibited binding of 125I-vasoactive intestinal peptide (125I-VIP), increased cellular cAMP, and stimulated amylase secretion. The increase in amylase secretion caused by a maximally effective concentration of PHI in combination with 8-bromo-cAMP, VIP, or secretin was the same as that caused by PHI alone. In contrast, the increase in amylase secretion caused by PHI plus bombesin, carbachol, or the C-terminal octapeptide of cholecystokinin was significantly greater than the sum of the increase caused by each secretagogue acting alone. From the abilities of PHI to inhibit binding of 125I-VIP, to increase cellular cAMP, and to increase amylase secretion, the apparent affinity of PHI for the VIP-preferring receptors on pancreatic acinar cells is approximately 25 times less than that of VIP but 10 times greater than that of secretin. From the ability of PHI to increase cellular cAMP, the apparent affinity of PHI for the secretin-preferring receptors on pancreatic acinar cells is approximately 300 times less than that of secretin but equal to that of VIP.
Effect of portacaval shunt on sulfur amino acid metabolism in rats
Authors: Benjamin L. E. , Steele R. D.
Published: December 2017

Male rats were subjected to portacaval shunts (PCS). Postoperative growth curves were similar between PCS and sham-operated control animals, with complete recovery of preoperative body weight occurring within 7 days. PCS rats had 30% smaller livers and 39% larger spleens at autopsy. Total liver levels of reduced glutathione were decreased by 38% in PCS rats. Sulfur amino acid metabolism was studied 6 wk after PCS by injection of L-[methyl-14C]- or L-[1-14C]methionine with 14CO2 collection or by similarly administering L-[35S]methionine or L-[35S] cysteine and measuring 24-h urinary 35SO4, [35S]taurine, and total 35S. There were no significant differences in 14CO2 production over an 8-h period between PCS and sham rats. PCS rats excreted 31% more 35SO4 and 25% more total 35S when injected with 0.9 mmol of [35S]methionine and excreted 38% less [35S]taurine than controls when injected with [35S]-cysteine. These results indicate altered sulfur amino acid metabolism in PCS rats, an animal model of portal-systemic shunting.
Prostaglandin E2-histamine in interactions on cAMP, cGMP, and acid production in isolated fundic glands
Authors: Levine R. A. , Kohen K. R. , Schwartzel E. H. , Ramsay C. E.
Published: December 2017

Relations among cAMP, cGMP, acid production [measured by the intraglandular accumulation of [14C]aminopyrine (AP)], and prostaglandin E2 (PGE2) activity were studied in isolated glands from rabbit fundic mucosa. AP, cAMP, and cGMP responses to histamine, PGE2, and 3-isobutyl-1-methylxanthine (IMX) were compared with controls. Histamine and PGE2 significantly increased glandular cAMP levels twofold, and histamine and IMX stimulated AP uptake two- to fourfold. PGE2 significantly inhibited both histamine- and IMX-stimulated AP accumulation, but it did not alter basal AP uptake. PGE2 also decreased histamine-stimulated cAMP production but only at a low concentration (10(-7) M). This dose of PGE2 was near to the endogenous PGE2 content found in unstimulated glands (10(-8) M). Intraglandular cGMP levels in unstimulated glands (10(-8) M). Intraglandular cGMP levels were increased by IMX but not by PGE2 or histamine. It is concluded that histamine stimulation of acid secretion is mediated by cAMP, that secretory and biochemical responses to histamine are modulated by PGE2 because PGE2 antagonized histamine-stimulated cAMP and AP uptake, and that the rise in cAMP induced solely by PGE2 appears to be localized within nonparietal cells because PGE2 alone did not stimulate AP accumulation.
Migrating action-potential complex activity in absence of fluid production is produced by B subunit of cholera enterotoxin
Authors: Sinar D. R. , Charles L. G. , Burns T. W.
Published: December 2017

The myoelectric response and fluid output from in vivo rabbit ileal loops injected with B subunits of purified cholera enterotoxin are compared with the response to the purified cholera holotoxin. Migrating action-potential complex (MAPC) frequency is similar after injection of purified cholera toxin or B subunits. In contrast, fluid output after B-subunit injection is significantly (P less than 0.05) less than fluid output after purified cholera toxin injection. Specific antiserum to the holotoxin incubated with holotoxin at equivalence significantly decreased both MAPC activity (P less than 0.05) and fluid output (P less than 0.001) from the purified toxin. Purified cholera toxin and B subunits, modified by reaction with 2-nitrophenylsulfonyl chloride to produce monomeric B fractions with decreased GM1 ganglioside-binding properties, produced significantly (P less than 0.05) less fluid output and MAPC activity. Binding of the toxin or B subunits in the aggregated form is essential for the expression of MAPC activity or fluid output. These results suggest that the B subunit of cholera toxin produces MAPC activity in the rabbit ileum in the absence of fluid production. Furthermore, previous assumptions that MAPC activity is linked to fluid secretion should be reconsidered. It appears that the gut responses to cholera toxin, fluid production, or MAPC activity are produced by separate mechanisms.
Permeability characteristics of bile duct in the rat
Authors: Smith N. D. , Boyer J. L.
Published: December 2017

To determine the permeability of the bile duct epithelium of the rat to several hydrophilic nonelectrolytes, isolated segments of rat bile duct (1-2 cm) were perfused with Ringer solution in situ. [14C]urea, [14C]erythritol, [14C]sucrose, or [3H]inulin was administered intravenously, and drops of duct perfusate were collected. Perfusate-to-plasma ratios for each solute were inversely related to their molecular weight (MW): inulin [0.13 +/- 0.06 (SD)], sucrose (0.20 +/- 0.08), erythritol (0.32 +/- 0.11), and urea (0.34 +/- 0.13). Permeability coefficients (P) expressed in cm.s-1 X 10(5) were determined for inulin (4.5 +/- 1.5), sucrose (8.5 +/- 2.6), erythritol (12.6 +/- 3.9), and urea (15.8 +/- 1.6). These values vary directly with their respective nonaqueous-aqueous partition coefficients (K) and inversely with their MW. Although P is directly related to K in both olive oil and isobutanol systems, the bile duct behaves as if its permeability barrier is more hydrophilic than isobutanol. These results indicate that the inert solutes urea, erythritol, sucrose, and inulin cross the epithelium of the rat bile duct by a polar route, possibly via intercellular junctions, and that erythritol may not be an ideal marker of canalicular bile flow.
Intestinal filtration-secretion due to increased intraluminal pressure in rabbits
Authors: Swabb E. A. , Hynes R. A. , Marnane W. G. , McNeil J. S. , Decker R. A. , Tai Y. H. , Donowitz M.
Published: December 2017

The mechanism of changes in small intestinal transport due to acutely increased intraluminal hydrostatic pressure (IHP) was investigated in detail using perfused in vivo rabbit intestinal segments. IHP affected passive transport in vivo by increasing effective mucosal surface area in the small intestine (indicated by 3HOH transport and tissue architectural changes) and increasing small intestinal permeability (indicated by a proportionately greater increase in mannitol than erythritol secretory clearance). IHP did not alter ileal blood flow rate measured by radioactive microspheres, despite grossly evident venous dilatation, or active intestinal transport in the ileum as measured by a) in vitro ion transport in the absence of elevated hydrostatic pressure, b) mucosal adenylate cyclase or Na-K-ATPase activities, and c) glucose-stimulated water and electrolyte absorption. Acutely increased IHP appears to influence the hydrodynamics of the mucosal microcirculation in the rabbit ileum to produce a driving force for passive filtration-secretion, which is associated with and possibly augmented by increased tissue permeability and effective surface area.
Gastric emptying and postprandial duodenogastric reflux in pylorectomized dogs
Authors: Muller-Lissner S. A. , Sonnenberg A. , Schattenmann G. , Hollinger A. , Siewert J. R. , Blum A. L.
Published: December 2017

A two-marker technique was used to determine gastric emptying rate and postprandial duodenogastric reflux rate without transpyloric intubation. The fractional gastric emptying rate in five dogs with normal pylorus was 3.0 +/- 0.3 (SE) X 10(-2)/min. In three dogs with circular pylorectomy, it was 5.8 +/- 0.8 X 10(-2)/min (P less than 0.01). The duodenogastric reflux rates were 0.72 +/- 0.23 (SE) ml/min and 3.21 +/- 0.97 ml/min. (P less than 0.05). The percentage of the test meal that by to-and-fro movements across the pylorus was emptied more than once was 2.3 +/- 1.0 (SE) in normal dogs and 15.5 +/- 2.4 after pylorectomy (P less than 0.005). Because the higher emptying rate was accompanied by more to-and-fro movements, the amount of the meal remaining in the stomach, and thus net gastric emptying, was similar in both groups. It is concluded that pylorectomy increases both reflux rate and emptying rate. This effect on emptying can only be detected by a method that includes the measurement of to-and-fro movements across the pylorus. The pylorus thus appears to prevent postprandial duodenogastric reflux and to slow gastric emptying.
Gastric and duodenal HCO3- transport in vitro: effects of hormones and local transmitters
Authors: Flemstrom G. , Heylings J. R. , Garner A.
Published: December 2017

Luminal application of acid was recently shown to stimulate surface epithelial HCO3(-) transport in stomach and duodenum. Effects of some potential transmitters of this response were therefore studied in amphibian gastric fundic and proximal duodenal mucosa in vitro. Duodenal HCO3- transport, which could be titrated directly, was stimulated by dibutyryl cAMP (DBcAMP, 10(-6) M), the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (10(-6) M), noradrenaline (10(-6) M), pancreatic glucagon (10(-8) M), and gastric inhibitory peptide (GIP, 10(-10) M). Stimulation by glucagon, but not by prostaglandin E2 (PGE2, 10(-6) M), required Cl- in the luminal solution and was prevented by furosemide (10(-3) M). This suggests that glucagon may affect HCO3(-)-Cl- exchange at the luminal membrane while transport stimulated by prostaglandins may be electrogenic. Stimulatory effects of glucagon and PGE2 were also additive. Gastric HCO3- transport, studied in tissues after inhibition of H+ secretion by histamine H2-antagonists, clearly differed from duodenum in that noradrenaline and GIP were inhibitory and DBcAMP was without effect. Stimulation of gastric HCO3- transport was observed with glucagon (10(-8) M), natural cholecystokinin (CCK, 10(-8) M), and CCK octapeptide (10(-7) M), CCK preparations had no effect in the duodenum. Although tested over a wide range of concentrations, no effect on either duodenal or gastric HCO3- transport was observed with histamine, pentagastrin, tetragastrin, urogastrone, ACTH, bombesin, motilin, secretin, serotonin, somatostatin, substance P, or vasoactive intestinal peptide.
Biphasic development of pentagastrin sensitivity in rat stomach
Authors: Garzon B. , Ducroc R. , Onolfo J. P. , Desjeux J. F. , Geloso J. P.
Published: December 2017

Rat stomach sensitivity to pentagastrin was examined in fetal (days 19--21) and newborn (5--day-old) preparations in vivo and in vitro. Gastric acidification in vivo was expressed as the gastric content pH and in vitro as the net transepithelial H+ fluxes determined in an Ussing chamber. In both preparations, fetal stomach first responded to pentagastrin on day 20. Dose-dependent H+ secretion was demonstrated in vitro for pentagastrin concentrations of 10(-8) to 10(-6) M, with half-maximal stimulations at 1.9 x 10(-7) and 4 x 10(-7) M on days 20 and 21, respectively. In contrast, isolated fundic mucosa of 5-day-old rat pups exhibited very low H+ secretion rates, and pentagastrin did not significantly stimulate acid output. Fetal serum immunoreactive gastrin was detected as early as day 16 in fairly constant concentrations (about 77.5 pg eq synthetic human gastrin/ml). These results indicate that, although immunoreactive gastrin is present in serum as early as day 165, pentagastrin does nt stimulate acid secretion until day 20 when fetal stomach exhibits active H+ secretion and decreased passive permeability. Pentagastrin sensitivity disappears during the 1st days of extrauterine life. These findings strongly suggest that the development of pentagastrin sensitivity in rat stomach is biphasic.
Mechanism of cholinergic regulation of electrolyte transport in rat colon in vitro
Authors: Zimmerman T. W. , Dobbins J. W. , Binder H. J.
Published: December 2017

Cholinergic agonists inhibit sodium and chloride absorption in the intestine and often produce secretion. To determine the mechanism of cholinergic regulation of intestinal electrolyte transport, the effects of bethanechol on ion transport were studied in the rat colon in vitro. The addition of 1 mM bethanechol produced an initially large but short-lived increase in short-circuit current (Isc) (171 +/- 19 microA/cm2). Bethanechol decreased net sodium and net chloride absorption (2.5 +/- 0.5 and 2.9 +/- 0.9 mueq . h-1 . cm-2, respectively) and increased Isc (0.8 +/- 0.3 mueq . h-1 . cm-2) during the steady-state period. All these effects were inhibited by 1 microM atropine, which alone had no effect on ion transport. The removal of either sodium or chloride also inhibited the effect of bethanechol. cAMP content did not increase in isolated enterocytes incubated with bethanechol; however, calcium removal from the serosal bathing solution inhibited the bethanechol-induced changes in ion transport. These results indicate that cholinergic muscarinic agonists alter sodium and chloride transport in the colon by inhibiting coupled NaCl absorption by a calcium-dependent, non-cAMP-mediated process.
Cyclic nucleotide antagonists of cholecystokinin: structural requirements for interaction with the cholecystokinin receptor
Authors: Barlas N. , Jensen R. T. , Beinfeld M. C. , Gardner J. D.
Published: December 2017

Previously, we have found that, in pancreatic acini, butyryl derivatives of cGMP antagonize the action of cholecystokinin by inhibiting binding of the peptide to its membrane receptors. In the present study, we found that derivatives of cAMP and cIMP can also inhibit binding of cholecystokinin as well as its actions on acinar cell function. Moreover, the inhibition caused by cyclic nucleotide derivatives did not require the presence of a butyryl moiety, because certain 8-bromo-cyclic nucleotides also inhibited the interaction of cholecystokinin with its receptors. Cyclic nucleotide derivatives can also increase pancreatic enzyme secretion; however, for the various cyclic nucleotides tested, there was no apparent correlation between their abilities to stimulate enzyme secretion and their abilities to antagonize the actions of cholecystokinin. Finally, cyclic nucleotide derivatives also inhibited binding of 125I-cholecystokinin to antibodies that were specific for the biologically active, C-terminal region of cholecystokinin. Thus, certain cyclic nucleotide derivatives possess a conformational structural which resembles that of the biologically active portion of cholecystokinin, and this structural similarity accounts for the abilities of these nucleotide derivatives to interact with cholecystokinin receptors and, by so doing, to inhibit the action of cholecystokinin on its target tissues.
Bile acid and bile salt disrupt gastric mucosal barrier in the dog by different mechanisms
Authors: Duane W. C. , Wiegand D. M. , Sievert C. E.
Published: December 2017

The present study was undertaken to assess the mechanism by which protonated taurocholic acid disrupts the gastric mucosal barrier. By the criterion of lecithin solubilization, the critical micellar concentration of taurocholic acid (pH 1) was 4.5 mM, as opposed to 3.0 mM for sodium taurocholate (pH 7). In canine Heidenhain pouches, taurocholic acid significantly increased net forward diffusion of Na+ and backdiffusion of H+ at concentrations of 9, 4.5, and 3.5 mM, indicating that micelle formation was not required for disruption of the gastric mucosal barrier by this bile acid. Saturation of the 9 mM taurocholic acid solution with lecithin (and cholesterol) did not prevent disruption of the gastric mucosal barrier. At 9 mM, taurocholic acid was absorbed from the pouches at a mean rate of 1,150 +/- 115 nmol/min in contrast to an absorption rate of 225 +/- 10 nmol/min for sodium taurocholate at the same concentration. These findings indicate that, unlike ionized bile salts, disruption of the gastric mucosal barrier by taurocholic acid is mediated largely by uptake of bile acid by the gastric mucosa rather than dissolution of mucosal membrane lipids.
Permeability of intestinal capillaries: effects of fat absorption and gastrointestinal hormones
Authors: Granger D. N. , Perry M. A. , Kvietys P. R. , Taylor A. E.
Published: December 2017

The purpose of this study was to determine whether the postprandial increase of intestinal lymphatic protein flux is due to an increased capillary permeability. Intestinal lymph flow and lymph (L) and plasma (P) protein concentrations were measured at various venous pressures under control conditions, after cream feeding, and during intraluminal perfusion with a bile-oleic acid solution. The osmotic reflection coefficient (sigma d), a measure of capillary permeability that is independent of surface area, was estimated under all conditions, assuming sigma d = 1 - L/P at high capillary filtration rates. The results acquired indicate that cream feeding and intraluminal perfusion with bile-oleic acid significantly increases intestinal capillary permeability. Pretreatment with indomethacin and antihistamines did not alter the permeability increase induced by intraluminal bile-oleic acid. Intra-arterial infusion of cholecystokinin and secretin did not increase intestinal capillary permeability. These studies indicate that the postprandial increase in intestinal lymphatic protein flux is due at least in part, to an increase in capillary permeability. Cholecystokinin, secretin, histamine, and prostaglandins do not appear to mediate the increased intestinal capillary permeability during fat absorption.
alpha 2-Adrenergic receptor regulation of ion transport in rabbit ileum
Authors: Chang E. B. , Field M. , Miller R. J.
Published: December 2017

Catecholamines are known to decrease short-circuit current (Isc), stimulate NaCl absorption, and inhibit HCO3 secretion in rabbit ileal mucosa in vitro. These effects appear to be mediated by alpha-adrenergic receptors because they are partially blocked by phentolamine and not by propranolol. To further characterize this receptor system, we determined the interactions of epinephrine (Epi) with alpha-subtype-selective antagonists. Prazosin (PZ), a specific alpha 1-antagonist, did not alter the Epi dose-response curve at concentrations up to 10(-5) M. Yohimbine (YO), a specific alpha 2-antagonist, completely inhibited the Epi effect on Isc. At 10(-5) M, YO increased by 70-fold the concentration of Epi required to produce a half-maximal effect (ED50; from 1.4 X 10(-7) M to 10(-5) M). YO and PZ by themselves had no significant effect on Isc in concentrations up to 10(-5) M. Clonidine, a specific alpha 2-agonist, decreased Isc with an ED50 similar to that of Epi; its effect was blocked by YO but not by PZ. Two alpha 1-selective agonists, methoxamine and phenylephrine, only caused a decrease in Isc in doses greater than 10(-5) M. This effect was reversed by YO but not by PZ. The effects of YO and PZ on Epi-modified Cl fluxes were also determined. YO completely aborted the effects of Epi on net Cl flux. No significant effects were seen with PZ. We conclude that the effects of Epi on ileal ion transport are mediated by a specific alpha 2-adrenergic receptor present in ileal mucosa and that no physiologic alpha 1-receptor function can be demonstrated.
Relationship of cholecystokinin receptor binding to regulation of biological functions in pancreatic acini
Authors: Sankaran H. , Goldfine I. D. , Bailey A. , Licko V. , Williams J. A.
Published: December 2017

Cholecystokinin (CCK) was conjugated to 125I-Bolton-Hunter reagent (125I-BH-CCK), and the binding of this ligand to CCK receptors in isolated mouse pancreatic acini was correlated with the regulation by CCK of both amylase release and the transport of 2-deoxyglucose and alpha-aminoisobutyric acid. Stimulation of amylase release by CCK was biphasic. At low CCK concentrations (less than 200 pM), amylase release was progressively stimulated, whereas at higher CCK concentrations (greater than 200 pM), amylase release was progressively reduced. In contrast, stimulation of 2-[3H]deoxyglucose transport and inhibition of alpha-[3H]aminoisobutyric acid transport were monophasic, being one-half maximal at 0.85 and 0.44 nM, respectively. Under incubation conditions identical to those employed for measuring biological functions, the binding of 125I-BH-CCK to receptors in acini was rapid and reversible. Competition-inhibition curves and Scatchard plots of equilibrium binding were compatible with two orders of binding sites. Employing a computer program for analysis of multiple binding sites, a high-affinity, low-capacity binding component having a Kd of 26 pM and a lower-affinity, higher-capacity binding component having a component Kd of 2.2 nM were resolved. Regulation of 2-[3H]deoxyglucose and alpha-[3H]aminoisobutyric acid uptake appeared, therefore, to be the result of fractional occupancy of the lower-affinity CCK receptors. Regulation of amylase released was more complex and appeared to be due to the concomitant occupancy of both the high- and low-affinity CCK receptors.
Mechanism of Cl- translocation across small intestinal brush-border membrane. I. Absence of Na+-Cl- cotransport
Authors: Liedtke C. M. , Hopfer U.
Published: December 2017

Kinetic predictions from a putative Na+-Cl- cotransport system were tested in vesicles of isolated rat intestinal brush-border membranes. For the conditions of isotope exchange at equilibrium, the model predicts activation of the Na+ and Cl- exchange rates by increasing concentrations of the counterion, at least for concentrations well below the Km of the counterion. When Cl- was the test ion (150 mM), K+ plus monactin replaced Na+. When Na+ was the test ion (150 mM), SO42(-) replaced Cl-. Contrary to the predictions of the cotransport model, the velocities of Na+ and Cl- exchange were constant regardless of the concentration of the putative cosubstrates Cl- and Na+, respectively. Cl- transport in the isolated vesicles was carrier mediated as judged by the criterion of saturability of transport (Km = 255 mM), and the pathways involved in net NaCl movements accounted for minimally 70 and 40% of the Na+ and Cl- exchange rates, respectively. These findings exclude a significant contribution of a Na+-Cl- cotransport mechanism to NaCl uptake across the intestinal brush-border membranes in the concentration range tested, i.e., above 25 mM. The findings are, however, consistent with a double exchange of Na+ for H+ and of Cl- for OH- (HCO3(-). A Donnan potential of 10 mV (inside negative) can explain differences in the equilibrium uptake of Na+, anions, and glucose by intestinal brush-border membranes.
Unstirred water layer in canine jejunum
Authors: Ryu K. H. , Grim E.
Published: December 2017

The thickness of the unstirred water layer in in vivo-lavaged canine jejunum has been estimated by observations on the kinetics of entrance of [14C]inulin into the intervillus space (IVS) from the luminal fluid. Concentrations of the inulin in the IVS at three different levels (upper, 350 micrometers; middle, 250 micrometers; and lower, 250 micrometers) were determined as a function of duration of lavage. The concentrations rose slowly, indicating that there was little or no convective mixing of the fluid between the villi. After 1-2 h of lavage, mean concentrations in the IVS were three to seven times higher than in the lavage fluid, indicating that water absorption occurred from the IVS and that solvent drag as well as diffusion played a role in the entrance of inulin into the IVS. Because the concentration was always greatest at the uppermost level of the IVS, water absorption from the IVS must have been restricted to that level. Analysis of the data also required the inclusion of a small secretory stream (5% of the absorptive flow) from the crypts to explain the experimental observations. The results demonstrate that substances absorbed into the villus tips must penetrate an unstirred layer of 500-1,000 micrometers; for those absorbed into the lateral surfaces of the villi, an additional barrier of as much as 800 micrometers exists.
Regulation of intestinal goblet cell secretion. I. Role of parasympathetic stimulation
Authors: Specian R. D. , Neutra M. R.
Published: December 2017

The in vivo effects of the parasympathomimetic drug pilocarpine on rat intestinal goblet cells were analyzed by autoradiography, light microscopy (LM), and electron microscopy (EM). Pilocarpine accelerated the release of mucus by compound exocytosis from crypt (but not surface) goblet cells throughout the small and large intestine. Pilocarpine-induced mucus secretion was blocked by atropine alone in ileum and colon, but total inhibition in proximal small intestine required a combination of atropine and tubocurarine. The sensitivity of morphological-autoradiographic methods for detection of goblet cell secretion was compared with that of a biochemical detection method, separation of labeled high-molecular-weight glycoproteins by Sepharose 4B gel filtration of luminal washings. Even when secretion of labeled mucus by compound exocytosis was clearly demonstrated by LM, EM, and autoradiography, gel filtration assay of luminal washings from pilocarpine-injected rats failed to reveal an increase in labeled high-molecular-weight glycoproteins. Autoradiographs of mucosal tissue after luminal washing showed that newly secreted, labeled mucus was retained in the crypts and was thus unavailable to the biochemical assay. Thus, direct observation of exocytosis in individual goblet cells provides a qualitative, but sensitive, assay for short-term acceleration of intestinal mucus secretion.
Regulation of intestinal goblet cell secretion. II. A survey of potential secretagogues
Authors: Neutra M. R. , O'Malley L. J. , Specian R. D.
Published: December 2017

The factors that regulate the rate of mucus secretion in intestinal goblet cells are only partially defined. Autoradiographic and ultrastructural studies demonstrated that muscarinic cholinergic agents accelerate the exocytosis of mucus from goblet cells in the crypts throughout the small and large intestine, both in vivo and in mucosal organ culture. The present study seeks to identify other factors that may alter mucous secretory rates. Mucosal explants were exposed to potential secretagogues and inhibitors in the organ-culture system and analyzed by light and electron microscopy, alpha- and beta-Adrenergic agents, gastrointestinal regulatory peptides, serotonin, histamine, and dibutyryl cyclic nucleotides were tested over wide concentration ranges. With the exception of histamine, none of these agents accelerated or inhibited the exocytosis of mucous granules. Histamine was effective at the concentration of 10(-4) M and induced rapid, compound exocytosis by crypt goblet cells in mucosal explants from the colon but not from small intestine. The response to histamine was unaffected by atropine. Goblet cells on the mucosal surface released mucus by compound exocytosis when exposed to mustard oil, a nonspecific chemical irritant, but not when exposed to histamine or cholinergic agents.
Structural requirements for action of cholecystokinin on enzyme secretion from pancreatic acini
Authors: Villanueva M. L. , Collins S. M. , Jensen R. T. , Gardner J. D.
Published: December 2017

Using dispersed acini prepared from guinea pig pancreas, we found that the structural requirements for cholecystokinin-induced stimulation of amylase secretion are the same as those for cholecystokinin-induced desensitization of amylase secretion. 1) The relative potencies with which various C-terminal fragments of cholecystokinin cause stimulation are the same as their relative potencies for causing desensitization. 2) With each fragment tested, desensitization occurs with peptide concentrations that are supramaximal for causing stimulation of amylase secretion. 3) Fragments of cholecystokinin less efficacious in causing supramaximal inhibition of amylase secretion are also less efficacious in causing desensitization of amylase secretion. In contrast, there is no obvious fixed relation between the ability of a cholecystokinin fragment to cause stimulation of enzyme secretion and its ability to cause residual stimulation of enzyme secretion. Cholecystokinin and its C-terminal hexadecapeptide are 25-40% more efficacious than the C-terminal decapeptide, octapeptide, and heptapeptide in causing residual stimulation, and the C-terminal pentapeptide and tetrapeptide caused no detectable residual stimulation. The C-terminal tetrapeptide, however, can prevent as well as reverse the residual stimulation caused by other cholecystokinin fragments, and the ability of the tetrapeptide to prevent cholecystokinin-induced residual stimulation is itself fully reversible.
Prevention of phenylbutazone ulcer in the rat by glucose: role of a glycoprivic receptor system
Authors: Mersereau W. A. , Hinchey E. J.
Published: December 2017

The mechanism by which the extragastric administration of phenylbutazone (PBZ) and other nonsteroid anti-inflammatory drugs induce a vagally mediated gastric hypercontractile response and ulceration is unknown. Glucose administration has been reported to protect the rat and the monkey from the ulcerogenic action of aspirin. It was postulated that by uncoupling oxidative phosphorylation PBZ might stimulate an energy-sensitive receptor system that results in the gastric contractile response. Glucose feeding or intravenous infusion was seen to prevent or abolish the gastric contractile response to the intraileal injection of 22.5 mg of PBZ in cervical-sectioned rats with miniature gastric balloons. Glucose treatment also significantly reduced ulceration and hemorrhage. Fructose infusion was somewhat less effective. Mannitol infusion had no effect on the PBZ-induced gastric contractile activity, and all animals developed severe ulceration and hemorrhage. Blood glucose levels fell significantly in starved rats treated with PBZ. Glucose feeding and glucose or fructose infusion prevented or reduced this effect. It is suggested that by alleviating the "glucoprivic state" induced by PBZ glucose abolishes the gastric contractile response and prevents ulceration and hemorrhage.
Role of capillary recruitment in the regulation of intestinal oxygenation
Authors: Shepherd A. P.
Published: December 2017

Increasing evidence indicates that capillary recruitment plays a significant role in regulating the oxygenation of intestinal tissue. Measurements of permeability-surface area product (PS) and capillary filtration coefficients (Kf) in isolated perfused gut loops indicate that changes in capillary density modulate oxygen extraction in a variety of experimental circumstances. Moreover, the intestinal microvasculature seems capable of independently regulating resistance and capillary exchange. Although "precapillary sphincters" have been identified in the intestine, the capillary density changes have not yet been confirmed by intravital microscopy, as they have been in skeletal muscle. Nevertheless, these changes in capillary density have quantitatively significant effects on oxygen extraction. For example, sympathetic stimulation depresses oxygen uptake in gut loops perfused at constant blood flow, presumably by reducing capillary density to such an extent that oxygen extraction becomes diffusion limited. The microvascular elements that control intestinal capillary density (presumably precapillary sphincters) are apparently under the control of neurogenic, myogenic, and local metabolic mechanisms, but the interaction among these mechanisms is poorly understood. In addition, the PS and Kf data, although well documented, could result from a redistribution of blood flow or an alteration in capillary permeability rather than a change in capillary density. Thus, the physiological mechanisms regulating capillary permeability and the intramural distribution of intestinal blood flow will have to be better understood before the role of capillary recruitment in regulating intestinal oxygenation will be firmly established.
Characteristics of intestinal glucose secretion in normal and diabetic rats
Authors: Levine G. M. , Shiau Y. F. , Deren J. A.
Published: December 2017

A method was developed to characterize and quantitate the transfer of glucose from the plasma to the intestinal lumen. In normal rats, there was a linear correlation between the blood glucose concentration and the rate of appearance of plasma glucose into the intestinal lumen perfused with Krebs-Ringer buffer (r = 0.88, P less than 0.01). Intestinal perfusion with buffers containing either mannitol, glucose, or phlorizin significantly increased the recovery of secreted glucose compared with plain buffer. Rats perfused with buffer containing mannitol or those undergoing plasma volume expansion with dextran demonstrated a change in water movement from net absorption to secretion coupled with a significant increase in glucose secretion. During luminal perfusion with a buffer containing 21 mM glucose, glucose secretion represented 14% of the net glucose absorption rate. Intestinal perfusion with phlorizin gave the highest measured recovery of glucose, probably by blocking active reabsorption of secreted glucose. A series of simultaneous perfusions performed in the jejunum and ileum revealed similar rates of glucose transfer in both segments of intestine. Measurement of glucose secretion in rats with streptozotocin diabetes gave the highest values for the plasma-to-lumen movement of glucose. Treatment with insulin reduced the blood sugar and glucose transfer rate. These data demonstrate that glucose moves bidirectionally across the rat intestine, and its secretion is a passive process.
Cholecystokinin-induced restricted stimulation of pancreatic enzyme secretion
Authors: Barlas N. , Jensen R. T. , Gardner J. D.
Published: December 2017

During a 5-min incubation with increasing concentrations of cholecystokinin, enzyme secretion from pancreatic acini increased, became maximal at 1 nM cholecystokinin, and then decreased progressively to 65% of maximal with concentrations of cholecystokinin above 1 nM. During a 20-min incubation with increasing concentrations of cholecystokinin, enzyme secretion increased, became maximal at 0.3 nM cholecystokinin, and then decreased progressively to 40% of maximal with concentrations of cholecystokinin above 0.3 nM. The configuration of the dose-response curve for cholecystokinin-stimulated enzyme secretion did not change when the incubation time was increased from 20 to 30, 45, or 60 min. Concentrations of cholecystokinin that were supramaximal for stimulating enzyme secretion abolished the stimulation caused by other secretagogues that promote mobilization of cellular calcium (e.g., carbamylcholine, bombesin, physalaemin, or A23187), as well as that caused by secretagogues that elevate cellular cAMP (e.g., vasoactive intestinal peptide or secretin). The submaximal stimulation caused by supramaximal concentrations of cholecystokinin reflects what we have termed "restricted stimulation" of enzyme secretion. Secretion is than the basal rate of release and is "restricted" in the sense that enzyme release is submaximal and cannot be increased by adding another secretagogue.
Stimulation of pancreatic acinar secretion: increases in cytosolic calcium and sodium
Authors: O'Doherty J. , Stark R. J.
Published: December 2017

Na+-selective and Ca2+-selective microelectrodes were used to examine the ionic mechanisms regulating acetylcholine (ACh) stimulation of pancreatic secretion. The cytosolic concentrations of free ionized Na+ and Ca2+ ([Na]i, [Ca]i) were determined in unstimulated acinar cells to be 10.5 +/- 0.4 mM and 0.43 +/- 0.03 microM, respectively. By measuring the induced changes in intracellular Ca2+, Na+, and membrane potentials (ECa, ENa, Em), we were able to demonstrate that 5 X 10(-8) M ACh depolarized Em by 4.3 +/- 0.2 mV and increased [Na]i and [ca]i to 12.2 +/- 0.3 mM and 0.58 +/- 0.02 microM, respectively. Stimulation with ACh at concentrations ranging from 10(-8) to 10(-5) M increased [Ca]i from 0.4 microM to between 0.5 and 1.0 microM. Amylase release reached a maximum at 10(-7) M ACh stimulation and progressively decreased at higher concentrations of stimulus. Increasing the stimulus above an optimal concentration appears to reduce or inhibit enzyme release. These experiments provide direct evidence supporting the concept that acinar cell secretion is triggered by increases in [Ca]i and of calcium's ability to act as primary intracellular mediator. Stimulation after removal of extracellular Ca2+ eliminated the increase in [ca]i that is usually observed in secreting cells, while producing the normal depolarization of Em and increase in [Na]i. These studies demonstrate the increases in [Ca]i are derived from an increase in membrane permeability to Ca2+ and the ability of ACh to depolarize the Em by a transmembrane movement of Na+ that is independent of the change in intracellular Ca2+.
Biliary excretion of [3H]-25-hydroxyvitamin D3 in the vitamin D-depleted rat
Authors: Gascon-Barre M.
Published: December 2017

The biliary excretion of [3H]-25-hydroxyvitamin D3 ([3H]25(OH)D3) was studied in vitamin D-depleted female rats over a 3-h period after intravenous or intraduodenal administration of intact [3H]25(OH)D3 and after the intraduodenal readministration of the [3H]25(OH)D3-derived biliary material. In each group four doses of 25(OH)D3 were administered (0.25, 2.5, 25, and 250 nmol/100 g). Over the dose range studied, the biliary excretion of [3H]25(OH)D3 could not be saturated, indicating that the biliary excretion of 25(OH)D3 is a reliable detoxification mechanism in circumstances of 25(OH)D3 intoxication. Analysis of plasma, liver, and bile suggests that the canalicular membrane seems to be rate limiting in the biliary excretion of 25(OH)D3. The intraduodenal administration of biliary excretion compounds derived from [3H]25(OH)D3 showed that they are efficiently reexcreted in newly secreted bile, confirming the existence of an enterohepatic circulation for 25(OH)D3. In this group of animals, however, the plasma analysis indicates that these compounds reach the systemic circulation in insignificant quantities, suggesting that the enterohepatic circulation probably plays a limited role in the body 25(OH)D3 economy.
Horseradish peroxidase transport across adult rabbit jejunum in vitro
Authors: Heyman M. , Ducroc R. , Desjeux J. F. , Morgat J. L.
Published: December 2017

Quantification and functional characteristics of intact protein uptake, metabolic behavior, and transmission across the intestinal wall were examined using horseradish peroxidase (HRP) transport through adult rabbit jejunum. Transepithelial HRP fluxes were determined with a modified Ussing apparatus. In Ringer solution, no significant difference was found between intact HRP fluxes from mucosa to serosa (JHRPm leads to s) and those from serosa to mucosa (JHRPs leads to m) (3.12 +/- 0.58 and 3.48 +/- 0.45 pmol.h-1.cm-2, respectively). In the presence of 10 mM glucose, slight net secretion was noted. The transport mechanism was shown to be sensitive to metabolic inhibitors, colchicine, and ammonia. Intracellular transfer and catabolism were estimated by measuring transepithelial fluxes of tritiated horseradish peroxidase (J[3H]HRP). Net absorption of 3H equivalent HRP (91 +/- 32 pmol.h-1.cm-2) occurred chiefly in the form of tritiated degraded catabolites of 2-4 kilodaltons. Comparison of the transepithelial fluxes of intact and 3H equivalent HRP made it possible to estimate that 97% of the HRP was degraded while crossing the tissue from mucosa to serosa and 88% while crossing from serosa to mucosa. The saturable absorption observed for JHRPm leads to s became a nonsaturable process for J[3H]HRPm leads to s. These results fit the existence of at least two functional pathways for intestinal protein transport. The main route seems to involve endocytosis, with striking intracellular degradation, possibly during passage through the lysosomal system. The HRP that escapes metabolic degradation is transported by an alternative route requiring the structural and metabolic integrity of the epithelial cells. Although this route only accounts for a small fraction of HRP transport, it may be of immunological importance.
Glucose absorption by in vitro perfused ileum of the fetal rat
Authors: Potter G. D. , Schmidt K. L. , Lester R. , Schultz S. G.
Published: December 2017

In vitro intraluminal perfusion of the fetal rat ileum at 19 and 20 days of gestation was employed to measure the rate of glucose absorption and the unidirectional fluxes of 3-O-methylglucose (3-O-MG). Fetal ileum was mounted on pipettes within an oxygenated bath and perfused with a solution containing glucose or 3-O-MG and polyethylene glycol with average molecular weight of 4,000 (PEG) as a marker substance. We verified that the PEG was not transported and did not diffuse across the fetal ileum. Scanning and electron microscopy before and after perfusion demonstrated preservation of mucosal anatomy. The rate of glucose absorption was 200 +/- 17 mumol.h-1.g-1 at 19 days and increased significantly to 378 +/- 12 mumol.h-1.g-1 at 20 days. The absence of sodium abolished this process. The flux of 3-O-MG from lumen to bath was 88 +/- 10 mumol.h-1.g-1 at 19 days and 160 +/- 16 mumol.h-1.g-1 at 20 days. Bath-to-lumen flux was -17 +/- 2 mumol.h-1.g-1 and did not vary with age. Active, rapidly developing transport of glucose and 3-O-MG is demonstrated by in vitro luminal perfusion of the fetal rat ileum at 19 days.
Sucrase metabolism in germfree rats
Authors: Olsen W. A. , Korsmo H. A.
Published: December 2017

We studied degradation of the intestinal brush-border protein sucrase-isomaltase in germfree animals as well as in ex-germfree animals and conventional controls to determine the mechanism by which intestinal bacteria alter disaccharidase levels. Our results indicate that sucrase-isomaltase turnover is as rapid in germfree animals as in the other groups and are consistent with surface removal of disaccharidases by pancreatic proteases under physiological conditions. Our results also suggest that elevated disaccharidase levels in germfree animals are in large part the consequence of an increased number of mature enterocytes, which persists for at least 2 wk after exposure of animals to a conventional microbial flora.
Response of the exocrine pancreas to quantitative and qualitative variations in dietary lipids
Authors: Saraux B. , Girard-Globa A. , Ouagued M. , Vacher D.
Published: December 2017

In the rat, pancreatic amylase and, to a lesser extent, lipase adapt quantitatively to the amount of their respective substrates in the diet by an increase in specific activity and total contents (range of variation, fivefold for amylase and twofold for lipase). Colipase responded to protein intake (r = 0.85, P less than 0.01) and not to lipids provided protein intake was below 3.5 g or above 6.0 g. With this latter amount of protein, a maximal level was obtained, even with 2% lipid in the diet. Between 3.5 and 6.0 g, lipid intake was found to modulate colipase in parallel with lipase. When different types of fat were compared, the degree of saturation was found to have no impact on lipase, colipase, and amylase. Diets containing medium-chain triglycerides (C8-C10) did not maximally increase specific activity and total content of lipase and colipase, whereas they did not repress amylase as much longer chain triglycerides did. With coconut oil (45% C12), lipase was maximally stimulated but amylase was not maximally repressed, showing that the regulation of the hydrolases may be partly reciprocal and partly independent.