bluuebunny/crossref_metadata_2025 huggingface dataset:
Measuring rates of O2 uptake in periportal and pericentral regions of liver lobule: stop-flow experiments with perfused liver
Authors: Matsumura T. , Thurman R. G.
Published: December 2017

Rates of oxygen uptake in periportal and pericentral regions of the hemoglobin-free perfused rat liver were measured successfully for the first time with a miniature oxygen electrode (tip diameter, 50–60 microns) by stopping the flow of perfusate and measuring the rate of decrease of oxygen concentration on the surface of the liver. Rates of oxygen uptake in periportal and pericentral areas were 131 +/- 9 (mean +/- SD) and 56 +/- 14 mumol X g-1 X h-1 in livers from fed, phenobarbital-treated rats, respectively. In livers from fasted rats, rates of O2 uptake of 141 +/- 12 and 89 +/- 11 mumol X g-1 X h-1 were observed in periportal and pericentral regions, respectively. Similar data were obtained in livers from normal rats. Thus, periportal hepatocytes have higher rates of oxygen uptake than pericentral cells in both the fed and fasted states. Rates of oxygen uptake were not affected in periportal regions by fasting. In contrast, rates of oxygen uptake by hepatocytes in pericentral areas were significantly (P less than 0.001) greater in livers from fasted than from fed rats. This significant increase in oxygen uptake in pericentral hepatocytes as a result of fasting is consistent with the hypothesis that glycolysis occurs predominantly in pericentral regions of the liver lobule.
Intestinal transudation, secretion, and lymph flow during volume expansion in the rat
Authors: Lee J. S.
Published: December 2017

The effect of volume expansion by intravenous infusion of saline on the rate of intestinal lymph flow (JL), serosal surface transudation (JT), and secretion (JS) from upper jejunum was determined. During saline infusion there was a large increase in JS and JT but a small increase in JL due to increased capillary filtration. About 20% of JL from the main intestinal lymph duct originated from the intestine and the rest from the mesenteric pedicle. JL (corrected for pedicle lymph flow), JT, and JS were estimated to account for 10, 30, and 60% of capillary filtrate from the intestine, respectively. Neither lymph nor secretion contained measurable protein, but transudation had a high protein concentration about half of that in the plasma. From these findings it is inferred that probably both JL and JS were derived from the capillary filtrate of mucosa and submucosa vascular beds and JT from that of muscular vascular bed and that capillaries and venules in the mucosa restricted the passage of protein molecules while those of the intestinal muscular tissue were highly permeable to protein.
Regionally perfused fatty acids augment acid-induced canine pancreatic secretion
Authors: Fink A. S. , Luxenburg M. , Meyer J. H.
Published: December 2017

To study interactions between hydrochloric acid and fatty acids on pancreatic secretion, six dogs with chronic gastric, pancreatic, and small intestinal cannulas received various combinations of the following intestinal perfusates: 20, 40, and 80 mM hydrochloric acid, oleate, dodecanoate, or 0.15 M saline. Regional intestinal perfusion (a proximal segment measuring 45 cm from the pancreatic duct versus the remaining small bowel) was utilized to separate the aqueous acid and lipid solutions. Both oleate and dodecanoate augmented the bicarbonate output induced by intraluminal acidification. In other experiments, intraluminal oleate, when combined with exogeneous intravenous secretin (12.5-900 ng . kg-1 . h-1), potentiated the secretin-induced bicarbonate output at low secretin doses. Dodecanoate also increased secretin-induced bicarbonate output. In all of these studies, protein outputs were increased by intestinal fatty acids. It is concluded that intestinal fatty acids can enhanced acid-induced canine pancreatic secretion.
Morphine versus motilin in the initiation of migrating myoelectric complexes
Authors: Sarna S. , Condon R. E. , Cowles V.
Published: December 2017

The roles of morphine and motilin in the initiation of migrating myoelectric complex (MMC) cycles were studied in four conscious dogs. Morphine or motilin boluses and morphine or motilin infusions were administered to healthy conscious dogs, each implanted with a set of 12 electrodes on the small intestine. The durations of premature phase IIIs initiated by morphine and motilin were not significantly different from each other or from control values. The premature phase IIIs initiated by morphine boluses propagated significantly faster over the 1st half of small intestine than the control or motilin bolus-initiated phase IIIs. The latent period for the onset of phase IIIs after morphine was not significantly different from that after motilin. Morphine infusion (50 micrograms X kg-1 X h-1) generally initiated one or two premature MMC cycles and then disrupted further MMC cycling. Motilin infusion (0.3 microgram X kg-1 X h-1) initiated one premature MMC cycle, and then further cycling continued at the normal rate. We conclude that morphine acts on both the MMC-initiating and MMC-propagating mechanisms, whereas motilin acts only on the MMC-initiating mechanism. Morphine has both excitatory and disruptive effects on MMC cycling, while motilin has only excitatory effects.
Regulation of cytosolic free Ca2+ concentration in acinar cells of rat pancreas
Authors: Streb H. , Schulz I.
Published: December 2017

Ca2+ uptake into isolated exocrine pancreatic cells with highly permeable plasma membrane was determined by measuring the decrease in free Ca2+ concentration of the surrounding incubation medium with a Ca2+-specific electrode. In the presence of Mg-ATP and respiratory substrates the free Ca2+ concentration of the incubation medium decreased rapidly after addition of leaky cells until a stable medium free Ca2+ concentration of 4.2 +/- 0.1 X 10(-7) mol/l was obtained. Changes in the medium free Ca2+ concentration at steady state by addition of Ca2+ or EGTA were buffered by cellular uptake or release, respectively, until the steady-state free Ca2+ concentration was reestablished. When nonmitochondrial Ca2+ uptake was determined in the presence of a combination of mitochondrial inhibitors (10(-5) mol/l antimycin, 5 X 10(-6) mol/l oligomycin, and 10(-2) mol/l azide), the rate of uptake was considerably reduced, while the steady-state concentration was unaltered. In contrast, mitochondrial uptake that could be observed in the presence of the ATPase inhibitor vanadate (2 X 10(-3) mol/l) proceeded at the same rate as the control, but the minimal medium free Ca2+ concentration reached was 2.4 +/- 0.1 X 10(-7) mol/l higher than the control. Addition of secretagogues at steady-state free Ca2+ concentration resulted in a Ca2+ release of 0.73 +/- 0.08 nmol/mg protein. The increase in medium free Ca2+ concentration was entirely transient and followed by reuptake to the prestimulation level. The data indicate that a cytosolic free Ca2+ concentration of 4 X 10(-7) mol/l can be regulated in pancreatic acinar cells by a nonmitochondrial Mg2+-dependent Ca2+ pool.
Amino acid inhibition of bile acid uptake by isolated rat hepatocytes: relationship to dissipation of transmembrane Na+ gradient
Authors: Blitzer B. L. , Ratoosh S. L. , Donovan C. B.
Published: December 2017

The effects of amino acids on bile acid uptake were studied in isolated rat hepatocytes. The Na+-dependent amino acid L-alanine inhibited [14C]taurocholate uptake in a nonlinear fashion (IC50, approximately 7 mM). Kinetic studies showed that alanine (30 mM) reduced the Vmax for taurocholate uptake from 1.7 +/- 0.1 to 1.1 +/- 0.1 nmol . mg protein-1 . min-1 but did not significantly affect taurocholate Km (42 +/- 7 vs. 35 +/- 7 microM). Taurocholate uptake was also inhibited by alpha-methylaminoisobutyric acid (which shares a common Na+-dependent transport pathway with alanine but is not metabolized) and by L-glutamine (undergoes Na+-dependent hepatic uptake via a carrier distinct from that for alanine). In contrast, the Na+-independent amino acid 2-aminobicyclo(2,2,1)heptane-2-carboxylic acid had no effect on hepatocyte bile acid uptake. Alanine induced a twofold elevation of intracellular sodium concentration as determined by the steady-state uptake of 22Na. These findings suggest that Na+-dependent amino acids noncompetitively inhibit hepatocyte taurocholate uptake by dissipating the transmembrane Na+ gradient and thereby reduce the driving forces for Na+-coupled bile acid entry. Dissipation of the Na+ gradient by substrates that undergo Na+-dependent hepatic transport may represent a novel mechanism of bile secretory failure.
Muscarinic receptors and guanylate cyclase in mammalian gastric glandular cells
Authors: Culp D. J. , Wolosin J. M. , Soll A. H. , Forte J. G.
Published: December 2017

To investigate the involvement of guanosine 3',5'-cyclic monophosphate (cGMP) in the cholinergic activation of gastric acid and pepsinogen secretion, we studied the subcellular and cellular relation between particulate guanylate cyclase and muscarinic cholinergic receptor sites. Subcellular fractionation of homogenates from rabbit gastric glands showed that particulate guanylate cyclase and muscarinic receptors were distributed in similar patterns, which differed from the pattern found for Na+-K+-ATPase, a marker for basal-lateral plasma membranes. Assuming a basal-lateral membrane localization for particulate guanylate cyclase and cholinergic receptors, these results suggested a heterogeneity of glandular basal-lateral membranes. The distributions of these markers among fractions enriched in isolated canine parietal or chief cells were also followed. Na+-K+-ATPase correlated with parietal cell distribution (r = 0.86) and guanylate cyclase with chief cell distribution (r = 0.76). The distribution of quinuclidinyl benzilate (QNB) binding sites indicated association of muscarinic receptors with both cell types. The similar subcellular and cellular distributions of guanylate cyclase and QNB binding sites may reflect a functional relationship of these markers in muscarinic-activated pepsinogen secretion. As seen in most other tissues, gastric glandular guanylate cyclase was not stimulated by various gastric secretagogues. We found that small changes in Ca2+ concentration, within the micromolar range, can regulate glandular guanylate cyclase activity. These results are discussed in terms of the cholinergic activation of parietal and chief cell function.
Lack of interaction between acid and pepsinogen secretion in isolated gastric glands
Authors: Hersey S. J. , Miller M. , May D. , Norris S. H.
Published: December 2017

Gastric glands isolated from rabbit stomach were employed to study the relation between acid and pepsinogen secretion. The effects of adenosine and guanosine nucleotides were examined for both secretory processes. cAMP, dibutyryl cAMP (DBcAMP), and 8-bromo-cAMP (8BrcAMP) were found to stimulate both acid and pepsinogen secretion with a potency sequence of 8BrcAMP greater than DBcAMP greater than cAMP. Adenosine, ATP, and AMP were ineffective, indicating that the responses to adenosine cyclic nucleotides do not involve an adenosine receptor. 8BrcGMP was found to produce a weak stimulation of both acid and pepsinogen secretions, while GMP, cGMP, and DBcGMP were ineffective. DBcGMP was found to inhibit competitively the stimulation of pepsinogen secretion by cholecystokinin (CCK)-like peptides. No inhibition was found with cGMP or 8BrcGMP. Stimulation of pepsinogen secretion by carbachol or isoproterenol was not inhibited by DBcGMP nor was the stimulation of acid formation by CCK-like peptides. Thiocyanate inhibited acid formation but did not affect pepsinogen secretion stimulated by 8BrcAMP or carbachol, indicating that stimulation of pepsinogen secretion does not require simultaneous acid formation. Costimulation of acid formation by histamine and pepsinogen secretion by isoproterenol showed no interaction between the two secretory processes. The results are interpreted to suggest that correlations between acid and pepsinogen secretion observed in vivo do not result from direct interactions between parietal and chief cells.
Effects of gastrointestinal hormones on ileal vascular and visceral smooth muscle
Authors: Premen A. J. , Soika C. Y. , Dabney J. M. , Dobbins D. E.
Published: December 2017

Blood levels of gastrin, secretin, gastric inhibitory polypeptide (GIP), and cholecystokinin octapeptide (CCK-8) increase after a meal and may affect vascular and/or visceral smooth muscle. To study this possibility, we measured the effects of local intra-arterial infusion of these hormones on ileal perfusion pressure and intestinal wall compliance. In pentobarbital sodium-anesthetized dogs, a segment of ileum was exteriorized and vascularly perfused at constant flow with arterial blood. Wall compliance was calculated from the pressure generated by incremental changes in intraluminal volume (delta V/delta P). Postprandial blood levels of these hormones did not affect ileal perfusion pressure. However, higher blood levels of secretin and GIP did significantly lower perfusion pressure. Wall compliance was significantly increased by postprandial blood levels of secretin and GIP, while postprandial blood levels of CCK-8 decreased compliance. Gastrin was without effect on compliance. These data suggest these hormones do not contribute to postprandial ileal hyperemia. However, secretin, GIP, and CCK-8 do affect the postprandial activity of ileal visceral smooth muscle.
Further studies on sudden potential drop in gastric mucosa
Authors: Kidder G. W.
Published: December 2017

The sudden potential drop (SPD) with its associated resistance drop, previously noted during anoxia when serosal pH was slightly decreased, can also be produced by substrate deprivation and reversed by addition of substrate. During a critical portion of the response, alternate stable high and low potential difference states can be selected by current pulsing. High Ca2+ in the serosal solution prevents the SPD response, and any condition preventing an SPD response will reverse the post-SPD potential. Although pH 1 mucosal solutions do not damage the tissue, an SPD under these conditions results in permanent loss of secretory activity, apparently due to increased H+ permeability in the post-SPD state. Cl-, Rb+, and urea fluxes are unchanged by the SPD. Since gastric anoxia and mild serosal acidosis might be expected during strong sympathetic stimulation, it is notable that an SPD can be produced in vivo by anoxia or vasoconstrictive drugs under conditions apparently in agreement with the in vitro requirements. This might provide a model system for studies of stress ulcer production. An equivalent circuit model for the SPD is presented, which agrees satisfactorily with the observations.
Backdiffusion of H+ in isolated frog gastric mucosa
Authors: Durbin R. P.
Published: December 2017

Backdiffusion of H+ was studied in isolated bullfrog gastric mucosa using direct titration to evaluate changes in luminal H+ level. In resting mucosae, the resulting permeability coefficient for H+ (uncorrected for electrical effects) was 0.4 X 10(-5) cm X S-1, which is of the same order of magnitude as that estimated from data in the literature for dog and rabbit gastric mucosa in vivo. With maximal stimulation of acid secretion, backdiffusion of H+ was considerably increased. In both resting and stimulated mucosae, an increase in Cl- flux from lumen to serosa was observed to accompany H+ backdiffusion. In experiments in which electrical activity of resting mucosae was monitored, instilled H+ lowered gastric potential difference but had little effect on the normal resistance. Sudden drops in resistance and potential were observed, independent of luminal acid; after such events instilled H+ had no effect on mucosal resistance. It appears that a substantial part of H+ backdiffusion occurs as the ion pair HCl.
Electrical and mechanical activity in the lower esophageal sphincter of the cat
Authors: Zelcer E. , Weisbrodt N. W.
Published: December 2017

Transmembrane electrical activity was correlated to isometric contractile activity for strips of circularly oriented smooth muscle from the feline lower esophageal sphincter (LES). Strips first were identified mechanically as being from the LES, and then either their cellular electrical activities were monitored with microelectrodes or their mechanical activities were monitored with force-displacement transducers. The mean resting membrane potential was -40.6 +/- 1.1 (SE) mV. Transmural electrical stimulation (0.2-8 Hz) induced only hyperpolarizations that were graded and increased as the frequency of stimulation increased. Mechanically, all strips developed tone spontaneously. Electrical stimulation induced only relaxations that likewise were graded and varied directly with the frequency of stimulation. When compared quantitatively, there was a correlation between the integral of the hyperpolarization and the integral of the relaxation. Thus, the tension exerted by LES smooth muscle appears to be related to the amount of current crossing the membrane of the smooth muscle cells.
Mechanism of active potassium absorption and secretion in the rat colon
Authors: Foster E. S. , Hayslett J. P. , Binder H. J.
Published: December 2017

To characterize and contrast the active potassium absorptive and secretory processes present in the rat colon, unidirectional 42K fluxes were performed under short-circuit conditions across isolated distal (D) and proximal (P) colonic mucosa of control rats and animals with hyperaldosteronism due to sodium depletion (aldosterone group). In the control D colon there was net potassium absorption (+0.51 +/- 0.07 mueq X h-1 X cm-2). The absorptive process appears electroneutral because net potassium flux ( JK net ) was unchanged in sodium-free Ringer solution (+0.76 +/- 0.12 mueq X h-1 X cm-2), whereas short-circuit current (Isc) was reduced to zero, and in chloride-free Ringer solution. In P colon of controls, net potassium secretion was -0.19 +/- 0.02 mueq X h-1 X cm-2 and was abolished by removal of sodium but not by removal of chloride. In both P and D colon aldosterone produced active potassium secretion (-0.39 +/- 0.06 mueq X h-1 X cm-2, P less than 0.001, and -0.90 +/- 0.07 mueq X h-1 X cm-2, P less than 0.001, respectively) that was sodium and chloride dependent. Although mucosal amiloride in D colon of aldosterone animals reduced net sodium flux to zero and reversed Isc from 4.1 +/- 0.6 to -1.1 +/- 0.1 mueq X h-1 X cm-2, net potassium secretion was not affected. Thus, in the presence of amiloride, Isc is accounted for by JK net (-0.93 +/- 0.12 mueq X h-1 X cm-2). These data indicate that 1) the active potassium absorptive process is electroneutral and could be explained by a potassium-proton exchange, and 2) the potassium secretory process is stimulated by aldosterone, is not inhibited by amiloride, and probably is electrogenic.
Bioactivity of cholecystokinin analogues: CCK-8 is not more potent than CCK-33
Authors: Solomon T. E. , Yamada T. , Elashoff J. , Wood J. , Beglinger C.
Published: December 2017

We determined the relative molar potencies of structural analogues of porcine cholecystokinin (CCK-39, CCK-33, CCK-8, and caerulein). Peptide concentrations delivered in infusates or present in bathing medium were measured by radioimmunoassay. The presence of albumin prevented loss of CCK-39 and CCK-33 from solution to a greater degree than loss of CCK-8 and caerulein from solution. As much as 10-fold differences in CCK-33 and CCK-39 concentrations were seen in albumin-containing versus nonalbumin-containing infusates. The potency estimates calculated from radioimmunoassay-corrected concentrations with CCK-8 as standard (potency 1.00) were canine pancreatic secretion in vivo: CCK-39 4.1, CCK-33 2.2, and caerulein 2.1; rat pancreatic secretion in vivo: CCK-39 2.1, CCK-33 5.4, and caerulein 5.4; rat pancreatic secretion in vitro: CCK-33 1.7, and caerulein 1.2; guinea pig gallbladder contraction in vivo: CCK-33 1.3, and caerulein 0.9; and guinea pig gallbladder contraction in vitro: CCK-33 1.8, and caerulein 5.8. Our data indicate that CCK-8 is not more potent than longer analogues and suggest that larger forms of CCK may be important mediators of the biological actions of CCK.
Calcium binding by lithocholic acid derivatives
Authors: Oelberg D. G. , Dubinsky W. P. , Adcock E. W. , Lester R.
Published: December 2017

Lithocholic acid (LCA) and its sulfate (LCS) and glucuronide (LCG) derivatives are potent cholestatic agents. During the course of LCG-induced cholestasis in rats, calcium (Ca) salts of LCG precipitate in bile. To characterize the affinity of bile salts for Ca, solutions of selected bile salts were titrated with Ca. Apparent equilibrium constants (KcaBS) were determined from the unbound Ca ion concentrations that were measured spectrophotometrically with metallochromic indicators antipyrylazo III or murexide or with a Ca-selective electrode. KCaBS values were 1.12 +/- 0.04 X 10(-4) M for LCS, 2.88 +/- 0.26 X 10(-4) M for LCG, 3.09 +/- 0.21 X 10(-4) M for LCA, 1.93 +/- 0.07 X 10(-3) M for taurocholic acid (TC), 2.69 +/- 0.08 X 10(-3) M for glycocholic acid (GC), and 6.07 +/- 0.27 X 10(-3) M for taurolithocholic acid sulfate (TLCS). The KCaBS for LCG measured by a Ca-selective electrode under identical conditions was 5.53 +/- 2.75 X 10(-4) M. Comparing relative cholestatic potential with affinity for Ca, cholestatic bile salts LCS, LCG, and LCA bind Ca 10-60 times more avidly than TC, GC, and TLCS. At the unbound Ca ion concentrations of serum or bile (approx 1 mM), only LCS, LCG, and LCA would be expected to bind significant amounts of Ca.
Clearance of 9-micron spheres and rubidium in the intestinal circulation
Authors: Gelman S. , Granger D. N. , Fowler K. , Smith L. R.
Published: December 2017

Rubidium clearance and 9-micron-sphere entrapment were studied and compared in isolated intestinal preparations under various physiological conditions in 10 dogs anesthetized with intravenous pentobarbital sodium. The chosen intestinal segment was pumped with aortic blood at a constant rate and pressure of about 90-100 mmHg. The temperature of the isolated loop was maintained at 37-38 degrees C with an electrical pad. A mixture of 86Rb and 9-micron-spheres labeled with 141Ce was injected into the arterial cannula supplying the intestinal loop while mesenteric venous blood was collected for activity counting. Three to four intestinal segments were used from each dog. The following three experimental conditions were randomly used for each intestinal segment preparation: 1) a mesenteric venous pressure (MVP) equaling 0 cmH2O and warmed normal saline infused into the lumen of segment; 2) an MVP equaling 0 cmH2O and 5% glucose in saline infused into the intestinal lumen; and 3) the reservoir with venous blood elevated to provide an MVP equaling 17 cmH2O and warmed normal saline infused into the intestinal lumen. A very strong and significant correlation was found between rubidium and microsphere clearances (r = 0.99, P less than 0.0001). Rubidium extraction was inversely associated with blood flow through the intestinal segment (r = 0.49, P = 0.02), while microsphere entrapment (extraction) was independent from intestinal blood flow (r = 0.16). The data suggest that the shunting of 9-micron spheres through tissue reflects the arteriovenous shunting of blood and, therefore, can be used as a tool to study the nutritive and nonnutritive blood flows in tissues.
Pluronic L-81: a potent inhibitor of the transport of intestinal chylomicrons
Authors: Tso P. , Gollamudi S. R.
Published: December 2017

We have shown previously that the acute administration of 0.5 mg/h of Pluronic L-81 (L-81), a non-ionic hydrophobic surfactant, markedly reduced the lymphatic lipid transport by the rat small intestine. This inhibition is quickly reversible. By studying two other Pluronic surfactants, 25R1 and P84, we assessed the importance of the positioning of the hydrophilic moiety relative to the hydrophobic chain and also the hydrophilic-to-hydrophobic ratio in the action of L-81. In 25R1 the hydrophilic moiety is at the center and the hydrophobic chain is at both ends; in L-81 the reverse is true. P84 has four times more hydrophilic moiety by weight than L-81. Four groups of intestinal lymph fistula rats were infused intraduodenally for 8 h with [3H]triolein, egg lecithin, sodium taurocholate, and 1 mg/h of either L-81, 25R1, or P84. The control group did not have a surfactant added. Both the absorption of lipid by the small intestine and the intestinal transport of the lipid into the lymph were measured. Similar to previous findings, infusion of 1 mg/h of L-81 produced a dramatic reduction in lipid transport by the small bowel. Although infusion of 1 mg/h of either 25R1 or P84 reduced significantly the intestinal lipid transport, both surfactants were markedly less effective than L-81. In conclusion, both the positioning of the hydrophilic moiety and the hydrophilic-to-hydrophobic ratio of L-81 are important for its action.
Regulation of pancreatic acinar cell insulin receptors by insulin
Authors: Mossner J. , Logsdon C. D. , Goldfine I. D. , Williams J. A.
Published: December 2017

In vivo pancreatic acini from normal mice are exposed to very high concentrations of insulin. To determine whether insulin receptors in these acini are downregulated by this endogenous insulin, insulin receptors on acini from both normal and diabetic mice were studied. Isolated acini from normal mice, which have accompanying islets of Langerhans, were studied under conditions where endogenous insulin was minimized. These acini bound 50% less 125I-insulin than acini from mice made diabetic with streptozotocin. Computer analysis of competition-inhibition curves showed a decrease in the number of insulin receptors in acini from normal mice when compared with acini from diabetic mice; however, the IC50 (a measure of receptor affinity) remained unchanged at approximately 1 nM. To study further the regulation of acinar cell insulin receptors, acini from diabetic mice were placed in suspension culture for 24 h. Addition of 1 microM insulin during the culture period led to a 30% decrease in subsequent 125I-insulin binding; the presence or absence of either epidermal growth factor or carbachol was without effect on insulin binding. The decrease in binding induced by insulin resulted from a change in receptor number without an alteration of the IC50. Measurement of total acinar cell insulin receptors by solubilization of these acini in 1% Triton X-100 showed that this insulin-induced decrease was due to a change in the total number of cellular insulin receptors. The present study suggests, therefore, that insulin can regulate its own receptor on pancreatic acini and that in vivo insulin receptors in normal pancreatic cells are downregulated, presumably due to high ambient insulin concentrations.
Interaction between transport of zinc and other solutes in human intestine
Authors: Steinhardt H. J. , Adibi S. A.
Published: December 2017

To investigate the kinetics of zinc absorption, a jejunal segment from healthy human volunteers was intubated with a triple-lumen tube, and isotonic NaCl solutions containing 0, 0.1, 0.3, and 0.9 mM ZnCl2 were infused. There was secretion of zinc when zinc was not added to the test solution but absorption when zinc was added. Over the range of zinc concentrations infused, there were linear increases in the rate of zinc absorption. There was net absorption of sodium and water during the infusion of isotonic saline solution but no net absorption when zinc (0.9 mM) was added to this solution. This impairment was not prevented by adding glucose to the test solution, but the rate of zinc absorption was significantly enhanced in the presence of glucose. The rate of glucose absorption was not affected by adding zinc to a glucose-saline solution. Zinc absorption was significantly stimulated by the addition of glycylleucine to the test solution, whereas the corresponding mixture of glycine and leucine had no effect. The data allow the following conclusions: a) zinc absorption is selectively stimulated by organic solutes and b) zinc inhibits net absorption of sodium and water in the jejunum.
Carbonic anhydrase activity and aminopyrine uptake in isolated gastric mucosal cells
Authors: Wollin A.
Published: December 2017

The role of carbonic anhydrase in the regulation and production of gastric acid was examined. Studies were done on isolated rabbit fundic mucosal cells, in which carbonic anhydrase activity and [14C]aminopyrine uptake were measured. The oxyntic cell-enriched cell fractions had the largest carbonic anhydrase content (4.2 +/- 0.1 U/10(6) cells) compared with other mucosal cells. The cellular carbonic anhydrase content of all isolated cell fractions was primarily a soluble enzyme, accounting for 10% of the total mucosal enzyme quantity. The remainder was found in the incubation medium from the mucosal dispersion procedure. The remaining cellular carbonic anhydrase activity in the oxyntic cell fraction was not enhanced by secretagogues. [14C]aminopyrine uptake increased dose dependently in the presence of histamine and dibutyryl cAMP. Acetazolamide (0.2 mM) inhibited the cellular carbonic anhydrase activity (99%) but did not interfere with the cellular uptake of [14C]aminopyrine. The present data from isolated cells suggest that cellular carbonic anhydrase in the oxyntic cell does not appear to be an integral step in the initiation of secretory function of isolated oxyntic cells. The lack of interference by the carbonic anhydrase inhibitor with H+ production does not exclude a role for carbonic anhydrase at high levels of acid secretion as it may occur in vivo, since isolated oxyntic cells probably do not achieve maximal rates of acid secretion and aminopyrine uptake reflects acid gradients and not rate of acid secretion.
Dissociated response of acid and pepsin secretion to omeprazole in an in vitro perfused mouse stomach
Authors: Fimmel C. J. , Berger M. M. , Blum A. L.
Published: December 2017

The effect of omeprazole, an inhibitor of the parietal cell H+-K+-ATPase, on pepsin and acid secretion was studied in an in vitro perfused whole mouse stomach model. Omeprazole inhibited basal and dibutyryl cAMP (DBcAMP)- and histamine-stimulated acid secretion in a dose-dependent fashion with a maximally effective dose of 10(-4) M. At the same time, omeprazole induced a dose-dependent increase of unstimulated pepsin release. This increase was not affected by pretreatment with 10(-3) M atropine or 10(-4) M cimetidine. It was, however, inhibited by preincubation with 10(-4) M carbonyl cyanide m-chlorophenylhydrazone (CCCP). Pepsin secretion after maximally effective doses of histamine or DBcAMP was not affected by 10(-4) M omeprazole. In a concentration of 10(-5) M, the effect of omeprazole was additive to the effect of submaximal concentrations of carbachol and histamine. NaSCN and imidazole mimicked the effect of omeprazole on acid secretion, but pepsin release was only stimulated with 10(-2) M imidazole. Another weak base, benzylamine, stimulated acid and pepsin in parallel. Luminal perfusion with solutions of high K+ concentration did not enhance basal pepsin release. The dissociated response of acid and pepsin secretion indicates that omeprazole does not act selectively on the parietal cell. The stimulation of pepsin secretion might be related to the weak base properties of the compound.
Analysis of hydrogen ion concentration in the gastric gel mucus layer
Authors: Engel E. , Peskoff A. , Kauffman G. L. , Grossman M. I.
Published: December 2017

Secretion of HCO-3 by the gastric epithelium has been thought to lower the concentration of H+ in the gastric mucus layer. This has been analyzed mathematically to include the HCO-3-H+ reaction, bulk water flow, diffusion, ion-ion electrical interaction, and ion-fixed charge interaction. The reaction-electrodiffusion problem is solved by use of singular perturbation theory. We show that there is a very thin layer for the reaction, equivalent to a sink of H+. In this layer there is negligible HCO-3 accumulation. A steady-state model is satisfactory if gastric mixing motions are more frequent than every 3 min. H+ concentration at the epithelium decreases with increased bicarbonate secretion, increased volume flow associated with bicarbonate secretion, increased thickness of the mucus layer, increased fixed negative charge of the mucus, and decreased cation flux into the lumen. The resultant lowering of H+ concentration may be as small as 5 mM but is probably considerably larger. Determining the actual drop will depend on more precise experimental measurements of the parameters of the problem.
Ethynylestradiol impairs bile salt uptake and Na-K pump function of rat hepatocytes
Authors: Berr F. , Simon F. R. , Reichen J.
Published: December 2017

Ethynylestradiol impairs bile flow and bile salt maximum secretory rate in rats, implying a secretory defect. In addition, Na-K-ATPase activity is decreased in liver surface membranes, suggesting abnormalities at the sinusoidal as well as the canalicular membrane. We investigated whether ethynylestradiol pretreatment affects bile salt uptake and Na-K pump function in isolated rat hepatocytes. Ethynylestradiol-treated cells were functionally intact as assayed with trypan blue exclusion, lactate dehydrogenase release, and oxygen consumption. Initial taurocholate uptake velocity was reduced by 73% in ethynylestradiol-treated hepatocytes [Vmax, 1.0 +/- 0.1 vs. 3.7 +/- 0.2 mumol X min-1 X (10(6) cells)-1; P less than 0.001; Km, 34 +/- 5 vs. 33 +/- 3 microM]. Na-K-ATPase activity in cell homogenates (36 +/- 5 vs. 27 +/- 4 mumol Pi X h-1 X mg prot-1; P less than 0.05), ouabain-suppressible rubidium-86 influx [6.8 +/- 1.1 vs. 4.8 +/- 1.0 nmol K+ X min-1 X (10(6) cells)-1; P less than 0.05], and intracellular potassium concentration (126 +/- 10 vs. 110 +/- 16 mmol/l; P less than 0.05) were reduced after ethynylestradiol. Taurocholate uptake measured at different temperatures between 25 degrees and 37 degrees was linear when plotted according to Arrhenius. The energy of activation was increased by 40% in ethynylestradiol-treated hepatocytes [17 +/- 4 vs. 23 +/- 4 kcal X mol-1 X (10(6) cells)-1; P less than 0.05], consistent with decreased membrane fluidity. These data suggest the possibility that during ethynylestradiol-induced cholestasis a disorder of the sinusoidal domain, caused perhaps by ethynylestradiol-induced alterations in membrane lipid composition, is an important contributing factor.
A contribution to analysis of three-compartment models for intestinal weak electrolyte absorption
Authors: Lucas M. L.
Published: December 2017

The flux ratio equation used to describe intestinal weak electrolyte absorption in terms of a three-compartment model, with an intermediate compartment of distinctive pH, was examined in detail. This took the form of fitting the function to experimental data from the literature, using several different parameter sets. Within wide limits, estimation of intermediate compartment pH is seen to be arbitrary due to redundancy in the model. Several pairs of pH values can satisfactorily fit experimental data. Inspection of the function reveals that it contains four basic submodels whose distinct identity depend on whether or not pH2 greater than pH, and which of the two membranes in series has the highest discrimination between ionized and non-ionized forms. Further analysis of the function reveals that it provides an infinite but bounded set of values for intermediate compartment pH. The model is therefore redundant, nonlinear function fitting reveals ill conditioning, and estimates of pH2 from the present model cannot be regarded as definitive.
Evidence for separate pathways of chylomicron and very low-density lipoprotein assembly and transport by rat small intestine
Authors: Tso P. , Drake D. S. , Black D. D. , Sabesin S. M.
Published: December 2017

Previously, we demonstrated that the hydrophobic surfactant Pluronic L-81 (L-81) inhibits the intestinal formation and transport of chylomicrons (CM) but not of very low-density lipoprotein-sized (VLDL) particles. The present study was undertaken to determine whether infusion of egg lecithin results mainly in secretion of VLDL by the small intestine and whether L-81 has any effect on their formation and secretion. Intestinal fistula rats were infused intraduodenally at a rate of 3 ml/h with a lipid emulsion containing 20 mM egg lecithin and 19 mM sodium taurocholate for 8 h. This was then followed by another 8 h of infusion of a similar lipid emulsion but with 0.5 mg/h of L-81 added. Lymphatic lipid output was measured, and lymph lipoproteins were sized by use of electron microscopy. Whether L-81 was present or not, no significant difference was detected in the lymphatic triglyceride, phospholipid, or cholesterol outputs. Based on agarose gel electrophoresis, sizing of intestinal lymph lipoproteins, and also the determination of lipid in the intestinal lymph CM and VLDL as separated by ultracentrifugation, VLDL were the major lipoproteins present in lymph during the infusion of egg lecithin. Thus, intraduodenal infusion of egg lecithin in the rat results mainly in the transport of VLDL and is not affected by the administration of L-81. The results suggest that CM and VLDL are assembled separately by the enterocytes and indicate the usefulness of L-81 in further investigating the pathways and regulation of intestinal lipoprotein synthesis, assembly, and secretion.
A map of membrane populations isolated from rat exorbital gland
Authors: Mircheff A. K. , Lu C. C.
Published: December 2017

We combined separation procedures based on three independent physical properties, sedimentation coefficient, density, and partitioning in an aqueous polymer two-phase system, to generate a three-dimensional subcellular fractionation of rat exorbital lacrimal gland. The distributions of protein and five enzymatic markers define a total of 13 physically and biochemically distinct membrane populations. These include epithelial cell apical membranes, purified 330-fold with respect to the initial homogenate; basal-lateral membranes, purified 80-fold; mitochondria, purified 19-fold; anda major endoplasmic reticulum population, purified 22-fold. Also apparent is a major Golgi population, which is extensively overlapped by other membrane populations; two populations that can be visualized as forming transitions between the endoplasmic reticulum and Golgi membranes; and several populations with unknown subcellular origins. Most of the markershave complex distributions among the isolated membrane populations; this complexity is consistent with current concepts of the synthesis and recycling of membrane constituents and the regulation of cytosolic electrolyte activities.
Characterization of cholecystokinin receptors on bovine gallbladder membranes
Authors: Steigerwalt R. W. , Goldfine I. D. , Williams J. A.
Published: December 2017

Cholecystokinin (CCK) binding to its receptors on a muscularis membrane fraction of bovine gallbladder was characterized using a biologically active CCK-33-[125I]Bolton-Hunter conjugate. Receptor binding was localized to the muscularis layer of the gallbladder; no binding was seen on either mucosal or serosal membranes. At 24 degrees C and pH 6.5, binding was maximal after 60–90 min of incubation, remained at a plateau for at least 240 min, and was reversed by the addition of unlabeled CCK-8. Optimal binding was seen at pH of 5.5 and required the presence of magnesium. Gallbladder binding data, best fit by a two-parameter model using a nonlinear least-squares computer program, was consistent with a single order of binding sites with a Kd of 618 +/- 168 pM and a binding capacity of 100.5 +/- 15.7 fmol/mg prot (mean +/- SE, n = 5). CCK-8 and CCK-33 inhibited 125I-CCK binding to gallbladder membranes with similar potencies, whereas desulfated CCK-8, gastrin I and II, and CCK-4 were at least 500 times less potent than CCK-33. The CCK antagonists dibutyryl cGMP and proglumide inhibited 125I-CCK binding with an IC50 of 31 and 600 microM, respectively. The present studies therefore demonstrate the existence of a specific CCK receptor on bovine gallbladder muscularis membranes with a high degree of selectivity for CCK analogues.
Colonic potassium and chloride secretion: role of cAMP and calcium
Authors: McCabe R. D. , Smith P. L.
Published: December 2017

Stripped rabbit colonic mucosa was studied in vitro in Ussing chambers to further investigate the role of Ca in regulating K and Cl secretion stimulated by the divalent cation ionophore A23187, prostaglandin E1 (PGE1), or 8-bromo-cAMP (8BrcAMP). To assess the effects of these secretagogues on the paracellular shunt permeability, we measured the Na concentration dependence of the serosal-to-mucosal Na flux in the absence or presence of these stimuli. Results from these studies reveal that changes in net K and Cl secretion produced by secretory stimuli cannot be accounted for by a change in shunt permeability. The possible involvement of Ca in the secretory response of the colon to these stimuli was investigated by measuring the changes in Cl and K transport elicited by A23187, PGE1, or 8BrcAMP in the absence or presence of trifluoperazine (10(-4) M) added to the serosal bathing solution. Trifluoperazine alone did not significantly alter basal Na or Cl fluxes or short-circuit current (Isc) but did decrease transepithelial conductance (Gt) and the serosal-to-mucosal K flux. Pretreatment of the tissues with trifluoperazine significantly reduced or abolished the changes in K fluxes elicited by A23187, 8BrcAMP, or PGE1 without altering the changes in Cl transport, Isc, and Gt. These results suggest that K secretion induced by these secretagogues involves an increase in intracellular Ca concentration and may be mediated by calmodulin.
Effect of divalent cations on gastrointestinal hormone release and exocrine pancreatic secretion in dogs
Authors: Inoue K. , Fried G. M. , Wiener I. , Sakamoto T. , Lilja P. , Greeley G. H. , Watson L. C. , Thompson J. C.
Published: December 2017

The purpose of this study was to examine the effect of three common divalent cations (Ca2+, Mg2+, and Zn2+) on the release of cholecystokinin (CCK-33), pancreatic polypeptide (PP), and gastrin. Five dogs with pancreatic and gastric fistulas were given 1-h intraduodenal infusions of calcium (5 mmol X kg-1 X h-1), magnesium (4 mmol X kg-1 X h-1), or zinc (1 mmol X kg-1h-1). At another time the same dogs were given an intravenous bolus followed immediately by a 1-h infusion of calcium (0.36 mmol/kg [bolus], 0.36 mmol X kg-1 X h-1), magnesium (0.25 mmol/kg [bolus], 0.25 mmol X kg-1 X h-1), or zinc (0.03 mmol/kg [bolus], 0.03 mmol X kg-1 X h-1). Intraduodenal infusions of calcium, magnesium, and zinc significantly stimulated CCK-33, PP, and gastrin release. Intravenous calcium stimulated CCK-33, PP, and gastrin release to 245, 193, and 155% of basal levels, respectively. Intravenous magnesium increased CCK-33 to 123% of basal levels but did not stimulate PP and gastrin levels. Intravenous zinc stimulated release of CCK-33, PP, and gastrin to 126, 185, and 124%, respectively. This study shows that calcium, magnesium, and zinc can stimulate release of CCK-33, PP, and gastrin in much the same manner. We suggest that these cations may have a nonspecific electrical action that results in an alteration of membrane permeability, which leads to release of gastrointestinal hormones.
Gastric mucosal protection by chronic restraint: effects of vagotomy
Authors: Wallace J. L. , Morris G. P. , Cohen M. M.
Published: December 2017

This study was performed to determine the effects of vagotomy on the gastric mucosal resistance to ethanol injury that develops in the rat in response to prolonged mild restraint. The resistance to ethanol injury up to 4 days after cessation of chronic mild restraint (CMR) was also examined. Intragastric administration of ethanol/acid to rats previously subjected to 10 days of CMR produced significantly (P less than 0.0001) less damage than to the mucosae of control rats. While previous exposure to CMR appeared to prevent the necrotic gastric damage induced by ethanol, damage to the surface epithelium was not prevented. When similar experiments were performed on CMR and control rats that had truncal vagotomy, the extent of ethanol/acid injury in the two groups was not significantly different. Intragastric administration of ethanol/acid to 8-day CMR rats produced 91% less (P less than 0.005) gastric damage than in control rats. When ethanol was administered 2 days after cessation of CMR, the gastric injury was still significantly less (P less than 0.01) than in control rats. However, when ethanol was administered 4 days after cessation of CMR, the resulting damage was not significantly different from that of control mucosae. These studies suggest that intact vagal innervation may be necessary for adaptation of the gastric mucosa to chronic mild restraint. These adaptive changes are still present up to 4 days after cessation of the restraint procedure.
Lactoferrin catabolism in the rat liver
Authors: Regoeczi E. , Chindemi P. A. , Debanne M. T. , Prieels J. P.
Published: December 2017

The hepatic uptake and degradation of human diferric 125I-lactoferrin by the liver of the intact rat were studied. After intravenous injection, the tracer was rapidly cleared by the liver, probably by adsorptive pinocytosis, as inferred from observations with a 3,470-fold dose range. Endocytosed lactoferrin was transferred, with a delay, from a light-density subcellular particle to an organelle that had a density similar to lysosomes. The loss of protein bound 125I from the liver was very slow (half-life 2.7 h), and its rate matched closely that of human asialotransferrin type 3. Lactoferrin was found to be a poor substrate for lysosomal hydrolases in vitro. Fucoidin effected the release of a portion of lactoferrin from the liver back into the plasma. By using this agent, indirect evidence was obtained suggesting that a fraction of lactoferrin is being repeatedly endo- and exocytosed (diacytosed) by the liver over prolonged periods of time. Fucosylation failed to impart lactoferrinlike properties on human asialotransferrin type 1, although the derivatized protein exhibited a less than or equal to 10-fold increase in affinity for the liver relative to the parent molecule.
Developmental maturation of D-glucose transport by rat jejunal brush-border membrane vesicles
Authors: Ghishan F. K. , Wilson F. A.
Published: December 2017

D-Glucose uptake into jejunal brush-border membrane vesicles was studied in suckling (2-wk-old), weanling (3-wk-old), and adolescent (6-wk-old) rats. The purity of the membrane vesicles from all age groups was validated by the finding that the specific activity of brush-border enzyme markers was severalfold greater in membrane vesicles compared with corresponding values in mucosal homogenate. D-Glucose uptake was inversely related to increasing medium osmolality, indicating that uptake of D-glucose was into the intravesicular space rather than binding. D-Glucose uptake was sodium dependent at all age groups; however, the initial uptake at 20 s was significantly greater in adolescent rats compared with suckling rats. The addition of valinomycin to KCl-preincubated vesicles in the presence of Na+ gradient resulted in a severalfold increase in D-glucose initial uptake over Na+ gradient alone, indicating that D-glucose uptake was electrogenic at all age groups. To delineate the mechanism for the decrease in the initial uptake in suckling rats, two experiments were performed: 1) an exchange tracer study that indicated the activity of D-glucose-Na+ transporters was similar in suckling and adolescent rats, and 2) a study that indicated 22Na uptake, as an indicator for Na+ permeability, was significantly greater in suckling rats compared with adolescent rats. These findings suggest that a Na+-dependent, electrogenic D-glucose uptake is already developed in the suckling period; however, because of the increased permeability to Na+, the Na+ gradient dissipates faster, resulting in a decrease in initial uptake.