bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential effects of corticosteroids on Na+ transport in rat distal colon in vitro
Authors: Jorkasky D. , Cox M. , Feldman G. M.
Published: December 2017

We studied rat distal colon during in vitro incubation with aldosterone and dexamethasone. Both hormones caused short-circuit current (Isc) to increase with a latency period of approximately 3 h. At the 7th h of incubation, control colons had a Isc of 72 +/- 8 microA . cm-2 while tissues incubated with 10(-5) M aldosterone and 10(-8) M dexamethasone, the respective maximal stimulatory concentrations, had similarly increased Isc, 211 +/- 21 and 185 +/- 18 microA . cm-2, respectively. The increase in Isc induced by steroids reflected increased net sodium transport: control, 3.4 +/- 0.8; aldosterone, 6.7 +/- 0.7 (P less than 0.05); and dexamethasone, 7.5 +/- 1.0 mueq . h-1 . cm-2 (P less than 0.025). Spironolactone inhibited the response to both steroids, but the molar ratio of antagonist to agonist was less for aldosterone (approximately 5,000:1) than for dexamethasone (approximately 50,000:1). Amiloride inhibited a greater fraction of aldosterone-induced Isc (0.70 +/- 0.07) than that of dexamethasone (0.37 +/- 0.07; P less than 0.025). The latter value was similar to the effect of amiloride on control tissues (0.35 +/- 0.04). These data provide evidence that the cellular mechanisms by which aldosterone and dexamethasone induce Na+ transport are different.
Effect of Ag+ on isolated bullfrog gastric mucosa
Authors: Rangachari P. K. , Matthews J.
Published: December 2017

In nitrate solutions, Ag+ added to the luminal side had marked effects on transmucosal conductance and potential difference (PD). Conductance increased quickly (85% within 60 s, 420% by 10 min); PD increased initially (11% within 30 s) and then fell precipitously (58% decreased within 2 min, 85% decreased by 10 min). During this period, no increase in mannitol permeability was found. These changes were essentially similar in histamine-stimulated, spontaneously secreting, and metiamide-inhibited fundic mucosae. Replacement of luminal Na+ by choline had no effect on the changes observed. Similar changes occurred also in the antrum. In SO2-4 media the increases in conductance occurred more slowly (40% within 2 min, 150% after 10 min); PD increased initially for 4-6 min and then slowly declined over 60 min to 74% of control values. After Ag+ treatment, replacement of luminal SO2-4 by nitrate led to an inversion of the PD by up to 20 mV (serosa -ve). Brief exposure of the mucosa (2 min) to Ag+ did not show any obvious damage, although surface cells were damaged following more prolonged exposures. After a 4-min treatment with Ag+, electrical and secretory parameters showed substantial recoveries. Ag+ appears to increase anion conductance; these effects appear to occur on the apical membranes of tubular and/or surface cells of the fundus and antrum.
Interaction of human lactoferrin with the rat liver
Authors: Debanne M. T. , Regoeczi E. , Sweeney G. D. , Krestynski F.
Published: December 2017

Binding of human lactoferrin (hLf) by purified rat liver plasma membranes was studied to clarify whether the liver possesses specific hLf receptors. The binding was rapid between 4 degrees and 37 degrees C, with a pH optimum close to 5.0. At 22 degrees C and in glycine-NaOH (5 mM, pH 7.4) containing 150 mM NaCl and 0.5% albumin, 1 microgram of membrane bound a maximum of 11.8 ng hLf. The dissociation constant of the interaction was 1.6 X 10(-7) M. Other proteins of high isoelectric points (lactoperoxidase, lysozyme, and particularly salmine sulfate) and a piperazine derivative inhibited hLf binding in a concentration-dependent manner. In contrast, monosaccharides (galactose, N-acetylgalactosamine, mannose, and fucose) were ineffective. By omitting NaCl from the incubation buffer, binding was increased 3.6-fold. Erythrocyte ghosts bound hLf less firmly and alveolar macrophages more firmly than hepatic plasma membranes. Liver cell fractionations performed after the intravenous injection of labeled hLf showed that approximately 88% of the hepatic radioligand was associated with parenchymal cells. When binding was expressed per unit of cell volume, however, more hLf was present in nonparenchymal than in parenchymal cells, implying that the above value was determined by the relative cell masses rather than affinities alone. It is concluded that the binding of hLf by hepatic plasma membranes is electrostatic, i.e., is mediated by the cationic nature of the ligand, and that it is explicable in terms of a "specific nonreceptor interaction" of the generalized type proposed by Cuatrecasas and Hollenberg (Adv. Protein Chem. 30: 251-451, 1976).
Dose-response effects of atropine on pancreatic response to secretin before and after truncal vagotomy
Authors: Singer M. V. , Niebel W. , Uhde K. H. , Hoffmeister D. , Goebell H.
Published: December 2017

In dogs with gastric and pancreatic fistulas, we studied the effect of intravenous atropine in doses ranging from 0.9 to 58 nmol X kg-1 X h-1 on the pancreatic secretory response to secretin before and after truncal vagotomy. Truncal vagotomy did not alter the incremental bicarbonate response to secretin. Before and after truncal vagotomy, 7 nmol X kg-1 X h-1 and all higher doses of atropine sulfate significantly decreased the bicarbonate response to low doses (5.2 and 10.3 pmol X kg-1 X h-1) of secretin but had no significant effect on responses to high doses (20.5 and 41 pmol X kg-1 X h-1). The inhibitory potency of the effective doses of atropine did not differ significantly. Secretin did not stimulate pancreatic protein output above basal. Truncal vagotomy reduced protein output basally and during secretin by about 50%. Before and after truncal vagotomy, 7 nmol X kg-1 X h-1 and all higher doses of atropine significantly decreased protein output basally and during secretin. Secretin and truncal vagotomy did not alter basal heart rate. Only the three highest doses (14, 29, and 58 nmol X kg-1 X h-1) of atropine significantly increased heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)
Measurement of regional gastroduodenal blood flow with iodo [14C]antipyrine autoradiography
Authors: Hudson D. , Scremin O. U. , Guth P. H.
Published: December 2017

Regional blood flow was measured in the gastroduodenal area by means of iodo[14C]antipyrine autoradiography. The tracer was given intravenously over a short period of time in awake rats followed by cardiac arrest and quick freezing of stomach and duodenum. Dry autoradiography of frozen sections provide a pictorial representation of radioactivity in the different tissue layers. This could be converted to blood flow after incorporation of the time course of blood radioactivity into an operational equation. A high level of resolution was achieved, allowing delineation of blood flow compartments of small dimensions such as single villi and regions within the fundic mucosa. The value of blood flow recorded in resting conditions were in agreement with previous observations with the microspheres technique. Hypotension induced a generalized decrease in blood flow, most marked in the corpus mucosa.
Ion transport studies with H+-K+-ATPase-rich vesicles: implications for HCl secretion and parietal cell physiology
Authors: Wolosin J. M.
Published: December 2017

A summary of recent studies on relations between the properties of the membrane incorporating the H+-K+-ATPase, the H+ motive force in gastric acid secretion, and the secretory state of the parietal cell is presented. Depending on tissue secretory state, two distinct H+-K+-ATPase-rich membranes predominate in tissue homogenates, the gastric microsomes derived from the intracellular tubulovesicles of the resting cell and the stimulation-associated (SA) vesicle derived from the apical membrane of the acid-secreting cell. Structural and chemical differences between both vesicular types lend support to the notion that the formation of an expanded, elaborated apical membrane in the secreting parietal cell results from fusion of tubulovesicles containing the H+-K+-ATPase to an apical membrane of different chemical composition. Comparison of polypeptide composition of microsomes and SA membranes provides a way to identify and isolate membrane and cytoskeletal components putatively involved in the membrane interconversion process. Comparison of transport properties between gastric microsomes and SA vesicles demonstrates that stimulation triggers the appearance of rapid K+ and Cl- permeabilities in the H+-K+-ATPase membrane, allowing efficient acid accumulation in SA vesicles by the combination of rapid KCl influx followed by ATPase-driven H+ for K+ exchange, i.e., by K+ recycling. These stimulation-triggered conductances are functionally independent. Nevertheless, their concurrent inhibition by certain divalent cations (Mn2+,Zn2+) suggests their location within a single physical domain. The compatibility of the K+-recycling model for HCl accumulation in SA vesicles with gastric HCl secretion and selected electrophysiological observations and certain implications of the findings for cellular mechanisms of transport regulation in the context of a membrane fusion and recycling model are discussed.
Evolution of portal hypertension and mechanisms involved in its maintenance in a rat model
Authors: Sikuler E. , Kravetz D. , Groszmann R. J.
Published: December 2017

In rats with portal hypertension induced by partial ligation of the portal vein, we have recently demonstrated an increased portal venous inflow that becomes an important factor in the maintenance of portal hypertension. The sequence of events that leads into this circulatory disarray is unknown. We evaluated chronologically the chain of hemodynamic changes that occurred after portal hypertension was induced by partial ligation of the portal vein. In this model it is possible to follow, from the initiation of the portal-hypertensive state, the interaction between blood flow and resistance in the portal system as well as the relation between the development of portal-systemic shunting and the elevated portal venous inflow. The study was performed in 45 portal-hypertensive rats and in 29 sham-operated rats. Blood flow and portal-systemic shunting were measured by radioactive microsphere techniques. The constriction of the portal vein was immediately followed by a resistance-induced portal hypertension characterized by increased portal resistance (9.78 +/- 0.89 vs. 4.18 +/- 0.71 dyn X s X cm-5 X 10(4), mean +/- SE, P less than 0.01), increased portal pressure (17.7 +/- 0.9 vs. 9.5 +/- 0.6 mmHg, P less than 0.001), and decreased portal venous inflow (3.93 +/- 0.26 vs. 6.82 +/- 0.49 ml X min-1 X 100 g body wt-1, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)
Capsaicin effects on muscularis mucosa of opossum esophagus: substance P release from afferent nerves?
Authors: Robotham H. , Jury J. , Daniel E. E.
Published: December 2017

The effects of capsaicin on the function and structure of muscularis mucosa of opossum esophagus were studied. In this tissue there are numerous nerves containing a substance P-like immunoreactive substance (SPLS), and electrical field stimulation (EFS) leads to a phasic response that appears to be due to release of acetylcholine, followed by a tonic response at higher frequencies of stimulation that appears to be due to release of a SPLS. The acetylcholine released by EFS and exogenous muscarinic agonists inhibits release of this SPLS (8). In the present study capsaicin (5 X 10(-5) M) was shown to cause a tonic submaximal contraction in most cases. This was prevented by substance P tachyphylaxis and by pretreatment with the partial agonist [D-Pro2, D-Trp7,9]substance P, the antagonist [D-Arg1, D-Trp7, Leu11]substance P, and tetrodotoxin. This response to capsaicin could not be repeated even after 2 h. Capsaicin also abolished the tonic response to high-frequency EFS without affecting phasic responses and reduced markedly the enhanced tonic response after atropine had abolished the phasic response. This occurred with or without a preliminary contraction to capsaicin. This tonic response to high-frequency EFS recovered completely 1-2 h after washing out capsaicin. Then, a further administration of capsaicin had no direct effect but again abolished tonic responses to EFS. Capsaicin reduced responses to exogenous substance P or carbachol only partially. When tissues were fixed and studied after capsaicin had abolished tonic responses to EFS, specific damage to nerve varicosities or synaptic vesicles in nerve varicosities could not be demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of 1,25(OH)2D3 and calcium channel blockers on cecal calcium transport in the rat
Authors: Favus M. J. , Angeid-Backman E.
Published: December 2017

To determine whether calcium transport across rat cecum is vitamin D dependent, we measured in vitro bidirectional calcium fluxes under short-circuited conditions across cecum from rats that were vitamin D deficient, vitamin D replete, or vitamin D deficient or vitamin D replete and injected with either 10, 25, or 75 ng of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] daily for 4 days before study. Vitamin D deficiency decreased net calcium absorption (Jnet) by reducing the mucosal-to-serosal absorptive flux (Jm----s) from 168 +/- 18 to 33 +/- 5 nmol X cm-2 X h-1 (mean +/- SE, P less than 0.0001). Twenty-five nanograms of 1,25(OH)2D3 raised Jm----s to 124 +/- 17 nmol X cm-2 X h-1, not different from values in vitamin D-replete rats. Although active calcium absorption by cecum appears to respond to vitamin D, calcium Jm----s is near maximal under normal conditions, and further stimulation follows only pharmacological doses of 1,25(OH)2D3. The in vitro addition of the calcium channel blocker verapamil (5 X 10(-5) M) to the mucosal side of cecum from vitamin D-replete rats reduced calcium Jm----s, but lower concentrations of verapamil or nitrendipine (10(-5) to 10(-9) M) did not reduce calcium Jm----s. The lack of inhibition by low concentrations of channel blockers suggest that the plasma membrane channels for calcium translocation across intestinal epithelium may not be analogous to voltage-dependent calcium channels in excitable tissue. The inhibition of cecal calcium transport that was blocked by high concentrations of verapamil may represent a nonspecific effect of the agent.
Calcium-activated, phospholipid-dependent protein kinase in pancreatic acinar cells
Authors: Noguchi M. , Adachi H. , Gardner J. D. , Jensen R. T.
Published: December 2017

In the present study we partially purified calcium-activated, phospholipid-dependent protein kinase (protein kinase C) from pancreatic acinar cells of the guinea pig using diethylaminoethylcellulose and Sephadex G-150 chromatography and characterized the dependence of the enzyme on calcium, phospholipids, diacylglycerol (diolein), and the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA). The enriched preparation of protein kinase C contained no cyclic nucleotide-dependent or calcium-dependent, calmodulin-dependent protein kinase activity. The values of Km for H1-histone and ATP were 0.74 +/- 0.22 and 13.1 +/- 3.2 microM, respectively. Pancreatic protein kinase C demonstrated an absolute requirement for calcium and phospholipid for its activation, and diolein or TPA increased the affinity of the enzyme for calcium by 10-fold. With phosphatidylserine the calcium concentration that caused a half-maximal activation (Ka) was 74 +/- 17 microM, whereas with phosphatidylserine and diolein or TPA the Ka for calcium was 7.9 +/- 1.6 or 6.8 +/- 1.3 microM, respectively. Adding phosphatidylethanolamine and phosphatidylserine decreased the Ka for calcium to 2.0 +/- 0.9 microM with diolein and to 0.7 +/- 0.4 microM with TPA. Activation of protein kinase C by TPA and diolein was identical with calcium concentrations greater than 1 microM, but at low calcium concentrations (less than 1 microM) in the presence of phospholipids, maximally effective concentrations of diolein caused only 55% of the activation seen with TPA. In addition to TPA, other phorbol esters such as phorbol dibutyrate and phorbol diacetate, but not phorbol itself, activated protein kinase C.(ABSTRACT TRUNCATED AT 250 WORDS)
Steroids alter ion transport and absorptive capacity in proximal and distal colon
Authors: Sellin J. H. , DeSoignie R. C.
Published: December 2017

Steroids are potent absorbagogues, increasing Na and fluid absorption in a variety of epithelia. This study characterizes the in vitro effects of pharmacological doses of gluco- and mineralocorticoids on transport parameters of rabbit proximal and distal colon. Treatment with methylprednisolone (MP, 40 mg im for 2 days) and desoxycortone acetate (DOCA, 12.5 mg im for 3 days) resulted in a significant increase in short-circuit current (Isc) in distal colon, suggesting an increase in basal Na absorption. Amiloride (10(-4) M) caused a significantly negative Isc in MP-treated tissue, demonstrating a steroid-induced, amiloride-insensitive electrogenic ion transport in distal colon. The effect of two absorbagogues, impermeant anions (SO4-Ringer) and amphotericin, were compared in control and steroid-treated distal colon. In controls, both absorbagogues increased Isc. Impermeant anions caused a rise in Isc in both MP and DOCA tissues, suggesting that the high rate of basal Na absorption had not caused a saturation of the Na pump. The steroid-treated colons, however, did not consistently respond to amphotericin. Amiloride inhibited the entire Isc in MP-treated distal colon that had been exposed to amphotericin; this suggested that amphotericin had not exerted its characteristic effect on the apical membrane of steroid-treated colon. In proximal colon, steroids did not alter basal rates of transport; however, epinephrine-induced Na-Cl absorption was significantly greater in MP-treated vs control (P less than 0.005). Steroids increase the absorptive capacity of both proximal and distal colon for Na, while increasing basal Na absorption only in the distal colon.(ABSTRACT TRUNCATED AT 250 WORDS)
Kinetic and energetic aspects of the inhibition of taurocholate uptake by Na+-dependent amino acids: studies in rat liver plasma membrane vesicles
Authors: Blitzer B. L. , Bueler R. L.
Published: December 2017

The kinetic and energetic aspects of the inhibition of taurocholate uptake by the Na+-dependent amino acid L-alanine were studied in rat basolateral liver plasma membrane vesicles. In the presence of an inwardly directed Na+ gradient, alanine (5 mM) reduced the initial velocity of taurocholate uptake to 60% of control and virtually abolished the overshoot. In the presence of a K+ gradient, the slow rate of Na+-independent taurocholate uptake was similar in the presence or absence of the amino acid. Inhibition of Na+-dependent taurocholate uptake increased nonlinearly with alanine concentration (half-maximal inhibition at approximately 1 mM) and plateaued at 5–10 mM. Kinetic studies showed that alanine significantly reduced the Vmax for taurocholate uptake from 6.32 +/- 0.22 to 3.68 +/- 0.21 nmol X mg prot-1 X min-1 but did not significantly affect taurocholate Km (38.4 +/- 3.6 vs. 29.0 +/- 4.9 microM). In contrast, the Na+-independent amino acid 2-aminobicyclo[2.2.1]heptane-2-carboxylic acid did not affect either the initial velocity or peak uptake of taurocholate. The effects of alanine on the driving forces for bile acid uptake were directly assessed by measuring vesicle uptake of 22Na. At early time points, 22Na uptake was faster in the presence of alanine than under control conditions. These findings provide further evidence that Na+-dependent amino acids noncompetitively inhibit Na+-dependent bile acid uptake in association with accelerated dissipation of the transmembrane Na+ gradient and extend previous observations of this phenomenon made in isolated rat hepatocytes [Am. J. Physiol. 245 (Gastrointest. Liver Physiol. 8): G399-G403, 1983].
Control of intestinal absorption by the renin-angiotensin system
Authors: Levens N. R.
Published: December 2017

In vivo angiotensin II (ANG II) exerts a dose-dependent dual action upon intestinal absorption. At low doses, ANG II stimulates sodium (Na) and water absorption from all intestinal areas. At high doses, ANG II inhibits absorption. The stimulation of jejunal absorption in response to ANG II is secondary to the release of norepinephrine (NE) from enteric sympathetic nerves. ANG II may act either within the brain or at the sympathetic nerve terminal to liberate NE. In contrast, the inhibition of absorption in response to ANG II is due to enteric prostaglandin production. At the present time it is unclear whether the changes in absorption in response to ANG II in vivo are due to changes in transport processes or secondary to alterations in enteric hemodynamics. ANG II also exerts a dose-dependent dual action on intestinal ion and water absorption in vitro. The mechanisms responsible for changes in absorption in vitro are unknown. However, since enteric sympathetic nerves are severed from their ganglia, it is unlikely that ANG II stimulates absorption in isolated preparations through release of NE. ANG II exerts a major control over intestinal absorption following volume depletion. The hormone controls colonic absorption through release of aldosterone and directly influences jejunal absorption via enteric sympathetic nerves. ANG II may control ileal absorption following volume depletion. All components of the renin-angiotensin system are present within the intestine. Furthermore, ANG II-like immunoreactivity is present within enteric nerves. The role of locally formed ANG II in the control of intestinal absorption has not been studied. Models illustrating the effect of ANG II on intestinal absorption are discussed.
Glucocorticoid receptors in isolated intestinal epithelial cells in rats
Authors: Lentze M. J. , Colony P. C. , Trier J. S.
Published: December 2017

There is evidence that glucocorticoid hormones influence a variety of epithelial cell functions in the small intestine. To exert their effect, glucocorticoids bind to cytoplasmic glucocorticoid receptors (GR), which, following translocation to the nucleus, stimulate mRNA transcription and then protein synthesis and ultimately trigger hormonal actions. To determine the distribution of GR in small intestinal villus and crypt cells, we measured GR activity in enriched villus and crypt cell fractions by use of [3H]dexamethasone. In normal rats GR activity was present in all cell fractions but was lowest in fully mature villus cells of the upper villus and greatest in immature crypt cells. In contrast, 1 wk after adrenalectomy and ovariectomy or sham operation, both of which reduced plasma corticosterone levels, GR activities were comparable in enriched villus cell and enriched crypt cell fractions. Kinetic studies indicated a single class of binding sites with comparable Kd values in villus and crypt cells of normal and steroid-depleted animals, suggesting that there are more glucocorticoid-binding sites in crypt than in villus cells of normal animals. Immature crypt cells may be more susceptible to glucocorticoid modulation than fully mature villus cells in normal rats in view of their higher GR activity.
Role of sodium or calcium in electrical depolarization of feline colonic smooth muscle
Authors: Snape W. J. , Tan S. T.
Published: December 2017

The aim of this study was to compare the role of Na+ and Ca2+ on the membrane potential and contraction of feline colonic circular smooth muscle. The changes in membrane potential were correlated with a change in tension using the double-sucrose gap technique. The estimated resting potential was -62.8 +/- 2.6 mV. A depolarizing current, passed during quiescent periods of the membrane, stimulated a spike potential and caused a concomitant increase in smooth muscle tension. The maximum depolarization rate of the active spike potential was rapid (580 +/- 75 mV/s) and unaffected by the amplitude of the depolarizing current. Reduction of extracellular calcium (0.0 mM Ca2+ plus 5 mM EGTA) or blockade of the calcium channels with verapamil (10(-6)M) slowed the maximum rate of membrane depolarization to 128 +/- 20 mV/s (P less than 0.001). The steady-state amplitude of the electrotonic potential and time constant also decreased in low-calcium solutions. The amplitude of smooth muscle contraction and the time between stimulus and onset of contraction were dependent on the amplitude of the depolarizing current and the concentration of extracellular calcium. Removal of sodium had no effect on the electrotonic potentials, maximum dV/dt of the spike, or the contraction of the smooth muscle. These studies suggest calcium plays a major role in the generation of an active spike potential, colonic smooth muscle contraction requires extracellular calcium and is associated with an active regenerative spike potential, and sodium plays a minor role in the generation of an active spike potential and in the initiation of a contraction in feline colonic smooth muscle.
Is intestinal peptide transport energized by a proton gradient?
Authors: Ganapathy Vadivel , Leibach Frederick H.
Published: December 2017

Transport of intact peptides, followed by intracellular hydrolysis in the intestinal mucosal cells, plays an important role in the absorption of protein digestion products in the mammalian small intestine. Even though earlier studies on peptide absorption in intact-tissue preparations have indicated that peptides are transported by an active Na+-dependent mechanism, recent studies with purified brush-border membrane vesicles have unequivocally demonstrated that Na+ does not play a direct role in the translocation of peptides across the membrane. Like most amino acids, peptides are also transported as zwitterions. However, peptide transport causes depolarization of the brushborder membrane in intact mucosal cells as well as in purified membrane vesicles, and the depolarization is the result of a net transfer of positive charge across the membrane during peptide transport. This electrogenic nature of peptide transport is observed even in the absence of Na+. Peptide transport is enhanced by an interior-negative membrane potential and inhibited by an interior-positive membrane potential. An inward proton gradient stimulates peptide transport, and this stimulation is reduced when the proton gradient is subjected to rapid dissipation by the presence of a proton ionophore. These observations strongly suggest that peptides are cotransported with protons in the intestine. There is substantial evidence for the existence of an inward proton gradient in the mammalian small intestine, and therefore it is very likely that this proton gradient is the in vivo energy source for the uphill transport of peptides. The Na+-H+ exchanger in the brush-border membrane, in conjunction with Na+-K+-ATPase at the basolateral membrane, is probably responsible for the generation and maintenance of the proton gradient and may thus be involved indirectly in the intestinal absorption of peptides.
Proglumide analogues: potent cholecystokinin receptor antagonists
Authors: Jensen R. T. , Murphy R. B. , Trampota M. , Schneider L. H. , Jones S. W. , Howard J. M. , Gardner J. D.
Published: December 2017

Proglumide [N-(benzoyl)-L-glutamic acid-1-di-n-propylamide] is a specific cholecystokinin receptor antagonist. In the present study we synthesized various analogues of proglumide and used pancreatic acini from guinea pig pancreas to examine the abilities of these analogues to function as cholecystokinin receptor antagonists. Each analogue inhibited cholecystokinin octapeptide-stimulated amylase secretion but did not stimulate amylase secretion when present alone. There was a close correlation between the ability of a particular analogue to inhibit the action of cholecystokinin on acinar cell function and its ability to inhibit binding of 125I-cholecystokinin. Structure-function studies demonstrated that neither the dipropylamide nor the benzoyl moieties are essential for inhibiting the action of cholecystokinin but that both groups are important in determining the inhibitory potency. Replacing the dipropylamide group with a hydroxyl group caused a 13-fold decrease in potency. Replacing the benzoyl moiety by an acetyl group caused a 30- to 40-fold decrease in inhibitory potency, whereas replacing the benzoyl moiety by a p-chlorophenoxyacetyl or phenoxyacetyl moiety caused a 75-fold increase in potency. Replacing both the dipropylamide moiety with a hydroxyl group and the benzoyl moiety with a phenoxyacetyl group resulted in a 5-fold decrease in inhibitory potency. Inhibition of cholecystokinin-stimulated amylase release by both the phenoxyacetyl and p-chlorophenoxyacetyl analogues was competitive in nature, fully reversible, and specific for those secretagogues that interact with the cholecystokinin receptor.(ABSTRACT TRUNCATED AT 250 WORDS)
Contractile patterns and transit of fluid in canine terminal ileum
Authors: Kruis W. , Azpiroz F. , Phillips S. F.
Published: December 2017

Earlier recordings of intraluminal pressure from the terminal ileum and across the ileocolonic sphincter of dogs revealed, in addition to the usual interdigestive and digestive patterns, pressure waves that appeared to have propulsive potential. One of these, which we designated as a “prolonged propagated contraction” (PPC), was a wave of high amplitude; it had a duration much longer than the ileal slow wave and migrated rapidly through the ileum, often into the proximal colon. The other pattern was one of “discrete clustered contractions” (DCC); these were propagated bursts of rhythmic phasic waves, distinct from phase III of the interdigestive myoelectric complex. These migrated through the ileum more rapidly than did phase III. Our aims were to record the electrical and mechanical equivalents of these pressure events using only extraluminal sensors and to evaluate the capacity of these contractions to propel fluids. PPCs and DCCs were recorded by extraluminal strain gauges, and flow was assessed by recovery of a nonabsorbable marker. Phase III of the migrating motor complex propelled fluid through the ileum, but in addition DCCs and, especially, PPCs were able to empty the ileum. These latter contractions have similarities to the ileal “peristaltic rush” described by others, and we believe these waves are an important force for ileal emptying.
Ion transport in goby intestine: cellular mechanism of urotensin II stimulation
Authors: Loretz C. A. , Howard M. E. , Siegel A. J.
Published: December 2017

The Na- and Cl-absorbing goby posterior intestinal epithelium is composed predominantly of mitochondria-rich, tall columnar cells. Glass intracellular microelectrode recording technique was applied to absorptive cells of this relatively leaky epithelium to measure apical cell membrane potential difference (psi mc) and apical membrane fractional resistance. As determined by ion-substitution studies, absorptive cells are characterized by a large, Ba2+-inhibitable apical K conductance, which is a major factor determining psi mc and smaller Cl and Na conductances. Inhibition of the apical Na-Cl-coupled influx directly by furosemide or indirectly by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine produced hyperpolarization of psi mc, consistent with the greater apical membrane conductance to Cl than Na. The urophysial neurosecretory peptide urotensin II, which stimulates Na-Cl-coupled absorption, markedly depolarized psi mc in posterior intestinal tissues from 5% seawater-adapted gobies. This response is consistent with a stimulatory effect of urotensin II at the apical membrane carrier rather than at the basolateral Na-K-ATPase. Urotensin II is without effect on psi mc in tissues from seawater-adapted fish and somatostatin, a natural analogue of urotensin II, is without effect on tissues from fish adapted to either salinity. This specificity parallels that determined using radiotracer fluxes.
Age-related changes in rat intestinal transport of D-glucose, sodium, and water
Authors: Esposito G. , Faelli A. , Tosco M. , Orsenigo M. N. , Battistessa R.
Published: December 2017

Experiments were performed with everted sacs of jejunum and ileum and brush-border membrane vesicles from four different age groups of rats: very young, young, adult, and old. The changes with age in several parameters, such as cell electrolyte and D-glucose concentrations, cell volume, net D-glucose, Na+ and water transport, and D-glucose uptake into vesicles, were studied. Differences in transport activities in the four age groups of animals were observed. In the jejunum the greatest transport was found in young rats and less in adult, very young, and old rats. In the ileum, the greatest transport activity was found in very young and young rats, while in adult and old animals transport activity was negligible. The cell volume of the enterocyte was significantly smaller in old rats. Changes in cell electrolytes (increased Na+ and decreased K+) were observed only in the jejunum of old rats. The overshoot of D-glucose in brush-border membrane vesicles varied considerably in the four different age groups of animals. In other words, the capacity for sugar uptake into vesicles is greater in young rats than in very young or adult animals. In old rats there was no overshoot, and a slow linear increase of sugar entry was observed. The results indicate that the changes in D-glucose transport with age might be explained in part by the changes in the amount of sugar that crosses the brush-border membrane of the enterocyte.
Initial plasma high-density lipoprotein distribution in the rat: effects of age, sex, and fasting
Authors: Cohn J. S. , Fidge N. H. , Nestel P. J.
Published: December 2017

The initial tissue distribution of high-density lipoprotein (HDL) was studied in the rat. Specific tissue-space measurements, calculated as the difference between HDL and albumin uptake in a tissue, 10 min after injecting radiolabeled lipoprotein, were taken to represent specific binding of HDL. Rat HDL (rHDL) and human HDL3 (hHDL3) were labeled directly with 125I or with prelabeled 125I-apolipoprotein A-I (125I-apoA-I). Specific tissue spaces were demonstrated for the liver and adrenals but not for spleen, jejunum, ileum, colon, muscle, or adipose tissue. The kidney showed a specific HDL space only when 125I-apoA-I-rHDL was injected. The adrenals bound rHDL to a greater extent than hHDL3, and the liver also bound from three to five times more rHDL than hHDL3. In male and female rats the liver accounted for about two-thirds of total HDL bound. Significantly more HDL was bound by adrenals of female than by male rats, but the reverse occurred for liver and kidney. The greater hepatic binding of HDL in males compared to females was consistent with measurements of HDL flux, calculated from constant infusions of labeled HDL; the fractional clearance of 125I-apoA-I-rHDL was 572 +/- 13 microliter plasma X h-1 X 100 g body wt-1 in males and 466 +/- 19 microliter plasma X h-1 X 100 g body wt-1 in females (P less than 0.01). Tissue-space measurements with 125I-rHDL were not affected by age. Fasting for 48 h increased HDL binding by liver but not by adrenals.(ABSTRACT TRUNCATED AT 250 WORDS)
Countercurrent exchange of water in canine jejunum
Authors: Ryu K. H. , Grim E.
Published: December 2017

The possibility of countercurrent exchange of water molecules in canine intestinal villi has been examined. Tritium-labeled water (3H2O) molecules were introduced either into the fluid lavaging the intestinal lumen or into the arterial blood supply for varying periods of time. Quickly frozen samples of intestinal tissue were sectioned such that isotopic concentrations at the villus tip, midvillus, villus base, and underlying submucosa and muscle could be determined. The villus concentration gradients observed were consistent with the existence of a countercurrent exchange but could also be explained by alternative arrangements. More convincing evidence of a countercurrent was obtained from experiments in which [14C]inulin was introduced simultaneously with 3H2O into the intestinal artery. The villus tip-to-base concentration ratio for 3H2O was less than one while the ratio for inulin was greater than one, thus vitiating the alternative explanations and leading to the conclusion that the labeled water molecules must have undergone a countercurrent exchange.
Influence of luminal pH on rat large bowel epithelial cell cycle
Authors: Lupton J. R. , Coder D. M. , Jacobs L. R.
Published: December 2017

The influence of luminal pH on the colonic epithelial cell cycle was studied by means of dietary modification to produce acidification of colonic contents. Forty male Sprague-Dawley rats were fed one of four diets: defined fiber free, fiber free diluted by either 100 g/kg lactulose or sorbitol, or 25 g/kg of MgSO4. After 2 wk, in vivo pH measurements were recorded at laparotomy under ether anesthesia in the cecum and proximal, mid-, and distal colon. Epithelial cells, isolated from these same regions, were measured for DNA content with flow cytometry in order to determine cell cycle stage. The pH values in all intestinal regions were highest with MgSO4 and then fiber free, sorbitol, and lactulose, the most acidic. In contrast, the percentage of cells in S phase (actively synthesizing DNA) was highest with lactulose and least with MgSO4. There was a significant inverse correlation between luminal pH and percent cells in S phase in the cecum (P less than 0.01), proximal colon (P less than 0.05), and distal colon (P less than 0.01). These results show that acidification of colonic contents by diet modification leads to increased epithelial cell proliferation.
Stimulation of pepsinogen secretion in permeable isolated gastric glands
Authors: Norris S. H. , Hersey S. J.
Published: December 2017

Rabbit isolated gastric glands were treated with digitonin so that stimulation of pepsinogen secretion could be studied in a permeable system. Criteria for permeabilization were the release of lactate dehydrogenase in response to digitonin as well as the finding that calcium stimulation and spermine inhibition required the presence of digitonin. Other evidence confirmed that digitonin directly permeabilized chief cells. Pepsinogen secretion was elicited from digitonin-treated gastric glands by a number of agents, including calcium, vanadate, cholecystokinin octapeptide (CCK-OP), 8-bromo-adenosine 3',5'-cyclic monophosphate, and forskolin. Spermine was found to inhibit secretion stimulated by each of these agents only in the presence of digitonin, suggesting an intracellular site of spermine action. We concluded that spermine inhibition of secretion could be used as a marker of secretion elicited from permeable chief cells. The ability to stimulate pepsinogen secretion by such agents as CCK-OP and forskolin suggests that stimulus-secretion coupling is virtually intact even in permeable chief cells. We felt that this preparation should offer unusual opportunities for investigating the mechanisms involved in the intracellular regulation and activation of pepsinogen secretion.
Cl- requirement for saliva secretion in the isolated, perfused rat submandibular gland
Authors: Martinez J. R. , Cassity N.
Published: December 2017

Replacement of perfusate Cl- with Br- reduced by 37% the volume of saliva secreted by isolated, perfused rat submandibular glands exposed to 10(-6) M acetylcholine. Replacement of perfusate Cl- with SO4(2-) reduced fluid secretion by 73%, while replacement of bicarbonate with HEPES or addition of acetazolamide had no effect on salivary flows or volumes. Furosemide (10(-3) M) reduced saliva secretion when added to Cl- -(73%) or Br- -containing (56%) perfusates and also to HEPES- (95%) or acetazolamide-containing (82%) perfusates. Perfusion of the glands with furosemide or SO4- containing perfusates resulted in significantly reduced salivary Cl- concentrations and increased residual anion (Na+-K+-Ca2+-Cl-) concentrations, while perfusion with solutions containing acetazolamide or with HCO3- -free (HEPES) perfusates resulted in opposite changes in salivary anions. Addition of furosemide to HEPES- or acetazolamide-containing perfusates reversed these changes and caused a reduction in salivary Cl- concentrations and an increase in residual anion concentrations. It is concluded that 1) extracellular Cl- is required for saliva secretion in the rat submandibular gland, 2) the required external Cl- enters the salivary cells by a furosemide-sensitive transport system, which is likely to be similar to a Na+-K+-Cl- cotransport system described in other epithelia, 3) HCO3- is not normally required for saliva secretion but can sustain it partially when Cl- transport is inhibited by either furosemide or Cl- replacement, and 4) salivary electrolyte changes induced by Cl- or HCO3- replacement or by furosemide probably represent combined effects on acinar secretion and transductal electrolyte transport.
Intracellular mediators of Na+-K+ pump activity in guinea pig pancreatic acinar cells
Authors: Hootman S. R. , Ochs D. L. , Williams J. A.
Published: December 2017

The involvement of Ca2+ and cyclic nucleotides in neurohormonal regulation of Na+-K+-ATPase (Na+-K+ pump) activity in guinea pig pancreatic acinar cells was investigated. Changes in Na+-K+ pump activity elicited by secretagogues were assessed by [3H]ouabain binding and by ouabain-sensitive 86Rb+ uptake. Carbachol (CCh) and cholecystokinin octapeptide (CCK-8) each stimulated both ouabain-sensitive 86Rb+ uptake and equilibrium binding of [3H]ouabain by approximately 60%. Secretin increased both indicators of Na+-K+ pump activity by approximately 40% as did forskolin, 8-bromo- and dibutyryl cAMP, theophylline, and isobutylmethylxanthine. Incubation of acinar cells in Ca2+-free HEPES-buffered Ringer (HR) with 0.5 mM EGTA reduced the stimulatory effects of CCh and CCK-8 by up to 90% but caused only a small reduction in the effects of secretin, forskolin, and cAMP analogues. In addition, CCh, CCK-8, secretin, and forskolin each stimulated ouabain-insensitive 86Rb+ uptake by acinar cells. The increase elicited by CCh and CCK-8 was greatly reduced in the absence of extracellular Ca2+, while that caused by the latter two agents was not substantially altered. The effects of secretagogues on free Ca2+ levels in pancreatic acinar cells also were investigated with quin-2, a fluorescent Ca2+ chelator. Basal intracellular Ca2+ concentration ([Ca2+]i) was 161 nM in resting cells and increased to 713 and 803 nM within 15 s after addition of 100 microM CCh or 10 nM CCK-8, respectively. Forskolin, secretin, and cAMP analogues had no effect on [Ca2+]i, nor did they either reduce or potentiate the rise in [Ca2+]i evoked by CCh.(ABSTRACT TRUNCATED AT 250 WORDS)
Influence of side-chain charge on hepatic transport of bile acids and bile acid analogues
Authors: Anwer M. S. , O'Maille E. R. , Hofmann A. F. , DiPietro R. A. , Michelotti E.
Published: December 2017

The importance of side-chain charge on hepatic uptake and biliary secretion of bile acids and analogues was studied using the isolated, perfused rat liver and the anesthetized rat with a bile fistula. Derivatives of cholic acid with negative, neutral, zwitterionic, or positive charges on the side chain were synthesized and studied. Hepatic uptake by the isolated perfused liver, determined by measuring the rate of disappearance of a single 20-mumol bolus added to the perfusate, was strongly influenced by side-chain charge. A fully positively charged bile acid derivative (cholylcholamine) and two fully zwitterionic bile acid derivatives (CHAPS and cholyllysine) showed no appreciable uptake (less than 1% of the uptake rate of cholyltaurine). Bile acid derivatives existing mostly in cationic form (cholylamine) at pH 7.4, in neutral form (cholylglycylhistamine), or in divalent anion form (cholylaspartate and cholylcysteate) had an uptake rate that was greater but only 7-19% that of cholyltaurine. Side-chain charge also appeared to influence the rate of secretion into bile. Bile acids existing in mono- or dianionic form were well secreted (greater than 95% of dose in 2 h) into the bile, but all other derivatives had much lower secretion rates (less than 20% of dose in 2 h). When the biliary secretion of each bile acid derivative was expressed in relation to the amount that had entered the liver, relative secretion rates (presumably from liver cell) into bile decreased in the following order: cholyltaurine greater than cholylaspartate and cholylcysteate greater than CHAPS greater than cholyllysine greater than cholylglycylhistamine approximately equal to cholylamine. In bile fistula rats, cholylaspartate was quantitatively secreted into bile when infused at rates below its secretory maximum, whereas only very low biliary secretion rates of CHAPS were observed even during relatively high infusion rates; cholylamine was cholestatic. The above data show that, although uncharged and anionic derivatives of cholic acid may be taken up by the liver at a moderate rate, only anionic derivatives (both monovalent and divalent) are well secreted from within the liver cell into bile. A single negative charge on the side chain appears to be required for optimal transport of a bile acid from sinusoidal blood to bile.
Intestinal control of gastric tone
Authors: Azpiroz F. , Malagelada J. R.
Published: December 2017

By use of a newly developed electronic barostat, we investigated chyme-mediated intestinal regulation of gastric tone in a canine model. In this model the proximal (3 dogs) or distal (3 dogs) small intestine was luminally isolated, maintaining neuromuscular continuity. Gastric tone was measured by recording variations in the volume of air within an intragastric bag that was maintained at a constant pressure (2 mmHg) by the electronic barostat. The isolated intestinal loop was perfused constantly (5 ml/min) with either isotonic saline (control) or with test infusates (osmolality, 300 mosmol/kg; pH 7.4) of carbohydrate (maltose), protein (casein hydrolysate), fat (sodium oleate), or a combination of all three nutrients. The combined nutrient solution, infused into either the proximal or the distal intestine, profoundly inhibited gastric tone. Fat infused into the proximal intestine induced gastric relaxation, whereas protein had only a modest effect and carbohydrate had no effect. In contrast, in the distal intestine carbohydrate and protein markedly reduced gastric tone, whereas fat had no effect. We conclude that nutrients in the small bowel regulate gastric tone by a mechanism that is nutrient and region specific.
Morphine initiates migrating myoelectric complexes by acting on peripheral opioid receptors
Authors: Telford G. L. , Hoshmonai M. , Moses A. J. , Szurszewski J. H.
Published: December 2017

The role of peripheral and central opioid receptors in morphine-induced migrating myoelectric complexes (MMECs) was studied in conscious dogs implanted with silver-silver chloride electrodes. In normal fasted dogs morphine (100-200 micrograms/kg iv) initiated phase III of the MMEC in the duodenum. Once initiated the MMEC propagated distally. This effect of morphine was blocked by the opioid receptor antagonists naloxone (2 mg/kg iv) and N,N-diallylnormorphinium bromide (4 mg/kg iv). Higher doses of morphine (300-600 micrograms/kg iv) initiated phase III activity in fed dogs as early as 20 min after feeding, while lower doses (150 micrograms/kg iv) initiated phase III activity routinely when administered 100 min after feeding. In dogs with bilateral vagotomies and bilateral thoracolumbar sympathetic chain ganglionectomies, morphine (150 micrograms/kg iv) initiated phase III activity in the duodenum, which then migrated distally. This study demonstrates that morphine initiates phase III of the MMEC by acting through peripheral opioid receptors.