bluuebunny/crossref_metadata_2025 huggingface dataset:
Identical patterns of somatostatin secretion from isolated antrum and fundus of rat stomach
Authors: Schubert M. L. , Saffouri B. , Makhlouf G. M.
Published: December 2017

The patterns of somatostatin secretion from the fundus, the main source of somatostatin, and the antrum, the site of paracrine regulation of gastrin secretion, were examined using perifused antral and fundic segments from rat stomach. Gastrin secretion fundic segments from rat stomach. Gastrin secretion could be obtained from antral segments only. Somatostatin secretion was obtained from both antral and fundic segments. 1,1-Dimethyl-4-phenylpiperazinium (DMPP) (10(-5) and 10(-4) M) and bombesin-14 (10(-8) and 10(-6) M) caused concentration-dependent increases in somatostatin secretion that were of the same magnitude in antral and fundic segments. These increases were also of the same magnitude as those obtained in the vascularly perfused whole stomach. Atropine (3 X 10(-7) M) inhibited the somatostatin response to DMPP (10(-4) M) to the same extent in antral (50 +/- 12% inhibition) and fundic (55 +/- 12% inhibition) segments. Hexamethonium (10(-5) M) also inhibited the response to DMPP to the same extent in antral (80 +/- 9%) and fundic (78 +/- 19%) segments. Methacholine caused a typically muscarinic decrease in somatostatin secretion that was of the same magnitude in antral (27 +/- 6%) and fundic (25 +/- 6%) segments. The identical patterns of somatostatin secretion from the two regions of the stomach imply that somatostatin secretion measured in the vascularly perfused whole stomach is a valid reflection of somatostatin secretion by the antrum.
Ursodeoxycholic acid choleresis: relationship to biliary HCO-3 and effects of Na+-H+ exchange inhibitors
Authors: Renner E. L. , Lake J. R. , Cragoe E. J. , Van Dyke R. W. , Scharschmidt B. F.
Published: December 2017

We have recently shown that substitution of Li+ for perfusate Na+ eliminates the HCO3(-)-rich choleresis produced by ursodeoxycholic acid (UDCA) in isolated perfused rat liver and that the increase in bile flow produced by both UDCA and taurocholic acid is partially inhibited by 1 mM amiloride. Although these findings are consistent with a role for Na+-H+ exchange in the choleresis produced by these bile acids, both Li+ substitution and amiloride affect other cellular processes, including Na+-K+-ATPase activity. We have now further explored both the relationship between UDCA-stimulated bile flow and biliary HCO3- secretion and the possible role of Na+-H+ exchange in this process by comparing the effects of amiloride with two of its more potent and presumably more specific analogues, 5-(N,N-dimethyl)amiloride hydrochloride (DMA) and 5-(N-ethyl-N-isopropyl)amiloride (EIA). In the absence of inhibitor, UDCA increased biliary HCO3- concentration ([HCO3-]) up to an apparent maximum of 60-70 mM, and bile flow and biliary HCO3- output appeared to be linearly related over a sixfold range of bile flow rates. Amiloride, DMA, and EIA each produced a concentration-dependent inhibition of UDCA-stimulated bile flow and biliary HCO3- output with an apparent rank order potency (EIA greater than DMA greater than amiloride) similar to that reported for inhibition of Na+-H+ exchange in other systems. None of the inhibitors significantly altered biliary UDCA output or the relationship between UDCA-induced bile flow and either biliary [HCO3-] or biliary HCO3- output. Effects of these inhibitors did not appear attributable either to nonspecific toxicity, as reflected by hepatic release of lactate dehydrogenase or K+, or to inhibition of hepatic Na+-K+-ATPase, measured as Na+-dependent uptake of 86Rb. In contrast to their effects on UDCA choleresis, these inhibitors had little or no effect on basal bile flow, biliary [HCO3-], and biliary HCO3- output. These findings indicate that UDCA-induced but not basal bile formation is closely coupled to biliary HCO3- concentration and output, and they provide additional evidence that UDCA choleresis requires an intact Na+-H+ exchange mechanism.
Microsphere estimates of blood flow: methodological considerations
Authors: von Ritter C. , Hinder R. A. , Womack W. , Bauerfeind P. , Fimmel C. J. , Kvietys P. R. , Granger D. N. , Blum A. L.
Published: December 2017

The microsphere technique is a standard method for measuring blood flow in experimental animals. Sporadic reports have appeared outlining the limitations of this method. In this study we have systematically assessed the effect of blood withdrawals for reference sampling, microsphere numbers, and anesthesia on blood flow estimates using radioactive microspheres in dogs. Experiments were performed on 18 conscious and 12 anesthetized dogs. Four blood flow estimates were performed over 120 min using 1 X 10(6) microspheres (15 microns) each time. The effects of excessive numbers of microspheres (13 million), pentobarbital sodium anesthesia (30 mg/kg), and replacement of volume loss for reference samples with dextran 70 were assessed. In both conscious and anesthetized dogs a progressive decrease in gastric mucosal blood flow and cardiac output was observed over 120 min. This was also observed in the pancreas in conscious dogs. The major factor responsible for these changes was the volume loss due to reference sample withdrawals. Replacement of the withdrawn blood with dextran 70 led to stable blood flows to all organs. The injection of excessive numbers of microspheres did not modify hemodynamics to a greater extent than did the injection of 4 million microspheres. Anesthesia exerted no influence on blood flow other than raising coronary flow. We conclude that although blood flow to the gastric mucosa and the pancreas is sensitive to the minor hemodynamic changes associated with the microsphere technique, replacement of volume loss for reference samples ensures stable blood flow to all organs over a 120-min period.
Cephalic phase response of pancreatic exocrine secretion in conscious dogs
Authors: Ohara I. , Otsuka S. , Yugari Y.
Published: December 2017

The effects of three taste solutions on the cephalic phase of pancreatic secretion were studied in conscious dogs. Male beagle dogs weighing 9-11 kg were prepared with gastric and duodenal fistulas. Gustatory receptors were stimulated for 5 min with 100 ml of 0.5% agar solutions containing 0.05, 0.12, and 0.3 M of either sodium chloride, sucrose, or monosodium glutamate (MSG). Pancreatic juice was collected every 5 min before and after stimulation, and volume flow and protein output were measured. Pancreatic secretory responses were found to vary with the type of taste stimulus. Sucrose was a better stimulus than MSG for both protein output and volume flow. Taste stimulation with sodium chloride produced a lower pancreatic response than those with sucrose or MSG.
Isolation and characterization of populations of mature and immature rat colonocytes
Authors: Ahnen D. J. , Reed T. A. , Bozdech J. M.
Published: December 2017

A nonenzymatic method is described for the isolation of viable populations of mature and immature rat colonocytes. Histology was used to monitor colocyte dissociation and to systematically characterize the amount of cross-contamination between populations of mature luminal cells and immature crypt cells. The mature colonocytes were 87 +/- 9% pure with respect to contamination from cells from the lower half of the colonic crypt, and the immature populations were 98% pure with respect to contamination with cells from the upper half of the colonic crypt. Neither population contained significant numbers of cells from the lamina propria. Cell viability and synthetic function were maintained for 10-12 h in short-term culture. Alkaline phosphatase activity was 1.59 +/- 0.01-fold higher in the mature cells than in the immature cells, and in vivo [3H]thymidine incorporation was 2.9 +/- 0.4-fold greater in the immature than the mature populations. Immature colonocytes synthesized protein in vitro at a rate of 2.5 +/- 0.4-fold higher than the mature cells, whereas fucoprotein synthetic rates and the secretory products were comparable in the two populations. Cell surface iodination revealed that the major iodinatable cell surface proteins were common to both cell populations. These studies demonstrate that highly enriched populations of mature and immature rat colonocytes that maintain viability and synthetic function in short-term culture can be prepared. The intrinsic rate of protein synthesis is higher in immature colonocytes, and a shift to synthesis of a higher percentage of fucoproteins occurs during colonocyte differentiation. In contrast to results in the small intestine, only modest gradients of differentiation markers and cell surface protein expression were observed between mature and immature colonocytes.
Selective modulation of hepatic and ileal Na+-K+-ATPase by bile salts in the rat
Authors: Simon F. R. , Sutherland E. , Sutherland J.
Published: December 2017

Sodium-potassium adenosinetriphosphatase (Na+-K+-ATPase) is modulated by functional demands. We determine whether Na+-K+-ATPase specific activity was changed by oral administration of different bile salts and whether upregulation in the liver is due to increased numbers of catalytic units. In rats after bile duct drainage for 18 h, Na+-K+-ATPase activity was reduced to 50% of control in liver and ileum but unchanged in jejunum and kidney. Increased Na+-K+-ATPase activity after short-term feeding of bile salts was noted only following trihydroxy bile salts, i.e., taurocholate (100 mg/100 g body wt) increased hepatic Na+-K+-ATPase 143% and ileum 138% above control, whereas jejunum and kidney were unchanged. Chronic feeding of trihydroxy bile salts for 4 days increased hepatic Na+-K+-ATPase (214-260%) and alkaline phosphatase (189-274%), whereas 5'-nucleotidase and Mg2+-ATPase activities were unchanged from control. Plasma membrane Na+-K+-ATPase activity significantly increased as early as 4 h after taurocholate administration, whereas homogenate activity did not rise until 16 h; both reached a new steady state between 24 and 48 h. Sixteen hours after bile salt feeding, increased Na+-K+-ATPase activity was blocked by cycloheximide, and in the liver increased enzyme activity (179%) was associated with a comparable change in sodium-dependent [gamma-32P]ATP binding (162%) to liver plasma membrane fractions. These studies show Na+-K+-ATPase activity adapts selectively in liver and ileum following administration of trihydroxy bile salts, and the process involves increased density of Na+-K+ pump sites on the liver plasma membrane.
pH regulatory mechanisms in rat pancreatic ductal cells
Authors: Stuenkel E. L. , Machen T. E. , Williams J. A.
Published: December 2017

The mechanisms underlying regulation of intracellular pH (pHi) by rat pancreatic duct cells were studied by use of the pH-sensitive, fluorescent, cytoplasmically trapped dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Cells exhibited a mean pHi of 7.18 +/- 0.14 in bicarbonate-buffered medium, as calculated from the BCECF fluorescence ratio. Removal of extracellular Na (Nao) caused an intracellular acidification that was rapidly reversed by Na replacement and occurred independently of Clo. Amiloride (10(-3) M) reversibly blocked Na-dependent recovery after Na-free-induced acidification. These results demonstrate the presence of a Na+-H+ exchange mechanism in pancreatic duct cells. Replacement of Clo with gluconate caused an intracellular alkalinization that was reversed by replacement of Cl. Application of the disulfonic stilbene derivatives, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) and dihydro-DIDS (2 X 10(-4) M), resulted in block of both Cl-dependent recovery from Na-gluconate and the onset of alkalinization of transition from NaCl to Na-gluconate. Chloride-dependent alteration of pHi occurred independently of Nao. These results demonstrate the presence of an anion exchange mechanism consistent with Cl--HCO3- exchange. Thus pancreatic duct cells contain both Na+-H+ and Cl--HCO3- exchangers.
Age-related loss of nongoblet crypt cells parallels decreased secretion in rabbit descending colon
Authors: Braaten B. , Madara J. L. , Donowitz M.
Published: December 2017

The effects of aging on active electrolyte transport and epithelial cell morphology were studied in rabbit descending colon. The rate of electrolyte transport was determined using the voltage-clamp technique, while computerized morphometric techniques were used to describe age-related and secretion-induced changes in histology. Comparison of percent water content of fecal pellets between young (2-3 mo) and mature (3.5-5 yr) animals demonstrated that mature animals had significantly decreased percent stool water. In mature animals, the total number of crypt epithelial cells was significantly less than in young animals, primarily due to the loss of crypt nongoblet cells. Crypt goblet cell number and area were not significantly changed from young to mature, while the crypt nongoblet cell number and area declined 38 and 28%, respectively, in the mature colon. Theophylline elicited dilatation of the crypt lumen. The decreased crypt nongoblet cell area correlated with a decreased theophylline-induced Cl- secretory response observed in the mature colon as measured by the change in short-circuit current (Isc). Also, a significant decrease in theophylline-stimulated active Cl- secretion was observed in mature vs. young animals in the presence of mucosal barium (5 mM) to eliminate active K+ secretion. The maximum theophylline plus barium-induced increase in Isc in young colon was 3.4 +/- 0.3 mueq.cm-2.h-1 and in mature colon 2.5 +/- 0.3 mueq.cm-2.h-1 (P less than 0.05). No significant difference in basal Isc and amiloride-inhibitable Na+ absorption was found between young and mature animals. The decreased capacity to secrete Cl- and the decrease in number and area of crypt nongoblet cells corresponds with the decrease in percent water content of mature fecal pellets.
Na+-glycine cotransport in canalicular liver plasma membrane vesicles
Authors: Moseley R. H. , Ballatori N. , Murphy S. M.
Published: December 2017

By use of purified rat canalicular liver plasma membrane (cLPM) vesicles, the present study determined the driving forces for glycine transport across this membrane domain. Initial rates of [3H]glycine uptake (10 microM) in cLPM vesicles were stimulated by an inwardly directed Na+ gradient but not by a K+ gradient. Na+ gradient-dependent uptake of glycine demonstrated cation specificity for Na+, dependence on extravesicular Cl-, stimulation by an intravesicular-negative membrane potential, and inhibition by dissipation of the Na+ gradient with gramicidin D. Na+ gradient-dependent glycine cotransport also demonstrated greater sensitivity to inhibition by sarcosine than 2-(methylamino)-isobutyric acid. Accelerated exchange diffusion of [3H]glycine was demonstrated in the presence of Na+ when cLPM vesicles were preloaded with glycine but not with L-alanine or L-proline. Substrate velocity analysis of net Na+-dependent [3H]glycine uptake over the range of amino acid concentrations from 5 microM to 5 mM demonstrated two saturable transport systems, one of high capacity (2.2 +/- 0.2 nmol.mg protein-1.15 s-1) and low affinity (11.2 +/- 1.7 mM) and one of low capacity (51 +/- 14 pmol.mg protein.15 s-1) and comparatively high affinity (66 +/- 12 microM). These results indicate that, in addition to previously described neutral and anionic amino acid transport systems, Na+ gradient-dependent glycine transport mechanisms are present on the canalicular domain of the liver plasma membrane. These canalicular reabsorptive mechanisms may serve to reclaim some of the glycine generated within the canalicular lumen from the intrabiliary hydrolysis of glutathione.
Characterization of calcium transport by basolateral membrane vesicles of human small intestine
Authors: Kikuchi K. , Kikuchi T. , Ghishan F. K.
Published: December 2017

The present studies investigated the mechanism of Ca2+ transport across basolateral membrane vesicles (BLMVs) prepared from human small intestine. Ca2+ uptake represented transport into the intravesicular space as evident by osmolality study and by the demonstration of Ca2+ efflux from the intravesicular space by Ca2+ ionophore A23187. Ca2+ uptake was stimulated by Mg2+-ATP. Kinetic parameters for ATP-dependent Ca2+ uptake revealed a Michaelis constant (Km) of 0.02 +/- 0.01 microM and a maximum rate of uptake (Vmax) of 1.00 +/- 0.03 nmol.mg protein-1.min-1.Ca2+ uptake in the absence of Mg2+ was inhibited by 75%. The Km of ATP concentration required for half-maximal Ca2+ uptake was 0.50 +/- 0.1 mM. Calmodulin (10 micrograms/ml) increased Vmax to 1.62 +/- 0.02 nmol.mg protein-1.min-1 (P less than 0.001). Km values were 0.017 +/- 0.001 microM, which was not significantly different from control values. Basolateral membranes depleted of calmodulin by EDTA osmotic shock decreased ATP-dependent Ca2+ uptake by 65%. Trifluoperazine, an anticalmodulin drug, inhibited ATP-dependent Ca2+ uptake by 50%, while no inhibition was noted in calmodulin-depleted membranes. Efflux of Ca2+ in the BLMVs was stimulated by trans-Na+. Na+-dependent Ca2+ uptake was saturable with respect to Ca2+ concentration and exhibited a Km of 0.09 +/- 0.03 microM and a Vmax of 1.08 +/- 0.01 nmol.mg protein-1.min-1. These results are consistent with the existence of a Na+-Ca2+ exchange system and ATP and Mg2+-dependent, calmodulin-regulated Ca2+, transport mechanism in BLMVs of human enterocytes.
Effect of methylene blue and N-ethylmaleimide on internal anal sphincter relaxation
Authors: Moummi C. , Rattan S.
Published: December 2017

The present studies were performed in vitro to define the participation of regulatory cyclic nucleotides in the relaxation of internal anal sphincter (IAS) smooth muscle in response to neural stimulation by electrical field stimulation (EFS) vs. exogenous vasoactive intestinal peptide (VIP). EFS and VIP both caused relaxation of the resting tone in the opossum-isolated IAS smooth muscle strips. The addition of permeant cyclic nucleotide derivatives, the guanylate cyclase stimulant sodium nitroprusside (SNP), and the adenylate cyclase stimulant forskolin caused a dose-dependent fall in the resting tension of IAS smooth muscle. The inhibitory effect of the agonists on the IAS smooth muscle was not modified by tetrodotoxin (TTX), a neurotoxin. TTX almost abolished the IAS responses to EFS. The effects of SNP and forskolin were selectively blocked by the putative inhibitors of corresponding enzyme systems, i.e., methylene blue (MB) (3 X 10(-5) M) for guanylate cyclase and N-ethylmaleimide (NEM) (10(-4) M) in the case of adenylate cyclase. NEM and not MB caused significant antagonism of the fall in IAS tension in response to both EFS and VIP during the control experiments. Such data suggest a common biochemical link (adenosine 3',5'-cyclic monophosphate as second messenger system) between the IAS smooth muscle relaxations with neural stimulation and VIP. In addition, a part of the IAS smooth muscle relaxation in response to EFS also involves the mediation of guanosine 5'-cyclic monophosphate.
Metabolism of gastrin and cholecystokinin by endopeptidase 24.11 from the pig stomach
Authors: Bunnett N. W. , Debas H. T. , Turner A. J. , Kobayashi R. , Walsh J. H.
Published: December 2017

The purpose of this investigation is to examine the metabolism and inactivation of human and porcine gastrin 17 (nonsulfated) (G-17) and cholecystokinin octapeptide (sulfated) (CCK-8) by gastric endopeptidase 24.11. Endopeptidase 24.11 was isolated by immunoaffinity chromatography using a monoclonal antibody to the kidney enzyme. Peptides were incubated with endopeptidase 24.11. The digests were either fractionated by reverse-phase high-pressure liquid chromatography and the products identified by amino acid analysis or they were used for bioassays. Digests of human gastrin were assayed for stimulation of acid secretion in the anesthetized rat, and cholecystokinin digests were assayed for the stimulation of amylase secretion from isolated rat pancreatic acini. Human G-17 was degraded by cleavage of the Trp4-Leu5,Ala11-Tyr12,Gly13-Trp14,Trp14 -Met15, and Asp16-Phe17-NH2 bonds, and the fragments (1-16), (1-13), (1-11), (1-4), (5-11), (5-13), (12-13), (12-14), (14-16), and (17-NH2) were identified. Porcine G-17 was degraded by hydrolysis of the Ala11-Tyr12,Gly13-Trp14, and Asp16-Phe17-NH2 bonds producing (1-16), (1-13), (1-11), (12-13), (14-16), and (17-NH2) fragments. CCK-8 was degraded by hydrolysis of the Gly4-Trp5 and Asp7-Phe8-NH2 bonds, and the fragments (1-7), (1-4), (5-7), (5-8), and (8-NH2) were identified. There was a progressive decline in the biological activity with incubation time.
Splanchnic nerve stimulation inhibits duodenal HCO3- secretion in the rat
Authors: Jonson C. , Fandriks L.
Published: December 2017

Sympathoadrenergic inhibition of HCO3- secretion by the duodenal mucosa was studied in chloralose anesthetized rats. Duodenal HCO3- secretion was measured in situ by pH-stat titration. Direct efferent electrical stimulation of the cut splanchnic nerves (10 Hz, supramaximal intensity) inhibited the duodenal alkaline output by approximately 50%. This inhibitory response was blocked by the administration of either the adrenolytic agent guanethidine or the alpha 2-adrenoceptor antagonist yohimbine. However, neither the alpha 1-adrenoceptor antagonist prazosin nor the beta-adrenoceptor antagonist propranolol blocked the response to splanchnic nerve stimulation. The present data suggest that electrical splanchnic nerve stimulation inhibits duodenal HCO3- secretion via activation of adrenergic nerve fibers and alpha 2-adrenoceptors within the peripheral nervous system.
Role of bicarbonate in biliary excretion of diisothiocyanostilbene disulfonate
Authors: Anwer M. S. , Nolan K. , Hardison W. G.
Published: December 2017

Hepatic transport of 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) was studied in isolated perfused rat livers and in isolated rat hepatocytes to determine if DIDS-induced decrease in biliary HCO3- excretion is due to a DIDS-HCO3- exchange and/or due to inhibition of Cl(-)-HCO3- exchange. In isolated perfused rat livers, DIDS reversibly decreased biliary HCO3- concentration and excretion. The changes in biliary HCO3- concentration were inversely related to biliary DIDS concentration. DIDS was concentrated in bile, indicating active hepatic transport. Replacement of perfusate HCO3- with equimolar dimethyloxazolidinedione (DMO) or tricine decreased biliary excretion, but not hepatic uptake, of DIDS. Biliary excretion of DIDS was also associated with a decrease in bile pH, and this decrease in pH was greater in the presence of HCO3-. HCO3-, but not DMO or tricine, stimulated DIDS efflux from preloaded hepatocytes. DIDS efflux was also temperature dependent and increased with increasing extracellular pH. Collectively, these results are consistent with the presence of a DIDS-HCO3- (OH-) exchange mechanism at the canalicular membrane. HCO3(-)-dependent Cl- uptake in hepatocytes was competitively inhibited by DIDS (Ki = 0.24 mM), confirming the presence of DIDS-inhibitable Cl(-)-HCO3- exchange. However, the ability of DIDS to decrease biliary HCO3- excretion persisted when perfusate Cl- was replaced by isethionate. Moreover, biliary HCO3- concentration returned to base line despite the presence of 2-6 mM DIDS in bile. Thus it seems unlikely that the inhibition of Cl(-)-HCO3- exchange by DIDS is a major mechanism of inhibition of HCO3- excretion. We, therefore, conclude that a DIDS-HCO3- (OH-) exchange at the canalicular membrane is the most likely explanation for the observed decrease in biliary HCO3- excretion.
Effect of ileal infusion of lipid on jejunal motor patterns after a nutrient and nonnutrient meal
Authors: Welch I. M. , Davison P. A. , Worlding J. , Read N. W.
Published: December 2017

To investigate how ileal lipid delays small bowel transit, pressure activity was recorded at multiple sites in the human small intestine during ileal infusion of either lipid or saline. Initial studies showed that ileal lipid reduced the contraction rate in the jejunum but not in the duodenum or ileum. The effect of ileal lipid was further investigated by recording pressures at seven sites in the jejunum after ingestion of either a nutrient or a nonnutrient meal. The nutrient meal induced an irregular motility pattern; ileal lipid significantly reduced the contraction rate, the percentage of contractions involved in propagated events, the mean length of propagation, and the propagation index. The nonnutrient meal induced a pattern containing discrete clusters of contractions. Ileal lipid significantly reduced the occurrence of contraction clusters and the mean length of propagation. Thus, although the delay in small bowel transit observed during ileal infusion of lipid can be explained by reductions in the rate and the degree of propagation of jejunal contractions, the mechanism varies according to the type of meal.
Effects of cholecystokinin on pancreatic ornithine decarboxylase gene expression
Authors: Rosewicz S. , Lewis L. D. , Liddle R. A. , Logsdon C. D.
Published: December 2017

The effects of cholecystokinin (CCK) on pancreatic ornithine decarboxylase (ODC) gene expression were studied in the rat. Plasma CCK concentrations were raised to levels comparable to postprandial values either by intravenous infusion of CCK octapeptide (CCK-8) or by intraduodenal perfusion of soybean trypsin inhibitor (SBTI). ODC mRNA levels were quantified using a cloned cDNA probe. ODC mRNA increased to 166 +/- 34% (n = 4) of control after 1 h, peaked at 254 +/- 39% (n = 4) of control after 24 h, and remained significantly elevated for up to 48 h of SBTI infusion. Intravenous infusion of CCK-8 for 24 h increased ODC mRNA levels to the same extent observed with SBTI infusion. The CCK receptor antagonist L364,718 by itself had no effect on ODC mRNA levels but totally abolished the induction of ODC mRNA by both intravenous CCK infusion and intraduodenal infusion of SBTI. These data therefore indicate that CCK plasma concentrations comparable to postprandial values regulate pancreatic ODC at a pretranslational level and that SBTI exerts its effects on pancreatic ODC via an increase in plasma CCK.
Evidence for inhibition of opossum LES through intrinsic gastric nerves
Authors: Schulze-Delrieu K. , Percy W. H. , Ren J. , Shirazi S. S. , Von Derau K.
Published: December 2017

We have studied the mechanical responses of the isolated opossum gastroesophageal junction to a variety of stimuli. Lower esophageal sphincter (LES) relaxations were readily produced by gastric stretch and by electrical stimulation of the intramural gastric nerves. Gastric stimulation also led in 60% of stimuli to a contraction of circular muscle (the off response) in the distal esophagus, but in less than 15% of stimuli to a contraction of longitudinal esophageal muscle (the duration response). Mechanical or electrical stimulation of the esophagus led to a mechanical response of the stomach (relaxation, contraction, or both) in 76% of stimuli. The LES relaxation produced by esophageal stimulation was not as long as that produced by gastric stimulation. Direct electrical stimulation of the esophageal or gastric muscle produced a ring contraction that spread readily across the gastroesophageal junction but did not produce a relaxation of the LES or a contraction of the longitudinal esophageal muscle. Thus intramural nervous pathways can coordinate the mechanical activity of the esophagus, LES, and stomach. LES relaxations may occur as part of intrinsic reflexes that mediate gastric accommodation to volume.
Effect of PCO2 on intracellular pH in in vitro frog gastric mucosa
Authors: Carter K. J. , Saario I. , Seidler U. , Silen W.
Published: December 2017

Steady-state intracellular pH (pHi) in 0, 5, and 10% CO2-buffered Ringer solution in sheets of in vitro frog gastric antral or fundic mucosa has been measured using the pH-sensitive fluorescent dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). In tissues perfused with N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES)-100% O2 buffer [extracellular pH (pHo) = 7.14], steady-state pHi in antral surface cells was 7.08 +/- 0.06 (n = 8), in fundic oxynticopeptic cells 6.91 +/- 0.03 (n = 13), in the muscularis mucosa 7.58 +/- 0.06 (n = 4). In mucosae perfused with 17.8 mM HCO3- -95% O2-5% CO2 buffer (pHo = 7.14), steady-state pHi in antral surface cells was 6.97 +/- 0.02 (n = 22), in fundic oxynticopeptic cells 7.00 +/- 0.04 (n = 18), and in fundic muscularis mucosa 7.39 +/- 0.05 (n = 8). In fundic oxynticopeptic cells perfused with 35.6 mM HCO3- -90% O2-10% CO2 (pHo = 7.14) steady-state pHi was 6.77 +/- 0.07 (n = 4). In tissues equilibrated initially with 100% O2 and changed to 5% CO2, antral surface cells acidified by 0.21 pH units and fundic oxynticopeptic cells by 0.10 pH units, with restoration of pHi to resting levels within 30 and 10 min, respectively. Exposure of tissues initially equilibrated with 5% CO2 to 100% O2 alkalinized antral surface cells by 0.22 pH units and fundic oxynticopeptic cells by 0.23 pH units, with only partial recovery of pHi by 30 min. These data suggest that steady-state pHi is equivalent in surface and oxynticopeptic cells and is lower than in the muscularis mucosa.(ABSTRACT TRUNCATED AT 250 WORDS)
Pathways mediating CRF-induced inhibition of gastric acid secretion in rats
Authors: Druge G. , Raedler A. , Greten H. , Lenz H. J.
Published: December 2017

The pathways involved in mediating the central nervous system actions of corticotropin-releasing factor (CRF) on gastric acid secretion were examined in conscious rats. CRF (0.1-2.0 nmol) given cerebroventricularly inhibited gastric acid secretion stimulated by pentagastrin (P less than 0.01). This effect was abolished by cerebroventricular but not intravenous administration of a specific CRF receptor antagonist, alpha-helical CRF-(9-41). Ganglionic blockade with chlorisondamine chloride, noradrenergic blockade with bretylium, or adrenalectomy abolished the gastric inhibitory action of CRF whereas truncal vagotomy or opiate blockade with naloxone did not. A vasopressin receptor antagonist significantly inhibited but did not abolish the gastric inhibitory action of CRF. An intravenous infusion of epinephrine that mimicked the epinephrine plasma concentrations which were observed after cerebroventricular administration of CRF did not alter pentagastrin-stimulated gastric acid secretion. These results indicate that CRF acts within the central nervous system to inhibit gastric acid secretion by a specific receptor-mediated event. Inhibition of gastric acid secretion by CRF in conscious rats is mediated by efferent fibers of the sympathetic nervous system and in part by a vasopressin-dependent pathway but not by the parasympathetic nervous system, adrenal epinephrine release, or opiate-sensitive pathways.
Interaction of peptides related to VIP and secretin with guinea pig pancreatic acini
Authors: Zhou Z. C. , Gardner J. D. , Jensen R. T.
Published: December 2017

The abilities of human and rat growth hormone-releasing factors (hGHRF, rGHRF), peptide histidine isoleucine or methionine (PHI, PHM) and the Gila monster venom peptides (helospectin I, helospectin II, and helodermin) to interact with guinea pig pancreatic acini were characterized and compared with vasoactive intestinal peptide (VIP) and secretin. Each peptide caused a sevenfold stimulation of amylase release, and the relative potencies were: VIP greater than helospectin I = helospectin II = helodermin = rGHRF greater than PHI = PHM greater than hGHRF greater than secretin. Each peptide inhibited 125I-labeled VIP binding, and the relative potencies agreed closely with those for stimulating enzyme secretion. Each peptide inhibited 125I-labeled secretin binding with the potencies: secretin greater than helospectin I = helospectin II = helodermin greater than rGHRF = PHI = VIP greater than PHM greater than hGHRF. Each peptide caused a 78-fold increase in adenosine 3',5'-cyclic monophosphate cAMP. VIP or rGHRF and PHI or PHM demonstrated high and low selectivity, respectively, for VIP receptors, secretin high selectivity for the secretin receptor, and helospectin I or II and helodermin a relatively high affinity for both VIP and secretin receptors. Correlation of the ability of each peptide to increase cAMP or amylase release and inhibit binding of 125I-VIP or 125I-secretin suggested all the actions of these peptides could be explained by the occupation of VIP or secretin receptors. To investigate this further, 125I-labeled helodermin was prepared, and binding was saturable, specific, and could be accounted for by the binding to VIP or secretin receptors.(ABSTRACT TRUNCATED AT 250 WORDS)
Regulation of intestinal biotin transport in the rat: effect of biotin deficiency and supplementation
Authors: Said H. M. , Mock D. M. , Collins J. C.
Published: December 2017

The effect of biotin deficiency and supplementation at pharmacological doses on the intestinal transport of the vitamin was examined in the rat using a brush-border membrane vesicle (BBMV) technique. Transport of biotin in both jejunal and ileal BBMV was significantly (P less than 0.05-0.01) higher in biotin-deficient rats compared with control (pair-fed) rats. This increase in biotin transport appeared to be specific because transport of D-glucose was similar in the two rat groups. The increase in biotin transport in the deficient rats appeared to be mediated through a marked increase (146-230%) in the Vmax of the biotin transport process (with minimal change in the apparent Km), suggesting an increase in the number of the transport carriers. In contrast, supplementation at pharmacological doses of biotin caused significant (P less than 0.05-0.01) and specific decrease (suppression) in biotin transport compared with (unsupplemented) controls. The suppression of biotin transport in the supplemented rats appeared to be mediated through a marked decrease (58%) in the Vmax of the biotin transport process (with minimal change in the apparent Km), suggesting a decrease in the number of the transport carriers. These results provide evidence that biotin transport in the intestine is regulated by the level of the vitamin in the diet (and/or body stores). Furthermore, the results demonstrate the ability of the small intestine to adapt to the challenge of deficiency of an essential nutrient, a capability that may be crucial for the survival of the animal.
Bombesin ingestion stimulates epithelial digestive cell proliferation in suckling rats
Authors: Puccio F. , Lehy T.
Published: December 2017

The characterization of a bombesin-like peptide in the breast milk of some mammals might suggest that this peptide may influence, in part, the postnatal development of the digestive tract. To test this hypothesis, our experiments investigated whether oral administration of bombesin affects epithelial progenitor cell proliferation in digestive organs of suckling and weaned rats. Four series of pups were given bombesin diluted in milk (20 micrograms/kg, 3 times daily) or milk alone, for 5 days during either the first, second, third, or fourth week of life. Pups were killed after [3H]thymidine pulse labeling. DNA labeling and mitotic indices were estimated in the oxyntic, antral, colonic mucosae, and exocrine pancreas. In all tissues examined, oral bombesin significantly increased over control values the two cell proliferative parameters studied during the suckling period (P less than 0.05 to P less than 0.001). In bombesin-treated rats, maximal stimulation of these parameters occurred in the second week of life. This effect of oral bombesin on the cell kinetics disappeared in all tissues after weaning. This study confirms the growth-promoting effect of bombesin observed on the digestive system of the neonatal rat after subcutaneous administration of the peptide and shows that bombesin, when given orally to suckling rats, is sufficiently resistant to proteolysis to enable it to exert a stimulatory effect on digestive cell proliferation. However, our findings as such do not prove that milk bombesin-like peptide has a physiological influence on the developing gastrointestinal tract and pancreas.
Effect of hypertonic stress on liver cell volume, bile flow, and volume-regulatory K+ fluxes
Authors: Haddad P. , Thalhammer T. , Graf J.
Published: December 2017

Net hepatic uptake and release of K+ were studied in the isolated-perfused rat liver subjected to a 10-min period of hyperosmotic stress by addition of 80 mM mannitol or sucrose to the perfusing solution. Bile flow and effluent Na+, K+, and Ca2+ activities were monitored throughout. Upon initiation of hypertonic stress, a sharp transient dilution of effluent ion activities indicated hepatic water losses that were larger and occurred more rapidly with sucrose than with mannitol. During continuous hyperosmotic perfusion, portocaval differences in K+ uncovered a steady net influx of the ion into the liver that reached a higher maximum and led to a greater accumulation in experiments with sucrose compared with mannitol. This hepatic K+ uptake was completely blocked by 1 mM ouabain. Upon return to isotonic conditions, a sharp transient concentration of effluent ion activities suggested hepatic water uptake that was again more rapid and pronounced in sucrose- than mannitol-treated livers. This was followed by a transient phase of net hepatic K+ release whose magnitude and duration were proportional to the water movements induced by the removal of each carbohydrate. Administration of 2 mM Ba2+ abolished this K+ efflux. These results indicate that mannitol equilibrates between extra- and intracellular compartments, whereas sucrose apparently does not. The data also suggest that net movements of K+ may be involved in the regulatory volume responses induced by hyperosmotic stress and return to normal tonicity, respectively.
Identification of the intestinal Na-phosphate cotransporter
Authors: Peerce B. E.
Published: December 2017

Na-dependent phosphate uptake in intestinal brush-border membrane vesicles was sensitive to arginine group-specific reagents in a substrate-sensitive manner. Four different arginine group-specific reagents were tested. All four reagents irreversibly inhibited Na-dependent phosphate uptake with the concentration for 50% inhibition, K0.5, varying between 150 and 40 microM. Maximum inhibition approached 80%. Addition of substrates during exposure to these reagents resulted in protection of Na-phosphate cotransport only in the presence of Na and phosphate. Na-phosphate cotransporter labeling at or near the phosphate site was accomplished using a pretreatment step with phenylglyoxal and substrates followed by a fluorescent phenylglyoxal-labeling step. Fluorescein isothiocyanate-phenylglyoxal (FITC-PG) specifically labeled a 130-kDa polypeptide on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) in a substrate-sensitive manner, consistent with its effect on Na-phosphate cotransport. n-Acetylimidazole (NAI) inhibited Na-phosphate cotransport in a Na+- but not K+ -sensitive manner. NAI or fluorescein n-acetylimidazole (FNAI) inhibited Na-dependent phosphate uptake with a K0.5 for inhibition of 38 microM. Maximum inhibition of Na-phosphate cotransport was 75%. On SDS-PAGE, FNAI labeled five polypeptide bands in a Na-sensitive manner including the 130-kDa polypeptide band labeled by FITC-PG. Of these five bands only the 130-kDa polypeptide lost substrate protectability against FITC-PG inhibition of Na-phosphate cotransport and FITC-PG labeling on prior exposure to NAI in the absence of Na+. On this basis the 130-kDa polypeptide is tentatively identified as the intestinal Na-phosphate cotransporter and this polypeptide band contains both the Na substrate site and the phosphate substrate site.
Endothelin has potent ulcerogenic and vasoconstrictor actions in the stomach
Authors: Wallace J. L. , Cirino G. , De Nucci G. , McKnight W. , MacNaughton W. K.
Published: December 2017

The role of endothelin, an endothelium-derived constricting factor, as a mediator of gastric ulceration was assessed using an ex vivo gastric chamber model in the rat. The rats were pretreated with indomethacin, and endothelin was infused intravenously or intra-arterially at various doses while the stomach was topically "challenged" with 20% ethanol. This concentration of ethanol did not, by itself, produce hemorrhagic damage in the stomach. However, infusion of endothelin rendered the mucosa vulnerable to damage induced by the ethanol. In a dose-dependent manner, endothelin increased the extent of hemorrhagic damage and the efflux of protein from the gastric mucosa. The effects of endothelin were less marked in rats not pretreated with indomethacin. The ulcerogenic actions of endothelin were not significantly affected by pretreatment with a platelet-activating factor antagonist or a leukotriene D4 antagonist. However, topical pretreatment with sodium nitroprusside produced a significant reduction in the damage induced by intravenous endothelin and topically applied ethanol. Endothelin also rendered the stomach vulnerable to damage induced by hydrochloric acid at a concentration (0.15 M) tolerated by control mucosa. Using an in vitro vascularly perfused rat stomach preparation, we found that endothelin produces marked increases in gastric vascular tone at nanomolar concentrations. These results suggest that the factors regulating the release of endothelin, and the balance between endothelial production of relaxing and contracting factors, may be important in the pathogenesis of ulcerative diseases of the stomach.
Development of rat jejunum: lipid permeability, physical properties, and chemical composition
Authors: Meddings J. B. , Theisen S.
Published: December 2017

This study reports the correlation between jejunal microvillus membrane's chemical composition, physical properties, and lipid permeability over the age range of 9-25 days in the rat. During this period of time the diet varies from entirely maternal milk (9 days, suckling) to milk plus chow (18 days, weaning) to finally predominantly chow (25 days, weaned). Lipid permeability was found to be greatest during the suckling period but decreased rapidly over the subsequent 2 wk of life. Alterations in lipid permeability were correlated with maturation of the microvillus membrane, both in terms of its lipid fluidity and chemical composition. The static component of membrane fluidity did not vary significantly over this time period, in agreement with a constant molar ratio of cholesterol-to-phospholipid (0.87 +/- 0.08, 0.94 +/- 0.07, and 0.84 +/- 0.04 at ages 9, 18, and 25 days, respectively). However, decreasing membrane lipid permeability correlated with decreasing lipid fluidity assessed by probes sensitive to the dynamic component of membrane lipid fluidity within the superficial regions of the bilayer. Furthermore, by measurement of the incremental change in free energy associated with a methylene group partitioning into the microvillus membrane, the hydrophobicity of the membrane could be assessed in vivo. These data demonstrate that suckling rats have the most hydrophobic microvillus membrane (-459 +/- 30 cal/mol), but with maturation a decline in membrane hydrophobicity occurred (-358 +/- 60 cal/mol). The results suggest that during the first 3 wk of life the jejunal microvillus membrane of the rat undergoes a maturation process that is well suited to the change in dietary nutrients ingested. Furthermore, changes in lipid permeability, in vivo properties of the microvillus membrane, and the associated change in lipid fluidity are similar to associations recently recognized in the adult animal.
Medullary sites for TRH analogue stimulation of gastric contractility in the rat
Authors: Garrick T. , Stephens R. , Ishikawa T. , Sierra A. , Avidan A. , Weiner H. , Tache Y.
Published: December 2017

Medullary sites at which the stable thyrotropin-releasing hormone (TRH) analogue, RX 77368 (p-Glu-His-[3,3'-dimethyl]-Pro-NH2), stimulates gastric contractility were investigated in rats under urethan anesthesia. The peptide analogue was microinjected in 50-100 nl of volume unilaterally into various brain stem nuclei using glass micropipettes (50 microns). Gastric contractility was recorded continuously with acutely implanted strain-gauge force transducers and traces analyzed by computer. RX 77368 (2.6-77 pmol) microinjected into the dorsal vagal complex (DVC) dose dependently stimulated gastric contractility. Peptide action (77 pmol) had a rapid onset with a peak response at 15 min, continued for 45 min after the microinjection, and was blocked by vagotomy. TRH microinjected into the DVC had a shorter duration of action. RX 77368 (0.7-77 pmol) microinjected into the nucleus ambiguus also dose dependently stimulated gastric contractions. In contrast, microinjection of RX 77368 (77 pmol) into the hypoglossal nucleus had no effect. These findings demonstrate that the DVC and nucleus ambiguus are sites of action for TRH-induced stimulation of gastric contractility in the rat. The effect is dose dependent, long lasting, site specific, and vagally mediated. These results are consistent with a possible physiological role for medullary TRH in the vagal regulation of gastric contractility.
Increased sinusoidal volume and solute extraction during retrograde liver perfusion
Authors: Bass N. M. , Manning J. A. , Weisiger R. A.
Published: December 2017

Retrograde isolated liver perfusion has been used to probe acinar functional heterogeneity, but the hemodynamic effects of backward flow have not been characterized. In this study, extraction of a long-chain fatty acid derivative, 12-N-methyl-7-nitrobenzo-2-oxa-1,3-diazol-amino stearate (12-NBDS), was greater during retrograde than during anterograde perfusion of isolated rat liver. To determine whether hemodynamic differences between anterograde and retrograde perfused livers could account for this finding, the hepatic extracellular space was measured for both directions of flow by means of [14C]sucrose washout during perfusion as well as by direct measurement of [14C]sucrose entrapped during perfusion. A three- to fourfold enlargement of the total hepatic extracellular space was found during retrograde perfusion by both approaches. Examination of perfusion-fixed livers by light microscopy and morphometry revealed that marked distension of the sinusoids occurred during retrograde perfusion and that this accounts for the observed increase in the [14C]sucrose space. These findings support the hypothesis that maximum resistance to perfusate flow in the isolated perfused rat liver is located at the presinusoidal level. In addition, increased transit time of perfusate through the liver and greater sinusoidal surface area resulting from sinusoidal distension may account for the higher extraction of 12-NBDS and possibly other compounds by retrograde perfused liver.
Putrescine stimulates DNA synthesis in intestinal epithelial cells
Authors: Ginty D. D. , Osborne D. L. , Seidel E. R.
Published: December 2017

Experiments were designed to examine the effects of exogenously supplied putrescine on the synthesis of DNA, RNA, and protein in cultured epithelial cells (IEC-6). Putrescine increased aphidicolin-sensitive DNA synthesis at concentrations as low as 0.3 microM putrescine with maximal stimulation (267% control) at 10 microM. This response appeared to be an effect of increases in the intracellular concentration of putrescine as the intracellular levels of spermidine and spermine did not change over the time period examined. Furthermore, pulse-chase experiments revealed that putrescine that entered the cell was not metabolized to another polyamine or degraded. In addition, 10 microM putrescine enhanced both cycloheximide-sensitive lysine incorporation and actinomycin D-sensitive uridine incorporation, indexes of protein and RNA synthesis, respectively. Incorporation of both lysine and uridine was maximal 12 h after the addition of putrescine, whereas thymidine incorporation was still increasing at 24 h, the longest time point examined. These data suggest that putrescine synthesis and/or transport during mucosal proliferation is directly involved in the stimulation of epithelial DNA, RNA, and protein synthesis.