bluuebunny/crossref_metadata_2025 huggingface dataset:
O2 uptake in periportal and pericentral regions of liver lobule in perfused liver
Authors: Matsumura T. , Kauffman F. C. , Meren H. , Thurman R. G.
Published: December 2017

O2 uptake by the perfused liver decreased at O2 concentrations considerably higher than levels that caused NADH reduction when the input O2 concentration was varied. The maximal rate of O2 uptake was two- to threefold higher in periportal (137 +/- 8 mumol . g-1 . h-1; O2 concentration = 478 +/- 37 microM) than pericentral regions (59 +/- 5 mumol . g-1 . h-1; O2 concentration = 263 +/- 21 microM); however, the O2 concentration required for half-maximal O2 uptake was similar (approximately 20 microM) in the two areas. The infusion of atractyloside, antimycin A, or KCN inhibited O2 uptake in both zones by 50–85%, indicating that O2 uptake in both regions was largely dependent on mitochondrial electron transport. The content of ATP and ADP and ATP:ADP were similar in microdissected samples from periportal and pericentral areas. In contrast, when livers were perfused in the retrograde direction, O2 uptake was two- to threefold greater in pericentral than in periportal regions. Maximal rates of O2 uptake correlated with the local O2 concentration irrespective of the direction of flow when the electrode was moved across the liver lobule with a micromanipulator. Lower rates of O2 uptake in pericentral areas were not altered appreciably by infusion of agents known to uncouple oxidative phosphorylation (DNP), increase ADP supply (fructose), or increase the NADH redox state (ethanol or octanoate). These data are consistent with the hypothesis that maximal rates of O2 uptake are regulated, in part, in the perfused liver by O2 concentrations far above the Km of cytochrome oxidase for O2.
Indomethacin and turnover of gastric mucosal cells in the rat
Authors: Baumgartner A. , Koelz H. R. , Halter F.
Published: December 2017

Mucosal morphology and the balance between cell loss and cell renewal were analyzed during treatment with a non-ulcerative dose of indomethacin. All rats were treated twice daily by subcutaneous injection of 2 mg/kg indomethacin or the solvent. The following parameters were assessed: cell proliferation on day 3 (determination of in vitro [3H]thymidine incorporation), cell migration on days 1 and 3 (autoradiography), cell shedding on days 7 and 14 (measurement of the remaining DNA-bound mucosal radioactivity after in vivo labeling with [3H]thymidine prior to treatment), mucosal morphology on day 14 (light microscopy), ex vivo mucosal prostaglandin E2 on day 14, and serum gastrin on days 0, 7, and 14. Indomethacin treatment had no effect on serum gastrin levels but reduced mucosal prostaglandin E2. Indomethacin produced a significant increase of [3H]thymidine incorporation, cell migration, and loss of mucosal DNA-bound radioactivity in the corpus and, to a lesser degree, in the antrum. Morphologically, this led to a hyperplasia of parietal cells (+15%, P less than 0.05) and chief cells (+45%, P less than 0.01) in the corpus, but antral morphology remained unchanged. We conclude that indomethacin stimulates the turnover of gastric mucosal cells. In the corpus, but not in the antrum, proliferation exceeds shedding, thus leading to increased mucosal volume.
Role of thyroxine in functional gastric development
Authors: Tseng C. C. , Johnson L. R.
Published: December 2017

The role of thyroxine (T4) on the functional development of chief and parietal cells was studied in the rat. Daily injection of thyroxine (0.1 microgram/g body wt) resulted in the precocious appearance of pepsinogen in the oxyntic gland mucosa and an increase in basal acid output. Thyroxine had no effect in adrenalectomized rats. In propylthiouracil-induced hypothyroid pups, pepsinogen content and basal acid secretion were low. Corticosterone acetate (200 micrograms/g body wt) injection increased pepsinogen content and basal acid secretion in the absence of normal levels of thyroid hormones. We conclude that the effect of thyroxine on the development of chief and parietal cells is primarily due to accompanying changes in serum corticosterone.
Intestinal blood flow and O2 uptake during hypoxemia in the newborn piglet
Authors: Nowicki P. T. , Hansen N. B. , Hayes J. R. , Menke J. A. , Miller R. R.
Published: December 2017

Previous work has indicated that the neonatal intestinal circulation responds to hypoxemia with vasoconstriction and subsequent intestinal ischemia. This work was carried out in newborn lambs, a ruminant species, and may not be representative of all newborns. Therefore, we measured intestinal blood flow, vascular resistance, tissue O2 uptake, and cardiac output during normoxemia and varying degrees of hypoxemia in newborn piglets, a nonruminant species. Hypoxemia was induced by adding N2 gas to the inspired gas mixture, and measurements were obtained over a wide range of arterial O2 contents (2.2–15.6 ml O2 X dl-1). Intestinal blood flow increased in response to moderate hypoxemia and decreased in response to severe hypoxemia. The changes in intestinal blood flow were primarily due to change in intestinal vascular resistance, not cardiac output. Intestinal O2 was independent of arterial O2 content until the latter decreased below approximately 6.5 ml O2 X dl-1. These data indicate that the response of the neonatal intestinal circulation to hypoxemia is species specific and that the nonruminant neonatal intestine is capable of vasodilation in response to moderate hypoxemia.
Adenosine export from the liver: oxygen dependency
Authors: Arnold S. T. , Cysyk R. L.
Published: December 2017

The liver is believed to be an important regulator of purine concentrations in the circulation. It has been an accepted notion that the liver exports the riboside adenosine to the circulation for use by other tissues. This phenomenon was reexamined using an artificial oxygen carrier to perfuse the isolated rat liver and high-performance liquid chromatography (HPLC) to analyze the purine content. It was found that perfusion with Krebs-Ringer-bicarbonate at a physiological flow rate as had been used by previous investigators results in a mildly hypoxic preparation, and it is this hypoxia that results in the export of adenosine. In a liver perfused with Fluosol-43, little (less than 0.05 microM) or no adenosine was released. However, if the oxygen content of Fluosol-43 was decreased, the liver could be induced to release adenosine at 1.0 microM levels. In addition, the liver was found to release adenine under control conditions; thus it is this purine base that is likely to be the important purine released by the liver for extrahepatic salvage, not adenosine as previously thought.
Colonic transit in rats: effect of ovariectomy, sex steroid hormones, and pregnancy
Authors: Ryan J. P. , Bhojwani A.
Published: December 2017

In vitro studies suggest that the female sex steroid hormones [estrogen (E) and progesterone (P)] can affect the myoelectric and mechanical activity of colonic smooth muscle. The present study was designed to examine the influence of the hormones on colonic transit in vivo. Transit was assessed by quantifying the distribution within the colon of a radiolabeled marker (0.5 microCi Na251CrO4), using the geometric center method of analysis. Studies were performed with adult male rats and the following groups of female rats: nonpregnant, ovariectomized, ovariectomy plus hormone pretreatment (100 micrograms X kg-1 X day-1 E + 2.5 mg X kg-1 X day-1 P for 4 days), and pregnant (day 18). Hormone-pretreated animals were studied 24 h following the fourth injection. The data can be summarized as follows. 1) Colonic transit was affected by the timing of the estrus cycle. Rats determined to be in proestrus-estrus had a geometric center value (1.97 +/- 0.50) significantly less than that of metestrus-diestrus animals (4.25 +/- 0.57). 2) Ovariectomy eliminated the biphasic transit pattern observed in estrus-cycling females and resulted in a geometric center value (4.19 +/- 0.17) comparable with that of the metestrus-diestrus animals. 3) E + P pretreatment of ovariectomized rats resulted in a significant decrease in the geometric center (1.94 +/- 0.19) compared with the untreated ovariectomized rats. 4) The geometric center value in pregnant animals (2.22 +/- 0.20) closely resembled the transit data for proestrus-estrus animals and hormone-pretreated animals.(ABSTRACT TRUNCATED AT 250 WORDS)
Plasma cholecystokinin and pancreatic growth during adaptation to dietary protein
Authors: Green G. M. , Levan V. H. , Liddle R. A.
Published: December 2017

The relationship among plasma cholecystokinin (CCK), pancreatic growth, and food intake was studied in rats over a 2-wk period of adaptation from a very low-protein to a very high-protein diet. Rats adapted to a control diet (5% casein) were killed at 0900 (without fasting) at 0 h, 12 h, 24 h, 48 h, 7 days, or 14 days after transfer to a high-protein diet (75% casein). CCK was measured by bioassay using isolated pancreatic acini. Plasma CCK in high protein-fed rats was increased approximately threefold in the first 24 h, but returned to control (approximately 2.5 pM) values by day 7. Pancreatic weight, DNA, protein, and chymotrypsin(ogen) significantly increased to maximal values by day 7 in high protein-fed rats. Food intake in high protein-fed rats was inhibited by 47% after 24 h but returned to control values by day 7. The results indicate that high-protein diets initially increase CCK release and increase pancreatic protease secretory capacity and that, when pancreatic protease secretion is sufficient to match protein digestive requirements, the stimulus for CCK secretion is reduced and plasma CCK returns to normal. The pronounced but transient inhibition of food intake in high protein-fed rats is consistent with a role for CCK in regulation of food intake.
Hemodynamic characterization of chronic bile duct-ligated rats: effect of pentobarbital sodium
Authors: Lee S. S. , Girod C. , Braillon A. , Hadengue A. , Lebrec D.
Published: December 2017

Systemic and splanchnic hemodynamics of the chronic bile duct-ligated rat were characterized by radioactive microspheres. Conscious and pentobarbital sodium-anesthetized, bile duct-ligated and sham-operated rats had cardiac output and regional organ blood flows determined. The conscious bile duct-ligated rat compared with the sham-operated showed a hyperdynamic circulation with an increased cardiac output (153.3 +/- 9.8 vs. 112.6 +/- 6.0 ml/min, P less than 0.005) and portal tributary blood flow (21.32 +/- 1.43 vs. 12.79 +/- 1.47 ml/min, P less than 0.005). Pentobarbital sodium anesthesia induced marked hemodynamic changes in both sham-operated and bile duct-ligated rats. The latter group was especially sensitive to its effects; thus, comparison of cardiac output and portal tributary blood flow between anesthetized bile duct-ligated and sham-operated rats showed no significant differences. We conclude that the rat with cirrhosis due to chronic bile duct ligation is an excellent model for hemodynamic investigations but should be studied in the conscious state, since pentobarbital sodium anesthesia eliminates the hyperdynamic circulation.
Proteins but not amino acids, carbohydrates, or fats stimulate cholecystokinin secretion in the rat
Authors: Liddle R. A. , Green G. M. , Conrad C. K. , Williams J. A.
Published: December 2017

Because of prior difficulties in measuring plasma cholecystokinin (CCK) levels, it has not been established which components of food stimulate CCK secretion in rats. In the present study, we used a sensitive and specific bioassay for measuring plasma CCK and determined the effects of proteins, protein hydrolysates, amino acids, fats, starch, and glucose on CCK secretion in this species. Intact proteins were the only stimulants of CCK release. Solutions of 18% casein and 0.2% soybean trypsin inhibitor caused prompt increases in plasma CCK levels from 0.5 +/- 0.2 to 7.9 +/- 1.9 and 8.0 +/- 2.0 pM, respectively, within 5 min of orogastric administration. The proteins lactalbumin and bovine serum albumin caused smaller elevations in circulating CCK. In contrast, hydrolysates of casein and lactalbumin and the amino acids L-phenylalanine and L-tryptophan did not stimulate CCK release. In addition, plasma CCK levels did not increase with the feeding of fat, starch, or glucose. The ability of proteins to stimulate CCK secretion paralleled their ability to inhibit trypsin activity in vitro. Furthermore, the plasma CCK response to casein was completely abolished by the simultaneous administration of trypsin. These studies indicate that proteins are the major food stimulants of CCK release in the rat and that the effects of proteins are related to inhibition of intraluminal protease activity.
Steady-state kinetic analysis of triacylglycerol delivery into mesenteric lymph
Authors: Mansbach C. M. , Arnold A.
Published: December 2017

The output of triacylglycerol in chylomicrons can be increased 60% by prefeeding rats with a 20% fat diet or 110% by including phosphatidylcholine in a lipid infusion. The present study was designed to determine whether the increment was due to an expansion of the chylomicron triacylglycerol precursor pool or an increase in its fractional turnover rate. A steady-state kinetic model was established in rats receiving 135 mumol glyceryl trioleate/h. The decay in specific activity of triacylglycerol after removal of radiolabeled glyceryl trioleate from the duodenal infusate was followed for 4 h and analyzed by the SAAM 23 program. It was found that the fractional turnover rate of the chylomicron precursor pool remained the same in each experimental condition. However, the pool was found to expand in direct proportion to the chylomicron triacylglycerol output. Functionally the infused [3H]glyceride-glycerol and tri[14C]oleate behaved the same in lymph chylomicrons and was 90% of infusate specific activity. In summary, these data suggest that increases in chylomicron triacylglycerol output are dependent on the size of the mucosal precursor pool and the monoacylglycerol acyltransferase synthetic pathway for its triacylglycerol.
Mechanism of action of calcitonin gene-related peptide in stimulating pancreatic enzyme secretion
Authors: Zhou Z. C. , Villanueva M. L. , Noguchi M. , Jones S. W. , Gardner J. D. , Jensen R. T.
Published: December 2017

In guinea pig pancreatic acini rat calcitonin gene-related peptide (CGRP) caused an eightfold increase in amylase release with various phosphodiesterase inhibitors present. Rat CGRP and rat [Tyro]CGRP caused half-maximal effect at 2 nM, and were threefold more potent than human CGRP. CGRP-stimulated amylase release was not inhibited by VIP-(10-28) or secretin-(5-27). CGRP stimulated cAMP and was augmented by phosphodiesterase inhibitors with the order of sensitivity being Ro-20-1724 greater than isobutylmethylxanthine greater than theophylline. CGRP did not increase 45Ca outflux or effect of 125I-VIP binding. CGRP specifically inhibited 125I-CGRP binding. The dose-response curves were broad and each peptide accelerated dissociation of bound 125I-CGRP. Computer analysis demonstrated two classes of CGRP-binding sites. Occupation of a high-affinity class (Kd 20 nM) correlated with stimulation of enzyme secretion and cAMP, and occupation of the low-affinity class (Kd 1 microM) correlated with accelerated dissociation. These studies demonstrate that CGRP interacts with specific pancreatic receptors, CGRP-stimulated cAMP is in a different compartment from that stimulated by other secretagogues, and CGRP differs from other agents that increase cAMP and amylase release in the relationship among receptor occupation, cAMP generation, and enzyme secretion.
Quantitative assessment of the two-component model of intestinal circulation
Authors: Kvietys P. R. , Navia C. A. , Premen A. J. , Granger D. N.
Published: December 2017

Recently a two-component model of the intestinal circulation was proposed to explain the effects of vasodilators on intestinal oxygenation. This model assumes that the intestine is composed of two regions: one region in which oxygen uptake is blood flow independent (well perfused and normoxic) and a second region in which oxygen uptake is blood flow dependent (under-perfused and hypoxic). The model predicts that total intestinal oxygen uptake is increased by a vasodilator only if the blood flow-dependent region is affected. We used a systems analysis approach to predict the various boundary conditions that must be imposed on the two-component model for it to simulate experimental observations. The mathematical model was based on current concepts and available data regarding intestinal hemodynamics and oxygen exchange. The model simulations predict that 30-70% of the intestine must be hypoxic (regions where oxygen uptake is blood flow dependent) for the two-component hypothesis to adequately explain published observations. Since the existence of such an extensive hypoxic region seems unlikely for the normal intestine, the predictive value of the two-component hypothesis may be of limited value for describing the effects of vasodilators on oxygen uptake in the normal intestine. However, the two-component model may be useful in predicting the effects of vasodilators on intestinal oxygen uptake in the ischemic intestine.
Stimulation of oxyntic and histaminergic cells in gastric mucosa by gastrin C-terminal tetrapeptide
Authors: Ruiz M. C. , Michelangeli F.
Published: December 2017

Gastrin tetrapeptide (TG) stimulation of H+ secretion and histamine release and their relationship were characterized in isolated amphibian gastric mucosa. TG released histamine and stimulated H+ secretion. Dose-response curves to TG showed nonparallel increases in both parameters. In tachyphylaxis experiments, there was no correlation between histamine release and H+ secretion. Comparison of cimetidine inhibitory dose-response curves of maximal TG or histamine stimulation showed a much higher sensitivity for TG-stimulated H+ secretion. This suggests that the pericellular histamine concentration released by TG was lower than that needed for maximal response. In mucosae maximally stimulated by histamine, TG induced a further increase in H+ secretion. In the presence of cimetidine, there was potentiation between TG and dibutyryl cAMP that was dependent on the presence of extracellular calcium. The results are interpreted to indicate that TG (or gastrin) stimulates H+ secretion through different mechanisms: 1) direct stimulation of the oxyntic cell dependent on extracellular calcium, 2) potentiation between gastrin and histamine, and 3) release of histamine from paracrine cells. Direct stimulation of the oxyntic cell by TG is not sufficient to trigger H+ secretion. Potentiation between TG and histamine at the oxyntic cell may result from interaction between TG-induced increases in intracellular Ca2+ and histamine-induced increases in intracellular cAMP.
Response of jejunal mucosa to electrical transmural stimulation and two neurotoxins
Authors: Perdue M. H. , Davison J. S.
Published: December 2017

We examined the mucosal response to endogenous neurotransmitters released from enteric nerves of guinea pig jejunum in vitro by 5 s of electrical transmural stimulation (TS). After TS, a rise in short-circuit current (Isc) occurred that peaked by 60 s and returned to base line by 3–6 min. The Isc response was associated with Cl- movement toward the luminal side of the tissue. The use of adrenergic and muscarinic cholinergic antagonists revealed that there was no adrenergic component but that the cholinergic component comprised up to 50% of the total response. Therefore, more than 50% of the response was due to the action of nonadrenergic, noncholinergic transmitter(s). The addition of the neurotoxin, tetrodotoxin (TTX), produced two effects: 1) an early fall in the base-line Isc and increased net absorption of Na+ and Cl-, and 2) a delayed inhibition of the response to TS. The former effect occurred at lower concentrations of TTX than the latter. Another neurotoxin, aconitine, blocked the response to TS without decreasing the base-line Isc or altering net ion transport. After aconitine, TTX still caused the Isc base line to fall. Because both neurotoxins prevented the Isc response to TS, we conclude that the response is due to the action of released endogenous neurotransmitters. Our results also suggest that TTX has an additional effect that is different from that of aconitine, acting either on the epithelium to enhance absorption or on a population of nerves that are relatively more TTX sensitive to block ongoing release of secretion-stimulating transmitter(s).
Functional role of carbonic anhydrase in intestinal electrolyte transport
Authors: Charney A. N. , Wagner J. D. , Birnbaum G. J. , Johnstone J. N.
Published: December 2017

We examined the role of carbonic anhydrase activity in intestinal transport by measuring the effect of systemic pH and PCO2 on electrolyte transport in the presence and absence of luminal acetazolamide. Adult Sprague-Dawley rats were anesthetized, and ileal and colonic segments were perfused with Ringer solution that was acetazolamide-free or that contained 0.1 mM sodium acetazolamide. Consecutive states of acute respiratory alkalosis and acidosis were created by changing the inspired CO2 from 0% (room air) to 8% CO2. In the ileum, acetazolamide perfusion did not affect the increment in net sodium and chloride absorption caused by a reduction in systemic pH. Mucosal carbonic anhydrase activity in this segment was measurable, although very low. In both the ascending and descending colon, acetazolamide perfusion reduced the increment in net sodium absorption caused by an increase in systemic PCO2. In addition, acetazolamide increased the chloride absorptive response to PCO2 in the ascending colon but did not affect the chloride response at all in the descending colon. Colonic mucosal carbonic anhydrase exhibited a proximal-to-distal gradient of activity: levels in the ascending colon were severalfold greater than in the descending colon. These findings suggest a functional role for carbonic anhydrase in mediating the colonic but not the ileal absorptive response to changes in systemic acid-base balance.
Age-related superior mesenteric arterial flow changes in piglets: effects of feeding and hemorrhage
Authors: Yao A. C. , Gootman P. M. , Frankfurt P. P. , DiRusso S. M.
Published: December 2017

Cardiovascular (CV) responses to feeding before and after 15% blood volume hemorrhage (H) were studied in lightly anesthetized piglets less than or equal to 2-days and greater than 2-wk-old. Superior mesenteric (Mes) and renal (Ren) arterial flows (F) were registered by electromagnetic probes before and continuously for 2 h after milk feeding (26 ml/kg) by gavage. Postprandially, in piglets less than or equal to 2-days-old MesF tended to increase (maximum change, mean +/- SE, 16.0 +/- 4.7%) at 30 min, whereas Mes vascular resistance (R) significantly decreased at 30, 90, and 120 min (17.3 +/- 6.2%). In piglets greater than 2-wk-old, MesF significantly increased by 30 min, which lasted 120 min (37.7 +/- 11.7%); MesR decreased by 20.0 +/- 5.8% at 90-120 min. Compared with the less than or equal to 2 days olds, the older piglets demonstrated greater and more sustained postprandial MesF increase. After H, regional F and pulse pressure (PP) decreased, heart rate and R increased in both groups. After stabilization, feeding induced insignificant CV changes in less than or equal to 2-day-old piglets. In contrast, increased MesF (44 +/- 14.4%) and PP (24 +/- 8.5%) and decreased MesR (31 +/- 8.9%) were observed in the greater than 2-wk-olds. MesF changes differed significantly between the age groups. The Ren vascular bed showed no consistent response in both age groups. Thus Mes vascular responses to feeding with or without preceding H in developing piglets were age related.
A hormonal mechanism for the interdigestive pancreatic secretion in dogs
Authors: Lee K. Y. , Shiratori K. , Chen Y. F. , Chang T. M. , Chey W. Y.
Published: December 2017

We investigated a hormonal mechanism involved with cyclic pancreatic secretion in interdigestive state in four dogs prepared with gastric and modified Herrera's pancreatic cannulas and four dogs prepared with gastric and Thomas' duodenal cannulas. Cholecystokinin-pancreozymin (CCK-PZ), secretin, pancreatic polypeptide (PP), and motilin were considered as candidate hormones that might be involved in the mechanism. Radioimmunoassays of the four hormones in serial plasma samples showed cyclic increases in only two hormones including motilin and PP, which coincided with the cyclic increase in pancreatic secretion. However, only motilin given intravenously produced a cyclic pancreatic secretion similar to spontaneous cyclic pancreatic secretion in interdigestive state. Although the magnitude of peak pancreatic secretion was not altered during intravenous infusion of motilin in doses of 0.06 microgram X kg-1 X h-1 or 0.06 microgram/kg, the peak secretion occurred more frequently than that during the control interdigestive state. Atropine administered intravenously abolished the cyclic increases in both plasma motilin concentration and pancreatic secretion. Exogenous secretin, CCK-PZ8 and PP failed to produce cyclic pancreatic secretion. To further elucidate the mechanism involved, the effect of intravenous infusion of a rabbit anti-CCK-PZ or antimotilin serum on the cyclic pancreatic secretion was studied. The antimotilin serum completely blocked the pancreatic secretory cycles in two dogs so studied, whereas rabbit anti-CCK-PZ serum did not influence the pancreatic cycle in two dogs. We conclude that circulating motilin plays an important role on the development of cyclic increase in the pancreatic secretion in two dogs so studied.(ABSTRACT TRUNCATED AT 250 WORDS)
Genesis of anal canal pressures in the opossum
Authors: Culver P. J. , Rattan S.
Published: December 2017

The purpose of the present investigation was to examine the role of the internal and external anal sphincters in the maintenance of resting pressures in the anal canal. The studies were performed in opossums anesthetized with alpha-chloralose. The radial and axial pressures in the anal canal were monitored using a continuously perfused catheter assembly. Electromyography of the external anal sphincter was monitored using bipolar tungsten hook electrodes. To examine the contribution of the external anal sphincter and surrounding skeletal muscle to the resting tone in the anal canal, pancuronium bromide was administered in a dose that abolished the electromyographic activity of the external anal sphincter muscle. The abolition of external anal sphincter activity did not modify the peak anal canal pressures, suggesting that these pressures are due to the internal anal sphincter. The alpha-adrenergic antagonist, phentolamine, did not modify the anal canal pressure, suggesting that basal internal anal sphincter pressure is not due to tonic adrenergic activity. Tetrodotoxin in a dose that produced obliteration of the anorectal reflex causing anal sphincter relaxation did not produce any change in the peak anal canal pressures. These studies show that the resting pressures in the anal canal of opossums are due to myogenic properties of the internal anal sphincter.
Cyclic nucleotide-dependent protein kinases in the lower esophageal sphincter
Authors: Miller C. A. , Barnette M. S. , Ormsbee H. S. , Torphy T. J.
Published: December 2017

The characteristics and regulation of adenosine 3',5'-cyclic monophosphate (cAMP)-dependent and guanosine 3',5'-cyclic monophosphate (cGMP)-dependent protein kinases (PKs) in opossum, canine, and human lower esophageal sphincter (LES) were investigated. As measured by the incorporation of 32P from [gamma-32P]adenosine 5'-triphosphate (ATP) into histone, LES homogenates from all three species contained three distinct types of PK: cAMP-dependent PK, cGMP-dependent PK, and cyclic nucleotide-independent PK. In all three species, cAMP-dependent PK comprised approximately 80%, cGMP-dependent PK comprised approximately 10%, and cyclic nucleotide-independent PK comprised approximately 10% of the total PK activity in the LES. Diethylaminoethyl-sepharose column chromatography of the supernatant fraction of opossum LES homogenates revealed that of the total cAMP-dependent PK, 10% was Type I and 90% was Type II. In contrast, equal amounts of Type I and Type II cAMP-dependent PK were present in both the human and canine LES. Isoproterenol-induced relaxation of the isolated opossum LES was accompanied by an increase in cAMP content and an activation of cAMP-dependent PK. The results of this study support the proposal that cyclic nucleotides and cyclic nucleotide-dependent PKs regulate LES tone.
The relationship between gastrointestinal motility and secretion
Authors: Greenwood B. , Davison J. S.
Published: December 2017

Few studies have addressed specifically or systematically the question of whether motility and secretion within the gastrointestinal tract are linked and if so by what mechanisms. The evidence for such a relationship is discussed in this review and we conclude that increased motor activity of the stomach is frequently associated with increased acid and pepsin secretion. Similarly, an increase in small intestinal motility is accompanied by elevated fluid and electrolyte secretion. Two possible mechanisms linking motility to secretion are considered. These could coexist. The first consists of parallel but separate neural pathways to smooth muscle and epithelium that might be activated synchronously and, therefore, produce simultaneous activation of motility and secretion. The existence of such parallel pathways in the stomach and small intestine are described, but their physiological significance is unresolved. The second mechanism we discuss is a sequential process in which increased motility provides a sensory stimulus for reflexly activated secretion. In the stomach the evidence for such a mechanism is largely deductive. In the intestine, however, we provide experimental evidence for an intrinsic neural mechanism activated by motor activity, which then stimulates fluid and electrolyte secretion. We conclude that such a sequential relationship exists and probably operates under physiological conditions but that further study is required.
Gastrin receptor characterization: affinity cross-linking of the gastrin receptor on canine gastric parietal cells
Authors: Matsumoto M. , Park J. , Yamada T.
Published: December 2017

We applied affinity cross-linking methods to label the gastrin receptor on isolated canine gastric parietal cells in order to elucidate the nature of its chemical structure. 125I-labeled Leu15-gastrin and 125I-labeled gastrin2(-17) bound to intact parietal cells and their membranes with equal affinity, and half-maximal inhibition of binding was obtained at an incubation concentration of 3.2 X 10(-10) M unlabeled gastrin. 125I-gastrin2(-17) was cross-linked to plasma membranes or intact parietal cells by incubation in disuccinimidyl suberate. The membrane pellets were solubilized with or without dithiothreitol and applied to electrophoresis on 7.5% sodium dodecyl sulfate polyacrylamide gels. Autoradiograms revealed a band of labeling at Mr 76,000 and labeling of this band was inhibited in a dose-dependent fashion by addition of unlabeled gastrin to the incubation mixture. Dithiothreitol in concentrations as high as 100 mM did not alter the electrophoretic mobility of the labeled band. After taking into account the molecular weight of 125I-gastrin2(-17), our results suggest that the gastrin receptor on parietal cells is a single protein of Mr 74,000 without disulfide-linked subunits.
Formation and actions of calcium-mobilizing messenger, inositol 1,4,5-trisphosphate
Authors: Putney J. W.
Published: December 2017

A variety of surface membrane receptors can activate a phospholipase C, which degrades phosphatidylinositol 4,5-bisphosphate liberating a calcium mobilizing second messenger, inositol 1,4,5-trisphosphate [(1,4,5)IP3]. The coupling of surface receptors to the phospholipase C involves one or more guanine nucleotide-dependent regulatory proteins that are similar but not identical to those that regulate adenylate cyclase. (1,4,5)IP3 has been shown to release Ca2+ from a portion of the endoplasmic reticulum and is believed responsible for the initial phase of Ca2+ mobilization ascribed to internal Ca2+ release. (1,4,5)IP3 acts by binding to a specific receptor that either is a component of, or regulates, a Ca2+ ion channel. The release of Ca2+ from the (1,4,5)IP3-sensitive component of the endoplasmic reticulum may secondarily activate the second phase of Ca2+ mobilization, which involves Ca2+ entry. (1,4,5)IP3 is metabolized by two pathways. One involves the action of a 5-phosphatase that degrades (1,4,5)IP3 to inositol 1,4-bisphosphate, whereas the other involves a 3-kinase that phosphorylates (1,4,5)IP3 to produce inositol 1,3,4,5-tetrakisphosphate. The significance of this dual metabolism is not known, but it may be important in rapidly extinguishing the Ca2+-releasing activity (1,4,5)IP3.
Calcitonin gene-related peptide inhibits acid secretion without modifying blood flow
Authors: Leung F. W. , Tallos E. G. , Tache Y. F. , Guth P. H.
Published: December 2017

Calcitonin gene-related peptide (CGRP) is a 37-residue peptide present in the central and peripheral nervous system. Based on previous reports of its localization in fibers associated with vascular smooth muscles of vessels and its potent inhibitory effect on acid secretion, we studied the influence of intravenous infusion of rat CGRP on gastric mucosal blood flow. The hydrogen gas-clearance technique was used to measure mucosal blood flow in urethan-anesthetized rats. CGRP infused intravenously in doses of 1 or 10 micrograms X kg-1 X h-1 did not significantly modify basal gastric corpus mucosal blood flow or mean-arterial blood pressure. Gastric acid secretion stimulated by pentagastrin infusion (20 micrograms X kg-1 X h-1) was suppressed by CGRP administration (10 micrograms X kg-1 X h-1), whereas neither gastric corpus mucosal blood flow nor mean arterial blood pressure were significantly changed. These results indicate that CGRP must exert its inhibitory action on gastric acid secretion by a mechanism other than decreasing gastric mucosal blood flow.
Inhibition of Na+-Pi cotransporter in small gut brush border by phosphonocarboxylic acids
Authors: Loghman-Adham M. , Szczepanska-Konkel M. , Yusufi A. N. , Van Scoy M. , Dousa T. P.
Published: December 2017

We examined the effect of phosphonoformic acid (PFA) and phosphonoacetic acid (PAA) upon Na+-Pi cotransport in brush-border membrane (BBM) from small gut of rat. Both PFA and PAA inhibited the Na+ gradient-dependent uptake of 32Pi by BBM vesicles (BBMV) prepared from intestinal mucosa but had no effect on Na+-dependent uptakes of D-[3H]glucose, L-[3H]proline, or [14C]succinate. The uptake in the absence of Na+ gradient, or uptake at equilibrium period (180 min), was not affected by PFA or by PAA. A chemical analogue of PFA and PAA, phosphonopropionic acid, had only a minor inhibitory effect and phenylphosphonic acid was inactive. Neither PFA nor PAA influenced the activity of rat intestinal BBM alkaline phosphatase. The BBMV from rat jejunum had a much higher capacity for Na+ gradient-dependent uptake of 32Pi than BBMV from duodenum or ileum. The inhibition of BBMV 32Pi transport across rat jejunum by PFA is competitive. We suggest that PFA and PAA are specific inhibitors of Na+ gradient-dependent uptake of Pi by BBMV from small intestinal mucosa and that they could serve as useful experimental tools for the studies of intestinal Na+-Pi cotransport.
Quantitative assessment of villous motility
Authors: Womack W. A. , Barrowman J. A. , Graham W. H. , Benoit J. N. , Kvietys P. R. , Granger D. N.
Published: December 2017

A videomicroscopic method was used to quantitatively analyze villous motility in the dog small intestine. The frequency and duration of villous contractions (retractions) were measured in the duodenum, midjejunum, and distal ileum under controlled conditions. A pronounced gradient of villous motility was evident along the bowel. The duodenum exhibited the highest frequency (7.3 +/- 0.1/min) and longest duration (2.6 +/- 0.1 s) of contraction; the jejunum exhibited an intermediate frequency and duration of contraction (4.0 +/- 0.1/min, 2.1 +/- 0.1 s), and the lowest values were measured in the ileum (2.0 +/- 0.1/min and 1.8 +/- 0.1 s). In contrast to the retraction movements, the frequency of pendular villous movements (whipping, swaying movements without shortening) was highest in the jejunum and lowest in the duodenum. The frequency and duration of villous contractions (retractions) remained relatively constant over a 2-h observation period. Reducing mucosal surface temperature from 38 to 30 degrees C caused the frequency of contraction to fall by 33% and the duration to increase by 106%. Varying the suffusate pH within the physiological range of 5.0-7.4 produced no significant effects on jejunal villous motility. Suffusion with glucose (140 and 280 mM) failed to alter villous motility. However, amino acid (15 and 30 mM) and fatty acid (10 mM) solutions significantly increased contraction frequency by 30-50% and 90%, respectively. The videomicroscopic method provides useful quantitative information, which should extend current knowledge regarding the regulation and physiological importance of villous motility.
CCK-5: sequence analysis of a small cholecystokinin from canine brain and intestine
Authors: Shively J. , Reeve J. R. , Eysselein V. E. , Ben-Avram C. , Vigna S. R. , Walsh J. H.
Published: December 2017

The purpose of this study is to purify and to characterize chemically cholecystokinin (CCK)-like peptides present in brain and gut extracts that elute from gel filtration after the octapeptide. Canine small intestinal mucosa and brain were boiled in water and then extracted in cold trifluoroacetic acid, and cholecystokinin-like immunoreactivity was determined by carboxyl-terminal specific radioimmunoassay. Gel permeation chromatography on Sephadex G-50 revealed a form of CCK apparently smaller than CCK-8. This peptide was purified by immunoaffinity chromatography and three successive reverse phase high-performance liquid chromatography steps. Microsequence analysis showed that the amino terminal primary sequence of this small CCK was Gly-Trp-Met-Asp. Immunochemical and chromatographic analysis indicated that the carboxyl-terminal residue was Phe-NH2 and thus the full sequence is Gly-Trp-Met-Asp-Phe-NH2. An antibody that recognizes synthetic CCK-8, CCK-5, and CCK-4 equally did not reveal the presence of significant amounts of CCK-4. These results indicate that CCK-5 is the major CCK form smaller than the octapeptide present in brain (19% of total CCK immunoreactivity) and small intestine (7% of total). This finding, coupled with the demonstration by others that CCK-5 interacts with high-affinity brain CCK receptors, indicates that CCK-5 may play a physiological role in brain function.
Effects of ion substitution on transport and choleretic effect of ouabain
Authors: Anwer M. S.
Published: December 2017

The role of inorganic ions in hepatic transport and choleretic effect of ouabain was studied in isolated perfused rat liver to verify whether Na+-coupled ouabain uptake into hepatocytes is responsible for the choleretic effect. Hepatic uptake and clearance of ouabain were not significantly affected when perfusate Na+ was replaced by Li+ or choline+, chloride by nitrate or isethionate, or bicarbonate by tricine. However, these ion substitutions, with the exception of Li+, significantly reduced ouabain-induced choleresis and biliary electrolyte excretion. When ouabain was infused at different rates followed by perfusion without ouabain, changes in bile flow paralleled biliary excretion of ouabain rather than hepatic uptake. These results indicate that hepatic uptake of ouabain is not Na+ dependent and that the osmotic effect of biliary excreted ouabain is responsible for its choleretic effect. A part of the choleretic effect (30%) must also involve other mechanisms, since a permeable anion-like nitrate failed to substitute for perfusate chloride. Results of infusion studies also showed that ouabain was concentrated in liver (liver/perfusate = 30) and in bile (bile/liver = 15), indicating that ouabain is transported against its concentration gradient across both sinusoidal and canalicular membranes.
Tachykinins: local gastric effects and brain stem responses
Authors: Barber W. D. , Stevenson G. D. , Burks T. F.
Published: December 2017

The gastric motor or mechanical effects of a group of peptides, the tachykinins, were evaluated in anesthetized cats to determine the relationship between local motor events and brain stem neurons that regulate gastric activity. The peptides evaluated were substance P, physalaemin, and eledoisin. The tachykinin-induced gastric changes were dose related and were characterized by initial distention-sustained contraction-late distention phases. At lower doses distention was the dominant effect with a sustained contraction-late distention response appearing as the dose increased. The sustained contraction-late distention phases were frequently accompanied by phasic contractions with a frequency of 2-4/min. Atropine had a significant effect on the sustained contraction phase but no effect on the phasic contractions or distention phases. Bilateral cervical vagotomy had a significant effect on the early distention phase, suggesting a link with brain stem mechanisms. The activity of brain stem units that responded to phasic distention of the stomach reflected the tachykinin-induced changes in gastric distention. Although the gastric effects of these tachykinins shared distinct similarities, certain differences in the time sequence of the distention-contraction interactions suggests the possibility that dissimilar receptor types may be involved in the mechanisms of action. Their mechanisms of action may also involve a direct effect on the effector organ.
Dependence of intestinal amino acid uptake on dietary protein or amino acid levels
Authors: Karasov W. H. , Solberg D. H. , Diamond J. M.
Published: December 2017

To understand how intestinal amino acid (AA) transport is regulated by dietary substrate levels, we measured uptake of seven AAs and glucose across the jejunal brush-border membrane of mice kept on one of three isocaloric rations differing in nitrogen content. In the high-protein ration, uptake increased by 77-81% for the nonessential, less toxic AAs, proline, and aspartate but only by 32-61% for the more toxic essential AAs tested. In the nitrogen-deficient ration, uptake decreased for the nonessential aspartate and proline but stayed constant or increased for essential AAs and for the nonessential alanine. These patterns imply independent regulation of the intestine's various AA transporters. With decreasing dietary AA (or protein), the imino acid and acidic AA "private" transporters are repressed, while activities of the basic AA transporter and the neutral AA "public" transporter decrease to an asymptote or else go through a minimum. These regulatory patterns can be understood as a compromise among conflicting constraints imposed by protein's multiple roles as a source of calories, nitrogen, and essential AAs and by the toxicity of essential AAs at high concentrations.
Comparison of different dietary amino acids as inducers of intestinal amino acid transport
Authors: Stein E. D. , Chang S. D. , Diamond J. M.
Published: December 2017

Intestinal amino acid (AA) transporters are known to be induced by raised levels of dietary protein or free AA mixtures, but little is known about whether certain AAs are more potent inducers than others. Hence we compared, in mouse jejunum, the inductive effects of seven different AAs (given to mice as dietary supplements) on the brush-border uptake of five solutes predominantly taken up via different transporters. The AAs tested as dietary supplements included one imino acid, two acidic AAs, two basic AAs, and two neutral AAs. The solutes whose uptakes we studied were D-glucose plus preferential substrates for the acidic AA, basic AA, neutral AA, and imino acid transporter. Mouse growth rates were consistently higher for dietary supplementation with nonessential than essential AAs, but there were no ration-related differences in intestinal morphometric parameters and almost none in active D-glucose uptake. AA transport is regulated independently of D-glucose transport. The four AA transporters are regulated semi-independently on each other: e.g., aspartate is a good inducer for only two of the four transporters, arginine for one or two, lysine for just one. Different AAs differ in their potencies at inducing the same AA transporter. In a few cases good substrates make good inducers (e.g., aspartate of the acidic AA transporter, valine of the neutral AA transporter). But often this is not true: the acidic AA aspartate is the best inducer of the basic AA transporter; the basic AA arginine but not lysine is a good inducer of the acidic AA transporter; and the imino acid proline is not a good inducer of the imino acid transporter. The adaptive significance of these discrepancies between inducers and transported substrates is unclear. Thus the differing dietary values of different AAs may be related to their differing values as inducers of AA transport, in addition to their well-known differing biosynthetic values as essential or nonessential nutrients.
Pancreatic calcification and stone formation: a thermodynamic model of calcium in pancreatic juice
Authors: Moore E. W. , Verine H. J.
Published: December 2017

CaCO3 is a major constituent of pancreatic stones, salivary stones, and many pigment gallstones. Elucidation of the physicochemical state of calcium is necessary for definition of calcium solubility in these systems. Pancreatic stones are observed in both humans and cattle, and are approximately 95% CaCO3 (calcite) in both species. Despite its importance, little is known about the physicochemical state of calcium in pancreatic juice. This paper presents an a priori model, based on established physicochemical principles, for the state of calcium in the juice at all levels of secretion. Two postulates of the model are the following: the limiting free [Ca2+] in the juice is governed by the solubility product (K' sp) for CaCO3; if K' sp is exceeded, the juice is supersaturated and precipitation of CaCO3 is thermodynamically possible; total calcium, [Ca], in the juice is the sum of four distinct species: free ionized calcium, Ca2+; calcium-bicarbonate complex, CaHCO3+; calcium carbonate ion-pair, CaCO3(0); and protein-bound calcium, CaProt. Overall equations of the model and graphical corollaries are presented. The model predicts an inverse hyperbolic relationship between [Ca2+] or [Ca] and [HCO3-]. Calcium solubility is maximal at low [HCO3-]; as [HCO3-] increases, both [Ca2+] and [Ca] decline to respective limiting values of approximately 0.015 and 0.15 mM. At low [HCO3-], most of [Ca] is present as Ca2+ and CaProt, whereas at high [HCO3-], most [Ca] is CaHCO3+ and CaCO3(0). Protein, HCO3-, and CO3(2-) ions are thus important buffers for Ca2+ in the juice. The model provides a quantitative framework for further elucidation of calcium lithogenicity in the pancreas, salivary gland, and biliary tract.