bluuebunny/crossref_metadata_2025 huggingface dataset:
Adenosine and hemodynamic alterations in cirrhotic rats
Authors: Champigneulle B. , Braillon A. , Kleber G. , Gaudin C. , Cailmail S. , Lebrec D.
Published: December 2017

This study evaluated the hypothesis that adenosine may participate in the hemodynamic alterations observed in conscious unrestrained cirrhotic rats. In sham-operated rats, adenosine (20 micrograms.100 g body wt-1.min-1 iv) induced hyperdynamic circulation and significantly increased portal pressure, mimicking the hemodynamic changes observed in cirrhosis. Although adenosine significantly increased hyperdynamic circulation and portal pressure in cirrhotic rats, these changes were significantly less marked than in sham-operated rats. 8-Phenyltheophylline (20 micrograms.100 g body wt-1.min-1 iv), a specific and potent adenosine antagonist, significantly decreased portal tributary blood flow in sham-operated rats (-18.0 +/- 5.6%) but did not have a significant effect in cirrhotic rats. The limited effect of 8-phenyltheophylline was not due to an insufficient dose, since the dose administered antagonized the hemodynamic effect of exogenous adenosine up to 40 micrograms.100 g body wt-1.min-1. We conclude that in certain circumstances, although adenosine may aggravate the hyperdynamic circulation, in normal conditions, the hemodynamic alterations observed in cirrhotic rats are not mediated by adenosine.
Gastrin-releasing peptide is a transmitter mediating porcine gallbladder contraction
Authors: Schjoldager B. , Poulsen S. S. , Schmidt P. , Coy D. H. , Holst J. J.
Published: December 2017

We studied the role of gastrin-releasing peptide (GRP) for porcine gallbladder motility. Immunohistochemistry visualized nerve fibers containing GRP-like immunoreactivity in muscularis. GRP concentration dependently stimulated contractions of muscularis strips (ED50, 2.9 nM). Neuromedin B was less potent (ED50, 0.1 microM), suggesting existence of GRP-preferring receptors. GRP-induced contractions were unaffected by muscarinic antagonism (1 microM atropine), axonal blockade (1 microM tetrodotoxin), cholecystokinin (CCK) receptor antagonism (10 microM MK-329), or substance P desensitization (1 microM), supporting the existence of myogenic GRP receptors. The bombesin (BN) analogue D-Phe6-BN-(6-13)propylamide (PA) stimulated contractions (ED50, 3.3 nM) with low efficacy (29% of that of GRP). D-Phe6-BN-(6-13)PA (1 microM) shifted GRP concentration-response curves one log to the right. D-Phe6-BN-(6-13)PA interacted specifically with GRP receptors; while abolishing responses to GRP (1 nM), responses to substance P (0.1 microM) and CCK-8 (1 nM) were unchanged. Electrical stimulation (10 Hz, 0.5 ms, 10 V) caused a rapid onset-slow offset, tetrodotoxin-sensitive excitation. Atropine reduced the amplitude to 58% and caused a delayed, slow onset-slow decline response. D-Phe6-BN-(6-13)PA reduced the amplitude to 59% and caused a very rapid onset-rapid decline response. Atropine plus D-Phe6-BN-(6-13)PA abolished responses to nerve stimulation. Nerve stimulation caused significant release of GRP-like immunoreactivity. Thus two neural inputs were defined: a cholinergic rapid onset-rapid offset excitation and a delayed, slow onset-slow offset excitation caused by release and subsequent binding of GRP to GRP-preferring receptors.
Effect of ischemia-reperfusion on lipid digestion and absorption in rat intestine
Authors: Fujimoto K. , Price V. H. , Granger D. N. , Specian R. , Bergstedt S. , Tso P.
Published: December 2017

The purpose of this study was to assess intestinal function after ischemia-reperfusion (I/R). In two groups of intestinal lymph fistula rats (experimental), the superior mesenteric artery (SMA) was isolated and occluded for 10 min. In the remaining two groups (controls), the SMA was isolated but not occluded. Twenty-four or forty-eight hours after I/R, a lipid test meal containing radioactive triolein was infused at 3 ml/h for 8 h. Radioactive lipid in lymph, lumen, intestinal wall, portal and systemic blood, epididymal fat pads, and liver was determined. Lymph radioactive lipid output was markedly depressed in the 24-h experimental rats compared with the other three groups, and this deficiency was restored 48 h after I/R. This reduction in lipid output in lymph appeared to be the result of an increased portal transport of the infused radioactive lipid rather than a deficiency of digestion or absorption of infused triolein. We have further validated the markedly increased portal transport of radioactive lipid after I/R by using Triton WR-1339, which blocks peripheral metabolism of hepatic very low-density lipoproteins (VLDL). When Triton WR-1339 was introduced in 24 experimental and control animals, the experimental rats accumulated significantly more radioactive lipid (12-14% of infused lipid) than the control animals (2-3% of infused lipid), indicating a marked increase in portal transport of radioactive lipid, which was taken up by the liver and then resecreted into circulation as VLDL. Thus intestinal lipid absorption is sensitive to the deleterious effects of ischemia followed by reperfusion, and therefore it may be used as a functional assessment of the small intestine after I/R-induced injuries.
Regulation of glucocorticoid receptors during adaptive liver growth
Authors: Thottassery J. V. , Yarbrough J. D.
Published: December 2017

Mirex, an organochlorine pesticide, is a potent inducer of liver hyperplasia and hypertrophy in intact (INT) rats. In contrast, mirex elicits predominantly hyperplastic liver growth in adrenalectomized (ADX) rats and hypertrophic liver growth in thyroidectomized (THX) rats. Supplements of glucocorticoids restore liver hypertrophy and inhibit DNA synthesis in ADX mirex-dosed rats. Because responsiveness to glucocorticoids is in part dependent on the number and affinity of glucocorticoid receptors (GR) we have measured hepatic GR levels and dexamethasone inducibility of tyrosine aminotransferase (TAT) in mirex-dosed INT, ADX, and THX rats. Specific [3H]dexamethasone binding sites decreased to 48, 49, and 59% of control values in mirex-dosed INT, ADX, and THX rats, respectively, with no changes in the apparent equilibrium dissociation constant at 48 h postdose. The significant depletion of hepatic cytosolic GR in all experimental groups dosed with mirex failed to impair both uninduced and dexamethasone-induced TAT levels in these groups. It appears that the decrease in steroid binding is neither a result of an interaction between mirex and hepatic GR nor a simple "dilution" of receptors due to the accompanying liver hypertrophy. Taken collectively, these data suggest that despite the ligand-independent downregulation of hepatic GR, responsiveness of hepatocytes from mixed-dosed rats to glucocorticoids is not altered. Therefore, glucocorticoid-mediated liver hypertrophy in mirex-dosed rats probably involves either 1) modulation of steps subsequent to ligand binding and activation translocation of hepatic GR, 2) glucocorticoid effects at extrahepatic sites that release factors that are the actual effectors of parenchymal cell enlargement, or 3) an unconventional receptor-mediated mechanism.
Effects of physical exercise on colonic motor activity
Authors: Dapoigny M. , Sarna S. K.
Published: December 2017

We investigated the effect of physical exercise on colonic motor activity in the fasted and fed states in six conscious dogs. Each dog was implanted with nine strain gauge transducers: three on the proximal, three on the middle, and three on the distal colon. The dogs ran for 1 h on a treadmill at 5 km/h (slope 5%). In the fasted state, the dogs exercised during the 5th h of recording after an overnight fast, and in the fed state during the 1st, 3rd, and 5th postprandial hour. In the fasted state, exercise significantly decreased the frequency of colonic migrating motor complexes (MMCs) but had no effect on the total or the mean duration of contractile states in the proximal, middle, and distal colon. Postprandially, exercise disrupted colonic MMCs and replaced them with nonmigrating motor complexes in all three periods of exercise (1st, 3rd, and 6th h). Exercise also increased the total duration per hour of contractile activity throughout the colon during the 1st and 3rd h and only in the distal colon during the 6th h after the meal. The dogs never defecated during rest in the fasted or the fed state. Shortly after the start of exercise in the fasted and fed states, giant migrating contractions (GMCs) occurred, and they were followed by defecation. In approximately 40% of the experiments, another GMC originated in the proximal colon, approximately 10 min after the first defecation, and migrated caudad up to the middle colon. These GMCs were not associated with defecation but caused mass movements.(ABSTRACT TRUNCATED AT 250 WORDS)
Intestinal vitamin D-dependent calbindin-D9k and alkaline phosphatase in spontaneously hypertensive rats
Authors: Cloney D. L. , Gray R. W. , Bruns M. E. , Burnett S. H. , Smith M. L. , Felder R. A. , Bruns D. E.
Published: December 2017

Intestinal Ca2+ malabsorption has been described in spontaneously hypertensive rats (SHRs), but the molecular basis for this defect is unknown. In this study, we measured intestinal alkaline phosphatase and vitamin D-dependent Ca(2+)-binding protein (calbindin-D9k), two proteins implicated in the active pathway of intestinal Ca2+ absorption. Both proteins were measured in the small intestines of SHRs and their normotensive controls, Wistar-Kyoto rats, before, during, and after development of hypertension (4, 9, 14, 18, and 28 wk of age). At all ages, alkaline phosphatase activity in duodenum (0-6 cm) was decreased by 30-57% (P less than 0.001) and by 47-75% in the 2nd intestinal segment (6-12 cm) (P less than 0.001-0.05). Calbindin-D9k was decreased similarly. The decreases of calbindin were statistically significant (P less than 0.001-0.05) in the duodena at 4, 14, 18, and 28 wk (9-30% decreases) and in the 2nd segment at 4, 14, and 18 wk (38-69% decreases; P less than 0.001-0.005). Decreased calbindin in SHRs was documented in animals from two suppliers. The deficiencies of calbindin-D9k and alkaline phosphatase could not be attributed to malnutrition or to a generalized brush-border defect as indicated by body weights and the intestinal marker enzyme sucrase. Although calbindin-D9k was decreased in young SHRs, the serum 1,25-dihydroxycholecalciferol [1,25(OH)2D3] was increased by 59 and 129% in 4- and 9-wk-old SHRs (P less than 0.001), respectively; by contrast, serum 1,25(OH)2D3 was unchanged or decreased in older SHRs.(ABSTRACT TRUNCATED AT 250 WORDS)
Intracellular mediators of bombesin action on rat pancreatic acinar cells
Authors: Matozaki T. , Zhu W. Y. , Tsunoda Y. , Goke B. , Williams J. A.
Published: December 2017

The effects of bombesin on physiological responses (amylase secretion, protein synthesis) and intracellular mediators [inositol 1,4,5-trisphosphate (1,4,5–IP3), [Ca2+]i, and diacylglycerol] were studied in isolated rat pancreatic acini and compared with the actions of cholecystokinin (CCK). Bombesin stimulated amylase secretion to the same extent as CCK. However, it failed to reproduce the inhibition of amylase secretion by high concentrations of CCK and likewise did not inhibit incorporation of [3H]leucine into protein in contrast to high concentrations of CCK. Low concentrations of bombesin (1–100 pM) induced repetitive oscillations in [Ca2+]i, whereas higher concentrations of bombesin (1–10 nM) induced a large transient increase in [Ca2+]i followed by a small sustained plateau. Bombesin (1–100 nM) induced an early peak of 1,4,5–IP3 at 5–15 s but was without measurable effect at lower concentrations. These effects on [Ca2+]i and 1,4,5–IP3 were similar to those seen with CCK except that bombesin was approximately 10-fold less potent than CCK. Bombesin induced an increase in acinar 1,2-diacylglycerol with a biphasic time course similar to CCK. However, the magnitude of the response to bombesin was much smaller than the response to CCK. The results suggest that bombesin receptors initiate similar intracellular messengers as does CCK. However, CCK induces a larger increase of diacylglycerol and probably an as yet unidentified messenger responsible for its inhibitory effects.
Expression of a liver fatty acid binding protein/human decay-accelerating factor/HLA-B44 chimeric gene in transgenic mice
Authors: Hansbrough J. R. , Lublin D. M. , Roth K. A. , Birkenmeier E. A. , Gordon J. I.
Published: December 2017

The intestinal epithelium is characterized by the rapid and continuous renewal of its four principal cell types and by its ability to establish and maintain remarkably complex spatial differentiation along its crypt-to-villus and duodenal-to-colonic axes. We have previously used transgenic mice containing liver fatty acid binding protein/human growth hormone (L-FABP/hGH) fusion genes to analyze the molecular mechanisms responsible for encoding positional information in this epithelium. Because these studies could not distinguish whether cis-acting sequences in the L-FABP promoter or hGH structural gene were responsible for the observed cellular and regional patterns of transgene transcription in the gut, a second model fusion gene has now been constructed. It consists of nucleotides -596 to +21 of rat L-FABP linked to a cDNA encoding a chimeric protein, human decay-accelerating factor (DAF, minus the site of attachment of its COOH-terminal glycophospholipid anchor), coupled to the transmembrane (TM) and cytoplasmic domains of human HLA-B44. RNA blot hybridization and immunocytochemical analyses revealed that the cell-specific and region-specific expressions of DAF-TM and hGH in adult mice appear identical along both axes of the gut, indicating that cis-acting elements contained within the 5' nontranscribed region of the L-FABP gene rather than in the reporter are largely responsible for these observed patterns of transgene expression. Unlike pre-hGH, a prototypical secreted protein, DAF-TM is a membrane protein. The ability to direct its expression along the length of both axes of the gut provides an opportunity to analyze in vivo the sorting pathways of membrane-associated proteins in normal epithelial cells as a function of their location and differentiation. Light microscopic studies indicate that DAF-TM is targeted to the basolateral and apical surfaces of villus-associated enterocytes.
Cionin, a protochordean hybrid of cholecystokinin and gastrin: biological activity in mammalian systems
Authors: Schjoldager Birgit , Park Jung , Johnsen Anders H. , Yamada Tadataka , Rehfeld Jens F.
Published: December 2017

The protochordean octapeptide cionin is structurally a hybrid of mammalian cholecystokinin (CCK) and gastrin, and thus their possible common ancestor. To determine whether cionin behaves like CCK or gastrin, we examined its effect on canine fundic somatostatin cells and on porcine and bovine gallbladder muscles. Cionin released somatostatin with a potency (ED50 0.15 nM) and efficacy (14.8% of cell content) similar to that of CCK-8 (ED50 0.12 nM, efficacy 16.7%). The efficacies but not the potencies of CCK-8 and cionin differed from those of sulfated gastrin (0.12 nM, 9.7%), nonsulfated gastrin (0.20 nM, 9.4%), and nonsulfated CCK-8 (0.30 nM, 10.4%). CCK and gastrin stimulated contractions of porcine gallbladder muscle strips in a concentration-dependent manner with no differences in efficacy but with characteristic differences in potency. CCK-8 and cionin displayed similar potencies of ED50 2.0 and 2.6 nM; both were significantly different from the ED50 of 0.4 μM for sulfated gastrin and 2.3 μM for nonsulfated gastrin. CCK radioligand binding to membrane-enriched preparations of porcine and bovine gallbladder muscularis was specific and of high affinity. The equilibrium data revealed that binding of CCK and gastrin peptides best fit a single site. CCK-8 and cionin displayed similar affinities [Kd 0.5 nM (porcine), 0.5 nM (bovine, CCK) vs. Kd 0.8 and 0.9 nM (cionin), respectively]. These differed again significantly from Kd 0.6 and 1.5 μM (sulfated gastrin) and 0.7 and 0.2 μM (nonsulfated gastrin). The results show that cionin behaves like CCK rather than gastrin in mammals.

gallbladder motility; somatostatin; receptors

Submitted on August 10, 1990

Accepted on December 19, 1990
Role of chloride ions in liver cell volume regulation
Authors: Haddad P. , Beck J. S. , Boyer J. L. , Graf J.
Published: December 2017

Hypotonic swelling of liver cells is followed by regulatory volume decrease (RVD), which has been shown to involve facilitated release of K+. In this study, the role of C1- in RVD was examined by videoplanimetric analysis of cell volume and measurement of membrane potential (Vm) and resistance (Rm) in single isolated rat hepatocytes, and by measurement of 36Cl efflux in the isolated perfused liver preloaded with the isotope. Liver cells subjected to hypotonic stress by removal of 50 mM external NaCl (70% of control osmolality) swelled from an initial volume of 6.68 +/- 0.77 to 8.27 +/- 0.88 pl (24.3 +/- 3.4% increase) within 1 min and exhibited RVD at an initial rate of 0.26 +/- 0.01 pl/min. A step decrease in external Cl- accelerated the initial rate of RVD to 0.53 +/- 0.08 pl/min. RVD was abolished in cells that had been depleted of Cl-. Vm and Rm displayed biphasic responses to hypotonic stress. An initial (less than 15 s) hyperpolarization of Vm from -35.4 +/- 2.2 to -38.8 +/- 2.6 mV was followed by a gradual depolarization reaching -30.2 +/- 2.0 mV by 1 min. In parallel, Rm initially (less than 15 s) increased from 101 +/- 13 to 121 +/- 17 M omega (19 +/- 3% increase) and then declined to 55 +/- 4 M omega (59 +/- 4% of initial Rm) within 1 min. These changes were reversible upon return to isotonicity.(ABSTRACT TRUNCATED AT 250 WORDS)
Contraction and accommodation of guinea pig duodenum in vitro
Authors: Schulze-Delrieu K. , Brown B. P. , Custer-Hagen T.
Published: December 2017

Because duodenal resistance to gastric emptying depends in part on duodenal capacity, we examined the changes of duodenal diameter, length, and luminal pressure that occur in response to injection of bolus volumes. Filling the duodenum led to a powerful, nonpropagating contraction of the duodenum. After the end of filling, sequential duodenal segments widened and duodenal pressure and length returned to baseline; i.e., there was accommodation. Accommodation was volume dependent and ceased at volumes greater than or equal to 1.2 ml. The entire duodenum unfolded almost immediately and the initial increase of pressure and length was abolished when the duodenal musculature was inhibited by exposure to tetrodotoxin or to Ca(2+)-free solution. Pressures and pressure accommodation were larger, occurred earlier, and lasted longer when the duodenal musculature was stimulated by exposure to carbachol. Filling of the duodenum from the distal end led to rapid distribution of the bolus through the duodenum and to accommodation similar to that seen with proximal filling. However, phasic duodenal contractions were less powerful on distal than on proximal injection. Spontaneous phasic contractions of the duodenum were accompanied by a similar sequence of changes in duodenal configuration as was observed with filling. We conclude that 1) the duodenum adjusts the tension of its walls at small volumes, and beyond this is fairly rigid; 2) filling the duodenum triggers contraction responses similar to those that occur with spontaneous contractions; and 3) the direction from which the duodenum is filled does not affect its accommodation. We postulate that the filling response of the duodenum may critically affect gastric emptying.
Hepatic venular pressures of rats, dogs, and rabbits
Authors: Bohlen H. G. , Maass-Moreno R. , Rothe C. F.
Published: December 2017

We tested the hypotheses that the hepatic venule pressures (Phv), just downstream from the hepatic sinusoids, are closely similar (less than 2 mmHg) either to the portal venous pressure (Ppv), indicating a high hepatic venous resistance, or to the inferior vena cava (Pivc) pressure, indicating a high portal-sinusoidal venous resistance, as reported by previous investigators. A micropipette servo-null pressure measurement technique was used with rats, dogs, and rabbits. Phv, referred to the anatomic level of the vena cava, averaged 5.1 +/- 1.0, 6.4 +/- 1.1, and 5.4 +/- 1.0 (SD) mmHg in the rats, puppies, and rabbits, respectively. Ppv averaged 8.0 +/- 1.4, 10.8 +/- 2.2, and 7.4 +/- 1.5 mmHg, respectively. Norepinephrine infusion into the portal vein (1-5 micrograms.min-1.kg-1) caused Ppv to increase and the portal venous flow to decrease but did not significantly affect Phv. The hepatic venous circuit contributed 44 +/- 17% (rats) and 31 +/- 26% (dogs) of the total liver venous vascular resistance under control conditions. We conclude that the portal and sinusoidal vasculatures are the dominant, but not exclusive, resistance sites of the liver venous vasculature both at rest and during norepinephrine-induced vasoconstriction.
Nutrient extraction by cold-exposed mice: a test of digestive safety margins
Authors: Toloza E. M. , Lam M. , Diamond J.
Published: December 2017

We examined the size of the "safety margin," if any, by which the small intestine's daily capacities to absorb nutrients exceed prevailing daily intakes of those nutrients. This safety margin, also known as reserve capacity, is widely assumed to be enormously large. As a test, we suddenly transferred mice from an ambient temperature of 22 to 6 degrees C and measured food intake, apparent digestive efficiency, intestinal morphometrics, and intestinal brush-border uptake capacities for D-glucose and L-proline over the next 28 days. Food intake jumped 68% within the first 12 h and rose in 2 days to a new plateau level 2.5 times the previous intake. Nevertheless, apparent digestive efficiency remained unchanged, even within the first 12 h, and intestinal transit times also remained unchanged, implying the existence of at least some safety margin. Masses of the small and large intestine, liver, kidneys, and spleen nevertheless increased within 4 days by 16-20%. Glucose and proline uptakes per milligram intestine increased by approximately 5%, so that the intestine's summed uptake capacities for these solutes increased by 24-26%. The animal's intestinal adaptation expressed in these increased uptake capacities implies that safety margins at the new plateau value of food intake would otherwise have been dangerously narrow. Comparison of calculated summed uptake capacities with measured dietary intakes suggests that safety margins are approximately 220-300% in mice at 22 degrees C, only 27-50% in mice at 6 degrees C before intestinal adaptation, but 60-88% in mice at 6 degrees C after intestinal adaptation.
Lipoprotein lipase enables triacylglycerol hydrolysis by perfused newborn rat liver
Authors: Gimenez-Llort L. , Vilanova J. , Skottova N. , Bengtsson-Olivecrona G. , Llobera M. , Robert M. Q.
Published: December 2017

Fasted 1-day-old rat liver has high heparin-releasable (endothelial) lipoprotein lipase (LPL) activity, and its hepatocytes synthesize LPL protein. To test the physiological role of this LPL, we perfused the isolated organ with a 0.8 mM triacylglycerol (TAG) (Intralipid + glycerol tri[3H]oleate) 6.3% serum medium. Samples of the recirculated perfusate were taken at different times to determine 3H in TAG, free fatty acid (FFA), and water-soluble (WS) fractions. In the medium [3H]TAG disappeared and [3H]FFA and [3H]WS fractions appeared linearly with time. This TAG hydrolysis was 1) absent when medium was recirculated without liver, 2) not affected by chloroquine addition, 3) inhibited by anti-LPL immunoglobulins, 4) absent when serum was omitted from the medium, and 5) restituted when apolipoprotein CII was added to the medium without serum. Therefore, lysosomal lipase is not involved in this TAG hydrolysis, the features of which are characteristic of LPL, not of the so-called "hepatic endothelial lipase." Thus LPL activity enables the neonatal rat liver to hydrolyze and take up circulating TAG, i.e., has the same function as extrahepatic LPL.
Bombesin/GRP-stimulated somatostatin secretion is mediated by gastrin in the antrum and intrinsic neurons in the fundus
Authors: Schubert M. L. , Jong M. J. , Makhlouf G. M.
Published: December 2017

The mechanism of action of bombesin, also known as gastrin-releasing peptide (GRP), on somatostatin secretion was examined separately in superfused segments of rat antral and fundic mucosa. Bombesin/GRP (1 nM) stimulated somatostatin secretion from both regions. In fundic segments, the somatostatin response was strongly inhibited (86%; P less than 0.01) by tetrodotoxin (5 microM) but augmented by atropine (1 microM) (P less than 0.01). In antral segments, both tetrodotoxin and atropine augmented the somatostatin response to bombesin/GRP by 42-45% (P less than 0.01), whereas the gastrin antagonist L 365260 (1 microM) abolished it. The gastrin antagonist augmented the gastrin response to bombesin/GRP by 103% (P less than 0.01). The results indicate that bombesin/GRP stimulates somatostatin secretion by distinct mechanisms in the fundus and antrum. In the fundus, bombesin/GRP acts indirectly on somatostatin cells by activating stimulatory noncholinergic neurons and, to a lesser extent, inhibitory cholinergic neurons. In the antrum, bombesin/GRP acts indirectly on somatostatin cells by stimulating release of gastrin and, to a lesser extent, by activating inhibitory cholinergic neurons. A dual paracrine pathway links gastrin and somatostatin secretion in the antrum.
Apical membrane localization of ouabain-sensitive K(+)-activated ATPase activities in rat distal colon
Authors: Del Castillo J. R. , Rajendran V. M. , Binder H. J.
Published: December 2017

This study sought to establish the presence of K(+)-activated adenosinetriphosphatase (ATPase) activity in the colonic mucosa of the rat distal colon. K(+)-activated ATPase activity was present in apical membranes but not in basolateral membranes. K(+)-activated ATPase activity in apical membranes represented an approximate 10-fold enrichment compared with that in the homogenate. Na(+)-K(+)-activated ATPase activity was also present in homogenate but was enriched less than fourfold in apical membranes. K(+)-activated ATPase activity in apical membranes had both ouabain-sensitive and ouabain-insensitive components. In contrast, Na(+)-K(+)-activated ATPase activity was completely inhibited by ouabain. Similar half-maximal concentrations for K+ and pH activation curves were found for both ouabain-sensitive and ouabain-insensitive fractions. In addition to K+, the ouabain-sensitive fraction of K(+)-activated ATPase activity was stimulated by Rb+, NH+4, and Cs+, whereas the ouabain-insensitive fraction was activated only by Rb+. K(+)-activated ATPase activity was significantly inhibited by vanadate but not by N-ethylmaleimide or omeprazole. In the proximal colon, in contrast to the distal colon, active K+ absorption is not present, and K(+)-activated ATPase is approximately 20% of that in the distal colon. These studies demonstrate that K(+)-activated ATPase is present in apical membranes of rat distal colon and permit the speculation that this enzyme represents a unique and distinct ATPase (compared with either Na(+)-K(+)-ATPase or gastric parietal cell K(+)-ATPase) and is likely linked closely to the active K+ absorptive process present in this epithelium.
Free fatty acid uptake by polyethylene: what can one learn from this?
Authors: Schwab A. J. , Goresky C. A.
Published: December 2017

Previous experiments have shown that fatty-acid uptake by isolated hepatocytes is inhibited by albumin, but this inhibition was less than expected from the decrease in the equilibrium concentration of fatty acid. The possible explanation of this observation by the effects of codiffusion of protein-bound and unbound fatty acid across the unstirred layer surrounding these isolated cells has recently been challenged on the basis of experiments in which uptake by monolayers of hepatocytes was compared with that by a polyethylene sheet [F.J. Burczynski et al., Am. J. Physiol. 257 (Gastrointest. Liver Physiol. 20): G584-G593, 1989]. In the present report, we reevaluate the theoretical basis for interpretation of these experiments by solving the differential equations describing diffusion into a sheet behind a linear barrier. The diffusion coefficient for palmitate in polyethylene is estimated to be approximately 10(-9) cm2/s. We conclude that when proteins are absent from the aqueous phase, diffusion across the unstirred layer is rate limiting for removal of fatty acids by cellular monolayers, and also rate limiting for net flux across the water-polyethylene interface. In contrast, if the aqueous phase contains either 5 microM albumin or 125 microM beta-lactoglobulin, diffusion within the polyethylene sheet will become rate limiting. The net flux of fatty acids into a polyethylene sheet becomes insensitive to an increase in protein concentration if the latter rises above a certain threshold. The polyethylene data provide no additional insight into the manner in which hepatocytes take up free fatty acids.
Measurement of hepatic blood flow after severe hemorrhage: lack of restoration despite adequate resuscitation
Authors: Wang P. , Ba Z. F. , Burkhardt J. , Chaudry I. H.
Published: December 2017

Although Ringer lactate (RL) is routinely used for resuscitation, it is not known whether the volume of RL that restores cardiac output after severe hemorrhagic shock also restores the depressed effective hepatic blood flow (EHBF). To study this, a 5-cm midline laparotomy was performed in rats (i.e., trauma induced), and the animals were then bled to and maintained at a mean arterial pressure of 40 mmHg until 40% of maximum bleedout volume was returned in the form of RL. Animals were then resuscitated with four or five times the volume of maximum bleedout with RL. EHBF was determined during hemorrhage and at various intervals thereafter by an in vivo indocyanine green (ICG) clearance technique and corrected by the appropriate hepatic extraction ratio for ICG. Cardiac output was determined by ICG dilution, and hepatic microvascular blood flow (HMBF) was measured with laser Doppler flowmetry. In addition, hepatic blood flow was assessed by using radioactive microspheres. Results indicate that resuscitation markedly improved but did not restore the depressed EHBF after trauma and hemorrhagic shock despite the fact that cardiac output was restored. Similar changes in EHBF, HMBF, and hepatic blood flow as determined by microspheres were observed, suggesting that the in vivo ICG clearance is a reliable method to assess effective hepatic perfusion. Thus the lack of restoration of EHBF may be responsible for the subsequent hepatocellular dysfunction after trauma and severe hemorrhage.
Perturbation of regulated secretion in the pancreatic acinar cell line, AR42J
Authors: Sachs E. , Jamieson J. D.
Published: December 2017

The regulated secretory pathway comprises accelerated discharge of proteins in response to hormonal stimuli, their presence in secretory granules (SG), and a long intracellular residence time. Dexamethasone induction of AR42J results in an increase in granule content and responsiveness to cholecystokinin (CCK). We studied the effects of conditions implicated in sorting of secretory proteins into the regulated pathway using [35S]methionine pulse-chase protocols that examine transport of secretory proteins from the rough endoplasmic reticulum (RER)----SG and specifically from the Golgi complex (GC)----SG. The latter uses a chase at 20 degrees C to allow accumulation of labeled proteins in the trans-Golgi, followed by a shift to 37 degrees C that initiates their transport to SG under test conditions. Quantitation of CCK-8-stimulated discharge of prestored amylase and of newly synthesized labeled proteins that have entered SG during the chase enables us to examine the effect of perturbants over selected parts of the pathway. The effects of acidic intracellular compartments, the cytoskeleton, protein synthesis, ATP, and temperature on pre- and post-Golgi entry of proteins into the regulated pathway were studied. NH4Cl, monensin, Na azide, incubation at 20 degrees C, and pertussis toxin retarded RER----SG transport without affecting amylase discharge. Only incubation with 20 mM NH4Cl or 1 microM monensin inhibited transfer of newly synthesized proteins from the late GC----SG. RER----Golgi or intra-Golgi transport thus appears to require ATP and possibly guanosine 5'-triphosphate (GTP)-binding proteins. Acidic compartments appear to be essential for sorting of secretory proteins from the GC----SG.
Effects of chloroquine and methylamine on lysosomal enzyme secretion by rat pancreas
Authors: Hirano T. , Saluja A. , Ramarao P. , Lerch M. M. , Steer M. L.
Published: December 2017

In vivo pancreatic secretion of the lysosomal hydrolase cathepsin B was found to be increased by infusion of the secretagogue caerulein. The basal as well as caerulein-stimulated in vivo rate of cathepsin B was further increased by infusion of either chloroquine or methylamine while neither the basal nor the secretagogue-stimulated rates of amylase secretion were altered by the lysosomotropic agents. These observations indicate that neutralization of the acidic prelysosomal compartment by administration of lysosomotropic agents results in lysosomal enzyme entry, by default, into the regulated secretory pathway. In vitro stimulation of pancreatic acini with caerulein was also found to stimulate cathepsin B secretion. That in vitro rate of cathepsin B secretion stimulated by caerulein was not increased in acini prepared from animals infused with caerulein, chloroquine, or methylamine, but the in vitro rate of cathepsin B secretion stimulated by caerulein was increased in acini prepared from animals infused with caerulein plus either chloroquine or methylamine. Under these conditions, redistribution of cathepsin B from the lysosome-enriched to the zymogen granule-enriched subcellular fraction was noted, and lysosomal enzyme-containing organelles became increasingly fragile. These observations indicate that in vivo secretagogue stimulation increases the degree of diversion of lysosomal hydrolases into the regulated secretory compartment when the prelysosomal compartment has been neutralized with lysosomotropic agents.
Human jejunal unstirred layer: evidence for extremely efficient luminal stirring
Authors: Levitt M. D. , Strocchi A. , Levitt D. G.
Published: December 2017

Previous studies employing the osmotic transient technique have suggested that the human jejunal lumen is poorly stirred with a resultant unstirred layer thickness of approximately 600 microns. However, assuming negligible epithelial resistance to glucose absorption, we recently estimated that the unstirred layer thickness seemingly could not exceed 48 microns in the human jejunum. Because disaccharidases are located on the brush border, the rate of disaccharide hydrolysis can be used to determine unstirred layer thickness, independent of epithelial transport. In the present report, we utilized published hydrolysis data for sucrose and maltose to calculate the unstirred layer thickness in the normal human jejunum. This calculation indicated that the unstirred layer thickness was only approximately 35 microns, less than one-fifteenth of previously reported 600-microns values obtained with the osmotic transient technique. Diffusion through a 600-microns unstirred layer would be the rate-limiting step in absorption of all rapidly transported compounds. In contrast, with a 35-microns unstirred layer, variations in epithelial function or luminal stirring could readily influence the absorption.
Nitric oxide as a putative nonadrenergic noncholinergic inhibitory transmitter in the canine pylorus in vivo
Authors: Allescher H. D. , Tougas G. , Vergara P. , Lu S. , Daniel E. E.
Published: December 2017

Antropyloroduodenal motility was recorded in seven anesthetized dogs to assess the role of nitric oxide and L-arginine metabolites in nonadrenergic noncholinergic (NANC) mediation of pyloric relaxation. Pyloric activity induced by duodenal field stimulation was inhibited by antral field stimulation and electrical vagal stimulation. Intra-arterial NG-L-arginine-methyl-ester (L-NAME) reduced the inhibition from antral or vagal stimulation (P less than 0.05). Intravenous infusion of L-NAME also blocked the inhibitory effect of vagal and antral stimulation but left the tetrodotoxin-insensitive action of intra-arterial vasoactive intestinal peptide (VIP) and sodium nitroprusside unchanged. L-Arginine reversed the effect of L-NAME whereas D-arginine did not. L-NAME enhanced pyloric contractions to intra-arterial acetylcholine. The NANC inhibition of the substance P-stimulated pyloric response in vitro was blocked by L-NAME and reversed by addition of L-arginine. Sodium nitroprusside was effective as a relaxant in vitro but VIP was not. These data suggest that metabolites of L-arginine mediate neural inhibition of canine pyloric motor activity.
Effect of diet on glucose transporter site density along the intestinal crypt-villus axis
Authors: Ferraris R. P. , Villenas S. A. , Hirayama B. A. , Diamond J.
Published: December 2017

High-carbohydrate diets stimulate intestinal brush-border glucose uptake and increase the number of glucose-protectable phlorizin binding sites, but it has been unknown where along the crypt-villus axis these effects are expressed. We attacked this problem by three methods. First, by measuring phlorizin binding to isolated mouse enterocytes fractionated along the crypt-villus axis by the Weiser method, we identified a high-affinity binding site predominating from villus tip to midvillus and a site of possibly lower affinity predominating in the crypts. A high-carbohydrate diet increased by severalfold the density of the villus sites and probably also of the crypt sites, without changing their binding constants. Second, autoradiography revealed increased glucose-protectable phlorizin binding along the whole crypt-villus axis on a high-carbohydrate diet. Finally, a polyclonal antibody against the Na(+)-glucose cotransporter recognized a protein in the brush-border membrane of villus cells. Hence, substrate-dependent upregulation of intestinal glucose transport involves increased numbers of transporters along the crypt-villus axis.
Vagus-dependent disruption of interdigestive canine motility by gastric distension
Authors: Dalton R. R. , Zinsmeister A. R. , Sarr M. G.
Published: December 2017

The purpose of this study was to determine the effect of proximal gastric distension on interdigestive patterns of canine gastrointestinal motility and to examine the role of extrinsic nerves in regulating such an effect. Serosal electrodes were placed on the antrum, duodenum, and jejunum. Animals were studied before and after transthoracic vagotomy or after neural isolation of the entire jejunoileum (extrinsic denervation). Proximal gastric distension for 5 h was provided by inflating with air a thin complaint bag placed into the proximal stomach after the onset of phase III of the migrating motor complex (MMC). Four volumes (0, 1.5, 12.5, and 25 ml/kg) were each tested four times in each animal. In neurally intact animals, gastric distension with volumes of 12.5 and 25 ml/kg consistently abolished the MMC in the antrum (100%), duodenum (96%), and proximal jejunum (greater than or equal to 62%), but less often in distal jejunum (greater than or equal to 25%). After vagotomy, gastric distension did not inhibit cycling of the MMC in the antrum, duodenum, or proximal or distal jejunum. After extrinsic denervation of the jejunoileum, gastric distension inhibited the MMC in the antrum and the duodenum but had no effect in the proximal or distal jejunum. These findings suggest that nonnutrient proximal gastric distension may contribute to postprandial changes in patterns of myoelectric activity in the upper gastrointestinal tract and that this effect is mediated by the vagus nerves.
ATP induces two cholecystokinin binding affinity states in permeabilized rat pancreatic acini
Authors: Blevins G. T. , Williams J. A.
Published: December 2017

The influence of adenine and guanine nucleotides on cholecystokinin (CCK) receptor binding was examined in streptolysin O-permeabilized rat pancreatic acini. Specific binding of tracer to intact acini was 12.1 +/- 0.4% per milligram protein, while permeabilized acini bound 34.6 +/- 2.9% (n = 7). The increase in binding was also seen when normalized to DNA. Binding to permeabilized acini was reduced by the presence of 1 mM ATP to 23.0 +/- 1.3%. Analysis of competitive inhibition of tracer binding by unlabeled CCK-8 was consistent with binding to two affinity states on intact acini, with the equilibrium dissociation constants for the high (KdH)- and low (KdL)-affinity states equal to 41 +/- 5 pM and 5.2 +/- 0.4 nM, respectively; permeabilized acini displayed a single binding site with Kd = 598 +/- 40 pM. In the presence of 1 mM ATP, two states were seen on permeabilized acini with KdH = 85 +/- 11 pM and KdL = 2.7 +/- 0.6 nM. ATP, ATP gamma S, GTP, and GTP gamma S all inhibited binding, with half-maximal inhibition occurring at greater than 1 mM, 21 microM, 5 microM, and 0.4 microM, respectively. GTP gamma S (1 microM) also induced two affinity states with KdH = 112 +/- 7 pM and KdL = 1.5 +/- 0.2 nM (n = 3). Binding of CCK to pancreatic membranes was also decreased by ATP, and a similar regeneration of two binding affinity states was observed. ATP also decreased binding of [125I-Tyr4]bombesin to permeabilized acini, but in contrast did not generate two measurable binding affinity states.(ABSTRACT TRUNCATED AT 250 WORDS)
Increased lymphatic flux of hyaluronan from cat intestine during fat absorption
Authors: Reed R. K. , Townsley M. I. , Pitts V. H. , Laurent T. C. , Taylor A. E.
Published: December 2017

During fat absorption, chylomicrons with sizes up to 5,000-10,000 A must traverse an interstitium that has estimated pore sizes of 120-200 A to reach the lacteals. The present experiments were performed to study the behavior of the interstitial matrix component hyaluronan during fat absorption from the intestine. Ileal segments were isolated and autoperfused in pentobarbital-anesthetized cats. A postnodal lymphatic was cannulated, and lymph flow, protein, and hyaluronan concentration in lymph were determined. In group 1, a mixture of oleic acid and taurocholate was infused into the ileal lumen, while in group 2 the animals were fed cream overnight. In group 1, control lymph flow and hyaluronan concentration averaged 53.3 +/- 16.0 (SD) microliters.min-1.100 g intestine-1 and 21.4 +/- 16.0 micrograms/ml, respectively. Administration of taurocholate and oleic acid increased lymph flow and lymph hyaluronan concentration by 100 and 50%, respectively, resulting in a nearly three-fold increase in hyaluronan flux. Subsequent increases in venous pressure increased lymph flow and reduced hyaluronan concentration in lymph to less than 3 micrograms/ml. Hyaluronan flux remained approximately 2 micrograms.min-1.100 g intestine-1 independent of lymph flow. In group 2, no lymph sample was available before administration of fat. Hyaluronan concentration at control venous pressure was 19.3 +/- 6.7 micrograms/ml and fell to 10 micrograms/ml at the highest lymph flow. Hyaluronan flux was approximately 10 micrograms.min-1.100 g intestine-1 at the highest lymph flow and venous pressure (P less than 0.05 compared with the same lymph flow in group 1).(ABSTRACT TRUNCATED AT 250 WORDS)
Enhanced sinusoidal glutathione efflux during endotoxin-induced oxidant stress in vivo
Authors: Jaeschke H.
Published: December 2017

Hepatic release of reduced glutathione (GSH) and its oxidation [glutathione disulfide (GSSG) formation] were investigated in male Fischer rats in vivo after administration of various doses (1-15 mg/kg) of endotoxin (Salmonella enteritidis). Endotoxin dose dependently enhanced basal plasma glutathione (9.64 +/- 0.80 microM) and GSSG (1.08 +/- 0.23 microM GSH equivalents) levels by up to 450 and 1,300%, respectively, 60 min after administration of the highest dose. Determination of arteriovenous differences of plasma glutathione and portal vein blood flow demonstrated an increase of basal sinusoidal glutathione efflux (18 nmol.min-1.g liver wt-1) by 300% 15 min after 5 mg/kg endotoxin. Activation of Kupffer cells by retinol enhanced endotoxin-induced release of GSH and its oxidation severalfold. Endotoxin enhanced plasma levels of catecholamines; however, only an epinephrine-induced not the endotoxin-induced stimulation of hepatic GSH efflux was inhibited by adrenergic blockers. Depletion of serum complement by cobra venom factor pretreatment completely abolished the endotoxin-induced increase of GSH release and enhanced GSSG formation. Zymosan-activated serum (source of C5a) increased GSSG formation and GSH release. It is concluded that endotoxin triggered an extracellular oxidant stress and an increased release of hepatic GSH indirectly through complement activation. Increased sinusoidal efflux of GSH and its extracellular oxidation may act as a local defense mechanism against the potentially deleterious effects of reactive oxygen generated by Kupffer cells during their physiological functions.
Guanylate cyclase inhibitors: effect on inhibitory junction potentials in esophageal smooth muscle
Authors: Conklin J. L. , Du C.
Published: December 2017

Electrical field stimulation (EFS) of nerves intrinsic to the opossum lower esophageal sphincter (LES) produces LES relaxation, an increase in its guanosine 3',5'-cyclic monophosphate (cGMP) content, and hyperpolarization of its circular muscle membrane potential difference. Activation of esophageal nerves produces an analogous hyperpolarization of the circular esophageal smooth muscle. These studies test the hypothesis that cGMP is an intracellular mediator of this hyperpolarization. The transmembrane potential difference of circular smooth muscle cells was recorded with glass microelectrodes. Nerve-mediated smooth muscle hyperpolarization was evoked by EFS (1 ms, 50 V pulses). Forskolin, an activator of adenylate cyclase, and sodium nitroprusside, an activator of guanylate cyclase, produced hyperpolarization. Cystamine and methylene blue, inhibitors of guanylate cyclase, blocked the hyperpolarization elicited by sodium nitroprusside, but not that by forskolin. Both also reversibly abolished the hyperpolarization evoked by EFS. Membrane-permeable derivatives of cGMP produced a concentration-dependent hyperpolarization. These data support the hypothesis that cGMP is an intracellular mediator of nerve-induced esophageal smooth muscle hyperpolarization.