bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation and distribution of MAdCAM-1 in endothelial cells in vitro
Authors: Oshima Tadayuki , Pavlick Kevin P. , Laroux F. Stephen , Verma S. Kris , Jordan Paul , Grisham Matthew B. , Williams Larry , Alexander J. Steven
Published: December 2017

Mucosal addressin cell adhesion molecule-1 (MAdCAM-1) is a 60-kDa endothelial cell adhesion glycoprotein that regulates lymphocyte trafficking to Peyer's patches and lymph nodes. Although it is widely agreed that MAdCAM-1 induction is involved in chronic gut inflammation, few studies have investigated regulation of MAdCAM-1 expression. We used two endothelial lines [bEND.3 (brain) and SVEC (high endothelium)] to study the signal paths that regulate MAdCAM-1 expression in response to tumor necrosis factor (TNF)-α using RT-PCR, blotting, adhesion, and immunofluorescence. TNF-α induced both MAdCAM-1 mRNA and protein in a dose- and time-dependent manner. This induction was tyrosine kinase (TK), p42/44, p38 mitogen-activated protein kinase (MAPK), and nuclear factor (NF)-κB/poly-ADP ribose polymerase (PARP) dependent. Because MAdCAM-1 is regulated via MAPKs, we examined mitogen/extracellular signal-regulated kinase (MEK)-1/2 activation in SVEC. We found that MEK-1/2 is activated by TNF-α within minutes and is dependent on TK and p42/44 MAPKs. Similarly, TNF-α activated NF-κB through TK, p42/44, p38 MAPKs, and PARP pathways in SVEC cells. MAdCAM-1 was also shown to be frequently distributed to endothelial junctions both in vitro and in vivo. Cytokines like TNF-α stimulate MAdCAM-1 in high endothelium via TK, p38, p42/22 MAPKs, and NF-κB/PARP. MAdCAM-1 expression requires NF-κB translocation through both direct p42/44 and indirect p38 MAPK pathways in high endothelial cells.
Stimulation of GLUT-1 glucose transporter expression in response to hyperosmolarity
Authors: Hwang Daw-Yang , Ismail-Beigi Faramarz
Published: December 2017

Glucose transporter isoform-1 (GLUT-1) expression is stimulated in response to stressful conditions. Here we examined the mechanisms mediating the enhanced expression of GLUT-1 by hyperosmolarity. GLUT-1 mRNA, GLUT-1 protein, and glucose transport increased after exposure of Clone 9 cells to 600 mosmol/l (produced by addition of mannitol). The stimulation of glucose transport was biphasic: in the early phase (0–6 h) a ∼2.5-fold stimulation of glucose uptake was associated with no change in the content of GLUT-1 mRNA, GLUT-1 protein, or GLUT-1 in the plasma membrane, whereas the ∼17-fold stimulation of glucose transport during the late phase (12–24 h) was associated with increases in both GLUT-1 mRNA (∼7.5-fold) and GLUT-1 protein content. Cell sorbitol increased after 3 h of exposure to hyperosmolarity. The increase in GLUT-1 mRNA content was associated with an increase in the half-life of the mRNA from 2 to 8 h. A 44-bp region in the proximal GLUT-1 promoter was necessary for basal activity and for the two- to threefold increases in expression by hyperosmolarity. It is concluded that the increase in GLUT-1 mRNA content is mediated by both enhanced transcription and stabilization of GLUT-1 mRNA and is associated with increases in GLUT-1 content and glucose transport activity.
Regulation of Cyr61 gene expression by mechanical stretch through multiple signaling pathways
Authors: Tamura Isao , Rosenbloom Joel , Macarak Edward , Chaqour Brahim
Published: December 2017

The cysteine-rich protein 61 (Cyr61) is a signaling molecule with functions in cell migration, adhesion, and proliferation. This protein is encoded by an immediate early gene whose expression is mainly induced by serum growth factors. Here we show that Cyr61 mRNA levels increase sharply in response to cyclic mechanical stretch applied to cultured bladder smooth muscle cells. Stretch-induced changes of Cyr61 transcripts were transient and accompanied by an increase of the encoded protein that localized mainly to the cytoplasm and nucleus of the cells. With the use of pharmacological agents that interfere with known signaling pathways, we show that transduction mechanisms involving protein kinase C and phosphatidylinositol 3-kinase activation partly blocked stretch-induced Cyr61 gene expression. Selective inhibition of Rho kinase pathways altered this stretch effect as well. Meanwhile, using inhibitors of the actin cytoskeleton, we show that Cyr61 gene expression is sensitive to mechanisms that sense actin dynamics. These results establish the regulation of Cyr61 gene by mechanical stretch and provide clues to the key signaling molecules involved in this process.
Flow-induced calcium oscillations in rat osteoblasts are age, loading frequency, and shear stress dependent
Authors: Donahue Seth W. , Jacobs Christopher R. , Donahue Henry J.
Published: December 2017

Bone adaptation to mechanical loading is dependent on age and the frequency and magnitude of loading. It is believed that load-induced fluid flow in the porous spaces of bone is an important signal that influences bone cell metabolism and bone adaptation. We used fluid flow-induced shear stress as a mechanical stimulus to study intracellular calcium (Ca[Formula: see text]) signaling in rat osteoblastic cells (ROB) isolated from young, mature, and old animals. Fluid flow produced higher magnitude and more abundant [Ca2+]ioscillations than spontaneous oscillations, suggesting that flow-induced Ca[Formula: see text] signaling encodes a different cellular message than spontaneous oscillations. ROB from old rats showed less basal [Ca2+]i activity and were less responsive to fluid flow. Cells were more responsive to 0.2 Hz than to 1 or 2 Hz and to 2 Pa than to 1 Pa. These data suggest that the frequency and magnitude of mechanical loading may be encoded by the percentage of cells displaying [Ca2+]ioscillations but that the ability to transduce this information may be altered with age.
Neurotrophin-3 inhibits HCO 3 − absorption via a cAMP-dependent pathway in renal thick ascending limb
Authors: Good David W. , George Thampi
Published: December 2017

Neurotrophins are expressed in the adult kidney, but their significance is unclear. We showed previously that nerve growth factor (NGF) inhibits HCO[Formula: see text] absorption in the rat medullary thick ascending limb (MTAL) via an extracellular signal-regulated kinase (ERK)-dependent pathway. Here we examined whether other neurotrophic factors affect MTAL HCO[Formula: see text] absorption. Brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor had no effect. In contrast, neurotrophin-3 (NT-3, 0.7 nM) inhibited HCO[Formula: see text] absorption by 40% (half-maximal inhibition at ∼0.4 nM). Inhibition by NT-3 was additive to inhibition by NGF. Inhibitors of ERK activation that block inhibition by NGF had no effect on inhibition by NT-3. In contrast, 8-bromo-cAMP or forskolin pretreatment blocked inhibition by NT-3 but not NGF. Inhibition by NT-3 was also blocked by the specific protein kinase A (PKA) inhibitor myristoylated PKI(14–22) amide and by vasopressin, which inhibits HCO[Formula: see text]absorption via cAMP. Inhibitors of phosphatidylinositol 3-kinase or protein kinase C did not affect NT-3-induced inhibition, but inhibition by NT-3 was eliminated by genistein, consistent with involvement of a receptor tyrosine kinase. These results demonstrate that NT-3 inhibits HCO[Formula: see text] absorption via a cAMP- and PKA-dependent pathway. NT-3 and NGF regulate MTAL ion transport through different signal transduction mechanisms. These studies establish a direct role for NT-3 in regulation of renal tubule transport and identify the MTAL as an important target for neurotrophins, which may be involved in the control of renal acid excretion.
Regulation of taurine transporter expression by NO in cultured human retinal pigment epithelial cells
Authors: Bridges Christy C. , Ola M. Shamsul , Prasad Puttur D. , El-Sherbeny Amira , Ganapathy Vadivel , Smith Sylvia B.
Published: December 2017

Taurine is actively transported at the retinal pigment epithelial (RPE) apical membrane in an Na+- and Cl−-dependent manner. Diabetes may alter the function of the taurine transporter. Because nitric oxide (NO) is a molecule implicated in the pathogenesis of diabetes, we asked whether NO would alter the activity of the taurine transporter in cultured ARPE-19 cells. The activity of the transporter was stimulated in the presence of the NO donor 3-morpholinosydnonimine. The stimulatory effects of 3-morpholinosydnonimine were not observed during the initial 16-h treatment; however, stimulation of taurine uptake was elevated dramatically above control values with 20- and 24-h treatments. Kinetic analysis revealed that the stimulation was associated with an increase in the maximal velocity of the transporter with no significant change in the substrate affinity. The NO-induced increase in taurine uptake was inhibited by actinomycin D and cycloheximide. RT-PCR analysis and nuclear run-on assays provided evidence for upregulation of the transporter gene. This study provides the first evidence of an increase in taurine transporter gene expression in human RPE cells cultured under conditions of elevated levels of NO.
HIF-1 expression in healing wounds: HIF-1α induction in primary inflammatory cells by TNF-α
Authors: Albina Jorge E. , Mastrofrancesco Balduino , Vessella Joseph A. , Louis Claudine A. , Henry William L. , Reichner Jonathan S.
Published: December 2017

The expression of the hypoxia-responsive transcription factor hypoxia-inducible factor (HIF)-1 during acute inflammation was investigated in experimental wounds. HIF-1α mRNA was maximally expressed in wound cells 6 h after injury. HIF-1α protein was detectable in wound cells 1 and 5 days after injury. Cells from 1-day-old wounds were not hypoxic, as determined by lack of pimonidazole hydrochloride adduct formation. Tumor necrosis factor (TNF)-α, but not interleukin-1β, increased the HIF-1α protein content of cells isolated 1 and 5 days after injury, and also of glycogen-elicited peritoneal cells, but not HIF-1α mRNA. HIF-1α did not accumulate in TNF-α-treated HeLa, NIH/3T3, NR8383, or RAW 264.7 cells. Nitric oxide from S-nitrosoglutathione did not induce HIF-1α accumulation or modulate the response to TNF-α. TNF-α did not increase oxygen consumption or result in the production of reactive oxygen intermediates by day 1 wound cells. Vascular endothelial growth factor mRNA in wound cells peaked 24 h after wounding. HIF-1 expression in early wounds may contribute to the regulation of inducible nitric oxide synthase and vascular endothelial growth factor, two HIF-1-responsive genes intimately related to the process of repair.
Expression and regulation of 4F2hc and hLAT1 in human trophoblasts
Authors: Okamoto Yoko , Sakata Masahiro , Ogura Kazuhiro , Yamamoto Toshiya , Yamaguchi Masaaki , Tasaka Keiichi , Kurachi Hirohisa , Tsurudome Masato , Murata Yuji
Published: December 2017

The neutral amino acid transport system L is a sodium-independent transport system in human placenta and choriocarcinoma cells. Recently, it was found that the heterodimer composed of hLAT1 (a light-chain protein) and 4F2 heavy chain (4F2hc), a type II transmembrane glycoprotein, is responsible for system L amino acid transport. We found that the mRNAs of 4F2hc and hLAT1 were expressed in the human placenta and a human choriocarcinoma cell line. The levels of the 4F2hc and hLAT1 proteins in the human placenta increased at full term compared with those at midtrimester. Immunohistochemical data showed that these proteins were localized mainly in the placental apical membrane. Data from leucine uptake experiments, Northern blot analysis, and immunoblot analysis showed that this transport system was partially regulated by protein kinase C and calcium ionophore in the human choriocarcinoma cell line. Our results suggest that the heterodimer of 4F2hc and hLAT1 may play an important role in placental amino acid transport system L.
Cytoplasmic dipeptidase activities of kidney, ileum, jejunum, liver, muscle, and blood.
Authors: Krzysik B A , Adibi S A
Published: December 2017

Peptide hydrolase activities against glycyl-L-leucine and glycylglycine were investigated in the soluble fractions of blood, liver, kidney cortex, skeletal muscle (gastrocnemius), and jejunal and ileal mucosa of rats. The maximal hydrolase activity in each tissue was determined when the incubation conditions, such as time, pH, substrate and enzyme concentrations, and ionic requirements were optimal. The kinetic constants (apparent Km and Vmax) were determined from Lineweaver-Burk double reciprocal graphs. Maximal hydrolysis rates against both dipeptides were many times greater by kidney and intestinal segments than by those of muscle, liver, or blood. The order of Vmax for hydrolase activity against glycylleucine was kidney greater than ileum greater than jejunum greater than liver greater than muscle greater than blood, and the order against glycylglycine was ileum greater than kidney greater than jejunum greater than liver greater than muscle. Those tissues that had the lowest Vmax values (liver and muscle), when calculated on the basis of tissue weights, were shown to have activities comparable to the others. Results of this study are consistent with our previous findings that: 1) glycylleucine half-life in plasma is shorter than that of glycylglycine, and 2) disappearance rates of these dipeptides from plasma are not affected by nephrectomy or enterectomy.
Fetal fuels II: contributions of selected carbon fuels to oxidative metabolism in rat conceptus.
Authors: Shambaugh G E , Koehler R A , Freinkel N
Published: December 2017

The effects of fasting on the oxidative disposition of selective fuels in tissues of the rat conceptus were examined on day 20 of gestation. Placentas and portions of fetal liver and brain from fed and 48-h fasted mothers were incubated in vitro with artificial mixtures containing glucose, lactate, and beta-hydroxybutyrate in concentrations simulating those that obtain in fed or 48-h fasted animals in vivo. Oxidative contributions from individual components were evaluated by separate incubations in which only one of the three fuels was 14C-labeled. As judged by the evolution of 14CO2, rates of oxidation of individual fuels by tissues of the conceptus appeared to be conditioned by ambient fuel concentrations rather than the dietary status of the mother. Additional studies indicated that evolution of 14CO2 from glucose or lactate may be depressed directly by adding beta-hydroxybutyrate to the incubation medium. This substitutive property of beta-hydroxybutyrate may "spare" glucose and lactate within the placenta for transfer to the fetus and preserve glucose and lactate availability for biosynthetic rather than oxidative disposition within the fetus.
Gluconeogenesis from alanine in vivo by the ovine fetus and lamb.
Authors: Prior R L , Christenson R K
Published: December 2017

Gluconeogenesis from alanine was determined with an intravenous infusion of [U-14C]alanine and [6-3H]glucose or [U-14C]glucose in five fetal lambs (3.6 +/- 0.1 kg; 127 days of gestation) and four growing ewe lambs (37 +/- 2 kg). Conversion of alanine to glucose (mmol/h) was 0.40 +/- 0.12 and 0.51 +/- 0.10 and accounted for 7.3 and 25.6% of the alanine turnover in fetal and growing lambs, respectively. Alanine contributed 2.3 and 1.1% of the glucose turnover and 22.3 and 1.1% of the lactate turnover in fetal and growing lambs, respectively. Lactate contributed 19.5% of the glucose turnover in growing lambs, and glucose synthesis from lactate accounted for 24.7% of the lactate turnover. Glucose turnover (mmol/h) was 10.2 and 25.1 in fetal and growing lambs, respectively. Results from these studies have shown that the fetal lamb at 127 days of gestation has a high rate of alanine turnover and conversion to glucose when compared with that of the growing lamb on a high plane of nutrition.
Storage telemetry of radionuclide tracers by implantable thermoluminescent dosimeters.
Authors: Bojsen J , Moller U , Christensen P , Lippert J
Published: December 2017

A storage telemetrical method using thermoluminescent (TL) dosimeters for long-term measurements of incorporated radioactive substances in unrestrained rats has been developed. The system has been used in combination with radiotelemetrical registration of the circadian temperature rhythm. By sequential replacement of double TL dosimeters (60 mg, CaSO4:Dy) through an implanted silicon tube, the concentration of different radionuclides can be determined over long periods. The persistence of the circadian temperature rhythm indicates that the animals were unaffected by the experimental conditions. The relative uncertainty of the dosimeter system and the temperature transmitter is approximately +/- 2% (SD) at 5 mR exposures and +/- 0.05 degrees C, respectively. The weight of the system in total is 5.7 g. Disappearance studies (36-48 h) have been performed with the beta-emitters, 32P nad 42K, in subcutaneous tissues and tumor tissue. This TL method permits the repetition of an experiment on the same rat several times, and thereby avoids errors due to biological variations between animals.
Origin of migrating myoelectric complex in sheep.
Authors: Ruckebusch Y , Bueno L
Published: December 2017

The electrical activity of the gastroduodenal junction was recorded in conscious sheep for 8 to 12 wk with chronically implanted electrodes. The flow of digesta was simultaneously recorded, and the duodenal bulb was isolated at the time of implantation. The mean slow-wave frequency of the antrum was 5.6 +/- 0.3/min with spike bursts randomly superimposed on about 60% of the slow waves. The activity of the duodenal bulb was characterized by an absence of slow-wave unpropagated spike bursts and by two types of propagated spike bursts. The first consisted of isolated bursts accompanied by a rapid movement of digesta through the entire duodenum and proximal jejunum. The second, an irregular series of 8-12 spike bursts was associated with total evacuation of the duodenal bulb, followed in turn by an inhibition of antral spiking activity and the development of a migrating myoelectric complex (MMC) in the distal duodenum. The results indicate that in sheep organization of the MMC is located at the duodenal level where the duodenal bulb has a reservoir function.
Regional differences in potassium content of smooth muscle from opossum esophagus.
Authors: Schulze K , Hajjar J J , Christensen J
Published: December 2017

Strips from the proximal part of the smooth muscle segment of opossum esophagus have a significantly higher potassium content (50 +/- 3 meq/kg) than those from the distal part (38 +/- 3 meq/kg). There are no significant differences between the two regions in content of sodium (65 +/- 4 meq/kg in proximal, 71 +/- 3 meq/kg in distal) or chloride (48 +/- 10 meq/kg in proximal, 42 +/- 5 meq/ kg in distal). The mean [14C]inulin uptake is 240 +/- 10 ml/kg in both proximal and distal strips. [14C]polyethylene glycol uptake is smaller and [14C]sucrose and [14C]mannitol uptake in both areas are larger than that of inulin. Intracellular potassium concentration (based on the inulin uptake as an estimate of the extracellular space volume) is significantly higher proximally (71 +/- 3 mM) than distally (52 +/- mM). Ouabain, 10(-4) M, increases the intracellular concentration of sodium and decreases the intracellular concentration of potassium in both the proximal and distal segment. The efflux of 86Rb, measured by a washout technique, is higher in the distal than in the proximal smooth muscle segment. A difference in membrane permeability to rubidium and hence, potassium between proximal and distal smooth muscle segments may account in part for the different intracellular potassium concentrations.
Cellular and paracellular calcium transport in rat ileum: effects of dietary calcium.
Authors: Nellans H N , Kimberg D V
Published: December 2017

The mechanism of calcium transport and its modulation by dietary Ca restriction in rat ileum have been investigated employing an in vitro voltage-clamp technique. Ca fluxes directed from mucosa-to-serosa (J(Ca)ms) and serosa-to-mucosa (J(Ca)sm) exhibit components consistent with both cellular and paracellular pathways. The cellular Ca fluxes are both dependent on medium Na and are abolished at 10 degrees C. In addition, a cellular component of J(Ca)ms displays voltage dependence. A low-calcium diet, which induces the formation of 1,25-dihydroxycholecalciferol, causes a marked increase in both cellular J(Ca)ms and Ca influx from media to cells with little absolute effect on the paracellular pathway. This evidence is consistent with the existence of electrogenic Na-Ca exchange pumps at both brush-border and basolateral membranes, driven in part by the Na electrochemical gradient. Dietary Ca conditioning may control the direction of net Ca transport by modulation of the saturable influx process at the brush border.
Glycogen synthase activation in human skeletal muscle: effects of diet and exercise.
Authors: Kochan R G , Lamb D R , Lutz S A , Perrill C V , Reimann E M , Schlender K K
Published: December 2017

We investigated the role of glycogen synthase in supranormal resynthesis (supercompensation) of skeletal muscle glycogen after exhaustive exercise. Six healthy men exercised 60 min by cycling with one leg at 75% VO2max, recovered 3 days on a low-carbohydrate diet, exercised again, and recovered 4 days on high-carbohydrate diet. Glycogen and glycogen synthase activities at several glucose-6-phosphate (G6P) concentrations were measured in biopsy samples of m. vastus lateralis. Dietary alterations alone did not affect glycogen, whereas exercise depleted glycogen stores. After the second exercise bout, glycogen returned to normal within 24 h and reached supercompensated levels by 48 h of recovery. Glycogen synthase activation state strikingly increased after exercise in exercised muscle and remained somewhat elevated for the first 48 h of recovery in both muscles. We suggest that 1) forms of glycogen synthase intermediate to I (G6P-independent) and D (G6P-dependent) forms are present in vivo, and 2) glycogen supercompensation can in part be explained by the formation of intermediate forms of glycogen synthase that exhibit relatively low activity ratios, but an increased sensitivity to activation by G6P.
Exercise stimulates interleukin-6 secretion: inhibition by glucocorticoids and correlation with catecholamines
Authors: Papanicolaou D. A. , Petrides J. S. , Tsigos C. , Bina S. , Kalogeras K. T. , Wilder R. , Gold P. W. , Deuster P. A. , Chrousos G. P.
Published: December 2017

In experimental animals, stress and catecholamines stimulate endogenous interleukin-6 (IL-6) secretion, whereas glucocorticoids inhibit it. To examine whether physical stress alters the secretion of IL-6 in humans, and to what extent this is correlated with catecholamines and modified by glucocorticoids, we performed high-intensity treadmill exercise test runs on 15 male volunteers, in a double-blind crossover design, after pretreatment with placebo, hydrocortisone, or dexamethasone. Plasma epinephrine and norepinephrine concentrations peaked 15 min after the start of exercise, whereas plasma IL-6 concentrations peaked twice, 15 min and 45 min after the onset of the test run. There was no difference in either the epinephrine or norepinephrine peaks among the three treatments, but the net area under the curve for IL-6 was smaller after hydrocortisone or dexamethasone than after placebo and smaller after dexamethasone than after hydrocortisone. A positive correlation was observed between peak plasma epinephrine or norepinephrine and IL-6 levels at 15 min. These findings suggest that IL-6 secretion is stimulated during exercise, possibly by catecholamines, whereas exogenous glucocorticoids attenuate this effect without affecting the catecholamine levels.
Importance of dietary amines in meal-induced gastrin release
Authors: Lichtenberger L. M. , Graziani L. A. , Dubinsky W. P.
Published: December 2017

The dietary chemical constituents responsible for initiating the gastrin secretory response to a meal have yet to be identified. The evidence supporting the importance of dietary amino acids in the initiation of the postprandial release of gastrin is both conflicting and unconvincing. In this study we investigated the role of the amino acid breakdown products ammonia and the amines in the regulation of gastrin release both in vivo and in vitro. Lyophilization of standard rat food under alkaline conditions results in the volatilization of both ammonia and the amines, which can be subsequently condensed in a cold trap. The normal postprandial release of gastrin is significantly reduced by approximately 50% when rats are fed this freeze-dried diet. Addition of the amine-containing condensate back to the freeze-dried diet completely restores this response to normal. Analysis of the completely restores this response to normal. Analysis of the condensate by thin-layer chromatography revealed that it contained ammonia, methylamine, ethylamine, dimethylamine, and a fourth unidentified aliphatic amine. All of the above compounds significantly stimulated the release of gastrin from isolated G cells. Similarly, addition of ammonia and a synthetic amine mixture to the freeze-dried diet completely restored the postprandial release of gastrin to normal levels. In conclusion, our results suggest that dietary amines and ammonia may play a key role in initiating the gastrin secretory response to a meal.
Experimental diabetes and intestinal barriers to absorption
Authors: Thomson A. B.
Published: December 2017

The unstirred water layer (UWL) and the brush-border membrane represent the major barriers to intestinal absorption. Enhanced uptake of several nutrients has been described in diabetes mellitus, and this study was undertaken in the rat to define whether these absorptive changes are due to alterations in the characteristics of these barriers. Using in vitro techniques the effective resistance of UWL was measured with lauryl alcohol, the rate of uptake (Jd) of which is limited by diffusion across the UWL. At all rates of stirring of the bulk phase, the effective resistance of UWL was less in diabetic than control rats. The Jd of a homologous series of saturated fatty acids (4:0-18:0) and cholesterol was higher than disks of intestine of diabetic than control intestine; this enhanced uptake of lipid could not be demonstrated using intestinal biopsies. The change in incremental free energy of transfer of fatty acid uptake into disks was higher in diabetic than control animals after correction for UWL effects. After correction for UWL, the Michaelis constant for Jd of D-glucose was similar in diabetic and control jejunum, and the greater Jd of glucose in diabetics was due to a higher maximal transport rate (Jmd) and a higher passive permeability coefficient. It is concluded that the enhanced uptake of glucose, fatty acids, fatty alcohols, and cholesterol into diabetic intestine is due to a reduction in the effective resistance of the UWL, an increase in the passive permeability properties of the membrane, and a rise in the Jmd for D-glucose.
Canalicular bile salt-independent bile formation: concepts and clues from electrolyte transport in rat liver
Authors: Graf J.
Published: December 2017

Studies on canalicular electrolyte transport are reviewed with reference to the concept that hepatocellular inorganic ion secretion may provide an osmotic drive for canalicular water flow. Cellular transport of electrolytes and of some nonelectrolytes appears directly or indirectly (cotransport or potential-sensitive transport) related to the activity of Na+-K+-ATPase of the sinusoidal cell membrane, but the role of the enzyme in regulating bile flow remains undetermined. Bile secretion of the isolated rat liver continues in the absence of either Na+, K+, Cl-, or HCO-3 when these ions are replaced in the perfusion medium by other permanent ions. Transepithelial salt concentration gradients, established experimentally, cause transient changes of bile flow and dissipate very quickly. Isotopic ion equilibration between sinusoids and bile proceeds faster than between sinusoids and liver cells. Both observations indicate extensive electrolyte diffusion through a paracellular shunt pathway. This pathway appears preferentially permeable to cations, and it restricts permeation of molecules of the size of sucrose (no apparent diffusion or effects of solvent drag) or bile acids (no backleak). In promoting canalicular osmotic water flow, transepithelial concentration gradients of NaCl are less effective than those of sucrose, revealing a reflection coefficient of NaCl of 0.3. By perfusion with hypertonic medium containing sucrose, bile flow is reduced. Bile production against this opposing osmotic gradient is accomplished by an increase in biliary organic anion concentration. Inorganic ion concentrations essentially conform to a Gibbs-Donnan distribution across the canalicular epithelium, established by the presence of impermeant anions in bile. Hence, the luminal electrical potential is expected to be negative with respect to the sinusoids. It is concluded that biliary secretion of endogenous organic anions is the major osmotic driving force for canalicular bile salt-independent bile flow and that transport of inorganic ions into bile results mainly from diffusion and solvent drag.
Cholecystokinin- and secretin-induced pancreatic secretion in normal and diabetic rats
Authors: Sofrankova A. , Dockray G. J.
Published: December 2017

The influence of the endocrine pancreas on exocrine pancreatic function was studied in rats made diabetic by administration of streptozotocin. In normal urethan-anesthetized rats the C-terminal octapeptide of cholecystokinin (CCK-8) stimulated the rate of flow and rates of amylase and trypsinogen release from the pancreas; the proportions of the two enzymes did not change with repeated stimulation. In diabetic rats CCK-8 (0.3-1.2 nmol . kg-1 iv) stimulated significantly greater increases in trypsinogen output and rate of flow compared with normal animals. In contrast, amylase responses to CCK-8 were significantly depressed in diabetic rats. There were no differences between normal and diabetic rats in the flow and total protein responses to exogenous secretin. The present results indicate that the effects of insulin deprivation on relative rates of enzyme synthesis are also expressed in the secretion of the intact pancreas in vivo. These results also raise the possibility that in the normal intact gland there may be nonparallel release of enzymes at different rates of secretion depending on the relative secretory activities of cells in the immediate vicinity of the islets of Langerhans and those distant to the islets.
Pepsinogen secretion from dispersed glands from rabbit stomach
Authors: Kasbekar D. K. , Jensen R. T. , Gardner J. D.
Published: December 2017

In dispersed glands from rabbit stomach, pepsinogen secretion was stimulated by carbamylcholine, the C-terminal octapeptide of cholecystokinin (CCK-8), and structurally related peptides physalaemin and A23187 but not by bombesin or histamine. Reducing the incubation temperature from 37 degrees to 4 degrees C or adding carbonyl cyanide m-chlorophenylhydrazone reduced basal as well as stimulated pepsinogen secretion. Dibutyryl cGMP inhibited the stimulation of pepsinogen secretion caused by cholecystokinin but not that caused by carbamylcholine; atropine inhibited the stimulation of pepsinogen secretion caused by carbamylcholine but not that caused by cholecystokinin. Each cholecystokinin-related peptide had the same efficacy for stimulating pepsinogen secretion. In terms of the concentration that caused half-maximal stimulation of pepsinogen secretion, the relative potencies of cholecystokinin-related peptides were caerulein greater than CCK-8 greater than [desSO3]CCK-8 greater than gastrin. Removing extracellular calcium did not alter basal or cholecystokinin-stimulated pepsinogen secretion. These results illustrate that dispersed glands from rabbit stomach constitute a suitable preparation for examining the actions of various agents on pepsinogen secretion in vitro.
Effect of cimetidine on histamine-stimulated gastric acid and electrolytes in dogs
Authors: Hirschowitz B. I. , Molina E.
Published: December 2017

Intravenous administration of cimetidine (0.25-2.0 mg X kg-1 X h-1) inhibited histamine-stimulated gastric acid secretion in both intact (Ki = 1.0 mg X kg-1 X h-1) and vagotomized (Ki = 1.75 mg X kg-1 X h-1) dogs. During histamine infusion, all doses of cimetidine reduced gastric volume output; high doses increased gastric juice pepsin and [Na+] and reduced [H+] and [Cl-]. Gastric juice [K+] was not affected during cimetidine infusion. The cimetidine-induced changes in electrolyte concentrations were qualitatively comparable with those observed on withdrawal of histamine stimulation. On termination of cimetidine infusion with continued histamine administration, gastric [K+] and volume output increased immediately, followed 30 min later by an increase in [H+] and a reciprocal decrease in [Na+]; [Cl-] did not recover. The changes in gastric juice electrolytes after termination of cimetidine, with the exception of [Cl-], mimicked the changes observed on initiation of histamine stimulation. These data indicate that the effects of cimetidine may be totally explained by its antagonism of histamine binding to the parietal cell H2-receptor, that vagotomy reduces cimetidine binding to the H2-receptor, and that cimetidine antagonism of histamine is rapidly reversed on removal of the antagonist.
Biliary transport of glutathione and methylmercury
Authors: Ballatori N. , Clarkson T. W.
Published: December 2017

The hepatobiliary transport of glutathione (GSH) and methylmercury (MM) was investigated in male and female rats anesthetized with pentobarbital sodium. When bile flow was altered with either sodium dehydrocholate (DHC), hypertonic sucrose infusion, or by hypothermia, the absolute rates of GSH and MM secretion into bile were not affected, resulting in parallel concentration changes in the bile fluid for both GSH and MM. Indocyanine green and sulfobromophthalein (BSP), but not BSP-glutathione complex, inhibited the biliary secretion of free GSH. This inhibition was accompanied by a parallel inhibition of MM secretion into bile and occurred without any changes in liver GSH or MM levels. On the other hand, the intravenous administration of cysteine, GSH, and penicillamine was associated with an increase in the secretion rate of reduced sulfhydryl groups into bile and an increase in the biliary secretion rate of MM. The increased biliary secretion rate of MM after phenobarbital pretreatment was also associated with an increased rate of secretion of GSH into bile. In addition, sex differences and individual variability in the biliary secretion of MM were correlated with differing abilities to secrete GSH into bile. The results suggest the presence of a biliary transport system for GSH that determines the biliary secretion of MM.
Different effect of starvation on activity of sucrase and lactase in rat jejunoileum
Authors: Yamada K. , Goda T. , Bustamante S. , Koldovsky O.
Published: December 2017

Activities of lactase and sucrase were determined in proximal, middle, and distal thirds of the jejunoileum of 15-wk-old male rats starved for 1, 2, and 3 days and in rats fed a high-sucrose diet for 24 h after 3 days of starvation. Sucrase activity (expressed per tissue protein or DNA as well as per intestinal segment) showed a progressive decrease during starvation in proximal and middle segments but not in the distal segment. Lactase activity expressed per tissue protein or DNA in all segments increased significantly. This was obviously due to the loss of tissue protein and DNA because total lactase activity per segment did not change. Refeeding the sucrose diet produced an increase of sucrase activity without influencing lactase activity. In serial tissue homogenate of jejunal villus-crypt columns prepared using cryostat sectioning, it was shown that, during starvation, activity of lactase (specific and total) increased in the upper and middle villus. Sucrase activity (specific and total) during starvation decreased and after refeeding increased in the lower and middle villus.
Concentrative uptake of alanine in hepatocytes from fed and fasted rats
Authors: Kristensen L. O. , Sestoft L. , Folke M.
Published: December 2017

The transport of alanine across the liver cell membrane was studied in hepatocytes isolated from fed and 48-h-fasted rats. Aminooxyacetate was used to render alanine nonmetabolizable. The steady-state intracellular-to-extracellular distribution ratio of alanine was maximal at extracellular concentrations below 0.5 mM and was increased from about 10 to about 20 by fasting. This increase was the net effect of a two- to threefold increase in the alanine influx and about a 50% increase in the rate constant of alanine efflux. The results suggest that alanine efflux occurred partly via the transport system mediating Na+-dependent alanine influx and partly by another pathway. The transmembrane Na+ electrochemical gradient remained unchanged by fasting and could apparently account for a maximal distribution ratio of alanine well above 20. In both nutritional states, the simplest kinetic model adequately describing the alanine influx implicated one saturable component besides a passive component. The apparent Vmax of the former was doubled by fasting while the apparent Km was insignificantly decreased. At low extracellular alanine concentrations, the rate of alanine consumption (aminooxyacetate absent) was only 40% of the alanine influx in the fed state but was increased at least fivefold by fasting and thereby balanced with the increased alanine influx. These results suggest a rate limitation at the transport level in the fasted state.
Oxygen consumption by rat liver: effects of taurocholate and sulfobromophthalein transport, glucagon, and cation substitution
Authors: van Dyke R. W. , Gollan J. L. , Scharschmidt B. F.
Published: December 2017

The proportion of total hepatic energy utilized for bile formation and transport of taurocholate (TC) and conjugated sulfobromophthalein (cBSP) has not been defined previously. To study this question we have measured changes in oxygen consumption by the isolated perfused rat liver and freshly isolated hepatocytes occurring in response to TC and cBSP administration, cation substitution, and glucagon infusion. The basal rates of bile formation and oxygen consumption varied considerably among different livers, and there was little or no relationship between these two variables. Administration of either TC or cBSP to the perfused liver elicited a marked choleresis but failed to alter steady-state oxygen consumption even at maximal rates of TC or cBSP transport. Similarly, incubation of hepatocytes with TC or cBSP did not alter oxygen consumption. In contrast, inhibition of Na-K-ATPase by removal of sodium and/or potassium from the medium reduced oxygen consumption by perfused rat liver and isolated hepatocytes by 27-37%, and glucagon administration increased oxygen consumption in both systems by 31-40%. These findings indicate that the oxygen requirement for bile formation and even maximal rates of TC and cBSP transport is small compared with that for the metabolic changes induced by glucagon or for hepatic Na-K-ATPase activity. This is in contrast to other epithelial tissues, such as kidney and rectal gland, in which oxygen utilization for transepithelial solute and water transport constitutes a large fraction of both total and Na-K-ATPase-dependent oxygen consumption.
Pancreatic acini in short-term culture: regulation by EGF, carbachol, insulin, and corticosterone
Authors: Logsdon C. D. , Williams J. A.
Published: December 2017

To define the hormonal regulation of the exocrine pancreas, acini were maintained for 24 h in suspension culture under various conditions and then examined morphologically and tested for their ability to synthesize and secrete protein. Acini cultured in the presence of 20% fetal calf serum (control conditions) retained their differentiated morphology as judged by light and electron microscopy. Under control conditions, stimulation with either cholecystokinin octapeptide (CCK8) or carbachol increased the release of amylase in a dose-dependent manner with a maximal threefold increase occurring at 200 pM CCK8 or 6 microM carbachol. Without inclusion of other factors in the medium during the culture period, the rate of protein synthesis measured in cultured acini was one-third the rate measured in freshly prepared acini. Inclusion of epidermal growth factor (EGF) (2 nM), carbachol (1 microM), or insulin (1 microM) during the culture period led to increases, whereas corticosterone (1 microM) led to decreases in functional parameters. Greatest effects were seen with a combination of EGF, carbachol, and insulin. This combination of factors led to a 160% increase over control in CCK8-stimulated amylase release and a 180% increase in [3H]leucine incorporation. These results indicate that isolated pancreatic acini can be maintained for up to 24 h and that EGF, carbachol, insulin, and corticosterone can regulate the long-term function of this tissue.
Amylase secretion by isolated pancreatic acini after chronic cholecystokinin treatment in vivo
Authors: Otsuki M. , Williams J. A.
Published: December 2017

Rats were given subcutaneous injections of synthetic cholecystokinin octapeptide (CCK8, 5 micrograms/kg) in a depot carrier twice daily for 7–14 days. The pancreatic wet weight increased by 20.6 and 30.9% in the rats treated with CCK8 for 7 and 14 days, respectively. The increase in pancreatic weight was associated with an increase in the amount of protein per DNA, indicating hypertrophy of the acinar cells, and with an increase in the total amount of pancreatic DNA. Moreover, CCK administration also increased the amylase content per DNA. In acini prepared from CCK8-treated rats, responsiveness to CCK8 was increased when amylase release was expressed relative to DNA but was decreased when calculated as the percentage of the initial content in the acini. The dose-response curves for CCK8 were similarly shaped in both CCK8-treated and control rats, but they were shifted 3- to 10-fold toward higher concentrations of CCK8 after 7 and 14 days of CCK8 treatment. There were no major changes in the affinity and capacity of CCK receptors determined by studying the binding of radioiodinated CCK, suggesting that alterations in pancreatic amylase release were due to changes at a postreceptor loci. In support of this hypothesis, the secretory response to carbachol, known to act on a different receptor but by a common intracellular mechanism, was altered in a manner identical to the response to CCK8. Thus chronic stimulation with CCK sufficient to induce pancreatic hypertrophy does not greatly alter CCK receptors and induces only moderate postreceptor desensitization.
Differentiation among inhibitory actions of omeprazole, cimetidine, and SCN- on gastric acid secretion
Authors: Wallmark B. , Jaresten B. M. , Larsson H. , Ryberg B. , Brandstrom A. , Fellenius E.
Published: December 2017

The action of the substituted benzimidazole omeprazole (H 168/68) was studied in three different in vitro preparations: the isolated guinea pig gastric mucosa, isolated intact and permeable rabbit gastric glands, and hog fundic microsomal membrane vesicles containing H+-K+-ATPase. The effects of omeprazole were compared with those of cimetidine and thiocyanate (SCN-). Under all the conditions studied, cimetidine only counteracted histamine-induced acid secretion, consonant with its H2-receptor antagonism. In contrast, omeprazole and SCN- were found not only to inhibit histamine-induced secretion but also basal acid formation and acid formation induced by dibutyryl cAMP and a high cell medium concentration of K+. Moreover, acid production induced by ATP in permeable gastric glands was antagonized by omeprazole and SCN-, whereas cimetidine was without effect. The interaction pattern of omeprazole and SCN- was differentiated by studies using the weak base antipyrine in the isolated mucosal preparation, where it was found that antipyrine could reverse the inhibition induced by SCN- but not that of omeprazole. Furthermore, omeprazole was found to inhibit the isolated H+-K+-ATPase, whereas cimetidine or SCN- was without effect. In the isolated mucosal preparation omeprazole caused an increase in K+ secretion rates in parallel with the inhibition of acid formation. This was in contrast to what was observed for cimetidine and SCN-, which exhibited no such increased K+ secretion. The results obtained from intact mucosa and isolated glands are in agreement with the ability of omeprazole to inhibit the isolated H+-K+-ATPase and thus provide evidence of a novel mechanism of action for this inhibitor.
Short-chain fatty acids stimulate motility of the canine ileum
Authors: Kamath P. S. , Hoepfner M. T. , Phillips S. F.
Published: December 2017

Based on earlier observations that colonic contents stimulated ileal motility in the dog, our hypothesis is that the ileum would respond to physiological amounts of short-chain fatty acids (SCFA). Four dogs had isolated ileocolonic loops constructed surgically and boluses of test solutions (15 ml) were instilled into the distal ileum through a small catheter. Intraluminal pressure catheters were used to record motility. Concentrations of SCFA (also called volatile fatty acids) comparable to those found in dog stool (108 mM; 66% acetic, 24% propionic, and 10% butyric acids) regularly stimulated motility with a dose-related effect. The response was not due to the pH of the SCFA solutions and was independent of the pH at which SCFA were instilled. Ricinoleic acid (4 mM) also stimulated motility, as did chenodeoxycholic acid; the bile acid was active only at supraphysiological concentrations (approximately 7.6 mM). Instillates that simulated the composition of ileal chyme in malabsorptive states were without effect. The results suggest that the ileum can "sense" the presence of colonic contents in the lumen and that SCFA are the responsible mechanisms. Stimulation of ileal motility by SCFA could be a response to coloileal reflux.
Role of somatostatin neurons in intestinal peristalsis: facilitatory interneurons in descending pathways
Authors: Grider J. R. , Arimura A. , Makhlouf G. M.
Published: December 2017

The role of somatostatin neurons in the regulation of peristalsis was examined in segments of rat colon that permit separate characterization of the ascending contraction and descending relaxation components of the peristaltic reflex. Release of somatostatin and vasoactive intestinal peptide (VIP) increased significantly only during descending relaxation. Preincubation of the segment with somatostatin antiserum (final concentration 1:40) decreased VIP release and descending relaxation. Addition of somatostatin (1 nM to 1 microM) augmented VIP release and descending relaxation in a concentration-dependent manner. Together the results implied that the increase in somatostatin release was coupled to, and responsible for, the increase in VIP release, which in turn was responsible for descending relaxation. The results are consistent with the topography of myenteric VIP neurons (which project into circular muscle) and somatostatin neurons (which project caudad within the plexus) and the pharmacological properties of the two peptides. Somatostatin antiserum had no effect on basal VIP release or ascending contraction, indicating that somatostatin neurons were not involved in the regulation of ascending contraction. The study suggests that somatostatin neurons of the myenteric plexus act as facilitatory interneurons in descending pathways.