bluuebunny/crossref_metadata_2025 huggingface dataset:
cGMP modulation of ileal ion transport: in vitro effects of Escherichia coli heat-stable enterotoxin
Authors: Guandalini S. , Rao M. C. , Smith P. L. , Field M.
Published: December 2017

Diarrheagenic strains of Escherichia coli have been shown to produce a heat-stable enterotoxin (ST) that simulates guanylate cyclase, increases short-circuit current (Isc), and inhibits active Cl absorption in the intestine. In rabbit ileum, the ion transport effects are smaller than those produced by cAMP-related agonists. Because ST may be a selective cGMP agonist, we further explored its mode of action in rabbit ileum. ST inhibits net Na and net Cl absorption. ST also inhibits the same fraction of Cl influx across the brush border that theophylline inhibits. At maximal doses, ST and 8-bromo-cGMP (8-Br-cGMP) had nearly equal, nonadditive effects of Isc that were about 66% of that produced by 8-Br-cAMP. ST increased mucosal cGMP concentration 16-fold, whereas epinephrine, an inhibitor of secretion, increased cGMP concentration by only 30%. This is insufficient to alter ion transport because doses of ST that increased cGMP concentration by 100% failed to alter Cl fluxes. Furthermore, epinephrine did not increase cGMP concentration in isolated enterocytes. We conclude that 1) cGMP mediates ST effects on ion transport, and 2) although ST and cAMP-related agonists have the same antiabsorptive effects, ST is less effective in stimulating electrogenic Cl secretion.
Uptake of vasoactive intestinal peptide by rat liver
Authors: Misbin R. I. , Wolfe M. M. , Morris P. , Buynitzky S. J. , McGuigan J. E.
Published: December 2017

We have investigated the uptake and degradation of vasoactive intestinal peptide (VIP) by rat livers. When liver was perfused with 125I-VIP, less than 20% of the radioactivity was recovered as intact peptide. 125I-VIp bound to specified high-affinity sites on isolated hepatocytes. Half-maximal inhibition of binding occurred at about 1 nM unlabeled VIP. Cell-bound 125I-VIP was degraded to low-molecular-weight products. The percent of 125I-VIP that was bound and degraded was approximately the same at both extremes of the range of VIP concentrations (25-250 pg/ml) reported in portal vein plasma. The lysosomotropic agent chloroquine inhibited 125I-VIP degradation and led to the accumulation of cell-bound 125I-VIP. We conclude that a) most of the VIP secreted from the gastrointestinal tract into portal blood is removed during its passage through the liver, b) VIP binds to specific high-affinity sites on hepatocytes and is probably internalized and degraded by lysosomes, and c) uptake of VIP by liver may serve to prevent the peptide from exerting deleterious systemic effects.
Dynamics of intestinal oxygenation: interactions between oxygen supply and uptake
Authors: Granger H. J. , Nyhof R. A.
Published: December 2017

The oxygenation of intestinal tissue is dependent on the interaction of three distinctive transport processes: 1) convection (i.e., blood flow), 2) diffusion, and 3) chemical reaction. Oxygen is transported to the capillary level by convection. Local adjustments of blood flow in accordance with tissue oxygen demand serve to stabilize capillary oxygen tension. After reaching the capillary, oxygen is transferred into the parenchymal cells by diffusion. Intrinsic modulation of the number of perfused capillaries allows vascular control of exchange surface area and effective capillary-to-cell diffusion distance. On entering the cell, molecular oxygen acts as the electron acceptor responsible for maintaining continuous mitochondrial respiration and the interlinked oxidative formation of ATP. The basic interaction of blood flow, diffusion, and mitochondrial respiration under a variety of conditions are illustrated utilizing a simplified graphic approach. The analysis demonstrates the ability of the flow and exchange controllers, operating in unison, to provide a wide margin of safety against development of cell hypoxia under a variety of stresses. Finally, the role of oxygen, adenosine, and prostaglandins as possible mediators of intrinsic vasoregulation in intestine is discussed.
Postnatal development of intestinal bile salt transport in the guinea pig
Authors: Heubi J. E. , Fondacaro J. D.
Published: December 2017

The postnatal development of intestinal bile salt transport was examined in the guinea pig. Using an in vitro technique, mucosal uptake of taurocholate was measured in jejunum and ileum at five monomeric concentrations from fetal, 1-day-old, 5-day-old, 10-day-old, 21-day-old, and adult animals. Jejunal taurocholate uptake was linear with respect to concentration and was not inhibited by taurochenodeoxycholate at all ages studied. In fetal and 1-day-old animals, ileal taurocholate uptake was linear and was not inhibited by taurochenodeoxycholate. A curvilinear relation between uptake and taurocholate concentration, which was inhibited by taurochenodeoxycholate, was observed in 5-day-old and older animals. These findings indicate that, in the guinea pig, passive diffusion of taurocholate is the only mode of intestinal transport in fetuses and newborns and the sole mode of jejunal transport at all ages. By 5 days, however, active ileal transport appears, which persists into adulthood and contributes to the development of an efficient enterohepatic circulation of bile salts.
Effect of pancreatic polypeptide on gallbladder pressure and hepatic bile secretion
Authors: Adrian T. E. , Mitchenere P. , Sagor G. , Bloom S. R.
Published: December 2017

Intraluminal gallbladder pressure, measured by radiotelemetry, and bile output were monitored during infusion of porcine pancreatic polypeptide (PP) at doses of 6, 25, 100, and 400 pmol . kg-1 . h-1 in healthy conscious pigs. Plasma PP concentrations during infusion of the three lower doses, measured by radioimmunoassay, were within the range seen postprandially in these animals. Gallbladder pressure fell in a dose-related manner during PP infusion by 2.2 +/- 0.9, 8.2 +/- 0.4, 11.6 +/- 0.7, and 14.8 +/- 0.8 mmHg, respectively. In addition, a significant reduction in the bile output was observed during infusion of the two higher doses of PP. In a separate series of experiments, using cholecystectomized pigs, PP had no effect on bile output. These findings suggest that the amount of PP released postprandially may be sufficient to influence gallbladder function but not hepatic secretion of bile in the pig.
A comparison of copper-loading disease in Bedlington terriers and Wilson's disease in humans
Authors: Su L. C. , Ravanshad S. , Owen C. A. , McCall J. T. , Zollman P. E. , Hardy R. M.
Published: December 2017

Eleven Bedlington terriers were found to have a mean hepatic copper concentration of 6,321 micrograms/g dry wt (normal, 200 micrograms/g dry wt) and renal copper concentration that was three or four times normal. Brain copper levels were normal in younger dogs, were elevated in two older dogs, and were 100 times normal in one dog that died of the disease. Increased concentrations of copper in the liver, kidney, and brain also characterize Wilson's disease. Erythrocyte survival was normal in three affected dogs, but serum glutamic-pyruvic transaminase levels were usually elevated. Unlike the hypoceruloplasminemia of patients with Wilson's disease, plasma ceruloplasmin activity was not only normal but was also slightly elevated in the terriers. Despite their normal or excessive ceruloplasmin, the Bedlington terriers could convert ionic 64Cu to radioceruloplasmin but did so only very slowly. These dogs accumulated significantly more 64Cu in their livers than normal, much like patients with Wilson's disease do before symptoms develop.
Effect of phenolphthalein on monkey intestinal water and electrolyte transport
Authors: Powell D. W. , Johnson P. T. , Bryson J. C. , Orlando R. C. , Fan C. C.
Published: December 2017

To assess Na-K-ATPase inhibiton and prostaglandin synthesis stimulation as the mechanism of the secretory (cathartic) action of phenolphthalein in the primate, we investigated water and electrolyte transport and Na-K-ATPase levels in monkey intestine. Both jejunum and colon were studied with in vivo perfusion and in vitro Ussing chamber techniques. Water, Na, and Cl absorption was inhibited or secretion was induced by phenolphthalein (10(-3) M) in the jejunum and colon when the drug was present in the mucosal bathing (perfusion) solution. Serosal addition of phenolphthalein (10(-4) or 10(-3) M) induced Na and anion absorption in the jejunum but not in the colon. Phenolphthalein inhibited Na-K-ATPase activity in the test tube, but assays of intestine previously perfused or bathed in the drug showed no inhibiton. Indomethacin, in doses sufficient to inhibit prostaglandin synthesis in the intestine, inhibited the secretion induced by phenolphthalein in the jejunum but not in the colon. These inconsistencies cast doubt on the role of Na-K-ATPase inhibition or the role of prostaglandin synthesis stimulation in the mechanism of action of phenolphthalein.
Protein synthesis inhibitors enhance secretagogue sensitivity of in vitro rat pancreatic acini
Authors: Otsuki M. , Williams J. A.
Published: December 2017

Isolated rat pancreatic acini were treated with cycloheximide and amylase release was measured. This agent increased the sensitivity to both synthetic octapeptide of cholecystokinin (CCK8) and carbamylcholine, the major secretagogues known to utilize Ca2+ as a second messenger. The mechanism of the cycloheximide effect was via inhibition of protein synthesis, as indicated by the following: 1) the concentration of cycloheximide used inhibited leucine incorporation by greater than 90%; 2) this effect was not instantaneous but increased up to a 2-h pretreatment; and 3) a similar effect was obtained with puromycin, a chemically different inhibitor of protein synthesis. Cycloheximide acted on the steps by which secretagogues mobilize cellular Ca2+ because the dose-response curve for 45Ca2+ efflux was shifted to the same extent as that for amylase release, whereas the dose-response curve for amylase release induced by the Ca2+ ionophore A23187 was not altered. The results suggest, therefore, that a rapidly turning-over protein present in pancreatic acinar cells exerts an inhibitory influence on Ca2+ mobilization by secretagogues.
Quantitative electron microscope autoradiographs of 125I-cholecystokinin in pancreatic acini
Authors: Williams J. A. , Sankaran H. , Roach E. , Goldfine I. D.
Published: December 2017

To morphologically evaluate the interaction of cholecystokinin (CCK) with its receptors on pancreatic acinar cells, we incubated isolated mouse acini at 37 degrees C with radioiodinated CCK and then prepared quantitative electron microscope autoradiographs. Specific binding of CCK to acini was one-half maximal at 2 min of incubation and maximal after 10 min. The cell-associated radioactivity was extracted and analyzed on Sephadex G-50. After 2 min, 90% of the total cellular radioactivity remained as intact CCK; after 30 min, the intact radioactivity decreased to 65% of total. At 2 min, the fraction of bound hormone that fixed to acini was 84% of total; this amount decreased to 78% after 30 min. Thus, the majority of radioactivity in the autoradiographs at both time points was intact CCK; however, at 30 min, a small amount was also degraded hormone. After both 2 and 30 min of incubation, silver grains were highly concentrated over the basolateral plasma membrane. A significant number of grains were in the cell interior at both time points, increasing from 13% of total grains at 2 min to 42% at 30 min. At both times, the largest fraction of internalized grains was localized over the endoplasmic reticulum. At 30 min, a significant concentration of CCK grains was observed over multivesicular bodies. The present study demonstrates, therefore, that CCK binds to specific receptors on the basolateral surface of pancreatic acinar cells. After binding, the hormone is internalized, locates predominantly on the endoplasmic reticulum, and is then degraded.
Hepatic transport kinetics: effect of anatomic and metabolic heterogeneity on estimates of the average transfer coefficients
Authors: Forker E. L. , Luxon B. A.
Published: December 2017

In the accompanying paper we explore the analysis of solute disappearance curves using conventional linear assumptions. In this study we extend the analysis to examine the possibility of using the same model to recover the average kinetic parameters when the liver lobule displays anatomic and metabolic heterogeneity. The results show that the linear model can be used to recover good estimates of the average transfer coefficients, even though the kinetic parameters that govern uptake, efflux, and excretion are nonlinear functions of sinusoidal length. The inhomogeneities that we have examined include a variable surface-to-volume ratio of the sinusoids, saturation kinetics at the canalicular face of the liver cells, and a lobular profile of metabolizing enzyme or excretory carrier units per unit length of sinusoid.
Effect of separate feeding of proteins and lipids on pancreatic adaptation in the rat
Authors: Bourdel G.
Published: December 2017

In agreement with what is known of pancreatic adaptation to dietary composition, a progressive lowering of amylase-to-chymotrypsinogen ratio was observed in the pancreases of rats fed mixed diets of increasing casein and decreasing carbohydrate contents. The same changes in ratio were found when casein alone was increased in otherwise isonitrogenous meals fed to rats provided ad libitum with a protein-free diet. Pancreatic accumulation of chymotrypsinogen was increased while that of amylase was decreased in spite of low-protein and high-carbohydrate intakes. Lowering the lipid content of the protein-free diet reduced the effectiveness of casein meals in lowering the amylase-to-chymotrypsinogen ratio. It is concluded that 1) the capacity of protein-rich diets to induce adaptative changes in pancreatic secretion does not depend on the absolute amount of proteins passing through the duodenum but rather on the increased protein concentration in the alimentary bolus, 2) protein concentration affects both amylase and chymotrypsinogen, and 3) lipids have a cooperative effect.
Effect of iron stores on hepatic metabolism of transferrin-bound iron
Authors: Wilms J. W. , Batey R. G.
Published: December 2017

Hepatic and splenic accumulation and hepatic subcellular distribution of iron from a tracer dose of purified 59Fe-labeled transferrin were studied in normal, iron-deficient, iron-loaded, and pregnant rats. Hepatic and splenic 59Fe content was determined at varying intervals and the subcellular distribution then studied. In normal rats hepatic accumulation of 59Fe was biphasic with 9-10% of the dose present in the liver in the first 2 h postinjection, followed by a plateau of 4 h and a second rise to 20-25% at 16-18 h. During iron deficiency, 5-6% of the dose accumulated in the liver in 2 h and remained at this level. Iron loading resulted in a rapid accumulation of 17% of the dose at 6 h, and the normal plateau was absent. Splenic iron accumulation was similar in the normal and iron-loaded groups with approximately 3% of the dose present in the spleen over the 7-day study. Iron deficiency resulted in a threefold increase in splenic iron content to 10% of the dose at 1 h postinjection. Hepatic and splenic iron accumulation was markedly depressed in the pregnant group. Subcellular distribution studies showed that the 59Fe moved rapidly into ferritin in all groups and was not at any time associated with either lysosomes or mitochondria. These studies present further physiological data of the effects of differing iron states on hepatic and splenic iron accumulation.
Mechanism of action of cholecystokinin octapeptide on rat antrum, pylorus, and duodenum
Authors: Scheurer U. , Varga L. , Drack E. , Burki H. R. , Halter F.
Published: December 2017

The mechanism of action of cholecystokinin octapeptide (CCK-OP) on tonic and phasic contraction of antral, pyloric, and duodenal smooth muscles was studied with a novel perfusion manometric system in isolated esophagogastroduodenal preparations of the rat. CCK-OP increased baseline pressure at each site, frequencies of phasic contractions in the antrum and pylorus, and amplitudes in the duodenum. It decreased antral and pyloric amplitudes and frequency of duodenal phasic contractions. CCK-OP action on tonic contraction was tetradotoxin (TTX) susceptible and its action on phasic contractions was TTX resistant. Phentolamine, phenoxybenzamine, propranolol, catecholamine depletion of preparations by reserpine-tetrabenazine, and the block of catecholamine synthesis at different levels significantly inhibited CCK-OP-induced tonic contraction, whereas atropine had no influence. Adrenergic and cholinergic neural actions on phasic contractions altered the level of amplitudes and frequencies on which CCK-OP action occurred. It is concluded that CCK-OP action on tonic contraction of the rat gastroduodenal junction is mediated by a neural noncholinergic pathway, whereas its effect on muscles responsible for phasic contractions is a direct one.
Separation of adaptive mucosal growth and transport after small bowel resection
Authors: Urban E. , Michel A. M.
Published: December 2017

In rats 70% of the small bowel was resected with preservation of duodenum and terminal ileum. Two and four weeks later transport of sodium, chloride, water, and galactose was studied in duodenum and ileum. Controls were sham-operated and unoperated rats. There was significant mucosal growth 2 and 4 wk after resection. By 2 wk postresection transport specific activities (transport per gram mucosa) were generally decreased. Mucosal growth compensated only sufficiently so that transport capacities (transport per centimeter segment length) remained unaltered from controls. By 4 wk postresection transport specific activities had either increased or were unchanged from controls. Therefore, in association with mucosal growth, transport capacities increased. The major adaptive increases for electrolytes and water occurred in duodenum; ileum was the site of increased galactose transport. The data indicate that 1) mucosal growth and functional transport changes occur as separate adaptive phenomena and 2) adaptive transport mechanisms are selectively localized to particular regions of the intestine.
Effect of vagus, gastric inhibitory polypeptide, and HCl on gastrin and somatostatin release from perfused pig antrum
Authors: Holst J. J. , Jensen S. L. , Knuhtsen S. , Nielsen O. V. , Rehfeld J. F.
Published: December 2017

The porcine antrum was isolated with the pancreas and perfused in vitro with an artificial medium supplemented with erythrocytes. The vagal innervation was preserved. Effluent was collected from the portal vein as well as from a vein directly draining the antrum. Electrical vagal stimulation increased gastrin output and inhibited somatostatin output. Intraluminal hydrochloric acid had the opposite effect. Gastric inhibitory polypeptide (GIP) in physiological concentrations (90 and 450 pmol/l) increased somatostatin output, inhibited gastrin output, and potentiated the effect of HCl on somatostatin release. Vagal stimulation, however, abolished the GIP effect on somatostatin output. Thus gastrin and somatostatin outputs were always inversely affected by the applied stimuli, suggestive of somatostatin-mediated control of gastrin secretion. GIP may exert its effects via local somatostatin release.
Role of calcium in the regulation of colonic secretion in the rat
Authors: Zimmerman T. W. , Dobbins J. W. , Binder H. J.
Published: December 2017

In vitro experiments were performed in rat colon to define the role of calcium in the regulation of electrolyte transport. Neither basal net sodium absorption (JNanet) nor JClnet was affected by varying serosal calcium from 0 to 3.0 mM, but both were decreased by 4.8 mM calcium. Removal of serosal calcium completely inhibited the effect of bethanechol, a muscarinic cholinergic agonist, which inhibits neutral sodium-chloride absorption in 1.2 mM calcium. In contrast, theophylline significantly decreased JNanet and JClnet both in the presence and absence of calcium, but the effects of theophylline were significantly less in calcium-free media. In 3.0 mM calcium bethanechol inhibited JCLnet significantly greater than JNanet and in 4.8 mM calcium bethanechol decreased JClnet equivalent to the increase in short-circuit current without significantly altering JNanet. We conclude that 1) high [Ca2+] inhibits net sodium and net chloride absorption; 2) the alteration of electrolyte transport by bethanechol is dependent on extracellular calcium, and the alteration of electrolyte transport by theophylline is not dependent on extracellular calcium but may be dependent on intracellular calcium; and 3) in addition to inhibition of neutral NaCl absorption, bethanechol stimulates chloride secretion.
Ca2+ in the control of active intestinal Na and Cl transport: involvement in neurohumoral action
Authors: Donowitz M.
Published: December 2017

Intracellular Ca2+ is a regulator of active intestinal Na and Cl transport. Most studies have been done with rabbit ileum. Increasing intracellular Ca2+ decreases active Na and Cl absorption and/or stimulates active Cl secretion; lowering intracellular Ca2+ stimulates Na and Cl absorption. Based on studies with microvillus membrane vesicles from rabbit ileum, a direct effect of Ca2+ and calmodulin on linked Na and Cl uptake is established. Intracellular Ca2+ and cAMP affect the same transport processes and act in a nonadditive manner. Intracellular Ca2+ does not act by changing intestinal cAMP or cGMP contents, and increasing cAMP mobilizes intracellular Ca2+. Whether this Ca2+ is involved in regulation of ion transport is not known. The aspects of Ca2+ handling identified as involved in regulation of active intestinal Na and Cl transport include entry of Ca2+ across the basolateral membrane, mobilization of Ca2+ from intracellular stores, and involvement of the Ca2+-binding protein calmodulin. Several neurohumoral substances alter intestinal transport by Ca2+-dependent mechanisms and appear to act primarily by increasing (serotonin, carbachol, substance P, and neurotensin) or decreasing (dopamine) Ca2+ entry across the basolateral membrane of intestinal epithelial cells.
Relative effects of systemic pH, PCO2, and bicarbonate concentration on ileal ion transport
Authors: Charney A. N. , Haskell L. P.
Published: December 2017

To determine the relative effects of systemic pH, CO2 tension (PCO2), and bicarbonate concentration on ileal electrolyte transport, states of acute metabolic acidosis and alkalosis were created in Sprague-Dawley rats by gavage feeding (NH4)2SO4 and NaHCO3, respectively. During in situ perfusion of the ileum in anesthetized animals, electrolyte transport was measured before and after respiratory compensation of the systemic pH. Acute respiratory acidosis and alkalosis also were studied by ventilating animals with 0, 3, or 8% CO2. When animals in all groups were considered, net sodium absorption correlated very well with blood pH (r = -0.97). Net bicarbonate secretion correlated with the plasma bicarbonate concentration (r = 0.91) independently of blood pH and PCO2. Net chloride absorption correlated with blood PCO2 (r = 0.92) and was altered when systemic pH and bicarbonate concentration changed in opposite directions. Alterations in luminal pH and PCO2 did not affect electrolyte transport. These results suggest that systemic pH affects a sodium chloride absorptive process and that the plasma bicarbonate concentration affects a chloride absorptive-bicarbonate secretory exchange process in the rat ileum.
Carnitine transport in rat small intestine
Authors: Shaw R. D. , Li B. U. , Hamilton J. W. , Shug A. L. , Olsen W. A.
Published: December 2017

Although L-carnitine has been given orally to patients with systemic carnitine deficiency with successful control of the disease and is present in a variety of dietary sources, there is little available information on the physiology of its absorption. We therefore studied intestinal carnitine absorption in the rat by measuring the uptake of radioactive L-carnitine by everted intestinal rings and sacs. Active transport was demonstrated in duodenum and jejunum, but not ileum, with intracellular concentrations higher than medium concentrations at steady state and by the prevention of concentration gradients with anoxia, metabolic inhibitors, and replacement of sodium ion. Studies of the relationship of uptake to carnitine concentration demonstrated the presence of two components of transport: a saturable component (with a Km of between 206 and 316 microM) that could be inhibited by the metabolically inactive D-isomer and by acetylcarnitine and a linear component that we presume represents diffusion.
Rat pancreatic response to intestinal infusion of intact and hydrolyzed protein
Authors: Green G. M. , Miyasaka K.
Published: December 2017

The effect of partial exclusion of pancreatic juice from the intestine on the pancreatic response to intraduodenal infusion of casein, casein hydrolysate, and trypsin inhibitor was investigated in conscious rats with chronic pancreatic and biliary fistulas. In controls all pancreatic juice collected was returned to the intestine. In partial diversion groups only 10% of the pancreatic juice collected was returned during each collection period. All bile was returned. Partial diversion of pancreatic juice slightly increased the response to NaCl, had no effect on the incremental response to casein hydrolysate, but doubled the incremental protein and volume response to casein infusion. Trypsin inhibitor infusion did not stimulate pancreatic secretion in controls but greatly increased pancreatic protein and fluid secretion in rats with partial diversion of pancreatic juice. The results confirm that protein hydrolysates are weak stimulants of pancreatic secretion in the rat compared with intact proteins and support the view that intact proteins and trypsin inhibitors stimulate pancreatic secretion in the rat by a common mechanism, i.e., by reducing feedback inhibition from luminal pancreatic proteases.
Glucose absorption by in vitro perfused colon of the fetal rat
Authors: Potter G. D. , Schmidt K. L. , Lester R.
Published: December 2017

The anatomic configuration of fetal rat colon resembles that of the small bowel. Accordingly, glucose and amino acid absorption were measured in order to see whether the fetal rat colon resembled the small bowel functionally. In vitro luminal perfusion of the fetal rat colon at 20 days of gestation was employed to measure the rate of glucose and L-alanine absorption and the unidirectional flux rates of 3-O-methylglucose (3-O-MG). The colon was mounted between pipettes in a heated oxygenated bath and perfused with the solute to be studied dissolved in buffered physiological solution and polyethylene glycol with average molecular weight of 4,000 (PEG) as a nonabsorbable marker substance. The PEG was not transported and did not diffuse across fetal colon. Scanning and transmission electron microscopy of perfused and control colon showed the presence of villi and the preservation of mucosal anatomy during perfusion. Glucose was absorbed at 173 +/- 16 mumol . h-1 . g-1 (8) and absorption was abolished in Na-free solution. 3-O-MG flux was 40 +/- 7 mumol . h-1 . g-1 (8) from lumen to bath and 7 +/- 1 mumol . h-1 . g-1 (8) from bath to lumen. L-Alanine flux was 130 +/- 15 mumol . h-1 . g-1 (8) from lumen to bath and 18 +/- 4 mumol . h-1 . g-1 (5) from bath to lumen, and the lumen-to-bath flux was only partially abolished by Na-free solutions.
A new technique for measuring intestinal calcium absorption in the rat
Authors: Marsh C. L. , LeBlanc A. D. , Johnson P. C. , Pool S. L.
Published: December 2017

A double-isotope technique that does not necessitate urine and fecal collections but requires only the extraction of the incisor teeth for isotopic analysis has been devised. A precalibrated dose of 45Ca in solution with stable carrier calcium is administered to the rat orally. An intraperitoneal injection delivers a precalibrated dose of 47Ca in isotonic saline. The ratio of the percentage uptake of the two radionuclides in the incisor tooth is equal to the fraction of the 45Ca and, therefore, the calcium absorbed by the gut. The fraction of calcium absorbed by 5-mo-old rats, as determined by collection and measurement of excreta, was found to be 39.1%. The ratio of uptake of the two calcium radionuclides in the incisor teeth yields an absorption measurement of 38.8%, nonsignificantly different from the value obtained from the excretion data. The measurement of radiocalcium uptake in the incisor tooth affords one an accurate in vivo determination of intestinal calcium absorption without the collection of excreta or multiple blood sampling.
Intestinal capillary exchange capacity and oxygen delivery-to-demand ratio
Authors: Kvietys P. R. , Perry M. A. , Granger D. N.
Published: December 2017

The relations between intestinal capillary exchange capacity and various determinants of tissue oxygenation were characterized in autoperfused, denervated preparations of the canine ileum. Ileal metabolic demand was either increased (intraluminal glucose) or decreased (graded reductions in intraluminal temperature) while measuring blood flow, arterial oxygen content, arteriovenous oxygen difference, and the capillary filtration coefficient (an index of capillary exchange capacity). No significant correlations were obtained between the capillary filtration coefficient and 1) blood flow), 2) oxygen delivery, or 3) oxygen demand. The capillary filtration coefficient was directly related to the arteriovenous oxygen difference and inversely related to the oxygen delivery-to-demand ratio. These observations support the hypothesis that intrinsic modulation of oxygen extraction is mediated by vascular elements which govern capillary exchange capacity and that capillary exchange capacity is inversely related to the oxygen delivery-to-demand ratio.
Resolution of apical and basal-lateral membrane populations from rat exorbital gland
Authors: Mircheff A. K. , Lu C. C. , Conteas C. N.
Published: December 2017

We performed analytical fractionation studies with the goal of isolating basal-lateral and apical membrane vesicles from epithelial cells of rat exorbital lacrimal gland. A density region designated window II contained elements of three physically and biochemically distinct membrane populations. These were resolved by countercurrent distribution in an aqueous polymer two-phase system. One population contained 50% of the NADPH-cytochrome c reductase activity recovered from window II and appeared to be of intracellular origin. A second population contained 70% of the recovered Na-K-ATPase, maximally enriched 42-fold with respect to the initial homogenate. This population was the major locus of alanine transport activity, roughly 85% of which was mediated by systems believed to be characteristic of epithelial cell basal-lateral membranes. It also contained portions of the alkaline phosphatase, galactosyltransferase, acid phosphatase, and NADPH-cytochrome c reductase activities. A third population accounted for 33% of the recovered alkaline phosphatase and was a secondary locus of Na-alanine transport activity, 45% of which could be attributed to systems believed to be characteristic of epithelial cell apical membranes.
Corticosteroid alteration of active electrolyte transport in rat distal colon
Authors: Foster E. S. , Zimmerman T. W. , Hayslett J. P. , Binder H. J.
Published: December 2017

To determine the effect of corticosteroids on active transport processes, unidirectional fluxes of 22Na, 36Cl, and 42K were measured under short-circuit conditions across isolated stripped distal colonic mucosa of the rat in control, secondary hyperaldosterone, and dexamethasone-treated animals. In controls net sodium and chloride fluxes (JNanet and JClnet) and short-circuit current (Isc) were 6.6 +/- 2.2, 7.6 +/- 1.6, and 1.3 +/- 0.2 mu eq X h-1 X cm-2, respectively. Although aldosterone increased Isc to 7.3 +/- 0.5 mu eq X h-1 X cm-2, JNanet (6.9 +/- 0.7 mu eq X h-1 X cm-2) was not altered and JClnet was reduced to 0 compared with controls. Dexamethasone also stimulated Isc but did not inhibit JClnet. In Cl-free Ringer both aldosterone and dexamethasone produced significant and equal increases in JNanet and Isc. Theophylline abolished JNanet in control animals but not in the aldosterone group. Aldosterone reversed net potassium absorption (0.58 +/- 0.11 mu eq X h-1 X cm-2) to net potassium secretion (-0.94 +/- 0.08 mu eq X h-1 X cm-2). Dexamethasone reduced net potassium movement to 0 (-0.04 +/- 0.12 mu eq X h-1 X cm-2). These studies demonstrate that 1) corticosteroids stimulate electrogenic sodium absorption and 2) aldosterone, but not dexamethasone, inhibits neutral NaCl absorption and stimulates active potassium secretion. The effects of mineralocorticoids and glucocorticoids on electrolyte transport are not identical and may be mediated by separate and distinct mechanisms.
Gastrointestinal blood flow and oxygen consumption in awake newborn piglets: effect of feeding
Authors: Nowicki P. T. , Stonestreet B. S. , Hansen N. B. , Yao A. C. , Oh W.
Published: December 2017

Regional and total gastrointestinal (GI) blood flow, O2 delivery, and whole-gut O2 extraction and O2 consumption were measured before and 30, 60, and 120 min after feeding in nonanesthetized, awake 2-day-old piglets. Cardiac output and blood flow to kidneys, heart, brain, and liver were also determined. Blood flow was measured using the radiolabeled microsphere technique. In the preprandial condition, total GI blood flow was 106 +/- 9 ml X min-1 X 100 g-1, while O2 extraction was 17.2 +/- 0.9% and O2 consumption was 1.99 +/- 0.19 ml O2 X min-1 X 100 g-1. Thirty minutes after slow gavage feeding with 30 ml/kg artificial pig milk, O2 delivery to the GI tract and O2 extraction rose significantly (P less than 0.05) by 35 +/- 2 and 33 +/- 2%, respectively. The increase in O2 delivery was effected by a significant increase in GI blood flow, which was localized to the mucosal-submucosal layer of the small intestine. O2 uptake by the GI tract increased 72 +/- 4% 30 min after feeding. Cardiac output and blood flow to non-GI organs did not change significantly with feeding, whereas arterial hepatic blood flow decreased significantly 60 and 120 min after feeding. The piglet GI tract thus meets the oxidative demands of digestion and absorption by increasing local blood flow and tissue O2 extraction.
Regulation of antral gastrin content
Authors: Johnson L. R. , Guthrie P. D.
Published: December 2017

Five groups of rats were fasted for 3 days and injected with either NaCl or 5, 10, 20, or 40 micrograms/kg bombesin every 8 h. The animals were killed, and their serum and antral gastrin levels were compared with those of normally fed rats. Fasting reduced serum gastrin to 14% of control; antral gastrin was reduced to 21% of control. All doses of bombesin significantly increased serum gastrin in fasted rats, and 20 and 40 micrograms/kg significantly increased antral gastrin. A group of normally fed rats was also compared with one fed a liquid diet for 7 days. Half of each of these was injected with 20 micrograms/kg bombesin (3 times/day) and the other half with NaCl. Bombesin significantly increased serum and antral gastrin in the rats fed solid food. The liquid diet lowered serum and antral gastrin to 17 and 59% of control values, respectively. Bombesin injection totally prevented these decreases. These data indicate that food in the gastrointestinal tract is not required for either gastrin release or synthesis. Furthermore, the data suggest that gastrin synthesis is regulated primarily by gastrin release or by direct stimulation by bombesin rather than by specific food products.
pH dependence of pepsinogen and acid secretion in isolated gastric glands
Authors: Norris S. H. , Hersey S. J.
Published: December 2017

Rabbit isolated gastric glands were used to investigate the dependence of pepsinogen and acid secretions on extraglandular pH. Changing pH from 8.0 to 6.7 caused small increases in pepsinogen secretory responses to isoproterenol, carbachol, cholecystokinin octapeptide, Boots' secretin, and hyperosmolarity but caused large increases in responses to 8-bromoadenosine 3',5'-cyclic monophosphate (8BrcAMP), 8-bromoinosine 3',5'-cyclic monophosphate (8BrcIMP), and forskolin. The similar effect of pH on responses to 8BrcAMP, 8BrcIMP, and forskolin was suggested to reflect a commonality in their proposed mechanisms of action. It was concluded that reducing extraglandular pH indirectly caused an increase in activity of cAMP-dependent protein kinase or of a subsequent step in cAMP-dependent regulation of pepsinogen secretion. 8BrcAMP-stimulated acid secretion also increased as pH was changed from 8.0 to 6.7, and a similar explanation of the effect was suggested. However, histamine-stimulated acid secretion and adenyl cyclase activity decreased markedly as pH was lowered over this range. It was suggested that cAMP was rate limiting for stimulation by histamine and that the effect of pH on histamine-stimulated acid secretion could be attributed to an effect of pH on adenyl cyclase activity.
Effects of KCl and insulin on benzimidazole-inhibited canine gastric secretion
Authors: Hirschowitz B. I. , Fong J.
Published: December 2017

The final step in acid secretion is believed to result from the H+-K+-ATPase-mediated exchange of H+ in the parietal cell, with K+ in the lumen. To study the K+ secretion we used Picoprazole and insulin separately and together to inhibit gastric secretion stimulated in gastric fistula dogs with histamine (100 micrograms X kg-1 X h-1). Picoprazole, a substituted benzimidazole (750 mg/kg), reduced gastric H+ concentration and volume with a rise in K+ concentration [( K+]) to 20–25 meq/l. Insulin alone inhibited acid output to the same extent as Picoprazole but with a marked fall in [K+]. Insulin (0.6 U/kg) given with Picoprazole did not alter inhibition of H+ but prevented the large decrease in gastric juice [K+]. An injection of KCl (1 meq/kg) 1 h after Picoprazole did not alter the effects of the inhibitor. Pepsin secretion after insulin was delayed by Picoprazole, whereas during bethanechol chloride infusion (80 micrograms X kg-1 X h-1) pepsin output was reduced for a shorter period and to a lesser extent than acid. We concluded that insulin affects gastric H+ and K+ secretion by a mechanism not related to H+-K+-ATPase and that Picoprazole affects pepsin secretion probably indirectly via its effect on the parietal cell, where its action is quite consistent with an effect limited to inhibition of the H+-K+-ATPase of the parietal cell.
Effects of hematocrit on oxygenation of the isolated perfused rat liver
Authors: Riedel G. L. , Scholle J. L. , Shepherd A. P. , Ward W. F.
Published: December 2017

The isolated perfused rat liver is used ubiquitously for metabolic and endocrine studies of hepatic function, yet few data are available regarding the inadequacy of the oxygenation of such preparations. Moreover, the isolated rat liver is usually deprived of its arterial supply and perfused via the hepatic portal vein with low-hematocrit or cell-free solutions. To investigate the efficacy of the oxygen supply, we determined the effect of hematocrit on the relation between oxygen consumption and perfusate flow. We then attempted to define a hematocrit at which hepatic oxygenation was maximal. Livers of male rats anesthesized with pentobarbital sodium were perfused via the portal vein with fresh canine red blood cells suspended in Krebs-Ringer-bicarbonate buffer. Perfusions were carried out at various flow rates, and the relation between perfusate flow and oxygen uptake was determined. At flow rates above 100 ml X min-1 X 100 g liver-1, oxygen uptake was independent of flow but below that value was flow limited, regardless of whether the hematocrit was 10, 20, or 40%. To determine the optimal hematocrit for hepatic oxygen uptake, hepatic portal venous and hepatic venous pressures were held at 10 and 0 mmHg, respectively. The hematocrit was lowered in steps from 80 to 10%. Blood flow increased exponentially as hematocrit fell while oxygen uptake increased to a maximum at approximately 20%. It is concluded that an hematocrit of approximately 20% provides the optimal combination of blood flow and oxygen-carrying capacity while maintaining physiological perfusion pressures, e.g., 10 mmHg.
Neural control of acid-induced serotonin release from rabbit duodenum
Authors: Kellum J. , McCabe M. , Schneier J. , Donowitz M.
Published: December 2017

The neural mediation of acid-stimulated serotonin release was studied in isolated sheets of rabbit duodenal mucosa mounted in Ussing chambers. The serosal side of the mucosa was exposed to Ringer-HCO3 at pH 7.4, and the mucosal side was exposed to citrate-phosphate buffer at pH 3–6.8. Immunoreactive serotonin release occurred onto the luminal surface at pH 6 and below and onto the serosal surface at pH 5 and below, but was greater on the luminal side at each pH. The effect of cholinergic and adrenergic agonists and antagonists on mucosal serotonin release was measured at luminal pH 7.4, 5, and 4. Acid-stimulated luminal release was significantly inhibited by atropine, hexamethonium, and propranolol at pH 4 and 5 but not by phentolamine. Serotonin release was stimulated at pH 7.4 and 4 by carbachol and isoproterenol but not by norepinephrine or nicotine at pH 7.4. It is concluded that acid-induced and nonacid-induced mucosal serotonin release is partly neurally mediated by muscarinic cholinergic and beta-adrenergic mechanisms.
Mobilization of copper(II) from plasma components and mechanisms of hepatic copper transport
Authors: Darwish H. M. , Cheney J. C. , Schmitt R. C. , Ettinger M. J.
Published: December 2017

The effects of plasma Cu(II) ligands on the kinetics of Cu(II) transport by rat liver parenchymal cells were determined to examine how Cu(II) is mobilized from plasma and transported into liver cells. Albumin markedly inhibited Cu(II) uptake at Cu(II)-to-albumin molar ratios of 3:1 or less. Kinetic analyses showed that albumin inhibits Cu(II) uptake by reducing the concentration of free Cu(II) in solution. Under conditions of excess albumin to Cu(II), histidine facilitated albumin-inhibited uptake of Cu(II). Threonine, glutamine, and most other amino acids were without effect. Moreover, the facilitation effect of a low-molecular-weight plasma fraction (less than or equal to 5,000) was largely accounted for by its histidine concentration. The tripeptide Gly-His-Lys also inhibited Cu(II) uptake into hepatocytes by the same mechanism as albumin. The inhibitory effects of albumin and Gly-His-Lys were additive with or without histidine. The active species in the Cu(II), albumin, and histamine mixtures was shown to be the His2Cu(II) complex. Vmax for this complex was identical to the Vmax for free Cu(II), but the Km was slightly higher [15 microM vs. 11 microM for free Cu(II)]. Concurrent determinations of [3H]-histidine and 64Cu(II) uptake showed that histidine was not transported with Cu(II) from His X Cu(II) or His2Cu(II) complexes. The data are consistent with histidine mobilizing Cu(II) from albumin by competing for Cu(II), interaction of the His2Cu(II) complex with the putative hepatic copper transport protein, and transport of copper as free ionic copper.
Effect of chronic ingestion of ethanol on in vitro uptake of lipids and glucose in the rabbit jejunum
Authors: Thomson A. B.
Published: December 2017

This study was undertaken to determine the effect of chronic feeding of ethanol on the in vitro jejunal uptake of lipids and glucose. The first group of rabbits was fed ad libitum (CAL); the food intake of a second control group [weight control (WC)] was restricted to match their gain in body weight with that of a chronically ethanol-fed group (ETH); and the food intake of a third control group [food control (FC)] was restricted to match the food intake with that of ETH. There was a marked decline in cholesterol uptake in WC and FC compared with CAL, and cholesterol uptake in ETH was intermediate between the higher value in CAL and the lower value in WC and FC. The uptake of fatty acids 4:0-12:0 was similar in the CAL, FC, WC, and ETH groups, both when the bulk phase was stirred and unstirred; the uptake of fatty acids 16:0 and 18:0 was lower in WC and FC than in CAL; and the uptake of fatty acids 14:0, 16:0, and 18:0 was even lower in ETH. The uptake of a homologous series of fatty alcohols was greater in WC and ETH than in CAL at five different rates of stirring of the bulk phase. When the uptake of fatty acids 6:0-12:0 was corrected for unstirred layer resistance, a linear relation was noted between fatty acid chain length and the natural logarithm of rate of uptake/aqueous diffusion coefficient, and the steeper slope in WC and ETH than in CAL represented a higher incremental change in free energy. Glucose uptake was similar in CAL, WC, and FC but was greater in ETH from 5 to 40 mM glucose. These studies demonstrate that 1) weight restriction, food restriction, and chronic ethanol feeding are associated with a change in the effective resistance of the unstirred layer and in the passive permeability properties of the rabbit jejunum, and 2) ethanol has a differential effect on passive permeation of short-, medium-, and long-chain fatty acids and cholesterol.
Characteristics of "on" and "off" contractions in esophageal circular muscle in vitro
Authors: Crist J. , Gidda J. S. , Goyal R. K.
Published: December 2017

The prevalence, amplitude, and latency periods of "on," "off," and "intermediate" contractions in response to transmural stimulation were recorded in transverse rings of circular muscle from different levels of the opossum esophagus. Ten-second train stimuli consistently produced off contractions. On contractions were not seen at lower stimulus frequencies (2 and 5 Hz); however, their incidence approached 90% at higher frequencies (40 Hz). Intermediate contractions occurred only at stimulus frequencies of 10 Hz or greater and were less frequent than on contractions. In general, the on and intermediate contractions had significantly lower amplitudes than the off contraction. The on contraction occurred with a latency period from initiation of the stimulus. This latency was greater in the more distal sites and decreased with increasing stimulus frequency. The off contractions occurred with a latency period from termination of the stimulus. This latency was not dependent on either stimulus frequency or site along the esophagus. Atropine antagonized the on and intermediate contractions but had no such effect on the off contraction. Tetrodotoxin abolished the on, off, and intermediate contractions. This study suggests that an intramural mechanism exists that upon stimulation produces atropine-sensitive on contractions. These contractions may play a role in esophageal peristalsis.
Mechanical and electrical activity of esophageal smooth muscle during peristalsis
Authors: Sugarbaker D. J. , Rattan S. , Goyal R. K.
Published: December 2017

Mechanical events and membrane potential changes in response to evoked swallows and cervical vagal stimulation (10 and 40 Hz) were recorded in anesthetized opossums. Miniature strain-gauge transducers monitored the mechanical activity of the two layers. A suction electrode recorded from the intact esophagus, from a proximally based pedicle flap of longitudinal muscle (LM), and from circular muscle (CM). The onset of swallowing was marked by the onset of mylohyoid activity. During swallows LM contraction preceded CM contraction and was of longer duration. The latencies of LM and CM contraction were 1,980 +/- 38 and 2,250 +/- 101 ms, respectively. The durations of contraction of LM and CM were 5,590 +/- 260 and 3,330 +/- 67 ms, respectively. LM showed no hyperpolarization but showed depolarization and spike burst. The CM showed prompt hyperpolarization followed by depolarization and spike burst. Responses to vagal stimulation were qualitatively similar to swallows. The different components of the responses were quantitatively modified by changes in stimulus frequency. These studies show that, during peristalsis in response to swallows and vagal stimulation, 1) LM contraction occurs before CM and is of longer duration, and 2) unlike CM, LM does not hyperpolarize prior to depolarization.