bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of glutathione in gastric mucosal cytoprotection
Authors: Robert A. , Eberle D. , Kaplowitz N.
Published: December 2017

Exogenous thiol compounds have been reported to protect the stomach from ethanol-induced necrotic lesions. The gastric mucosa contains high levels of an endogenous thiol, glutathion (GSH). Because of the known role of glutathione in protecting against hepatic injury, its role in gastric mucosal cytoprotection was of interest. By use of an animal model for acute gastric injury from ethanol, a close parallel relation between depletion of endogenous mucosal GSH and induction of mucosal protection was demonstrated. Surprisingly, mucosal protection varied inversely with the level of mucosal GSH obtained after treatment with specific GSH-depleting agents (diethyl maleate and cyclohexene-1-one). Depletion of gastric mucosal GSH was associated with an increase in the mucosal content of prostaglandins 6-keto F1 alpha and F2 alpha but not E2. The protective effect induced by GSH-depleting agents was partially reversed by indomethacin in some but not all studies. Although GSH depletors increased gastric juice volume, protection with these agents persisted after the volume and mucosal GSH had returned to control levels and also was not reversed by increasing the dose of ethanol threefold to overcome a possible dilutional effect. We conclude that, contrary to apparent predictions, depletion of endogenous gastric GSH protects the stomach from acute ethanol-induced injury. Although the mechanism of this protection is unknown, a mediation by endogenous release of prostaglandins seems to play a minor role since diethyl maleate was protective even in indomethacin-treated animals.
Chemical adrenalectomy by aminoglutethimide and the pancreas in suckling rats
Authors: Lerner A. , Lee P. C. , Lebenthal E.
Published: December 2017

The role of corticosterone in the development of pancreatic enzymes of suckling rats was studied through a partial and transient blockade of steroidogenesis by aminoglutethimide. Rats were injected with aminoglutethimide the night before their 14th day of age. Ten hours later they showed a transient decrease of serum total corticosterone level as compared with rats injected only with the vehicle. At 34 and 58 h after injection, their corticosterone levels returned to that of control rats. Pancreatic weight, protein, DNA contents, and total activities of amylase, lipase, and trypsinogen were depressed only in the aminoglutethimide-treated pups 34 h after injection. These pancreatic parameters returned to the control level 58 h after injection. Hydrocortisone given to another group of rats completely abolished the effect of aminoglutethimide on the pancreas. Thus, a transient suppression of serum corticosterone level caused a delay in the developmental accumulation of pancreatic exocrine enzymes that resumed only after the serum corticosterone returned to the control level. These results further confirm that corticosterone is an important modulator of pancreatic enzyme development in the rat.
Characteristics of cysteine uptake in intestinal basolateral membrane vesicles
Authors: Lash L. H. , Jones D. P.
Published: December 2017

Uptake of cysteine in intestinal basolateral membrane vesicles was independent of Na+, was sensitive to medium osmolarity, exhibited saturation kinetics, and was selectively inhibited by other amino acids in a concentration-dependent manner, indicating transport by a carrier-mediated process. The kinetics indicated the existence of two transport systems: a high- and a low-Km system with Km and Vmax values that differed by greater than one order of magnitude. The substrate specificity pattern indicated two principal transport systems for cysteine: one corresponding to the high-Km system and one to the low-Km system. The high-Km system was inhibited primarily by neutral amino acids with small or polar side chains (alanine, serine, threonine, and glycine), resembling the ASC system in its specificity. The low-Km system was inhibited primarily by neutral amino acids with large, nonpolar side chains (leucine, phenylalanine, and methionine) and by the leucine analogue beta-2-aminobicyclo(2,2,1)heptane-2-carboxylic acid, identifying it as the L system. The two systems also exhibited trans stimulation, but only with those amino acids that caused cis inhibition.
Hydrocortisone inhibits mucin secretion from guinea pig gallbladder
Authors: Moore J. R. , Turner B. S. , LaMont J. T.
Published: December 2017

We studied the effects of hydrocortisone, an inhibitor of phospholipase A2, on the secretion of mucin and release of prostaglandins from guinea pig gallbladder explants. We measured mucin using [3H]glucosamine as a precursor and prostaglandins by radioimmunoassay of 6-keto-prostaglandin F1 alpha. Mucin secretion and prostaglandin release were studied under basal conditions and after arachidonate stimulation. Hydrocortisone sodium succinate reversibly inhibited basal secretion of mucin by 24% at 10(-5) M (P less than 0.05 compared with control) and 34% at 10(-4) M (P less than 0.01). Hydrocortisone, 10(-4) M, also reversibly inhibited arachidonate-stimulated secretion of mucin (P less than 0.01 compared with controls incubated with arachidonate alone). Release of prostaglandin F1 alpha was significantly inhibited by hydrocortisone under basal (P less than 0.01) and arachidonate-stimulated (P less than 0.01) conditions. The inhibitory effect of hydrocortisone was mediated by inhibition of hydrolysis of arachidonate from membrane phospholipids, suggesting that exogenous arachidonate is incorporated into membrane phospholipids prior to conversion to prostaglandins.
Swallowing induces sequential activation of esophageal longitudinal smooth muscle
Authors: Sugarbaker D. J. , Rattan S. , Goyal R. K.
Published: December 2017

We examined the mechanical activity of the longitudinal and circular muscles of the esophagus at three different levels (9, 5, and 1 cm above the lower esophageal sphincter) during peristalsis induced by swallows or vagal stimulation in anesthetized opossums with miniature strain gauges applied in the axis of muscle fibers. The onset of longitudinal muscle contraction occurred in an aboral sequence with swallows but simultaneously with vagal stimulation. The speed of longitudinal muscle activation with swallows was 7.6 +/- 1.7 cm/s. Circular muscle contraction occurred in an aboral sequence with vagal stimulation and swallowing with speeds of 4.1 +/- 0.8 and 2.3 +/- 0.1 cm/s, respectively. Longitudinal muscle contracted before the circular muscle at all sites. The duration of longitudinal muscle contraction increased aborally (P less than 0.05) with swallowing or vagal stimulation. These studies show that 1) during swallowing, esophageal longitudinal and circular smooth muscle contract in a sequential fashion, 2) the longitudinal muscle sequential contraction is due to central mechanisms, whereas circular muscle sequential contraction may be due to both central and peripheral mechanisms, and 3) peripheral neuromuscular mechanisms produce regional differences in the duration of longitudinal muscle contraction.
Permeation patterns of polar nonelectrolytes across the guinea pig biliary tree
Authors: Tavoloni N.
Published: December 2017

The biliary permeation of polar nonelectrolytes was studied in anesthetized, bile duct-cannulated guinea pigs with functional cholecystectomy and nephrectomy. During spontaneous secretion, the steady-state bile-to-plasma ratio (B/P) of [14C]urea, [14C]erythritol, [14C]mannitol, [3H]sucrose, and [3H]inulin was 1.02, 0.90, 0.38, 0.12, and 0.04, respectively. Differently structured hydroxy bile acids, but not taurodehydrocholate, reversibly diminished [14C]erythritol and [14C]mannitol B/P during choleresis, and with some of them, particularly taurocholate and glycochenodeoxycholate, the biliary clearance of either solute declined below precholeretic levels. For any given hydroxy bile acid, the degree of B/P diminution was directly related to the molecular radii of these two inert carbohydrates. All bile acids failed to decrease [14C]urea, [3H]sucrose, and [3H]inulin B/P. On the contrary, most of them irreversibly increased [3H]sucrose and [3H]inulin permeability. These results suggest that in the guinea pig 1) hydroxy bile acids diminish the size or rearrange the architecture of the canalicular membrane "aqueous pores" through which [14C]erythritol and [14C]mannitol enter the canaliculus, and 2) solutes of the size of or smaller than [14C]mannitol enter bile primarily through a transcellular route, whereas [3H]sucrose, and [3H]inulin permeate mainly via a transjunctional shunt pathway. These studies indicate that [14C]erythritol and [14C]mannitol cannot be used to estimate canalicular bile flow in this species.
Effect of arterial carbon dioxide tension on amiloride-sensitive sodium absorption in the colon
Authors: Kurtin P. , Charney A. N.
Published: December 2017

To examine the nature of the electroneutral sodium chloride absorptive process affected by arterial carbon dioxide tension (PCO2), we measured the effects of amiloride on colonic sodium absorption at concentrations (0.75 mM) known to inhibit cell membrane sodium-hydrogen ion exchange. During sequential in situ perfusions of distal colon with amiloride-free and amiloride-containing solutions, water and electrolyte transport was measured in anesthetized, mechanically ventilated rats during normocapnia, respiratory alkalosis, or respiratory acidosis. During amiloride-free perfusions, alkalosis decreased and acidosis increased net water, sodium, and chloride absorption without changing the transmural potential difference. Perfusion of amiloride (0.75 mM) caused a similar fractional decrease in net sodium absorption in alkalotic (-53.3 +/- 10.2%), normocapnic (-46.3 +/- 6.5%), and acidotic rats (-57.2 +/- 5.2%). Net water (-43%) and chloride absorption also exhibited equivalent fractional reductions in the three acid-base states during amiloride perfusion, although net chloride absorption was reduced only about 20%. These results suggest that the specific colonic sodium absorptive process affected by arterial PCO2 is an amiloride-sensitive, sodium-hydrogen ion exchange process. Arterial PCO2 probably also affects a mucosal chloride-bicarbonate exchange process that results in its overall effect on electroneutral sodium chloride absorption by the distal colon.
Three-dimensional dynamic x-ray-computed tomography imaging of stomach motility
Authors: Seide K. , Ritman E. L.
Published: December 2017

The dynamic spatial reconstructor (DSR), an x-ray-computed, tomography-based imaging machine, scans a cylindrical volume up to 39 cm in transaxial diameter and 21.5 cm in axial height with scan repetition rate up to 60 per second. We applied this technique to three dogs in order to investigate the accuracy with which stomach shape, dimensions, and motility can be measured. Single peristaltic waves of one dog's stomach filled with air and two other dogs' stomachs filled with different volumes of contrast-enhanced semisolid meals (10% Gastrografin) were scanned at 2-s intervals at scan apertures between 0.011- and 1-s duration. On completion of the scan sequence, images of oblique sections perpendicular to the local long axis of the stomach fundus, corpus, and antrum were computed from the DSR scan data. Measurements of differential motion of defined points on the stomach wall surface, propagation velocities, acceleration, and amplitudes of peristalsis as well as gastric volume determinations were made. This approach overcomes problems of superposition and ambiguity inherent in projection imaging. Measurements of the volumes of ingested first meal were accurate to within 1.5% (of the actual volume of solid food introduced into the stomach) using a 0.40-s scan aperture. Wall motion could be detected with an SEE of 1.5 mm (pixel size used was 1.4 mm) using a 0.40-s scan aperture.
Two distinct adaptive responses in the synthesis of exocrine pancreatic enzymes to inverse changes in protein and carbohydrate in the diet
Authors: Schick J. , Verspohl R. , Kern H. , Scheele G.
Published: December 2017

Rates of synthesis of 16 individual pancreatic exocrine proteins; tissue concentrations of amylase, trypsinogen, and chymotrypsinogen; and morphological assessment of pancreatic acinar cells were studied in the exocrine pancreas in response to inverse changes in protein and carbohydrate in the diet, administered for 12 days. Two distinct patterns of response were observed. During adaptation to diets containing normal protein (22%) or increased levels of protein (30, 45, 64, and 82% protein) and correspondingly decreased levels of carbohydrate, amylase and the majority of protease zymogens were synthesized in direct proportion to the nutritional substrates carbohydrate and protein, respectively, in the diet. With increases in dietary protein, anticoordinate patterns of response in the synthesis of exocrine isoenzymes were observed: 0.4- to 2.0-fold increases in trypsinogen forms 1 and 2, chymotrypsinogen forms 1 and 2, proelastase 1, and procarboxypeptidases A and B; 5- to 7-fold decreases in amylase forms 1 and 2; and insignificant changes in trypsinogen 3, proelastase 2, lipase, and ribonuclease. During adaptation to diets containing normal protein (22%) or decreased levels of protein (0 or 10% protein) and correspondingly increased levels of carbohydrate, amylase and the majority of protease zymogens were synthesized in inverse proportion to nutritional substrates in the diet.(ABSTRACT TRUNCATED AT 250 WORDS)
Short-term effects of feeding raw soya flour on pancreatic cell turnover in the rat
Authors: Oates P. S. , Morgan R. G.
Published: December 2017

Pancreatic acinar cell turnover was studied after a 48-h fast and in rats fed raw soya flour (RSF) for up to 28 days. Feeding RSF for 2 days resulted in a significant increase in pancreatic weight and RNA content while protein was increased by the 4th day compared with rats fasted for 48 h. RSF also resulted in a significant increase in RNA by the 4th day and weight and protein by the 7th day compared with rats fed heated soya flour (HSF). This pancreatic hypertrophy was maintained for the rest of the study period. Two days after starting RSF, pancreatic DNA synthesis, measured bythe rate of incorporation of [3H]thymidine into pancreatic DNA, had increased sixfold compared with that in animals fedHSF but returned to control values again by the 4th day on the diet. Autoradiography showed that this increase in DNA synthesis occurred in both acinar and duct cells, with turnover in acinar cells preceding that in duct cells. A second moregradual rise in DNA synthesis was seen from the 7th to 28th day. This peak in DNA synthesis was associated with an increased total pancreatic DNA content and occurred predominately in duct cells with a smaller contribution from acinar cells. Histological studies of the pancreas during the 1st wk showed cell damage and tissue necrosis, possibly due to exposure to high levels of cholecystokinin released by RSF. The first peak in DNA synthesis may be a regenerative response to this damage. The second more delayed peak appears to be hyperplasia in response to a trophic stimulus, again possibly mediated by cholecystokinin.
Regulation of intestinal goblet cell secretion. III. Isolated intestinal epithelium
Authors: Phillips T. E. , Phillips T. H. , Neutra M. R.
Published: December 2017

Cholinergic secretagogues evoke mucus secretion from goblet cells in the crypts of small and large intestinal mucosa in vivo and in organ culture. It was not known whether this response reflected a direct action on epithelial cell receptors or an indirect effect involving intermediate neurons of the enteric nervous system. To resolve this, carbachol was applied to isolated intestinal epithelium maintained in vitro. Intact sheets of epithelium, measuring 10–200 mm2, were isolated from the ileum and colon of adult rats following short intravascular perfusion with 30 mM EDTA. The isolated epithelia lacked a basal lamina and cytoplasmic blebs formed on the basal cell surfaces, but cell ultrastructure was normal and intercellular junctions were intact. Autoradiography revealed that both goblet and columnar cells continued to incorporate [3H]glucosamine into nascent secretory macromolecules for at least 45 min after isolation. When exposed to 20 microM carbachol for 5 min, crypt goblet cells discharged their stored mucin granules by compound exocytosis, whereas goblet cells in portions of the epithelium derived from villi or mucosal surfaces were unresponsive. We conclude that cholinergic secretagogues act directly on crypt epithelial cells to elicit mucus secretion.
A23187-induced changes in colonic K and Cl transport are mediated by separate mechanisms
Authors: Smith P. L. , McCabe R. D.
Published: December 2017

Stripped rabbit colonic mucosa was studied in vitro in Ussing chambers to determine 1) effects of the divalent cation ionophore A23187 on K and Cl fluxes and electrical properties; 2) effects of the prostaglandin (PG) synthesis inhibitor indomethacin on A23187-, PGE1-, and arachidonic acid-induced changes in electrical parameters and K and Cl fluxes; and 3) changes in PGE2 release in response to A23187, arachidonic acid, indomethacin, or indomethacin and either A23187 or arachidonic acid. Results from these studies demonstrate that A23187, PGE1, and arachidonate increase net K and Cl secretion. Results with indomethacin reveal that this agent abolishes the increase in Cl secretion stimulated by A23187 or arachidonate but not by PGE1. Indomethacin also abolished net K secretion stimulated by arachidonate but not by A23187 or PGE1. These results together with the finding that A23187 like arachidonate increases PGE2 release in the absence but not the presence of indomethacin suggest that A23187-stimulated Cl secretion occurs by a PG-dependent mechanism, while A23187-induced K secretion occurs by an alternate Ca-dependent mechanism.
Kinetics of zinc absorption by luminally and vascularly perfused rat intestine
Authors: Steel L. , Cousins R. J.
Published: December 2017

Zinc absorption by intestines of rats fed either zinc-deficient or zinc-adequate diets was measured by simultaneous luminal and vascular perfusion. The rate of absorption increased steadily for the first 30-40 min of perfusion over the entire lumen zinc concentration range examined (8-234 microM). During the last 10 min of perfusion the absorption rate did not change appreciably with time (steady state), and absorption by intestines from the zinc-depleted rats showed evidence of both carrier-mediated (saturable) and nonmediated (nonsaturable) components. The former had a Km of 55 microM and a Jmax of 3.3 nmol X min-1. In contrast, the absorption rate during the last 10 min of the perfusion period was a sigmoidal function of the luminal zinc concentration with intestines from zinc-adequate rats. The cytosol 65Zn concentration increased proportionately with increased luminal 65Zn concentration but was significantly greater in intestines from zinc-depleted rats. Both high-molecular-weight species and metallothionein accounted for this increase in cytosolic 65Zn. An increase in the vascular bed zinc concentration increased the amount of zinc transferred to the mucosal cytosol but did not increase the amount transferred to the lumen. These results suggest a second mechanism of absorption may be induced during a dietary zinc depletion that is carrier mediated. Moreover, while zinc is transferred in the vascular-to-mucosal direction from the vascular supply, little actually enters the lumen.
Intestinal triglycerides are derived from both endogenous and exogenous sources
Authors: Shiau Y. F. , Popper D. A. , Reed M. , Umstetter C. , Capuzzi D. , Levine G. M.
Published: December 2017

Although studies have indicated that the small intestine is capable of utilizing endogenous substrates for triglyceride synthesis in the absence of dietary lipid, the importance of the endogenous contribution to total intestinal triglyceride production during absorption has not yet been defined. In this study we have examined the quantitative contribution of endogenous triglyceride production during different luminal lipid loads. By use of a mesenteric lymph fistula rat model with total parenteral nutritional support, mesenteric lymphatic triglyceride transport was investigated. Our results indicate that, during absorption, a substantial fraction (greater than 50%) of total triglyceride is derived from endogenous sources. Increased luminal fatty acid loads lead to an increase in both endogenous and exogenous triglyceride production. Incorporation of luminally infused oleic acid into triglyceride carried by chylomicrons is dependent on the luminal fatty acid load, while incorporation of oleic acid into very low-density lipoprotein (VLDL) triglyceride is saturable. We conclude that both chylomicron and VLDL are involved in transporting triglyceride derived from both endogenous and exogenous sources. The different patterns in the partition of endogenous and exogenous triglyceride into chylomicrons and VLDL suggest that these two lipid-carrying lipoproteins are probably packaged differently in the small intestine.
Gastric H+ and HCO3- secretion in response to sham feeding in humans
Authors: Feldman M.
Published: December 2017

Sham feeding (SF) was used to evaluate the effect of physiological vagal stimulation on gastric acid (H+) and bicarbonate (HCO3-) secretion in humans, as well as on parietal and nonparietal volume secretion. A recently validated method, derived from a two-component model of gastric secretion, was employed. SF increased both H+ secretion from parietal cells (P less than 0.001) and HCO3- secretion from nonparietal cells (P less than 0.01), although the H+ response was greater and more prolonged. Atropine significantly inhibited not only H+ secretion but also HCO3- and nonparietal volume secretion. Peak H+ secretion during SF averaged approximately 27 mmol/h, whereas peak HCO3- secretion averaged approximately 6 mmol/h. When H+ secretion was already maximally stimulated by an intravenous pentagastrin infusion, SF actually reduced gastric juice acidity and osmolality due to neutralization of H+ by HCO3- and to dilution of H+ by nonparietal secretions. These studies therefore indicate that vagal stimulation induced by SF increases both H+ and HCO3- secretion in humans and that this process is cholinergically dependent.
Ca2+ metabolism during cholinergic stimulation of acid secretion
Authors: Muallem S. , Sachs G.
Published: December 2017

Carbachol-induced changes in 45Ca fluxes and cytosolic free Ca2+ were characterized in rabbit gastric glands and isolated dog parietal cells. Cholinergic stimulation was expressed as changes in the membrane permeability of the parietal cell to Ca2+ without Ca2+ release from intracellular stores. The changes in the membrane permeability to Ca2+ were sustained as long as the cells were exposed to carbachol, independent of extracellular Ca2+, and had the properties of a passive pathway across which Ca2+ distributed according to its chemical gradient. As a consequence of the changes in membrane permeability to Ca2+, carbachol caused a sustained increase in free cytosolic Ca2+ from a resting level of 134 +/- 11 to 533 +/- 81 nM (n = 14). After carbachol stimulation, calcium ions were sequestered in mitochondrial and probably nonmitochondrial compartments. When cell stimulation was terminated by atropine or La3+, the cells restored the resting level of the intracellular Ca2+ activity ([Ca2+]in), independent of uncoupling of mitochondrial oxidation phosphorylation. Reduction in [Ca2+]in was mainly through Ca2+ efflux across the plasma membrane of the parietal cell. Manipulation of intracellular Na+ ion activity in intact cells and studies with basal-lateral membrane vesicles from gastric mucosa indicated the absence of extracellular Na+-intracellular Ca2+ exchange activity in the plasma membrane of the parietal cell. A calmodulin-regulated, ATP-dependent Ca2+ pump that could maintain active Ca2+ extrusion from parietal cells was found in the basal-lateral membrane of the parietal cells.
Sulfobromophthalein inhibition of glutathione and methylmercury secretion into bile
Authors: Ballatori N. , Clarkson T. W.
Published: December 2017

The mechanism through which sulfobromophthalein (BSP) inhibits the biliary secretion of glutathione (GSH) and methylmercury was examined in male rats anesthetized with pentobarbital sodium. The biliary secretion rates of GSH and methylmercury were measured following the bolus intravenous administration of various doses of BSP, the GSH conjugate of BSP (BSP-SG), and phenol-3,6-dibromphthalein disulfonate (DBSP, a nonmetabolizable analogue of BSP). The effects of BSP on GSH secretion were dose dependent; at a dose of 120 mumol/kg the rate of GSH secretion fell close to zero. DBSP also inhibited GSH secretion, although the inhibition was not as complete as observed after BSP administration; at a dose of 180 mumol/kg GSH secretion fell to 18% of control. BSP-SG, in contrast, had no effect on GSH secretion into bile when given at a dose of 120 mumol/kg. At doses of 240 and 360 mumol BSP-SG/kg, there were only minor changes in the rate of GSH secretion. The changes in GSH secretion induced by these dyes were accompanied by proportional changes in glutathione disulfide (GSSG) secretion into bile, so that the molar ratio of GSSG to GSH in bile remained within the range of 0.07–0.18. In all experiments the changes in methylmercury secretion were parallel to the changes in GSH secretion. The results suggest that the BSP-induced inhibition of GSH, GSSG, and methylmercury secretion into bile is due to the direct inhibition of the biliary GSH transport process.
Structure-activity relation among macrolide antibiotics in initiation of interdigestive migrating contractions in the canine gastrointestinal tract
Authors: Itoh Z. , Suzuki T. , Nakaya M. , Inoue M. , Arai H. , Wakabayashi K.
Published: December 2017

The relation between the chemical structure of commercially available macrolide antibiotics and their activity in inducing interdigestive migrating contractions (IMC) was studied in conscious dogs. It was found that the 14-membered macrolides erythromycin and oleandomycin are active in inducing IMC in the stomach in association with the endogenous release of motilin. These erythromycin- and oleandomycin-induced contractions in the stomach migrated through the small intestine in a caudad direction. Conversely, 16-membered macrolide antibiotics such as leucomycin, acetylspiramycin, and tylosin do not induce any contractions in the stomach or stimulate endogenous release of motilin. These findings suggest that the IMC-inducing activity in macrolides seems to be closely related to their chemical configuration, i.e., the structure of 14-membered macrolides with dimethylaminosugar (desosamine) bound at C-5 and neutralsugar at C-3 in glycosidic linkage in parallel is likely to be necessary for IMC-inducing activity. The mechanisms by which erythromycin and oleandomycin stimulate endogenous motilin release are not known.
Mucin depletion in the intestine of malnourished rats
Authors: Sherman P. , Forstner J. , Roomi N. , Khatri I. , Forstner G.
Published: December 2017

The effects of malnutrition on mucosal goblet cell mucin levels were studied in rats deprived of 50% of their daily intake, as judged by pair-fed, age-matched control animals, for 5 wk. Average daily weight gain was 0.7 g/day compared with 5.8 g in age-matched (AM) rats; final weight was 246 +/- 9 g compared with 406 +/- 4 g. Immunoassayable mucin, sucrase, protein, and DNA were assayed in mucosal scrapings from the proximal, middle, and distal segments of the small intestine in malnourished rats, AM rats, and a third group of low-weight, less mature (LM) rats. Total protein, total DNA, and protein-to-DNA ratios in malnourished rats were unchanged compared with AM control rats and often higher than levels in LM control rats. In malnourished animals, mucin concentration per milligram protein was significantly decreased below AM control animals in the upper two segments and below LM control animals in all segments. Mucin concentration per milligram DNA was significantly lower in malnourished rats than in all segments of both control groups. In contrast, sucrase activity per milligram protein or DNA was either unchanged or increased in the malnourished rats, indicating that the reduction in mucin concentration was selective and did not reflect all surface glycoproteins. Isolated mucins from malnourished and AM control rats were chemically similar, and the affinity and number of antigenic determinants were the same. Malnutrition therefore leads to an absolute decrease in intestinal mucin rather than reduced molecular antigenicity. Impaired capacity to maintain mucosal mucin content may be a factor in reducing intestinal resistance to enteric infection in malnutrition.
Hepatic uptake and disposition of human polymeric IgA1 in perfused rat liver: evidence for incomplete biliary excretion and intrahepatic degradation
Authors: Finck M. H. , Reichen J. , Vierling J. M. , Kloppel T. M. , Brown W. R.
Published: December 2017

The hepatic uptake of polymeric immunoglobulin A (IgA) is mediated by secretory component; the resulting secretory IgA is excreted intact into bile. To define the hepatic metabolism of polymeric IgA, we quantitated the uptake and transport of human polymeric IgA1 after a single pass through the perfused rat liver. Uptake of polymeric IgA1 was compared with that of asialoorosomucoid, a glycoprotein whose uptake is mediated by the asialoglycoprotein receptor. Single-pass hepatic uptake of 125I-polymeric IgA1 and of 125I-asialoorosomucoid averaged 18.0 +/- 3.1% (SE) and 71.8 +/- 2.8%, respectively. The uptake of 125I-polymeric IgA1 was inhibited by excess unlabeled polymeric IgA1 but not by asialoorosomucoid. Only 13.0 +/- 1.6% of the 125I-polymeric IgA1 extracted by the liver was excreted into bile, whereas three-fourths was released into the hepatic venous effluent in degraded form. Thus, both the uptake and biliary excretion of polymeric IgA1 by the rat liver are inefficient processes. Polymeric IgA1 follows two distinct pathways after uptake by the liver: a small proportion is excreted intact into bile, while the majority is degraded and released back into the circulation.
Role of calcium in cholecystokinin-stimulated phosphoinositide breakdown in exocrine pancreas
Authors: Pandol S. J. , Thomas M. W. , Schoeffield M. S. , Sachs G. , Muallem S.
Published: December 2017

In dispersed acini from guinea pig pancreas cholecystokinin octapeptide (CCK-OP) stimulated breakdown of the phosphoinositides phosphatidylinositol (PI) and its phosphorylated derivative, phosphatidylinositol 4,5-bisphosphate (PI-P2), as measured by a decrease in the mass of PI and decreases in the content of [3H]PI and [32P]PI-P2 in acini prelabeled with myo-[2-3H]inositol or H3(32)PO4. The breakdown occurred in the absence of extracellular Ca2+ and when the CCK-OP-induced rise in free intracellular Ca2+ ([Ca2+]i) was ablated by loading the acini with the Ca2+-selective indicator and chelator quin-2 in the absence of extracellular Ca2+. In contrast to CCK-OP, the calcium ionophore A23187 caused breakdown of PI and PI-P2 in the presence but not in the absence of extracellular Ca2+, although like CCK-OP A23187 stimulated 45Ca outflux, a measure of cellular Ca2+ mobilization, and amylase release during the first 5-10 min of incubation independent of extracellular Ca2+. In the absence of extracellular Ca2+ A23187 did not inhibit the ability of CCK-OP to cause PI breakdown. These results indicate that CCK-OP stimulates breakdown of PI and PI-P2 and that this breakdown is independent of extracellular Ca2+, mobilization of intracellular Ca2+, and the CCK-OP-induced rise in [Ca2+]i. These findings suggest that one of the initial events resulting from CCK-OP interaction with its receptor is phosphoinositide breakdown.
Acid formation by permeable gastric glands: enhancement by prestimulation
Authors: Hersey S. J. , Steiner L.
Published: December 2017

Digitonin was used to render isolated gastric glands permeable. This procedure was found to release cellular lactic dehydrogenase without disrupting the parietal cell's ability to generate proton gradients. Optimal conditions for permeabilizing the glands were found to depend on the ratio of digitonin to gland concentration. Stimulation of the glands with histamine, forskolin, or 8-bromo-cAMP prior to digitonin treatment resulted in a marked enhancement of the subsequent ATP-dependent acid formation. This enhancement was not found with the cholinergic agonist carbachol. These results indicate that preservation of the active secreting state does not require the continued presence of soluble factors. Characterization of the ATP-dependent acid formation in prestimulated permeable glands showed a dependence on exogenous substrate and inhibition by the mitochondrial inhibitors oligomycin and atractyloside. Moreover, it was found that ADP could replace ATP in promoting acid formation. These results are interpreted to show that mitochondrial oxidative phosphorylation can serve as an in situ ATP-recycling system to provide a local supply of ATP for proton transport. The overall study demonstrates that the digitonin-permeabilized gastric gland preparation is a valuable model system for studying mechanisms of gastric proton transport.
Gastric vasoconstrictor actions of leukotriene C4, PGF2 alpha, and thromboxane mimetic U-46619 on rat submucosal microcirculation in vivo
Authors: Whittle B. J. , Oren-Wolman N. , Guth P. H.
Published: December 2017

The gastric vasoconstrictor actions of the arachidonate lipoxygenase products leukotrienes B4, C4, and D4 and the prostanoids prostaglandin F2 alpha (PGF2 alpha) and the endoperoxide analogue U-46619 have been investigated in vivo in the submucosal microcirculation of the anesthetized rat using direct microscopy. Topical application of PGF2 alpha (1-100 microM) to the exposed submucosa reduced vessel diameter of the venules, with peak vasoconstriction occurring within 1 min and remaining during the 3-min period of administration. Constriction of the arterioles by PGF2 alpha was less pronounced. U-46619 (1-1,000 nM), a thromboxane mimetic, induced vasoconstriction in both arterioles and venules, reaching plateau responses within 1.5-2.0 min of application. Leukotriene C4 (25-400 nM) induced vasoconstriction in the venules, which was more pronounced than in the arterioles, reaching peak responses within 1-1.5 min, which were unaffected by indomethacin administration. No significant vasoactive action with leukotrienes B4 or D4 in the submucosal microcirculation could be detected. With both leukotriene C4 and U-46619 intense focal vasoconstriction in the venules was observed, leading to sluggish blood flow or stasis within the vessel. In contrast, norepinephrine had no significant action on submucosal venules at concentrations that substantially reduced arteriolar vessel diameter. Such potent vasoconstrictor actions of leukotriene C4 and U-46619 in the gastric submucosa identify this leukotriene and thromboxane A2 as potential endogenous proulcerogenic agents and suggest that these arachidonate products could play a role in microcirculatory events accompanying gastric damage.
Gastric mucosal barrier: hydrophobicity of stretched stomach lining
Authors: Hills B. A. , Lichtenberger L. M.
Published: December 2017

Surface hydrophobicity of the luminal lining of the canine stomach has been studied as a very convenient means of following the adsorbed monolayer of surfactant believed to provide the gastric mucosal barrier. Hydrophobicity has been measured as the contact angle (theta) produced when a drop of saline is placed upon the surface. theta was found to decrease from 82 to 62 degrees upon 50% linear extension of samples of oxyntic mucosa from 10 dogs. When the phospholipid believed to cause the hydrophobicity was absorbed to glass slides, the contact angle was found to decrease with lower surface concentration. Thinning or "crazing" of the absorbed surfactant monolayer imparting the very hydrophobic nature of the luminal lining is discussed as a possible reason why ulcers tend to form at the crests of the folds, i.e., at points where the surface has been stretched and the monolayer disrupted.
Saturable and nonsaturable copper and calcium transport in mouse duodenum
Authors: Bronner F. , Yost J. H.
Published: December 2017

Duodenal copper and calcium absorption was evaluated in 30-day-old normal male Swiss mice by an in situ loop procedure. For both ions, the 90-min absorption values yielded a curve that was resolvable into a hyperbolic (saturable) and a linear (nonsaturable) function. The two ions differed, however, in total absorption and the relative importance of the two functions. For copper, the maximum saturable component of transepithelial movement (Jmax) was 127 +/- 2.4 (SE) pmol in 90 min, the apparent half-saturation constant of the saturable process (Kt) was 4.3 +/- 0.7 microM, and the slope of the nonsaturable function was 0.011 +/- 0.006. Thus, when luminal copper equaled plasma copper (approximately equal to 15 microM), only 8% was absorbed, nearly all of which was by the saturable component. For calcium, on the other hand, Jmax was 4.8 +/- 0.1 mumol, the Kt was 27 +/- 2 mM, and the slope was 0.10 +/- 0.01. At luminal calcium concentrations equal to the inorganic plasma calcium (1 mM), calcium absorption was 75%, but only 80% of that was moved by the saturable process. The findings suggest the existence of separate transport mechanisms for copper and calcium.
Coupled Na+-H+ exchange in isolated acinar cells from rat exocrine pancreas
Authors: Hellmessen W. , Christian A. L. , Fasold H. , Schulz I.
Published: December 2017

Isolated acinar cells from the rat exocrine pancreas were loaded with 6-carboxyfluorescein diacetate (CFDA), and the intracellular pH (pHi) was estimated from the pH-dependent fluorescence intensity of trapped 6-carboxyfluorescein liberated from CFDA by intracellular esterases. The intracellular fluorescence intensity was calibrated by equilibrating the internal and external pH with nigericin in K+ buffers. In the absence of Na+ (130 mmol/l K+) a pHi of 6.86 +/- 0.04 was found; in its presence (130 mmol/l Na+) a pHi of 7.17. Acute addition of Na+ increased intracellular pH with increasing Na+ concentrations, reaching a maximum at 150 mmol/l with an apparent Km of approximately 40 mmol/l. Of the different cations tested on pHi, such as Li+, K+, Rb+, and Cs+, only Li+ showed an effect on pHi similar to that of Na+. Amiloride dose dependently inhibited both Na+- and Li+-induced alkalinization (apparent Km approximately 10(-5) mol/l). In the presence of ouabain pHi was decreased by 0.2 pH units. Intracellular acidification induced by permeable buffers such as acetic acid-acetate or CO2-HCO3- was dissipated more rapidly in the presence of Na+ compared with K+ or with Na+ and amiloride in the medium. In Li+-preincubated cells intracellular acidification was higher in the absence of Li+ in the extracellular medium than in its presence. This Li+ gradient-induced acidification was dependent on the extracellular pH, was highest at an extracellular pH of 7.05, and decreased with increasing pH to 7.5. The results allow the conclusion that a coupled Na+-H+ exchange is present in pancreatic acinar cells and that the intracellular pH rather than the extracellular Na+ concentration regulates this transport mechanism.
Nonprotein sulfhydryl compounds in canine gastric mucosa: effects of PGE2 and ethanol
Authors: Miller T. A. , Li D. , Kuo Y. J. , Schmidt K. L. , Shanbour L. L.
Published: December 2017

By use of an in vivo canine chambered stomach preparation in which the gastric mucosa was partitioned into two equal halves, the effect of topical 16,16-dimethyl PGE2 (DMPGE2) (1 microgram/ml of perfusate) and 8% and 40% ethanol on tissue levels of nonprotein sulfhydryl compounds was assessed. Both DMPGE2 and 8% ethanol significantly increased (P less than 0.005) mucosal levels of nonprotein sulfhydryls when compared with corresponding mucosa bathed with saline alone. In contrast, mucosa bathed with 40% ethanol showed significantly decreased levels. If mucosa was bathed with DMPGE2 or 8% ethanol prior to exposing the stomach to 40% ethanol, this depletion in sulfhydryl compounds was not observed. Since other experimental observations have shown that exogenously administered prostaglandins and mild irritants (such as low-dose alcohol) can prevent gastric mucosal damage by necrotizing agents (such as high-dose alcohol), our findings are consistent with the hypothesis that nonprotein sulfhydryls may play a role in mediating gastric mucosal protection.
Role of lymph flow in intestinal chylomicron transport
Authors: Tso P. , Pitts V. , Granger D. N.
Published: December 2017

In this study we investigated the influence of lymph flow on chylomicron transport. We examined the effects of varying the hydration of the interstitial matrix on chylomicron appearance time and on lymphatic lipid transport rate when a lipid test meal containing oleic acid and 1-monoolein was infused intraduodenally at a constant rate. The three groups of rats tested were control rats (normal interstitial hydration), rats receiving intravenous saline infusion (expanded interstitial matrix), and rats with an attenuated water absorption rate (dehydrated interstitial matrix). This study shows that lymph flow has a profound effect on intestinal chylomicron transport. As lymph flow increased, the chylomicron appearance time (time between the placement of radioactive fatty acid into the intestinal lumen to the appearance of radioactive lipid in the central lacteal) was reduced. When lymph flow exceeded 40 microliter/min, the chylomicron appearance time reached a minimum value of 13.6 min. This minimum chylomicron appearance time probably represents the time required for assembly of absorbed lipid, formation of chylomicrons, and their subsequent discharge into the lymphatics. The chylomicron appearance time lengthened as lymph flow fell. The results of this study underscore the necessity of using steady-state lymphatic lipid output data to assess factors affecting the cellular packaging and release of chylomicrons in the small intestine.
Characterization of segmental collateral blood flow in the small intestine
Authors: Bulkley G. B. , Womack W. A. , Downey J. M. , Kvietys P. R. , Granger D. N.
Published: December 2017

Collateral blood flow and the pressures and resistances determining that flow were measured between two adjacent segments of canine jejunum following acute occlusion of the arterial branch perfusing one of the segments (the “recipient” segment). Collateral flow was approximately 55% of control flow in the recipient segment. This flow was provided by an equal increment in arterial flow to the nonischemic (“donor”) segment, such that pressures, resistances, and flows in the donor segment were not affected. Virtually all of the total collateral flow was derived from precapillary channels and was therefore available to the capillary bed of the recipient segment. Collateral flow was adequate to maintain the recipient segment in a nonischemic state, as indicated by the absence of a reactive hyperemia following release of the arterial occlusion. Selective occlusions of intramural or extramural collateral channels indicate that about two-thirds of the total collateral flow is derived from the extramural (marginal) vessels, while the remainder is supplied by intramural collaterals. For the most part collateral flow between adjacent segments is determined simply by the pressure gradient between connecting collateral channels.
Evidence for protein kinase C as a regulator of intestinal electrolyte transport
Authors: Fondacaro J. D. , Henderson L. S.
Published: December 2017

We examined the possibility that the Ca2+-and phospholipid-dependent protein kinase, protein kinase C, may regulate intestinal electrolyte transport. By use of two active phorbol esters, known activators of protein kinase C, we studied the secretory response in rat small intestine. In the in vivo enteropooling assay, 4 beta-phorbol 12-myristate 13-acetate given by gavage produced intestinal fluid secretion and accumulation comparable with that of known secretagogues. The response was dose dependent and only partially blunted at higher doses by atropine. Known inactive phorbol esters failed to elicit a secretory response. In Ussing chamber preparations, 4 beta-phorbol 12,13-dibutyrate applied on the serosal side produced a dose-dependent increase in short-circuit current (Isc). This response was totally dependent on the presence of Cl ion, and as seen in vivo atropine only partially attenuated the Isc response to high concentrations of phorbol ester. Only a minimal increase in Isc was observed when the ester was applied to the mucosal side. Protein kinase C was found to phosphorylate the microvillus membrane of the enterocyte, and the phosphorylation was stimulated by phorbol ester in a concentration-dependent manner. Two membrane proteins of Mr 51,000 and 46,000 were the primary substrates of the enzyme. These studies demonstrate that phorbol esters, specific activators of protein kinase C, elicit the secretory response in rat small intestine both in vivo and in vitro and that this response is mediated by an increase in Cl ion secretion. Furthermore, protein kinase C-mediated phosphorylation of specific microvillus membrane proteins suggests that protein kinase C may modify the functional state of the microvillus membrane of the enterocyte.
Microcirculation in periportal and pericentral regions of lobule in perfused rat liver
Authors: Conway J. G. , Popp J. A. , Thurman R. G.
Published: December 2017

A noninvasive method was developed to quantitate the vascular space and the fraction of fluid entering the liver via the hepatic artery or portal vein in periportal and pericentral regions of the lobule. Fluorescence of fluorescein-dextran measured with a light guide placed on the surface of livers perfused via the portal vein in situ correlated closely with liver vascular space (r = 0.85). Thus, fluorescein-dextran fluorescence can be used to measure vascular space. Livers were then perfused simultaneously via the hepatic artery and portal vein at flow rates of 8 and 24 ml/min, respectively. Fluorescein-dextran (12 microM) was infused via the hepatic artery and portal vein separately or simultaneously. The sum of fluorescence increases due to fluorescein-dextran infused via the artery and vein equaled the increases due to simultaneous infusion via the artery and vein. From these measurements, the fraction of fluid that entered the vascular space via the artery or the portal vein was calculated. Vascular space was similar in hilar and tip areas of the left lateral lobe; however, threefold more fluid entered the liver via the hepatic artery in hilar regions than in tip areas. Micro-light guides were placed on periportal and pericentral areas of the liver lobule to monitor fluorescein-dextran fluorescence. Fluorescence changes indicated that the vascular space was about twice as large in pericentral as in periportal areas, whereas the fraction of fluid that entered the liver via the hepatic artery was similar in both regions. In addition, morphometric analysis of sections of liver indicated that the vascular space was 60% greater in pericentral than periportal regions.(ABSTRACT TRUNCATED AT 250 WORDS)