bluuebunny/crossref_metadata_2025 huggingface dataset:
Ethanol stimulates leucine uptake by rat fetal hepatocytes via trans-stimulation
Authors: Henderson G. I. , Frosto T. A. , Heitman D. W. , Schenker S.
Published: December 2017

Prior studies showed that exposure of cultured rat fetal hepatocytes to ethanol increased sodium-independent transport of alpha-amino-isobutyric acid and cycloleucine. Using leucine (Leu) as a probe, we now show that this is a reflection of trans-stimulation of system L inward flux. Transport of Leu was entirely sodium independent and beta-2-aminobicyclo(2,2,1)-heptane-2-carboxylic acid inhibitable. Uptake kinetics indicated two components, likely systems L1 and L2 reported for the adult hepatocyte. The low-affinity Km was in the 0.5 mM range, whereas the high-affinity Km was 2% of that value. Under optimal growth conditions, approximately 65% of the Leu was transported by the latter system. Strong bidirectional exchange was shown with Leu loading, stimulating initial Leu uptake by 66%. Externally directed transport was enhanced 2.9 times against 5 x 10(-3) M Leu vs. no external Leu. A 24-h exposure to ethanol (2 mg/ml) increased Leu uptake by up to 100%, an effect that could be mimicked by arrested cell replication. Both enhanced rates could be reversed by amino acid depletion, reflecting intracellular amino accrual that induced trans-stimulation of Leu uptake. Enhanced uptake was also reproduced in replicating cells by loading with increasing concentrations of Leu.
Omeprazole and cimetidine versus pentagastrin in canine ex vivo gastric chamber
Authors: Larsen K. R. , Ives M. M. , Jensen N. F. , Carlsson E. , Larsson H.
Published: December 2017

The effects of acid inhibitory doses of omeprazole were compared with equieffective doses of cimetidine in the canine ex vivo stomach model (n = 30). Systemic blood pressure, temperature, stomach fluid and ion fluxes, potential difference, blood flow rates, and arterial and venous blood gases were monitored during each of nine 30-min periods. Two resting periods preceded seven periods of pentagastrin stimulation. During the last four of these, the drug effect was recorded (cimetidine 1.2 or 4.8 mumol.kg-1.h-1; omeprazole 0.3, 0.6, or 1.2 mumol/kg). Omeprazole (1.2 mumol/kg) produced 100% inhibition of stimulated acid efflux, no significant decrease in total gastric blood flow (venous outflow), 90% return of potential difference (PD) toward resting values, and a 55% reduction in stimulated oxygen consumption. Omeprazole also showed a dose-dependent K+ efflux at the two lower doses. Cimetidine (4.8 mumol.kg-1.h-1) given during pentagastrin stimulation showed a 70% decrease in total gastric blood flow, a 40% return of PD toward resting, and a 77% reduction in stimulated oxygen consumption. Neither drug showed significant changes in mucosal blood flow from resting values, thus supporting the principle that changes in gastric acid secretion and changes in blood flow are not necessarily correlated.
Capsaicin-sensitive nerves are involved in bile-oleate-induced intestinal hyperemia
Authors: Rozsa Z. , Jacobson E. D.
Published: December 2017

The purpose of the present study is to assess the role of capsaicin-sensitive afferent nerves of the gut in bile-oleate-induced intestinal hyperemia. In anesthetized rats, intestinal blood flow (BF) was determined with a pulsed Doppler flowmeter. Systemic arterial blood pressure and heart rate were also measured. Test solutions containing either 40 or 80 mM oleic acid, combined with 10% natural bile, were introduced into the jejunum and produced abrupt increases in BF (64 +/- 12 and 118 +/- 14% of control, respectively). The vasodilator response was abolished by pretreatment with systemic capsaicin in neonatal life and by topical application of either capsaicin or lidocaine to the mucosa in adult animals. The response was inhibited 69 +/- 6% by an antiserum to vasoactive intestinal peptide. We found no significant inhibition of the vasodilator response by pretreating animals with antisera to cholecystokinin octapeptide or substance P, nor with hexamethonium, atropine, or reserpine. It appears that bile-oleate-induced intestinal vasodilation involves primary afferent nerve fibers of gut that release vasoactive intestinal peptide.
Determinants of glutathione efflux and biliary GSH/GSSG ratio in perfused rat liver
Authors: Ballatori N. , Truong A. T. , Ma A. K. , Boyer J. L.
Published: December 2017

Utilizing the isolated perfused rat liver, we examined several factors influencing efflux of glutathione [reduced glutathione (GSH) and glutathione disulfide (GSSG)] into perfusate and bile, including the effects of perfusate composition, oxygen delivery to the liver, and acivicin (AT-125), an inhibitor of gamma-glutamyl transferase activity. When livers were perfused with a recirculating Krebs-Ringer bicarbonate buffer only 7-26% of released glutathione was excreted into bile, mainly in its oxidized form (71-90% as GSSG). In contrast, when 20% bovine red blood cells or 20% fluorocarbon emulsion were utilized as perfusates, biliary glutathione accounted for a larger fraction of total hepatic efflux (16-41%), and only 39-65% was excreted as GSSG. To determine whether O2 delivery to the liver could explain some of these differences, biliary and sinusoidal efflux of glutathione were measured as O2 delivery was varied by 1) increasing the perfusion flow rate, 2) altering the concentration of fluorocarbon emulsion (5, 10, and 20%), and 3) changing the PO2 (95% O2-5% CO2 vs. 50% O2-5% CO2-45% N2). Under all experimental conditions, an increase in O2 delivery was accompanied by an increase in bile flow and in the concentration and rate of glutathione efflux into bile but no significant change in sinusoidal efflux of glutathione. Hepatic tissue GSH and GSSG levels were not affected by the various treatments. When gamma-glutamyl transferase activity was inhibited with AT-125, biliary glutathione increased to levels of approximately 50% of total hepatic efflux in fluorocarbon-perfused livers, and only 24-29% of the glutathione was excreted as GSSG.(ABSTRACT TRUNCATED AT 250 WORDS)
Brush-border inositol transport by intestines of carnivorous and herbivorous teleosts
Authors: Vilella S. , Reshkin S. J. , Storelli C. , Ahearn G. A.
Published: December 2017

Transport characteristics of myoinositol by isolated brush-border membrane vesicles of two fish, the herbivorous tilapia (Oreochromis mossambicus) and the carnivorous eel (Anguilla anguilla), were measured. [3H]myoinositol uptake by vesicles of both fish was stimulated by a transmembrane Na gradient, was electrogenic, and was inhibited by phloridzin. Kinetic analysis of myoinositol influx disclosed species differences (tilapia, K = 0.15 mM, Jmax = 0.2 nmol.mg protein-1.min-1; eel, K = 2.6 mM, Jmax = 0.8 nmol.mg protein-1.min-1). D-glucose inhibition of myoinositol influx was shown to be noncompetitive. Additional inhibition studies with a range of sugars demonstrated that aldohexoses in the C-1 chair conformation were preferred substrates. Myoinositol had no effect on D-glucose transport. Preloading vesicles with myoinositol transstimulated [3H]myoinositol uptake, while the use of internal D-glucose was without effect. These results suggest that the intestinal brush border may have a pathway for myoinositol transport entirely separate from that for D-glucose but inhibited by D-glucose via binding to a regulator site on the myoinositol transporter. Markedly dissimilar influx kinetic constants suggest possible differences in myoinositol needs by carnivorous and herbivorous fish.
Changes in hepatic blood volume on galactose and indocyanine green uptake by cat liver
Authors: Greenway C. V. , Innes I. R. , Pushka K. L. , Scott G. D. , Sitar D. S.
Published: December 2017

The liver has important functions as a blood volume reserve and in uptake and metabolism of many substrates. This study examines whether changes in hepatic blood volume modify the uptakes of model substrates galactose and indocyanine green (ICG) in cats anesthetized with pentobarbital sodium. A hepatic venous long-circuit technique with an extracorporeal reservoir was used to control hepatic flow and venous pressure and to allow repeated sampling of arterial, portal, and hepatic venous blood without depletion of the cat's blood volume. Hepatic blood volume was measured by plethysmography. Galactose and ICG were infused intravenously at constant rates for 200 min in each of three series of experiments. The first series were time controls. In the second series, hepatic blood volume was increased by raising hepatic venous pressure. In the third series hepatic blood volume was decreased by hepatic nerve stimulation and infusions of norepinephrine and angiotensin. Hepatic congestion resulted in small increases in blood galactose levels, suggesting mild impairment of hepatic galactose metabolism. Decreases in liver blood volume did not modify hepatic galactose metabolism. Increases in hepatic blood volume facilitated while decreases inhibited ICG uptake, but the effects were small. Sinusoidal velocity and transit time have minor effects on uptake even for protein-bound substrates. In summary, large changes in hepatic blood volume had minor effects on galactose and ICG blood concentrations, suggesting that the metabolic functions of the liver are essentially independent of the blood reservoir function.
Effects of cations and pH on apical membrane potential of in vitro Necturus antrum
Authors: Rutten M. J. , Delcore R. , Soybel D. I. , Moore C. D. , Cheung L. Y.
Published: December 2017

The surface epithelial cells of the gastric mucosa transport Na+ from lumen to serosa. The first step in this process is the entry of Na+ through an amiloride-sensitive Na+ channel at the apical membrane. The exact function(s) of this Na+ transport are unknown, but it has been suggested that it might help the stomach to withstand an acid load. The present study was undertaken to examine the effects of low luminal pH and the alkali cations Li+, K+, Rb+, and Cs+ on the amiloride-sensitive Na+ permeability of the apical membrane of Necturus antral cells by measuring the changes in apical membrane voltage (Vmc) using conventional microelectrode techniques. Isosmolar replacement of luminal NaCl (pH 7.25) with LiCl caused a depolarization of the Vmc, a decrease in transepithelial resistance (Rt), and an increase in the transepithelial potential (Vmc), whereas replacement with KCl, RbCl, or CsCl caused a hyperpolarization of the Vmc, an increase in Rt, and a decrease in the Vmc. Luminal acidification from pH 7.25 to pH 3.00 caused very similar changes with all the cation solutions tested, hyperpolarizing the Vmc, increasing Rt, and reducing the Vmc to near 0 mV. Acidification of the luminal NaCl solution from pH 7.25 to pH 2.00 caused a progressive hyperpolarization of the Vmc similar to the effects seen with luminal amiloride (10(-4) M) in pH 7.25 NaCl solutions or luminal Na+-free (N-methyl-D-glucamine) Ringer at pH 7.25. These results demonstrate that 1) of the cations tested only Li+ can substitute for Na+ in maintaining the Vmc, and 2) external H ions (low luminal pH) block cation permeability of the apical membrane.
EGF content in the gastrointestinal tract of rats: effect of age and fasting/feeding
Authors: Schaudies R. P. , Grimes J. , Davis D. , Rao R. K. , Koldovsky O.
Published: December 2017

Immunoreactive rat epidermal growth factor (EGF) was measured in the pancreas and in the mucosa and lumen of the stomach, duodenum, jejunum, midjejunum, ileum, and colon of fed or fasted 5- and 12-day-old suckling, and 3- to 4-month-old adult male rats using a homologous radioimmunoassay. The EGF levels in the pancreas in sucklings were lower than in adults and were unaffected by fasting. Both gastrointestinal mucosal and luminal EGF levels were higher in suckling rats than in adults. Fasting caused a significant decrease in gastrointestinal levels of EGF in the suckling rats but resulted in minimal changes in the adults. Our results show that the content of EGF in gastrointestinal tract is dependent on both age and dietary status. Together with the fact that milk contains a large amount of EGF (O. Koldovsky and W. Thornburg, J. Pediatr. Gastro. Nutr. 6: 172-196, 1987) and that labeled EGF is absorbed to a considerable extent by the gastrointestinal tract of suckling rats (P.A. Gonella et al., J. Clin. Invest. 80: 22-32, 1987: W. Thornburg et al., Am. J. Physiol. 246: G80-G85, 1984), our present study implicates milk as an important source of EGF in the suckling period.
Putrescine uptake and release by colon cancer cells
Authors: McCormack S. A. , Johnson L. R.
Published: December 2017

We have investigated the uptake and release of [3H]putrescine by a human colon adenocarcinoma cell line (LoVo) maintained on filter inserts. This culture system permits the cells to develop morphological polarity and provides separate access to the basolateral and apical surfaces of the cells. [3H]putrescine was taken up more readily by the basolateral than by the apical side of the cells. [3H]putrescine uptake could be stimulated greater than 300 times by either 10 mM asparagine or 10% fetal bovine serum. [3H]putrescine was accumulated to a concentration gradient of approximately 300-fold; uptake could be inhibited 50% by 7.5 microM unlabeled putrescine and was not dependent on Na+. The release of [3H]putrescine into the apical medium was inhibited by asparagine or fetal bovine serum. Usually, less than one-thousandth of the [3H]putrescine taken up into the cells was released into the apical medium. Release of [3H]putrescine did not correspond to the accumulation of [14C]-inulin in the apical medium. For these reasons we concluded that putrescine release was not simply passive leakage but was responsive to intracellular demand. The [3H]putrescine taken up by the cells as well as that released into the apical medium was greater than 90% unmetabolized at 4h.
Rapid regulation of D-glucose transport in basolateral membrane of rat jejunum
Authors: Cheeseman C. I. , Maenz D. D.
Published: December 2017

D-Glucose transport and D-glucose inhibitable [3H]cytochalasin B binding to jejunal basolateral membrane vesicles were measured to investigate the possible association between changes in transport activity seen in hyperglycemia and density of transporter sites. Comparison was made between hyperglycemic animals, noninfused rats, and a group infused with sorbitol. Vascular infusion of D-glucose produced a rapid increase in D-glucose transport followed by a delayed and smaller increase in [3H]cytochalasin B binding. The Vmax for glucose uptake was increased after only 30 min of glucose infusion and continued to rise up to 6 h. Comparison with noninfused and sorbitol-infused controls showed that 2 h of glucose infusion produced a 3.5-fold increase in the Vmax for D-glucose uptake while D-glucose-inhibitable binding of [3H]cytochalasin B was unaffected. Six hours of hyperglycemia resulted in the further stimulation of glucose transport (4.1-fold) and a significant 1.8-fold increase in cytochalasin B binding over that for noninfused animals. Vesicles prepared from animals 4 h after an in vivo injection of cycloheximide showed an 80% reduction in glucose transport with no significant change in the cytochalasin B binding density. These results suggest that D-glucose transport in the basolateral membrane is regulated by a combination of a modulation of carriers already in the membrane and subsequent changes in carrier site density.
Insulin modulates rat intestinal glucose transport: effect of hypoinsulinemia and hyperinsulinemia
Authors: Westergaard H.
Published: December 2017

The current studies were designed to evaluate the role of plasma insulin and glucose as regulators of intestinal glucose transport in vivo. Initially, rats received either intravenous glucose infusion or intraperitoneal streptozotocin to induce sustained hyperglycemic hyperinsulinemia or hyperglycemic hypoinsulinemia. Net jejunal uptake rates of glucose were measured in vivo at several perfusate concentrations, and the kinetic constants, corrected for diffusion barrier resistance, were derived. Maximal velocity (Jmax) was increased 1.8-fold by hyperglycemic hyperinsulinemia and 2.6-fold by hyperglycemic hypoinsulinemia compared with controls, whereas Km and passive permeability of glucose were unchanged. The rate of L-proline uptake at saturation conditions was not increased by these experimental interventions. The corrected kinetic constants for jejunal glucose transport in streptozotocin diabetic rats kept normoglycemic and normoinsulinemic with insulin were similar to controls. Finally, induction of normoglycemic hyperinsulinemia by intravenous glucose-insulin infusion increased Jmax 1.8-fold, similar to hyperglycemic hyperinsulinemia, but induction of hyperglycemic normoinsulinemia by intravenous glucose-somatostatin infusion did not change Jmax. In conclusion, changes in plasma insulin but not glucose concentration cause a specific and reversible increase in Jmax of intestinal glucose transport. Hypoinsulinemia is a more potent signal than hyperinsulinemia. The membrane level, microvillus or basolateral, at which insulin induces an increased number of glucose transporters in intestinal epithelial cells remains to be defined.
Plasma secretin, CCK, and pancreatic secretion in response to dietary fat in the rat
Authors: Green G. M. , Taguchi S. , Friestman J. , Chey W. Y. , Liddle R. A.
Published: December 2017

The role of fat in regulation of pancreatic secretion was studied in conscious rats by measuring pancreatic secretion and plasma cholecystokinin (CCK) and secretin responses to intraluminal infusion of fat, protein, or trypsin inhibitor via the duodenum. In rats with pancreatic juice continuously returned to the intestine, intraduodenal infusion of 20% emulsified fat (Liposyn), 10% casein, and 0.4% ovomucoid trypsin inhibitor (OMTI) stimulated equivalent increases of approximately threefold in pancreatic protein output. Proglumide reduced fat-stimulated pancreatic protein secretion by greater than 90% but did not inhibit the response to OMTI. Fat significantly increased plasma CCK from basal levels of 0.5 pM to 2-3 pM, but it was a weaker stimulant of CCK secretion than casein (peak CCK levels greater than 10 pM) or OMTI (peak CCK levels 5-6 pM). Fat significantly stimulated secretin release (21.7 pM) compared with casein (6.8 pM), OMTI (4.4 pM), and NaCl (3.5 pM). The inhibition of fat-stimulated pancreatic secretion by proglumide indicates that the small amounts of CCK released by fat are necessary for a normal pancreatic response, suggesting that this response may be the result of potentiation between secretin and small amounts of CCK.
Characterization of an 80-kDa phosphoprotein involved in parietal cell stimulation
Authors: Urushidani T. , Hanzel D. K. , Forte J. G.
Published: December 2017

When isolated rabbit gastric glands were stimulated with histamine plus isobutylmethylxanthine, a redistribution of H+-K+-ATPase, from microsomes to a low-speed pellet, occurred in association with the phosphorylation of an 80-kDa protein (80K) in the apical membrane-rich fraction purified from the low-speed pellet. Histamine alone or dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP), but not carbachol, also stimulated both the redistribution of H+-K+-ATPase and phosphorylation of 80K. Under stimulated conditions, 80K copurified in the apical membrane fraction along with H+-K+-ATPase and actin; whereas purified microsomes from resting stomach were highly enriched in H+-K+-ATPase but contained neither 80K nor actin. Treatment of the apical membranes with detergents, salts, sonication, and so on, led us to conclude that 80K is a membrane protein, unlike actin; however, the mode of association of 80K with membrane differed from H+-K+-ATPase, an integral membrane protein. Isoelectric focusing and peptide mapping revealed that 80K consists of six isomers of slightly differing pI, with 32P occurring only in the three most acidic isomers and exclusively on serine residues. Moreover, stimulation elicited a shift in the amount of 80K isomers, from basic to acidic, as well as phosphorylation. We conclude that 80K is an apical membrane protein in the parietal cell and an important substrate for cAMP-dependent, but not calcium-dependent, pathway of acid secretion.
Ouabain-sensitive H+-K+ exchange mechanism in the apical membrane of guinea pig colon
Authors: Suzuki Y. , Kaneko K.
Published: December 2017

The K+ uptake process across the apical membrane was investigated in relation to the ouabain-sensitive H+ secretion and the active transepithelial K+ absorption in guinea pig distal colon. The isolated colon was mounted between Ussing chambers or everted and fixed over a polyethylene tube (86Rb uptake measurements). The H+ secretion rate was determined from changes in pH of the weak-buffered mucosal bathing solution. K+ and Rb+ in the mucosal bathing solution powerfully stimulated H+ secretion. Cs+ also activated H+ secretion, though less than K+ or Rb+, whereas Na+, Li+, or choline scarcely did so. The increase in K+ concentration on the mucosal side reduced the degree of inhibition of H+ secretion by mucosal ouabain. 86Rb influx across the apical membrane (5.4 mM Rb+ in mucosal solution) was inhibited by approximately 90% by mucosal ouabain with the half-maximal effective dose being 3.9 +/- 1.0 X 10(-6) M; the half-maximal dose is not different from that for the inhibition of H+ secretion under similar conditions. The ouabain-sensitive component of 86Rb influx and the ouabain-sensitive H+ secretion rate were closely correlated when these rates were altered with either changes in the mucosal Rb+ concentration or addition of inhibitors such as acetazolamide, indomethacin, or 2,4-dinitrophenol. In the presence of K+ on the mucosal side, the ouabain-sensitive 86Rb influx was significantly reduced. Finally, the active transepithelial 42K absorption under short-circuit conditions was inhibited by approximately 50% with 4 X 10(-6) M and almost abolished with 10(-4) M ouabain on the mucosal side. It is concluded that the ouabain-sensitive K+ (Rb+) uptake mechanism, which is closely associated with H+ secretion, is present in the apical membrane of the colonic epithelial cells; the molecular mechanism of this uptake may be a H+-K+-ATPase. This K+ uptake is likely to mediate the apical membrane step of active transepithelial K+ absorption.
Regulation of plasma motilin by opioids in the dog
Authors: Poitras P. , Boivin M. , Lahaie R. G. , Trudel L.
Published: December 2017

In the first part of this study, we compared the effects of morphine and trimebutine, two opioid receptor agonists, on small intestinal motility and plasma motilin in dogs. Morphine (100 micrograms/kg iv for 10 min) induced first a typical vomiting myoelectric profile followed subsequently by a migrating electrical activity mimicking phase III of the migrating myoelectric complex; trimebutine (5 mg/kg iv for 10 min) initiated only a migrating phase III-like activity. Despite their different initial contractile effects, both agents induced a significant and similar rise in plasma motilin that preceded the beginning of the premature phase III. In the second portion of the study, naloxone, an opioid receptor antagonist, was infused to verify the influence of endogenous opiates on plasma motilin and on the migrating motor complex. Naloxone (2 mg/kg, then 0.5 mg.kg-1.h-1 iv) delayed significantly the cyclic recurrence of plasma motilin peak increases and of the phase IIIs. In some animals, where naloxone abolished the phase IIIs, the amplitude of the motilin peak increases was significantly diminished. These results suggest 1) that opioid administration increases plasma levels of motilin by a mechanism that is independent of the intestinal contractile activity, and 2) that endogenous opioids could be physiological inducers of plasma motilin increases in the conscious dog.
Portal venous pressure and portasystemic shunting in experimental portal hypertension
Authors: Geraghty J. G. , Angerson W. J. , Carter D. C.
Published: December 2017

The relationship between portal venous pressure and the degree of portasystemic shunting was studied in portal vein-ligated and cirrhotic rats anesthetized with halothane. One day after partial portal vein ligation there was a strong positive correlation (r = 0.80, n = 7) between portal pressure and shunting of mesenteric venous blood as measured by injection of radioactive microspheres. The relationship subsequently underwent rapid change but stabilized by 14 days postligation, when higher levels of shunting were again associated with higher portal pressures up to a limit of approximately 70% shunting, above which pressures did not increase further. This relationship was well described by a quadratic function (r = 0.75, n = 17). In cirrhotic rats there was no relationship between portal pressure and shunting (r = -0.01, n = 10). The results suggest that in the prehepatic model there is little inherent variability in capacity to develop shunts, which open to a degree directly related to portal pressure, but that this relationship may be altered in cirrhotic portal hypertension.
Carbachol-induced protein phosphorylation in parietal cells: regulation by [Ca2+]i
Authors: Brown M. R. , Chew C. S.
Published: December 2017

1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester (BAPTA/AM), an intracellular calcium [( Ca2+]i) chelator, was used to investigate the role of [Ca2+]i in acid secretory activity and protein phosphorylation in parietal cells from rabbit. Chelation of extracellular calcium [( Ca2+]o) with ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid did not prevent the initial carbachol-induced elevation of [Ca2+]i as measured with the fluorescent Ca2+ probe, fura-2, and only partially inhibited [14C]-aminopyrine (AP) accumulation, an indirect indicator of acid secretory activity. [Ca2+]i chelation with BAPTA/AM eliminated carbachol-stimulated increases in [Ca2+]i and AP accumulation but only transiently reduced histamine stimulation of AP accumulation. Carbachol increased phosphorylation of a 36-kDa, pI approximately 7 protein (pp36) and transient phosphorylation of a 28-kDa, pI approximately 5 protein (pp28), whereas histamine increased phosphorylation of 40-kDa, pI approximately 6.5 (pp40) and 27-kDa, pI approximately 6.2 (pp27) proteins. Phosphorylation of pp36 and pp28 were mimicked by the protein kinase C activator, 12-O-tetradecanoylphorbol-13-acetate (TPA) and the calcium ionophore, ionomycin, respectively. Two other phosphoproteins with molecular weights of 66,000 and pIs of 5.7 and 5.9 were also phosphorylated in response to TPA and carbachol. Chelation of [Ca2+]i and [Ca2+]o blocked carbachol-induced phosphorylation of pp28 and pp36 and ionomycin phosphorylation of pp28 but not TPA-stimulated phosphorylation of pp36 or the two pp66s or histamine-stimulated phosphorylation of pp27 or pp40. Chelation of [Ca2+]i alone did not block increases in [Ca2+]i or phosphorylation of pp28 in response to ionomycin. Both pp28 and pp36 were localized in both microsomal and cytosolic fractions of cells, which suggests involvement in cytoskeleton-membrane interactions. These phosphoproteins could be common elements of Ca2+-dependent stimulus-secretion coupling as similar proteins were phosphorylated by carbachol and cholecystokinin (CCK) in chief cells. Based on data with TPA and ionomycin, both protein kinase C and an as yet unidentified Ca2+-dependent protein kinase(s) appear to be activated upon stimulation with cholinergic agonists and CCK.
A microelectrode study of responses to secretagogues by epithelial cells on villus and crypt of rat small intestine
Authors: Stewart C. P. , Turnberg L. A.
Published: December 2017

The cellular origin of the response to secretagogues in small bowel epithelium was investigated by recording the effect of 5-hydroxytryptamine (5-HT, 10(-4) mol/l), acetylcholine (10(-4) mol/l), and prostaglandin E2 (PGE2, 10(-5) or 10(-4) mol/l) on apical membrane potentials (Va) of crypt and villus cells of rat ileum and jejunum in vitro using intracellular microelectrodes. Experiments were performed under visual control; addition of secretagogues and other manipulations were carried out during single impalements. Under basal conditions, apical membrane potential differences were consistently higher in jejunum than ileum (-72 +/- 1 vs. -47 +/- 2 mV, respectively, for villus impalements; -61 +/- 2 mV vs. -57 +/- 1 mV, respectively, for crypt impalements), and in jejunum villous membrane potentials exceeded those in the crypt. In the ileum, this crypt-villus gradient was reversed. The three secretagogues increased transmural potential difference and transiently reduced Va in cells in both crypt and villus regions by 8 mV or more. Fractional apical membrane resistance (FR) declined in ileum by approximately 30% in response to 5-HT and PGE2, whereas little change in FR was observed in jejunal recordings. PGE2 was ineffective in crypt and villus when Cl- was replaced by gluconate in both the luminal and serosal perfusates but depolarized the apical membrane in both regions after serosal restoration of Cl- from -76 +/- 4 to -56 +/- 8 mV in villus and from -58 +/- 4 to -45 +/- 6 mV in crypt. Rapid luminal Cl- substitution depolarized Va on the villus from -77 +/- 2 to -74 +/- 3 mV, but this effect was enhanced in the presence of PGE2, reducing Va from -65 +/- 8 to -43 +/- 12 mV. Prior to PGE2 addition, Va was -81 +/- 4 mV for this group of experiments. FR rose in the nominal absence of luminal Cl- from 0.69 +/- 0.09 to 0.77 +/- 0.06. It is concluded that because a Cl(-)-dependent depolarization of apical membrane potentials occurs in villi and crypts, net secretion in the small bowel is probably not confined to the crypts and may also occur from villous epithelium.
Hydrocortisone treatment increases the sensitivity and responsiveness to cholecystokinin in rat pancreas
Authors: Otsuki M. , Okabayashi Y. , Nakamura T. , Fujii M. , Tani S. , Ohki A. , Baba S.
Published: December 2017

The effects of hydrocortisone treatment on the secretory abilities of pancreatic acini to various secretagogues were studied. Rats were given subcutaneous injections of hydrocortisone at doses of 1.25, 2.5, or 5.0 mg/kg body wt once daily for 7 days. Hydrocortisone led to a small dose-dependent increase in pancreatic wet weight per 100 g body wt, which was associated with an increase in both total protein and DNA contents. In acini prepared from hydrocortisone-treated rats, both the responsiveness and the sensitivity to cholecystokinin octapeptide (CCK-8) was increased. The concentration dependence of cellular Ca2+ mobilization in response to CCK-8 was also shifted to lower concentrations in acini from hydrocortisone-treated rats compared with control rat acini. In vivo administration of hydrocortisone caused a significant increase in the affinity of 125I-CCK-8 binding to high-affinity receptors. The secretory responsiveness to carbamylcholine and bombesin, but not to secretin, was also increased but without any change in the sensitivity. Moreover, the hydrocortisone treatment increased the secretory responsiveness of acini to the Ca2+ ionophore A23187 and the phorbol ester 12-O-tetradecanoylphorbol-13-acetate but did not to an adenosine 3',5'-cyclic monophosphate analogue, 8-bromoadenosine 3',5'-cyclic monophosphate. The present observations suggest that in vivo glucocorticoid administration affects both the CCK receptors and a postreceptor loci.
Effect of duodenectomy on interdigestive pancreatic secretion, gastrointestinal motility, and hormones in dogs
Authors: Malfertheiner P. , Sarr M. G. , Spencer M. P. , DiMagno E. P.
Published: December 2017

We tested the hypothesis that the duodenum is necessary to coordinate interdigestive pancreatic trypsin secretion with gastrointestinal motility and determined whether duodenectomy altered interdigestive cycles of plasma motilin and pancreatic polypeptide and their relationship to trypsin secretion and motility. Consequently, in normal and duodenectomized dogs, we measured trypsin secretion, gastrointestinal motility, and plasma concentrations of motilin and pancreatic polypeptide during the interdigestive period. After duodenectomy, peaks of trypsin secretion continued to cycle at normal intervals (102 +/- 15 min), but the amounts of trypsin were reduced during peaks of secretion (P = 0.02) and throughout the entire cycle (P = 0.02). Trypsin secretory cycles after duodenectomy, however, were not coordinated with cycles of interdigestive motility, and the plasma concentrations of motilin (P = 0.02) and pancreatic polypeptide (P = 0.05) were reduced and had no cyclic pattern. In addition, we confirmed that duodenectomy alters canine interdigestive antral motility, interrupts coordination between antral and intestinal motility, and shortens the period of jejunal migrating motor complexes. We conclude that duodenectomy disrupts the relationship between the cycles of interdigestive gastrointestinal motility and trypsin secretion and reduces the amount of interdigestive trypsin secretion. These effects of duodenectomy may be due to interruption of the duodenopancreatic neural connections or the hormonal abnormalities we have described. The loss of the cyclic pattern of plasma pancreatic polypeptide after duodenectomy suggests that the duodenum controls the release of pancreatic polypeptide by either a neural or hormonal mechanism.
Rat intestinal lymph osmolarity during glucose and oleic acid absorption
Authors: Bohlen H. G. , Unthank J. L.
Published: December 2017

The two major purposes of this study were to determine 1) how glucose and oleic acid absorption by the intestinal villi influenced the osmotic composition of lymph as it exited the villus base and 2) what if any changes in lymph osmolarity occurred as the lymph traversed through the bowel wall. The rat jejunum was used in all studies and lymph was collected from individual lymphatics at 0.5-1 nl/min during control states and luminal exposure to 35-550 mg% glucose solutions (isotonic in saline) and 5 and 20 mM oleic acidtaurocholate solutions. Lymph collected from the base of villi during vigorous motility had an osmolarity of 403 +/- 15 mosM at rest and was only increased 30-50 mosM more except during exposure to 550 mg% glucose, where osmolarity increased over 100 mosM. Under comparable conditions, the submucosal lymph osmolarity at rest was 302 +/- 3.5 mosM and increased to 330-350 mosM during exposure to all of the solutions tested. When intestinal motility was virtually stopped, the submucosal lymph osmolarity was isotonic for all solutions tested. These observations indicate that absorption of glucose and oleic acid increased the osmolarity of lymph, leaving the villus only 30-50 mosM unless a glucose concentration of 550 mg% was present. Furthermore, the increased flow of villus lymph during absorption raised the osmolarity of the submucosal lymph when bowel motility assisted the lymph propulsion. This movement of materials from the villus to the submucosa by venular blood and lymph flow provides an opportunity for the villus tissue to influence the composition of the submucosal interstitial environment.
TRH: immunocytochemical distribution in vagal nuclei of the cat and physiological effects of microinjection
Authors: Hornby P. J. , Rossiter C. D. , Pineo S. V. , Norman W. P. , Friedman E. K. , Benjamin S. , Gillis R. A.
Published: December 2017

In the present study, we have applied antiserum to thyrotropin-releasing hormone (TRH) and avidin-biotin immunocytochemistry to determine the distribution of TRH-like immunoreactivity in the vagal nuclei of the cat. A dense network of TRH-immunoreactive (TRH-IR) fibers and terminals is noted in the dorsal motor nucleus of the vagus (DMV) from 0 to 2.5 mm rostral to the obex. Horseradish peroxidase conjugated wheat germ agglutinin (HRP-WGA)-labeled neurons are noted in this region of the DMV after application of the tracer to the musculature of the pylorus. In dual-stained sections, TRH-IR fibers and terminals appear to terminate in close proximity to HRP-WGA-labeled neurons in the DMV. In contrast, a moderate to low density of TRH-IR fibers and terminals is noted in the nucleus ambiguus (NA), and no HRP-WGA-labeled neurons are noted in this nucleus. To determine the physiological significance of TRH fibers in these vagal nuclei, TRH was microinjected into the DMV and NA while monitoring gastric (antrum and pylorus) and duodenal motility as well as mean blood pressure (MBP) and heart rate. Microinjections of TRH (16-500 ng) into the DMV resulted in increases in pyloric and antral motility (minute motility index increased from 1.28 to 8.70 in the pylorus, P less than 0.05, and from 2.29 to 4.25 in the antrum, P less than 0.05). TRH microinjection also increased the intraluminar pressure in the stomach by 6.1 +/- 1.3 mmHg. No significant changes in duodenal motility, MBP, or heart rate were noted.(ABSTRACT TRUNCATED AT 250 WORDS)
Postprandial changes in intestinal slow-wave propagation reflect a decrease in cell coupling
Authors: Terasaka D. , Bortoff A. , Sillin L. F.
Published: December 2017

The purpose of these studies was to determine the effects of feeding on jejunal slow-wave propagation velocity (SWPV). Nine cats were instrumented with six pairs of electrodes implanted 4 cm apart on the jejunum. Electrical activity was recorded at the end of an 18-h fast after which each animal was fed 60 g of canned cat food. Recordings were continued during feeding and for several hours thereafter. This procedure was repeated at least twice for each cat. Average SWPV (cm/s) decreased from a fasting level of 2.28 +/- 0.20 (mean of means +/- SE) to 1.93 +/- 0.16 at 10-20 min, 1.51 +/- 0.11 at 1 h, and 1.37 +/- 0.10 at 3 h postprandially. Corresponding SW frequencies (SWFs) were 19.6 +/- 0.3, 18.7 +/- 0.2, 19.2 +/- 0.2, and 19.0 +/- 0.2 cycles/min, respectively. The differences between the fasting SWPV and that at 1 and 3 h were significant (P less than 0.05). When SWPV was plotted as a function of SWF, the slopes of the corresponding curves were also found to decrease postprandially (P less than 0.05, fasting vs. 1 and 3 h). There was no apparent change in SW amplitude, maximum rate of SW depolarization, or threshold. In the absence of changes in these parameters, the divergence of the slopes at lower SWFs indicates that the decrease in SWPV is because of increased internal resistance, probably the result of uncoupling of intestinal muscle cells. The change is rapid in onset and long in duration, suggesting that an uncoupling factor is released during ingestion of a meal, and that its effect persists for several hours.
Prostanoids in regulation of postprandial jejunal hyperemia and oxygen uptake
Authors: Chou C. C. , Alemayehu A. , Mangino M. J.
Published: December 2017

The role of prostanoids in regulation of jejunal blood flow (JBF) was studied in anesthetized dogs. Intra-arterial infusions of arachidonate produced biphasic changes and dose-dependent decreases in jejunal vascular resistance (JVR) in untreated and aspirin-pretreated dogs, respectively; mefenamate abolished these responses. The jejunum released prostaglandin I2 (PGI2) greater than PGE2 greater than thromboxane A2 (TXA2) (radioimmunoassay) under resting conditions, and food enhanced the release of PGE2 greater than PGI2 greater than TXA2 greater than PGF2 alpha. Addition of arachidonate to food enhanced TXA2 and PGF2 alpha releases and decreased PGI2 and PGE2 releases, while inhibiting the food-induced increases in JBF and O2 uptake; mefenamate inhibited these arachidonate actions. A TXA2 receptor antagonist (SQ-29548) reversed the arachidonate vascular and metabolic actions. Intra-arterial infusions of PGI2 or PGE2 decreased, whereas TXA2 analogue U-44069 or PGF2 alpha increased JVR. A mixture of these prostanoids infused at blood concentrations similar to the increase observed during food placement did not alter JVR. At concentrations similar to the increases observed when arachidonate was added to luminal food, the infusions increased JVR and abolished the food-induced decrease in JVR. In conclusion, jejunal productions of PGI2, PGE2, TXA2, and PGF2 alpha increase during nutrient absorption. Addition of arachidonate to food attenuates the former two and enhances the latter two releases, which act to attenuate food-induced jejunal hyperemia.
Identification of neurotransmitters by selective protection of postjunctional receptors
Authors: Grider J. R.
Published: December 2017

The neurotransmitter responsible for relaxation of gastric smooth muscle was identified by a technique involving the use of selective ligands to protect postjunctional receptors combined with inactivation of all other receptors with N-ethylmaleimide (NEM). Relaxation in response to field stimulation (80 V, 1 ms, 0.5-8 Hz) and to maximally effective concentrations of vasoactive intestinal peptide (VIP; 1 microM), ATP (1 mM), isoproterenol (1 mM), dibutyryl adenosine 3',5'-cyclic monophosphate (cAMP; 1 mM), and forskolin (1 microM) was measured in muscle strips from guinea pig gastric fundus before and after treatment with NEM (5 microM) for 1 h. Protection of VIP receptors with VIP or the VIP antagonist VIP10-28 fully protected relaxation induced by VIP and by field stimulation, but did not protect relaxation induced by ATP or isoproterenol. Protection of ATP receptors with ATP protected only the response to ATP, but did not protect the response to field stimulation, VIP, or isoproterenol. Relaxation induced by either forskolin or dibutyryl cAMP was not altered by treatment with NEM alone or in the presence of protective ligands, indicating that at the concentrations used NEM inactivated membrane receptors without affecting intracellular relaxation mechanisms. These studies indicate that VIP but not ATP is the neurotransmitter responsible for neurally induced relaxation in the gastric fundus.
Effect of diet on triolein absorption in weanling rats
Authors: Flores C. A. , Brannon P. M. , Wells M. A. , Morrill M. , Koldovsky O.
Published: December 2017

To determine the effect of altered dietary fat intake on the rate of fat absorption in the intact animal, we fed male weanling rats either a high fat-low carbohydrate (HF-LC) (calories: 67% fat, 10% carbohydrate, 20% protein) or low fat-high carbohydrate (LF-HC) (calories: 10% fat, 67% carbohydrate, 20% protein) diet for 8 days. Absorption of [14C]triolein was estimated by determining 1) 14CO2 expiration in breath, 2) intestinal triglyceride output using Triton WR-1339, an inhibitor of lipoprotein lipase, and 3) quantitating the disappearance of labeled triolein from the gastrointestinal tract. Changes in the activity of pancreatic lipase and amylase confirmed the adaptation to altered fat and carbohydrate intake. Animals fed the HF-LC diet exhibited approximately twofold greater triolein disappearance, oxidation, and intestinal triglyceride output compared with animals fed LF-HC. There was also a highly significant linear relationship between 14CO2 excretion and intestinal triglyceride output in both diet groups. These data show that high dietary fat content markedly enhances in vivo fat absorption in the weanling rat.
Effects of osmotic stresses on isolated rat hepatocytes. II. Modulation of intracellular pH
Authors: Gleeson D. , Corasanti J. G. , Boyer J. L.
Published: December 2017

To assess the roles of acid-base transport systems in cell volume regulation in rat hepatocytes, intracellular pH (pHi) was measured in subconfluent monolayers loaded with 2'-7'-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF) after exposure to hypotonic and relative hypertonic media, interventions that stimulate regulatory volume decrease (RVD) and increase (RVI), respectively. During RVD, pHi decreased from 6.98 +/- 0.11 to 6.85 +/- 0.08 in the absence of HCO3- and from 7.26 +/- 0.10 to 7.19 +/- 0.06 in its presence. Omission of Na+ or addition of 1 mM amiloride prevented the decline in pHi. Acute withdrawal or replacement of Na+ in hypotonic medium resulted in a slower rate of fall or recovery in pHi, respectively, than when the same maneuvers were carried out in isotonic medium. In contrast, during RVI, pHi increased from 6.86 +/- 0.11 to 7.15 +/- 0.15 in the absence of HCO3-, a rise in pHi that was also completely abolished by Na+ removal or by 1 mM amiloride. In the presence of HCO3-, the rise in pHi was less marked than in its absence, although net acid efflux was greater because of a greater intracellular buffering capacity. Cl- removal in the presence of HCO3- had no effect on the change in pHi during either RVD or RVI. Perfusion with 0.5 mM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) during RVD lowered pHi further and accentuated the subsequent pHi rise seen after the return to isotonic medium. These data suggest that Na(+)-H+ exchange in rat hepatocytes is downregulated during RVD and activated during RVI. Cl(-)-HCO3- exchange does not appear to be involved in hepatocyte volume regulation.
Hypertonic fluid absorption from rabbit descending colon in vitro
Authors: Bleakman D. , Naftalin R. J.
Published: December 2017

Fluid and solute movements across rabbit distal colonic mucosa were investigated to determine the solute concentration of the absorbate and to characterize the absorption process. With isotonic mucosal and serosal bathing solutions the osmolality of the absorbate was 492 +/- 22 mosmol/kg. When the absorbate concentration was corrected for passive components of water and salt flux, the concentration of the "active" component was 1,062 +/- 206 mosmol/kg. Octanol (2 mM) caused a decrease in net solute and water absorption and in the concentration of the absorbate. Cytochalasin D (20 microM) increased the absorbate tonicity and decreased the hydraulic conductance of the active route for water movement. Correlations were made with measurements of the total crypt and crypt luminal cross-sectional areas. Ouabain, octanol, deoxycholate, and theophylline increase the cross-sectional area of the crypt lumen relative to that of the total crypt. These findings suggest that the hypertonic component of fluid absorption is via the crypts. The large osmotic pressure across the crypt wall could provide the considerable fluid tension (5 atm) required to dehydrate feces.
Cholecystokinin downregulates receptors for vasoactive intestinal peptide and secretin in rat pancreatic acini
Authors: Katsushima S. , Adachi H. , Honda T. , Sato S. , Kusui T. , Onishi S. , Aoki E. , Noguchi M. , Konishi J.
Published: December 2017

We examined the effect of cholecystokinin (CCK) on the receptors for vasoactive intestinal peptide (VIP) and secretin in rat pancreatic acini. CCK decreased the specific binding of 125I-VIP and 125I-secretin by 42 and 51%, respectively. This CCK-induced inhibition was caused by an apparent decrease in the capacity of high-affinity binding sites of VIP and secretin receptors. CR 1409, a specific antagonist of CCK, abolished CCK-induced binding inhibition, whereas 12-O-tetradecanoylphorbol-13-acetate, A23187, and cycloheximide did not affect the binding of the radioligands. Both N2,O2-dibutyryl guanosine 3',5'-cyclic monophosphate (Bt2cGMP) and nitroprusside inhibited the specific binding of 125I-VIP. This inhibition, however, was because of an apparent decrease in the capacity of low-affinity binding sites on VIP receptors. CCK-induced downregulation of VIP and secretin receptors was associated with the diminished acinar response to VIP or secretin-induced adenosine 3',5'-cyclic monophosphate accumulation and amylase secretion, whereas neither Bt2cGMP nor nitroprusside affected VIP-induced amylase secretion. Data suggest that CCK-induced downregulation is mediated by the initial interaction of CCK with CCK receptors followed by some postreceptor process, which appears unrelated to protein kinase C, calcium mobilization, decrease in protein synthesis, or cellular cGMP increases. This downregulation, at least in part, accounts for CCK-induced restricted stimulation of amylase secretion by VIP and secretin.