bluuebunny/crossref_metadata_2025 huggingface dataset:
Binding of Escherichia coli heat-stable enterotoxin to receptors on rat intestinal cells
Authors: Giannella R. A. , Luttrell M. , Thompson M.
Published: December 2017

This study was performed to determine whether receptors for Escherichia coli heat-stable enterotoxin (ST) exist on intestinal epithelial cells. Binding sites for 125I-ST were found on rat jejunal and ileal villus cells. Binding was rapid, reversible, linear with cell number, saturable, and temperature dependent. Significant degradation of 125I-ST occurred when incubated with cells at 37 degrees C but not at 25 degrees C. Binding was specific to ST since binding of 125I-ST was competitively inhibited by increasing concentrations of human or porcine ST but not by E. coli heat-labile, cholera, or staphylococcal enterotoxins. Addition of excess unlabeled ST to cells preincubated with 125I-ST resulted in dissociation of much but not all of the bound 125I-ST. Binding of 125I-ST to jejunal and ileal cells occurs with two affinities, and this is due to the phenomenon of negative cooperativity. The potency of ST for inhibiting the binding of 125I-ST was identical to the potency of ST in stimulating cGMP production. These data support the existence of receptors for ST on intestinal cells, and these receptors may be involved in the action of ST.
Manganese action on pancreatic protein synthesis in normal and diabetic rats
Authors: Korc M.
Published: December 2017

The effects of manganese on [3H]phenylalanine incorporation into protein were studied in pancreatic acini prepared from normal and streptozotocin-induced diabetic rats. In the absence of added Ca2+ manganese exerted a biphasic effect on [3H]phenylalanine incorporation in both groups of acini. Significant stimulation occurred at 3 X 10(-5) M manganese. At higher concentrations manganese inhibited incorporation. The magnitude of stimulation was similar in all acini, whereas the magnitude of inhibition was greater in acini from normal rats. Addition of Ca2+ to incubation media abolished the stimulatory effect of manganese in normal rat acini and greatly enhanced it in diabetic rat acini, significant stimulation now occurring at 10(-5) M manganese. The magnitude of inhibition was again greater in acini from normal rats. Insulin in vivo partially reversed the diabetes-induced alterations in acinar cell responsiveness to manganese. The present findings suggest that streptozotocin-induced diabetes is associated with postreceptor alterations in the pancreatic acinar cells.
Effect of chloroquine on intestinal lipid metabolism
Authors: Mansbach C. M. , Arnold A. , Garrett M.
Published: December 2017

Most studies that have quantitated recovery of infused lipid in the intestinal mucosa and mesenteric lymph have only been able to recapture 50-75%. One possibility is that the missing lipid enters a triacylglycerol (TG) storage pool in the enterocyte and is hydrolyzed by lysosomal lipase, and the free fatty acid released is transported by the portal vein. This postulate was tested by comparing glyceryl trioleate (TO)-infused rats pretreated with the lysosomotropic drug, chloroquine (6.3 mg.kg-1.h-1) with saline controls. Chloroquine increased mucosal TG from 94 +/- 6 to 128 +/- 8 mumol. Additionally, the specific activity of the mucosal TG relative to the infused [3H]TO was reduced in the treated rats. The mucosal TG increase was not due to impaired TG output, which remained the same as controls. We conclude that the TG in the acid lipase-sensitive pool derives most of its glyceride-glycerol from endogenous sources. Furthermore, the increment in mucosal TG caused by chloroquine is not enough to explain the majority of the acyl groups unaccounted for in the mucosa and lymph after a TG infusion. For these a direct passage of acyl groups through the enterocyte is postulated.
Secretagogue-induced changes in intracellular pH and amylase release in mouse pancreatic acini
Authors: Carter K. J. , Rutledge P. L. , Steer M. L. , Silen W.
Published: December 2017

The response of the intracellular pH (pHi) to stimulation of enzyme secretion in pancreatic acini was measured using the fluorescent dye 2'-7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. Acini suspended in pH 7.40 buffer demonstrated cytoplasmic alkalinization of 0.17, 0.14, and 0.15 pH units 2 min after addition of the secretagogues carbachol (10(-5) M), caerulein (10(-10) M), and bromo-A23187 (10(-6) M). Corresponding net stimulated amylase secretion over 30 min was 9.2, 10.3, and 5.6% of total content, respectively. Pretreatment of acini with atropine blocked the pHi rise induced by carbachol; addition of atropine 2 min after the carbachol did not reverse the alkalinization. Acini suspended in Ca2+ free buffer containing 0.1 or 0.2 mM ethylene glycol tetraacetic acid showed 0.21 and 0.10 pH unit alkalinization in response to caerulein (10(-10) M) and carbachol (10(-5) M) but no change in pHi after addition of bromo-A23187. Amylase release in response to increasing concentrations of caerulein was maximal at 10(-10) M, with decreasing rates of amylase release at higher drug concentrations (10(-8), 10(-7) M). Alkalinization in response to stimulation of secretion was maximal at 10(-8) M caerulein (0.30 pH units at 2 min) but was of lesser magnitude at 10(-7) M. Pancreatic acini demonstrated autoregulation of pHi over a range of external pH from 7.4 to 7.1. Net amylase release over 30 min in response to 10(-5) M carbachol was sustained at normal levels in buffers of pH varying between 7.7 and 6.5. In contrast, cytoplasmic alkalinization in response to carbachol occurred only in buffers with pH values between 7.40 and 7.10. These results indicate that amylase release occurs over a wide range of pHi and is not invariably associated with secretagogue-induced alkalinization.
T84 cell receptor binding and guanyl cyclase activation by Escherichia coli heat-stable toxin
Authors: Guarino A. , Cohen M. , Thompson M. , Dharmsathaphorn K. , Giannella R.
Published: December 2017

Escherichia coli heat-stable enterotoxin (STa) induces intestinal secretion by binding to enterocyte receptors and activating the guanylate cyclase-guanosine 3',5'-cyclic monophosphate (cGMP) system. The intermediate steps between binding of STa and secretion are poorly understood, due in part to the lack of a convenient system to study the effects of STa at the cellular level. To establish such a model, we investigated the binding of 125I-STa, STa activation of guanylate cyclase, and STa-induced increase in cGMP production in a well-characterized human colonic cell line, T84. Binding was specific, linear with cell number, and time, temperature and pH dependent, and reversible. ST may also be internalized by these cells. Addition of unlabeled STa competitively inhibited binding of 125I-STa. These parameters closely resemble those described in intact rat enterocytes and cell-free membrane preparations. STa stimulated guanylate cyclase and cGMP production in a dose-related manner. The similar dose-response relationships for binding, guanylate cyclase stimulation by STa, and cGMP production suggest that the guanylate cyclase-cGMP system is coupled to ST occupancy of specific receptors. These data, together with the fact that STa induces chloride secretion from T84 cells suggest that T84 cells are a suitable and convenient system to study the cellular mechanism of action of STa.
Norepinephrine uptake by rat jejunum: modulation by angiotensin II
Authors: Suvannapura A. , Levens N. R.
Published: December 2017

Angiotensin II (ANG II) is believed to stimulate sodium and water absorption from the small intestine by enhancing sympathetic nerve transmission. This study is designed to determine whether ANG II can enhance sympathetic neurotransmission within the small intestine by inhibiting norepinephrine (NE) uptake. Intracellular NE accumulation by rat jejunum was concentration dependent and resolved into high- and low-affinity components. The high-affinity component (uptake 1) exhibited a Michaelis constant (Km) of 1.72 microM and a maximum velocity (Vmax) of 1.19 nmol.g-1.10 min-1. The low-affinity component (uptake 2) exhibited a Km of 111.1 microM and a Vmax of 37.1 nmol.g-1.10 min-1. Cocaine, an inhibitor of neuronal uptake, inhibited the intracellular accumulation of label by 80%. Treatment of animals with 6-hydroxydopamine, which depletes norepinephrine from sympathetic terminals, also attenuated NE uptake by 60%. Thus accumulation within sympathetic nerves constitutes the major form of [3H]NE uptake into rat jejunum. ANG II inhibited intracellular [3H]NE uptake in a concentration-dependent manner. At a dose of 1 mM, ANG II inhibited intracellular [3H]NE accumulation by 60%. Cocaine failed to potentiate the inhibition of [3H]NE uptake produced by ANG II. Thus ANG II appears to prevent [3H]NE accumulation within rat jejunum by inhibiting neuronal uptake.
Function and structure of parietal cells after H+-K+-ATPase blockade
Authors: Fryklund J. , Helander H. F. , Elander B. , Wallmark B.
Published: December 2017

Omeprazole was administered to rabbits as a single dose or daily for 1 wk. H+-K+-ATPase and isolated gastric glands were prepared from the oxyntic corpus mucosa and used for functional and quantitative morphological studies. Both 10 and 100 mumol omeprazole/kg increased the pH of the gastric content when measured at death. The stimulated oxygen uptake and the rate of aminopyrine (AP) uptake were both inhibited in the isolated gastric gland preparations. Morphometric studies of biopsy specimens taken from the corpus mucosa and isolated gastric glands showed that omeprazole treatment increased the volume density of the acid compartments. This expansion provides an increased accumulation space for AP. Therefore, an increased AP uptake might be seen in glands isolated from omeprazole-treated animals. Blockade of the H2-receptor by ranitidine transformed the morphology of the cell into a more resting type and, furthermore, reduced the omeprazole-induced increase in the volume density of the acid compartments in the parietal cell. The H+-K+-ATPase activity measured in membrane fractions from the omeprazole-treated animals was decreased dose dependently and inhibited by 95% after 100 mumol omeprazole/kg. However, the concentration of the enzyme in these fractions did not change. These results indicate a specific inhibitory action of omeprazole on the H+-K+-ATPase.
Contractile effects of manganese on taenia of guinea pig cecum
Authors: Lategan T. W. , Brading A. F.
Published: December 2017

The present study was undertaken to examine Mn as a contractile agent in its own right in the absence of extracellular Ca and after the depletion of Ca from agonist-releasable stores. The results show that isolated strips of taenia coli depolarized by high-K, Ca-free solution will contract when Mn is present. Similarly, carbachol will evoke contractions in tissues incubated in Ca-free, Mn-containing solutions. In addition, it seems possible to stimulate contraction by releasing Mn from an agonist-releasable intracellular store in the absence of extracellular Ca and Mn. Therefore the possibility exists that cations employed as Ca antagonists may in fact support contraction.
Gastrin: levels and trophic action during advancing age
Authors: Majumdar A. P. , Edgerton E. A. , Dayal Y. , Murthy S. N.
Published: December 2017

Changes in antral and serum gastrin levels as well as gastrin (G) and somatostatin (D) cell density were examined in 4- to 16-mo-old Fischer-344 rats. In these rats, the responsiveness of the gastric mucosa to the trophic action of gastrin was also examined. It was observed that whereas serum gastrin levels declined steadily between 4 and 16 mo of age, antral gastrin levels rose sharply during this period. In the antrum of 16-mo-old rats, the density of G-cells, but not D-cells, was found to be lower than in their 4-mo-old counterparts. Thus, when D- to G-cell ratios were calculated, 16-mo-old rats revealed a 50% higher D- to G-cell ratio than the 4-mo-old animals. To assess the trophic action of gastrin, groups of 4-, 8-, and 16-mo-old rats were infused subcutaneously (osmotic minipump) with either saline or gastrin (G-17-I; 250 ng.kg-1.h-1) for 14 days. The gastric mucosa was assayed for thymidine kinase (an indicator of proliferative activity) and DNA and protein content. In the saline-infused rats, gastric mucosal thymidine kinase activity increased sharply between 4 and 16 mo of age without significantly affecting DNA or protein content (expressed as milligrams per 100 g of body weight), suggesting that the age-associated rise in proliferative activity is not accompanied by increased mucosal growth.(ABSTRACT TRUNCATED AT 250 WORDS)
Ca2+ channel blockers interact with alpha 2-adrenergic receptors in rabbit ileum
Authors: Homaidan F. R. , Donowitz M. , Wicks J. , Cusolito S. , el Sabban M. E. , Weiland G. A. , Sharp W. G.
Published: December 2017

An interaction between Ca2+ channel blockers and alpha 2-adrenergic receptors has been demonstrated in rabbit ileum by studying the effect of clonidine on active electrolyte transport, under short-circuited conditions, in the presence and absence of several Ca2+ channel blocking agents. Clonidine, verapamil, diltiazem, cadmium, and nitrendipine all decrease short-circuit current and stimulate NaCl absorption to different extents with clonidine having the largest effect. Exposure to verapamil, diltiazem, and cadmium inhibited the effects of clonidine on transport, whereas nitrendipine had no such effect. Verapamil, diltiazem, and cadmium, but not nitrendipine, also decreased the specific binding of [3H]alpha 2-adrenergic agents to a preparation of ileal basolateral membranes explaining the observed decrease in the transport effects of clonidine. The effective concentrations of the Ca2+ channel blockers that inhibited the effects of clonidine on transport were fairly similar to the concentrations needed to inhibit its specific binding. The displacement of clonidine by calcium channel blockers is ascribed to a nonspecific effect of these agents, although the possibility that their effects are exerted via their binding to the calcium channels is not excluded.
Kinetics of hepatic alanine uptake and urea synthesis in pigs
Authors: Vilstrup H. , Skovgaard L. T.
Published: December 2017

The kinetics of hepatic alanine uptake and urea synthesis in relation to sinusoid alanine concentration was investigated in seven anesthetized pigs weighing 63 kg, using liver vein catheterizations. Each experiment consists of four steady-state periods of 40 min with alanine concentrations in the range of 0.4-27 mmol/l. The process rates were measured as the products of transhepatic concentration gradients and hepatic blood flow rate, determined by indocyanine green. The data suggest that both processes follow saturation kinetics, that there exists a sinusoidal concentration of alanine below which net removal is limited, and that urea synthesis consists of two components: one alanine independent and one depending on alanine concentration according to Michaelis-Menten kinetics. The kinetic parameters were estimated iteratively by the maximum likelihood method. The maximum rate of alanine uptake was 1.13 +/- 0.74 mmol.min-1.kg liver wt-1 (mean +/- SD), the alanine concentration resulting in half-maximum alanine uptake rate was 1.69 +/- 0.99 mmol/l, and the removal-limiting alanine concentration was 0.27 +/- 0.09 mmol/l. The maximum rate of urea-N synthesis was 1.49 +/- 0.87 mmol.min-1.kg liver wt-1, the alanine concentration resulting in half-maximum urea-N synthesis rate was 2.32 +/- 1.11 mmol/l, and the alanine concentration-independent urea-N synthesis rate was 0.13 +/- 0.10 mmol.min-1.kg liver wt-1.
Developmental intestinal vascular responses to venous pressure elevation
Authors: Crissinger K. D. , Kvietys P. R. , Granger D. N.
Published: December 2017

The response to venous pressure elevation is an important criterion for determining whether metabolic or myogenic mechanisms are involved in local vasoregulation. We studied the effects of venous pressure elevation on intestinal hemodynamics and oxygenation in 20 mixed-breed piglets, divided equally among 1-day-, 3-day-, 2-wk-, and 1-mo-old animals. A venous circuit was established between the superior mesenteric and jugular veins, which allowed measurement of superior mesenteric blood flow, venous pressure, capillary pressure, and arteriovenous oxygen difference at venous pressures between 0 and 20 mmHg. The resting intestinal oxygen uptake in 1-day-old piglets was significantly higher than in 2-wk-old and 1-mo-old piglets. The vascular response to venous pressure elevation in 1-day-old piglets was characterized by reductions in total and precapillary resistance and increased oxygen uptake, while older animals responded to venous pressure elevation with increases in total and precapillary vascular resistance and reductions in oxygen uptake. These results indicate that metabolic factors exert a dominant influence on the intestinal vasculature of the newborn, while myogenic factors predominate in older animals in response to venous pressure elevation.
CNS blockade of acoustic stress-induced gastric motor inhibition by kappa-opiate agonists in dogs
Authors: Gue M. , Honde C. , Pascaud X. , Junien J. L. , Alvinerie M. , Bueno L.
Published: December 2017

The influence of the kappa-opioid substances dynorphin-(1-13), ethylketocyclazocine (EKC), and U 50488 and mu-opioid substance [D-Ala2-N-Me, p-nitro-Phe4-Gly5-ol]enkephalin (DAGO) on gastric motor inhibition induced by acoustic stress (AS) was investigated in fasted dogs with strain-gauge transducers chronically implanted on the antrum and proximal jejunum. AS induced by 1 h of music (80-90 dB) was delivered through earphones. Starting 40-50 min after the last migrating motor complex (MMC), AS delayed by 114% the occurrence of the next gastric MMC, whereas intestinal motility was unaffected. During AS plasma cortisol increased (P less than 0.05) by 215%, 15 min after the beginning of noise and reached a peak at 30 min. When administered intracerebroventricularly at doses higher than 20 ng/kg, dynorphin abolished the AS-induced lengthening of the gastric MMC cycle. Similar blockade was observed for EKC and U 50488 at doses of 10 and/or 20 ng/kg, but DAGO was unable to affect the AS-induced gastric inhibition at any dosage tested (20-200 ng/kg icv). At doses effective against AS-induced hypomotility, both dynorphin-(1-13) and EKC reduced significantly (P less than or equal to 0.05) the associated maximal increase in plasma cortisol level. Plasma cortisol was unmodified by intracerebroventricular administration of DAGO. None of the agonists affected basal plasma cortisol levels or the increase (0-90 min) in response to intravenous adrenocorticotropic hormone (ACTH, 5 IU). Both EKC (50 ng/kg) and U 50488 (20 ng/kg) were unable to antagonize the inhibitory effect of ovine corticotropin-releasing factor (CRF, 100 ng/kg icv).(ABSTRACT TRUNCATED AT 250 WORDS)
Norepinephrine induces Na+-H+ and Cl -HCO3 exchange in Amphiuma intestine: locus and response to amiloride
Authors: White J. F. , Hinton C. F.
Published: December 2017

Catecholamines stimulate Na+-dependent acid secretion by Amphiuma small intestine. Studies were undertaken to localize the response within the mucosa and characterize the effect on Na+ and Cl- transport. Stripped segments of jejunum were mounted in tissue chambers that permitted isolation of villus or intervillus epithelium. In Cl-free medium, norepinephrine (NE) stimulated the transepithelial voltage (Vms) in both villus and intervillus epithelium, whereas galactose and valine elevated Vms predominately in the villus. Paired segments of whole mucosa were maintained under short circuit while the rate of acid secretion (JH) was measured by titration of the unbuffered serosal medium and unidirectional fluxes of Na+ were measured by 22Na. NE significantly stimulated net Na+ absorption (JNanet), short circuit current (Isc), and JH. Amiloride reduced JH and Isc in NE-stimulated tissues and blocked the stimulation of JNanet by NE. The NE-induced current was nearly completely and reversibly inhibited by replacement of luminal medium HCO3- or CO2. NE significantly stimulated net Cl- absorption without changing Isc or JH. It is concluded that cells throughout the mucosa respond to catecholamines with enhanced Na+ and Cl- absorption, possibly through induction or stimulation of Na+-H+ and Cl- -HCO3- exchange.
Dietary regulation of intestinal transport of the dipeptide carnosine
Authors: Ferraris R. P. , Diamond J. , Kwan W. W.
Published: December 2017

Uptake of the dipeptide L-carnosine was measured in everted intestinal sleeves of mice whose dietary protein level or else proportion of protein in the form of free amino acids was varied experimentally. Carnosine uptake was highest in the jejunum, regardless of ration. Compared with a low-protein (18%) ration, a high-protein (72%) ration stimulated carnosine uptake by 30-70% in duodenum and jejunum (but not in ileum). This stimulation was observed even in the presence of peptidase inhibitors that inhibit cell surface hydrolysis of dipeptides. Measured carnosine hydrolysis was low or negligible. Carnosine uptake was the same in mice fed 54% unhydrolyzed casein, 54% partly hydrolyzed casein, and 54% free amino acids formulated so as to stimulate a complete hydrolysate of casein. Thus carnosine uptake is regulated by dietary levels of amino acids, peptides, and proteins, all of which seem equally effective at inducing carnosine transporters.
Effect of sulfidopeptide leukotrienes D4 and E4 on ileal ion transport in vitro in the rat and rabbit
Authors: Smith P. L. , Montzka D. P. , McCafferty G. P. , Wasserman M. A. , Fondacaro J. D.
Published: December 2017

Effects of leukotrienes D4 and E4 (LTD4 and LTE4) on electrolyte transport were examined, employing stripped segments of rat and rabbit ileum mounted in Ussing chambers. Addition of LTD4 or LTE4 to the serosal but not the mucosal bathing solution elicited a transient increase in short-circuit current (Isc) with maximal responses seen at 10(-5) M and 10(-8) M in rat and rabbit respectively and a sustained decrease in transepithelial conductance (Gt) in the rat only. In the rat, Cl replacement, reduction of bathing solution [Ca2+] to 1 microM or pretreatment with 1 microM indomethacin or meclofenamic acid inhibited the LTD4- or LTE4-induced Isc changes with no effect on the decrease in Gt. LTD4 (10 microM) transiently increased net Cl secretion and produced a sustained decrease in both unidirectional and net Na transport and mucosal-to-serosal Cl flux in rat ileum. The decrease in unidirectional Na fluxes is accounted for predominantly by a change in the potential independent flux of Na. These results suggest that the increase in Isc in both rat and rabbit is mediated by arachidonic acid metabolites, whereas the decrease in Gt and net Na absorption in rat ileum is mediated by a cyclooxygenase-independent pathway.
Continuous monitoring of portal vein and hepatic artery hemodynamics in unrestrained rats
Authors: Braillon A. , Brody M. J.
Published: December 2017

Continuous measurement of portal vein and hepatic artery blood flows during physiological experimental conditions, even in large animals, poses difficult problems. We report the successful use of miniaturized flow probes and pulsed Doppler flowmetry for chronic monitoring of hepatic artery and portal vein flows in intact unrestrained rats and describe the probe construction and implantation. Proportionality between portal vein velocity and portal flow was made possible by a technique for stabilizing the diameter of the venous segment from which velocity is recorded. The accuracy of the method in detecting changes in portal vein flow was established by the high statistically significant correlation between changes in velocity recorded simultaneously from portal vein and superior mesenteric artery in a series of rats with ligated celiac and inferior mesenteric arteries. In these preparations all portal vein flow is derived from the superior mesenteric artery. Complex dynamic changes in the hepatic circulation of conscious unrestrained rats were recorded in response to systemic injections of glucagon and angiotensin II. In the resting state several characteristic velocity patterns were recorded from the portal vein. Oscillations linked to respiration were not observed while the animals rested quietly but were noted during sleep and anesthesia. Two hitherto unrecognized patterns produced respectively by the pulsations of the superior mesenteric artery and by spontaneous contractions of the portal vein were also observed. The method described here provides the first opportunity to study hepatic circulation in chronically instrumented rats during physiological experimental conditions.
Role of pancreatic polypeptide in the regulation of pancreatic exocrine secretion in dogs
Authors: Shiratori K. , Lee K. Y. , Chang T. M. , Jo Y. H. , Coy D. H. , Chey W. Y.
Published: December 2017

The effect of intravenous infusion of synthetic human pancreatic polypeptide (HPP) or a rabbit anti-PP serum on pancreatic exocrine secretion was studied in 10 dogs with gastric and Thomas duodenal cannulas. The infusion of HPP, at a dose of 1 microgram.kg-1.h-1, achieved a plasma PP concentration that mimicked the peak plasma concentration of PP in both interdigestive and postprandial states. This dose of HPP significantly inhibited pancreatic secretion in the interdigestive state. By contrast, immunoneutralization of circulating PP by a rabbit anti-PP serum resulted in significant increases (P less than 0.05) in both interdigestive and postprandial pancreatic secretion, including water, bicarbonate, and protein. The increase in the pancreatic secretion paralleled a decrease in circulating PP level, which lasted for as long as 5 days. Furthermore, the anti-PP serum blocked the inhibitory action of exogenous HPP on pancreatic exocrine secretion. The present study indicates that endogenous PP plays a significant role in the regulation of the pancreatic exocrine secretion in both interdigestive and digestive states. Thus we conclude that PP is another hormone regulating pancreatic exocrine secretion in dogs.
Ketocyclazocine, a kappa-opioid receptor agonist, and control of intestinal myoelectric activity in dogs
Authors: Telford G. L. , Caudill A. , Condon R. E. , Szurszewski J. H.
Published: December 2017

The role of kappa-opioid receptors in the control of fed and fasted myoelectrical activity of the stomach and small intestine was studied in conscious dogs implanted with bipolar silver electrodes. In fasted dogs, migrating myoelectric complex (MMC) cycle times were 105 +/- 14 min in the duodenum. Administration of ketocyclazocine (1 mg/kg iv) inhibited contractile activity, blocked migration of distally propagating MMCs, and increased the MMC cycle time to 246 +/- 56 min (P less than 0.0005). Pretreatment with naloxone (2 mg/kg iv) 5 min before administration of ketocyclazocine (1 mg/kg iv) prevented the disruption by ketocyclazocine of the distally propagating MMC but did not completely antagonize the effect of ketocyclazocine on MMC cycle time. MMC cycle time was 102 +/- 14 min before naloxone plus ketocyclazocine administration and 138 +/- 22 min after administration (P less than 0.005). Although MMC cycle times were still significantly prolonged over control after naloxone plus ketocyclazocine, cycle times were significantly decreased compared with ketocyclazocine administration alone (P less than 0.005). Ketocyclazocine (1 mg/kg iv) completely inhibited the fed pattern of myoelectric activity for 74 +/- 26 min when administered 15 min after feeding. Bethanecol (2 mg sc)-initiated spike activity was not blocked by ketocyclazocine. These studies suggest that endogenous opioids and kappa-opioid receptors may play a role in the inhibition of gastric action potentials and small intestinal spiking activity.
Characterization of the effects of neurokinins on canine antral muscle
Authors: Koelbel C. B. , Mayer E. A. , van Deventer G. , Snape W. J. , Patel A.
Published: December 2017

The excitation of longitudinal antral muscle by substance P (SP) involves both a myogenic and a cholinergic effect. To examine if these responses are mediated by different neurokinin receptors, we studied the mechanical response and the release of [3H]acetylcholine from antral muscle strips in response to SP, substance P methylester (SPME), neurokinin A (NKA), neurokinin B (NKB), and several non-mammalian tachykinins. All peptides studied showed a dose-dependent inotropic and chronotropic effect on spontaneous phasic contractions. This ionotropic effect in longitudinal muscle was partially atropine sensitive for SPME, SP, and NKB but not for NKA, whereas neither atropine nor tetrodotoxin had an effect in circular muscle. In longitudinal muscle, all three neurokinins were equipotent. In longitudinal muscle treated with atropine and in circular muscle, the rank order of potency for the inotropic response was NKA greater than NKB greater than SP greater than SPME. For the chronotropic response the rank order was SPME, SP greater than NKA greater than NKB. NKA, NKB, and SP caused a dose-dependent, tetrodotoxin-sensitive increase in [3H]acetylcholine release from strips preincubated with [3H]choline. NKA was significantly more potent to release [3H]acetylcholine than either NKB or SP. The stimulated release was inhibited by [D-Ala2,D-Met5]methionine enkephalinamide and the SP antagonist, spantide. These results are consistent with the hypothesis that NKA is the natural ligand mediating the myogenic inotropic response in both muscle layers and the cholinergic response in longitudinal muscle.
Neuropeptide responses and mechanics of the proximal and distal feline colon in vitro
Authors: Merlo A. , Cohen S.
Published: December 2017

Mechanical properties and responses to neuropeptides were compared for proximal and distal feline colonic muscle. Proximal longitudinal (PL), proximal circular (PC), distal longitudinal (DL), and distal circular (DC) muscles were studied in vitro under isometric conditions. Total tension in DL [1.636 +/- 0.009 (SE) kg/cm2] was greater than in DC (0.699 +/- 0.004 kg/cm2) or PC (0.710 +/- 0.005 kg/cm2, P less than 0.05). Longitudinal muscle developed proportionately more active tension than circular muscle at each region (80.9% in DL vs. 54.1% in DC and 77.1% in PL vs. 52.3% in PC, P less than 0.01). Neuropeptides varied in potency and efficacy. Cholecystokinin octapeptide (CCK-8) was the most potent and efficacious in PL and substance P was the most efficacious in PC muscle (P less than 0.05). Substance P was more efficacious whereas CCK-8 and neurotensin were less efficacious in PC than PL muscle (P less than 0.01). DL muscle did not respond to CCK-8. DC muscle did not respond to CCK-8 or neurotensin. Isometric contractions to each neuropeptide were insensitive to tetrodotoxin. We conclude that 1) mechanical properties of circular and longitudinal colonic muscle differ and 2) responses to neuropeptides depend on anatomic region and intrinsic properties.
Handling of tracer norepinephrine by the dog liver
Authors: Goresky C. A. , Bach G. G. , Cousineau D. , Schwab A. J. , Rose C. , Lee S. , Goresky S.
Published: December 2017

Norepinephrine handling by the dog liver was appraised by carrying out tracer-transient, multiple-indicator-dilution studies within steady-state conditions in a basal situation, during norepinephrine infusion and after the uptake inhibitor desipramine. In controls, tracer norepinephrine extraction averaged 61%, whereas bulk norepinephrine extraction was approximately 31%; intrahepatic secretion of unlabeled norepinephrine accounted for the difference. Infusion of norepinephrine, raising arterial levels more than an order of magnitude, constricted the hepatic vascular space but did not change tracer extraction; norepinephrine secretion remained essentially unchanged, and with this, bulk extraction approached tracer extraction. A theoretical analysis of norepinephrine uptake was developed. Analysis of tracer data with this indicated that the permeability surface products for influx and efflux, expressed per gram liver, did not change. Desipramine did not affect the uptake kinetics, indicating that the uptake process was virtually completely nonneurogenic. Late efflux of tracer normetanephrine product was detected but was small prior to recirculation. The study demonstrates that norepinephrine secretion ordinarily coexists with uptake and provides an approach to quantitating both.
Pentagastrin induction of spermine/spermidine N1-acetyltransferase and mucosal polyamines
Authors: Seidel E. R. , Snyder R. G.
Published: December 2017

The trophic response of the gastrointestinal mucosa to treatment with the hormone gastrin includes a polyamine-dependent step. Because gastrin does not induce ornithine decarboxylase, experiments were designed to determine whether pentagastrin induced the polyamine interconverting enzyme, spermine/spermidine N1-acetyltransferase (SAT). Eight hours after intraperitoneal treatment of rats with either spermidine (0.8 mmol/kg) or pentagastrin (250 micrograms/kg) oxyntic gland mucosal SAT activity was increased from roughly 400 to 800 pmol [14C]acetate.mg protein-1.h-1. In contrast, colonic mucosa was not sensitive to pentagastrin even though spermidine treatment induced nearly a 400% increase in SAT activity. Measurement of both oxyntic gland and colonic mucosal polyamine concentrations showed that by 16 h after pentagastrin (250 micrograms/kg ip) putrescine, acetylspermidine, and spermidine levels all were increased to a level approximately 200% of that observed in NaCl-treated rats. By 24 h mucosal polyamine content of pentagastrin-treated rats was not different from control. Essentially the same results were found in animals treated with difluoromethylornithine, thus demonstrating that the increase in mucosal polyamine concentration was not related to the induction of ornithine decarboxylase. The results of these experiments demonstrate that unlike most hormones, the hormone gastrin induces the polyamine converting enzyme, SAT, rather than ornithine decarboxylase during stimulation of polyamine-dependent cell growth and/or division.
Central neurotensin affects rat gastric integrity, prostaglandin E2, and blood flow
Authors: Zhang L. , Colony P. C. , Washington J. H. , Seaton J. F. , Kauffman G. L.
Published: December 2017

The aim of this study is to define the effect(s) of centrally administered neurotensin (NT) on gastric mucosal integrity, prostaglandin E2 (PGE2) generation, and blood flow during stress induced by cold-water restraint (CWR) in rats. Intracerebroventricular (icv) NT reduced macroscopic and microscopic damage. The former effect was dose dependent and was totally blocked by indomethacin pretreatment. Gastric mucosal PGE2 increased 27 and 30% at 30 and 60 min, respectively, in nonrestrained rats given icv NT. PGE2 generation was reduced in control rats during CWR but was maintained in CWR rats treated with icv NT. Gastric mucosal blood flow (GMBF) was significantly reduced in control rats during CWR. Mucosal blood flow was maintained at nonrestraint levels in the presence of icv NT during CWR; however, this effect was abolished by parenteral indomethacin pretreatment. Similarly, intravenous 16,16-dimethyl-PGE2 (200 micrograms.kg-1.h-1) maintained GMBF of non-CWR levels as well as preventing the macroscopic damage normally associated with CWR. These data suggest a protective role for central NT on the gastric mucosa, mediated, at least in part, by PGE2 generation and gastric mucosal blood flow.
Characterization of acetylcholine release from enzyme-dissociated myenteric ganglia
Authors: Yau W. M. , Dorsett J. A. , Parr E. L.
Published: December 2017

Longitudinal muscle strips adhered with myenteric plexus were subjected to enzyme digestion under controlled conditions in a Krebs-bicarbonate buffer solution containing a mixture of collagenase, deoxyribonuclease, protease, choline chloride, and bovine serum albumin for 30 min at 37 degrees C. Myenteric ganglia, singly or in multiple aggregates, were harvested with micropipette and labeled with [3H]choline for [3H]acetylcholine (ACh) release studies. When examined by light or electron (transmission or scanning) microscopy, the ganglia exhibited their normal structural characteristics with axon bundles, dendrites, cell bodies, and vesiculated processes. Depolarization with elevated potassium or veratrine hydrochloride significantly elevated the efflux of [3H] ACh. Perfusion with tachykinins (substance P and substance K), vasoactive intestinal peptide, forskolin, or serotonin also significantly increased the release of [3H]ACh. This study demonstrated that enzyme-dissociated myenteric ganglia, notably free of muscle or connective tissue components, were structurally well preserved and were amenable to functional studies targeted specifically for the enteric plexus neurons.
Neutral endopeptidase inhibitors potentiate substance P-induced contraction in gut smooth muscle
Authors: Djokic T. D. , Sekizawa K. , Borson D. B. , Nadel J. A.
Published: December 2017

To determine the role of endogenous neutral endopeptidase (NEP), also called enkephalinase (EC 3.4.24.11), in regulating tachykinin-induced contraction of gut smooth muscle, we studied the effects of NEP inhibitors on the contractile responses to substance P (SP) in isolated longitudinal strips of ileum or duodenum in rats and ferrets. Leucine-thiorphan and phosphoramidon shifted the concentration-response curves of SP to lower concentrations in all tissues studied, but the sensitivity to SP was greater and the effect of leucine-thiorphan was less in the ferret, a finding that correlated with the observation that the ferret ileum contained substantially less NEP activity than rat ileum. Captopril, bestatin, MGTA, leupeptin, and physostigmine did not alter contractile responses to SP, suggesting that kininase II, aminopeptidases, carboxypeptidase N, serine proteinases, and acetylcholinesterase do not modulate the SP-induced effects. These studies suggest that, in the ileum and duodenum, NEP modulates the actions of SP and, furthermore, that the sensitivity of tissues may be determined, at least in part, by the amount of enzymatically active NEP present.
Uptake of bumetanide into isolated rat hepatocytes and primary liver cell cultures
Authors: Petzinger E. , Muller N. , Follmann W. , Deutscher J. , Kinne R. K.
Published: December 2017

Uptake of bumetanide into rat liver cells was investigated using isolated hepatocytes and primary cell cultures. The kinetics of [3H]-bumetanide uptake revealed two saturable components in addition to an unsaturable component. Saturable bumetanide uptake consists of a high-affinity, sodium-dependent uptake and a low-affinity transport system. Bumetanide uptake into isolated rat hepatocytes is energy dependent and temperature sensitive. At low temperatures, bumetanide uptake is due to diffusion with a permeability coefficient of 1.16 x 10(-6) cm/s. In primary liver cell cultures, uptake of bumetanide decreases rapidly over 3 days. AS-30D ascites hepatoma cells do not take up bumetanide but bind small amounts of the loop diuretic. Hepatocytes metabolized bumetanide extensively. The metabolites were secreted into the surrounding incubation buffer. Two hydroxylated and at least one conjugated biotransformation product could be separated by thin-layer chromatography. Isolated rat hepatocytes possess carrier proteins for uptake of bumetanide and very likely also for uptake of other loop diuretics like furosemide, piretanide, and torasemide. Several inhibitors of multispecific transport systems in the kidney and liver were tested as potential inhibitors of hepatocellular bumetanide or furosemide uptake. Probenecid, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, iodipamide, digitoxin, bile acids, and bromosulfophthalein inhibited uptake of loop diuretics. Inhibition by taurocholic acid was competitive with a Ki of 24 microM. Taurocholic acid inhibited [3H]bumetanide uptake in the presence but not in the absence of Na+. Deoxycholic acid and bromosulfophthalein were noncompetitive inhibitors of hepatocellular bumetanide uptake.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of Yersinia enterocolitica on intestinal mucin secretion
Authors: Mantle M. , Thakore E. , Hardin J. , Gall D. G.
Published: December 2017

Mucin and glycoprotein synthesis and secretion were evaluated in the upper, mid, and distal small intestine and in the proximal colon of rabbits infected with Yersinia enterocolitica (YE). Infected (INF) animals were examined on day 6 and compared with pair-fed controls and unmanipulated weight-matched rabbits. Tissue mucin content in vivo and mucin secretion in vitro, measured by a specific immunoassay, were significantly elevated in all four regions of the gut of INF rabbits compared with both control groups. In vitro secretion of stored glycoprotein, prelabeled with [3H]glucosamine, was not increased in the upper and mid small intestine of INF animals but was significantly elevated in the distal small intestine and proximal colon. In vitro incorporation of [14C]glucosamine was increased in all four regions of the gut of INF rabbits, but secretion of newly synthesized [14C]glycoprotein was only significantly elevated in the distal small intestine and proximal colon. A graded response was observed down the intestinal tract of INF rabbits, with the greatest increase in mucin content, synthesis and secretion occurring in the distal small intestine and proximal colon where the morphological impact of disease is also most severe.
Stimulation of oxygen uptake by glucagon is oxygen dependent in perfused rat liver
Authors: Kizaki Z. , Thurman R. G.
Published: December 2017

Livers from well-fed female Sprague-Dawley rats (100-150 g) were perfused at flow rates of 4 or 8 ml.g liver-1.min-1 to deliver O2 to the organ at various rates. During perfusion at normal flow rates (4 ml.g-1.min-1), glucagon (10 nM) increased O2 uptake in perfused liver by approximately 40 mumol.g-1.h-1. In contrast, glucagon increased O2 uptake by nearly 100 mumol.g-1.h-1 when livers were perfused at high flow rates. Increase in O2 uptake was directly proportional to flow rate and was blocked partially by infusion of phorbol myristate acetate (100 nM) before glucagon. Increase in O2 uptake due to elevated flow was not due to enhanced glucagon delivery, since infusion of 120 nM glucagon at normal flow rates only increased O2 uptake by approximately 40 mumol.g-1.h-1. On the other hand, when O2 tension in the perfusate was manipulated at normal flow rates, the stimulation of O2 uptake by glucagon increased proportional to the average O2 tension in the liver. Infusion of 8-bromo-adenosine 3',5'-cyclic monophosphate (BrcAMP; 25 microM) also increased O2 uptake more than twice as much at high compared with normal flow rates. In the presence of angiotensin II (5 nM), a hormone that increases intracellular calcium, glucagon increased O2 uptake by nearly 100 mumol.g-1.h-1 at normal flow rates. Infusion of glucagon or BrcAMP into livers perfused at normal flow rates increased state 3 rates of O2 uptake of subsequently isolated mitochondria significantly by approximately 25%. In contrast, perfusion with glucagon or BrcAMP at high flow rates increased mitochondrial respiration by 50-60%. Glucagon addition acutely to suspensions of mitochondria, however, had no effect on O2 uptake. These data are consistent with reports that glucagon administration in vivo or treatment of intact cells with glucagon increases O2 uptake of subsequently isolated mitochondria, a phenomenon that can account for the observed increase in O2 uptake in livers perfused at high flow rates with glucagon. Furthermore, these results are consistent with the hypothesis that the effect of glucagon on mitochondria is O2 dependent in the perfused liver. This is most likely due to an effect of intracellular calcium on a mechanism mediated via cAMP.(ABSTRACT TRUNCATED AT 250 WORDS)
Atrial natriuretic factor binding sites in the jejunum
Authors: Bianchi C. , Thibault G. , De Lean A. , Genest J. , Cantin M.
Published: December 2017

We have studied the localization and the characterization of atrial natriuretic factor (ANF) binding sites by radioautographic techniques. Quantitative in vitro radioautography with a computerized microdensitometer demonstrated the presence of high-affinity, low-capacity 125I-ANF-(99-126) binding sites (Kd, 48 pM; Bmax, 63 fmol/mg protein) mainly in the villi of 20-microns slide-mounted transverse sections of the rat jejunum. Competition curves showed 50% inhibitory concentrations of 55 and 1,560 pM for ANF-(99-126) and ANF-(103-123), respectively. In vivo electron microscope radioautography showed that 80% of the silver grains were localized on the lamina propria fibroblast-like cells, 18% on mature enterocytes, and 2% on capillaries. Bradykinin and adrenocorticotropin did not compete with ANF binding. These results demonstrate that ANF binding sites in the rat jejunum possess the pharmacological characteristics of functional ANF receptors encountered in other rat tissues, and ultrastructural radioautographs show their cellular distribution. Taken together, these results demonstrate the presence and the localization of specific binding sites for ANF in the jejunal villi of the rat small intestine.
Peripheral reflex pathways involving abdominal viscera: transmission of impulses through prevertebral ganglia
Authors: King B. F. , Szurszewski J. H.
Published: December 2017

In neurophysiological terms, divergence describes the transmission of impulse traffic from a single afferent line, through an integrating nervous system, and out into multiple efferent lines. This feature has been ascribed to the vertebrate central nervous system and invertebrate ganglionic systems but has not yet been associated with the autonomic nervous system in mammals. Therefore, this study investigated the degree of divergence of afferent impulse traffic through a mammalian autonomic ganglion, the inferior mesenteric ganglion (IMG) in guinea pig. Multiunit discharges were recorded extracellularly from the peripheral nerves, which emerge from the IMG, to determine the lines of efferent outflow (i.e., divergence) of impulse traffic generated by stimulating central efferent and peripheral afferent nerves. Pathways interrupted by a cholinergic ganglion synapse were identified by using hexamethonium. Pathways running directly through the IMG were identified by studying the effects of dividing nerves surgically. A complex arrangement of ascending and descending pathways was revealed, showing a neural network that interconnects the upper gastrointestinal tract, distal colon, and pelvic viscera via prevertebral ganglia.
Cross-linking of neuropeptide Y to its receptor on rat brain membranes
Authors: Mannon P. J. , Taylor I. L. , Kaiser L. M. , Nguyen T. D.
Published: December 2017

The receptor for neuropeptide Y (NPY) was identified on rat brain membranes after covalent labeling with 125I-NPY using the homobifunctional cross-linkers disuccinimido suberate and disuccinimido dithiobis(propionate) and the heterobifunctional photoactive cross-linker succinimido 4-azidobenzoate. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by autoradiography revealed the presence of two bands at Mr 62,000 and 39,000. Both species showed the same high affinity for 125I-NPY. Exposure to reducing agents did not change the migration of these bands. When the NPY receptor complex was solubilized from the membranes with 1% Triton X-100 and analyzed by gel filtration chromatography, it eluted from a Fractogel TSK 55F column as a peak at approximately 65 kDa. This peak was asymmetric with a shoulder of radioactivity that probably reflects the smaller receptor species. These data indicate that the NPY receptor on rat brain membranes is a monomeric 58-kDa unit (62 kDa minus the mass of the cross-linked NPY) without covalently or noncovalently linked subunits. The smaller 39-kDa species may be an immature form of the 62-kDa species, a second distinct receptor, or a degradation product of the 62-kDa band.