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Biomedical subjects

A Barber

Publications and source records attributed to A Barber.

At least 37 records · Page 2Linked to original sources

Cytoskeleton involvement on intestinal absorption processes.

It has been recently demonstrated in the laboratory that the cytoskeletal inhibitor cytochalasin E has an indirect inhibitory effect on the function of the intestinal Na+-sugar cotransporter (SGLT1). The present work confirms that cytochalasin E inhibits SGLT1 activity through cytoskeleton disruption, showing that in anaerobic conditions (N2 bubbling), which implies low cytosolic ATP levels, the inhibition is not observed. As it occurs in sugar transport, the Na+-dependent intestinal transport of phenylalanine decreases if cytochalasin E is present in the incubation medium. However, the activity of the brush border enzymes sucrase, amino peptidase N and gamma-glutamyl transferase is not affected by the inhibitor. These enzymes only have one transmembrane domain and the active center is projected to the intestinal lumen. Therefore, cytoskeleton changes that could modify the transmembrane enzyme segment do not alter the activity of these enzymes. Examination of the intestine morphology after 30 min incubation with cytochalasin E shows only light modifications which do not seem to explain the inhibitory effects of the toxin on Na+-sugar or Na+-phenylalanine cotransporters function. On the whole, these results indicate that the inhibition of cytochalasin E on galactose and phenylalanine intestinal transport is secondary to its action on cytoskeleton through protein structure modifications.

Animals↗

Hemeoxygenase expression in human placenta and placental bed implies a role in regulation of trophoblast invasion and placental function.

The purpose of this study was to examine the expression of hemeoxygenases HO-1 and HO-2, which are responsible for the production of carbon monoxide (CO), in the human placenta and placental bed and to determine the role of inhibitors of HO on placental perfusion pressure. We hypothesized that HO is expressed within the placenta and that invading cytotrophoblast cells (CTB) express HO isoforms. The expression of HO-1 and HO-2 was studied on placenta and placental bed biopsies, obtained using a transcervical sampling technique, from normal human pregnancies between 8 and 19 wk gestation and at term. In the placenta, HO-2 immunostaining was prominent in syncytiotrophoblast in the first trimester and reduced toward term (P<0.0005). HO-2 endothelial immunostaining was weak in the first trimester, but increased by term (P<0.0005). Within the placental bed, HO-2 was expressed by CTB in cell columns, the cytotrophoblast shell, and cell islands. Both intravascular CTB and interstitial CTB expressed HO-2. HO-1 immunostaining was low in the placenta but intense on the CTB within the placental bed. A striking feature was the absence of HO-1 from the proximal layers of cell columns, with strong expression on the more distal CTB layers of the cell columns. In placental perfusion studies, a significant dose-dependent increase in perfusion pressure was observed in the presence of zinc protoporphyrin, an inhibitor of HO. These results suggest a role for CO in placental function, trophoblast invasion, and spiral artery transformation. Hemeoxygenase expression in human placenta and placental bed implies a role in regulation of trophoblast invasion and placental function.

Blotting, Western↗

Hemoxygenase and nitric oxide synthase do not maintain human uterine quiescence during pregnancy.

The nitric oxide (NO)-cGMP pathway has been proposed as a mechanism for relaxation of myometrium during pregnancy and as a modulator of labor. Carbon monoxide (CO), produced by hemeoxygenases (HO-1 and HO-2), also activates soluble guanylate cyclase to increase cGMP. A recent study reported a large increase in HO-1 and HO-2 proteins during pregnancy, suggesting that the HO-CO pathway may be important in the maintenance of uterine quiescence during pregnancy. In this study we used Western blotting, reverse transcription-polymerase chain reaction, and immunohistochemistry to determine HO-1 and HO-2 expression in nonpregnant, pregnant, and laboring myometrium. Immunolocalization of HO was also compared with endothelial and inducible nitric oxide synthases (eNOS and iNOS). In contrast to HO-1 protein, which was not detected in myometrium, HO-2 protein and mRNA were constitutively expressed, although there were no differences in expression between the groups. eNOS was expressed in endothelial cells but not in myometrial smooth muscle. iNOS protein was not detected in myometrium. These data do not support an up-regulation of HO-1 and HO-2 during pregnancy and are not consistent with a role for NO or a major role for CO in human myometrial quiescence. Our results are also in keeping with HO-2 being an noninducible protein.

Blotting, Western↗

Attenuating tumor necrosis factor alpha does not ameliorate other cytokine and peroxidase products during sepsis.

BACKGROUND: Recent trials utilizing single anticytokine agents have shown no consistent survival benefit in improving the outcome of sepsis. Since an entire cascade of mediators contributes to the underlying pathophysiology, it is not surprising that monotherapy has proven unsuccessful. The purpose of this study was to measure the effects of attenuating tumor necrosis factor (TNF)alpha early in sepsis. METHODS: Three groups of Sprague-Dawley rats were studied. All animals were infused with live Escherichia coli, with group I and group II rats additionally receiving a matrix metalloproteinase inhibitor. Serum levels of TNFalpha, interleukin (IL)-6, malondialdehyde (MDA), and lipid hydroperoxide (LOOH) were compared. RESULTS: TNFalpha showed a significant decrease, yet IL-6, MDA, and LOOH (markers of sepsis) levels remained abnormally elevated. CONCLUSION: Despite significantly attenuating TNFalpha, the septic response continued. This supports the concept that in sepsis, monotherapy directed at attenuating a single cytokine cannot overcome the tissue-damaging effects of an entire cascade of mediators.

Animals↗

Alterations in carbohydrate and lipid metabolism induced by a diet rich in coconut oil and cholesterol in a rat model.

OBJECTIVE: The type of dietary fat as well as the amount of cholesterol occurring in the diet have been associated with several metabolic disorders. Thus, the aim of the present study was to investigate the influence of a hypercholesterolemic diet enriched with coconut oil and cholesterol on carbohydrate and lipid metabolism in a rat model. METHODS: Twenty male Wistar rats weighing about 190 g were assigned to two dietary groups. One group received a semipurified control diet and the other was given a diet enriched in coconut oil (25% by weight) and cholesterol (1% by weight) for 26 days. RESULTS: Our results indicated a significant increase in serum total cholesterol (+285%; p<0.001), low-density lipoproteins (+154%; p<0.01), liver cholesterol (+1509%; p<0.001), as well as a significant increase in liver weight (+46%; p<0.001) in those rats fed the hypercholesterolemia-inducing diet as compared to controls. Moreover, a significant decrease in serum high-density lipoproteins (-67%; p<0.001), triacylglycerols levels (-33%; p<0.05), and abdominal fat weight (-39%; p<0.01) were found. The observed alterations in serum lipid and lipoprotein profile resembled a situation of type IIa hyperlipidemia in humans. Measurement of several enzymes concerned with lipid utilization revealed a significant increase in 3-hydroxy-3-methylglutaryl-CoA reductase activity (+68%; p<0.01) in the liver of animals fed the hypercholesterolemic diet, while a significant reduction in plasma lecithin-cholesterol acyltransferase activity (-66%; p<0.001) was found. The situation of hypoglycemia (-18%; p<0.05) was accompanied by lower levels of serum insulin (-45%; p<0.01) and liver glycogen (-30%; p<0.05) in the hypercholesterolemic rats. Furthermore, glucose utilization was altered since lower glucose-6-Pase (-33%; p<0.05) and increased glucokinase (+212%; p<0.001) activities in the liver were found in the rat model of hypercholesterolemia. CONCLUSION: These results provide new evidence that a diet-induced hypercholesterolemia in rats is associated with several adaptative changes in carbohydrate metabolism. These findings may be of importance not only considering the role of western diets on cholesterogenesis, but also in other metabolic disturbances involving lipid and carbohydrate metabolism.

Animals↗

Effects of GR-89696 and the novel peripherally selective OP2 agonists, EMD-61569 and EMD-61747, against focal cerebral ischemia in the rat.

We examined whether increases in blood-brain barrier (BBB) permeability occurring after stroke can be exploited to apply protective substances selectively to ischemic tissue. To do this, the actions of the peripherally selective OP2 agonists, EMD-61569 and EMD-61747, have been compared with those of the centrally acting OP2 agonist, GR-89696, in the rat permanent focal ischemia model. EMD-61569, EMD-61747 and GR-89696 all bound with high affinity to OP2 receptors and were potent agonists in the rabbit vas deferens functional assay. These substances also potently inhibited electrically-induced overflow of dopamine from slices of rat nucleus accumbens. EMD-61747 and EMD-61569 penetrate poorly into the CNS under normal conditions and reverse haloperidol-induced L-DOPA accumulation in the nucleus accumbens of the rat only at high doses, in contrast to GR-89696. Permanent unilateral occlusion of the middle cerebral artery (MCAO) was associated with a disruption of the BBB and an increase in the concentration of EMD-61747 in the area of the infarct. GR-89696 at a dose of 0.1 mg/kg s.c. produced a reduction in infarct volume by 38% after MCAO, EMD-61569 and EMD-61747 had no influence on swelling and ischemic damage. We conclude that EMD-61747 and EMD-61569 are potent OP2 agonists, which usually have a limited ability to penetrate the BBB. The change in the properties of the BBB in ischemic tissue was not sufficient to elicit neuroprotection, since both EMD-61747 and EMD-61569 were inactive in the focal ischemia model. Conversely, GR-89696 had a robust protective action, and probably powerful OP2-typical side effects as a consequence of its unrestricted central activity.

Animals↗

CCK-mediated response in the activation of 5-HT receptor types in the guinea-pig ileum.

The possible interaction between cholecystokinin (CCK) and 5-hydroxytryptamine (5-HT) was evaluated in vitro in the longitudinal muscle-myenteric plexus of the guinea-pig ileum. Devazepide and L-365,260 were used to block CCKA and CCK(B) receptors and ondansetron and tropisetron to block 5-HT3 and 5-HT4 receptors, respectively. The CCK receptor antagonists blocked, in a dose-dependent manner, the response to 5-HT and to the selective agonists at 5-HT3 and 5-HT4 receptors, 2-methyl-5-hydroxytryptamine (2-Me-5-HT) and 5-methoxytryptamine (5-MeOT), respectively. The blockade was almost complete on the first phase of the concentration response curve to 5-HT and for all the concentrations of 5-MeOT tested. In the 2-Me-5-HT-induced contractile response there was a component with the same sensitivity to devazepide and to the selective NK1 receptor antagonist, GR 82334, and another resistant component that was abolished by atropine. However, the blockade of the NK1 receptor did not produce a significant increase in the inhibition obtained when atropine or devazepide were separately tested on the 5-MeOT-induced response. These results suggest that CCK is involved in the 5-HT-induced contractile response, particularly in the response induced by 5-HT4 receptor stimulation.

Animals↗

Galactose transport inhibition by cytochalasin E in rat intestine in vitro.

Cytochalasins are cytoskeleton disrupters, and cytochalasin E has been reported to increase intestinal paracellular permeability. In this study, the cytochalasin E effect on galactose transport has been investigated. Ussing-type chamber experiments show an inhibitory effect of 20 microM cytochalasin E on unidirectional mucosal to serosal flux of galactose. On the contrary, the opposite unidirectional flux is not modified by the inhibitor. Results using intestinal everted sacs and rings confirm that galactose uptake by the tissue is diminished by cytochalasin E. The effect appears already after 5 min incubation, depends on cytochalasin E concentration, and does not occur in the absence of Na+. The inhibition is accompanied by an increase in the apparent K(m) of the active sugar transport (11.5 vs.15.8 mM) without significant change in the VmaX (10.6 vs. 9.1 micromol x g(-1) wet weight x 5 min(-1)). Cytochalasin E does not modify either galactose uptake by brush border membrane vesicles or Na(+)-K(+) ATPase activity in the enterocytes, indicating that the inhibitory effect on the Na(+)-dependent sugar transport cannot be explained as a direct effect on SGLT1 activity or as an indirect effect through the Na(+)-K(+) ATPase. Thus, our results suggest that cytochalasin E decreases SGLTI activity indirectly through cytoskeleton disruption.

Animals↗

Presence of leptin receptors in rat small intestine and leptin effect on sugar absorption.

Leptin is involved in food intake and thermogenesis regulation. Since leptin receptor expression has been found in several tissues including small intestine, a possible role of leptin in sugar absorption by the intestine was investigated. Leptin inhibited D-galactose uptake by rat small intestinal rings 33% after 5 min of incubation. The inhibition increased to 56% after 30 min. However, neither at 5 min nor at 30 min did leptin prevent intracellular galactose accumulation. This leptin effect was accompanied by a decrease of the active sugar transport apparent Vmax (20 vs. 4.8 micromol/g wet weight 5 min) and apparent Km (15.8 vs. 5.3 mM) without any change in the phlorizin-resistant component. On the other hand, immunohistochemical experiments using anti-leptin monoclonal antibodies recognized leptin receptors in the plasma membrane of immune cells located in the lamina propria. These results indicate for the first time that leptin has a rapid inhibitory effect on sugar absorption and demonstrate the presence of leptin receptors in the intestinal mucosa.

Animals↗

Effect of different beta-adrenergic agonists on the intestinal absorption of galactose and phenylalanine.

Nutrient transport across the mammalian small intestine is regulated by several factors, including intrinsic and extrinsic neural pathways, paracrine modulators, circulating hormones and luminal agents. Because beta-adrenoceptors seem to regulate gastrointestinal functions such as bicarbonate and acid secretion, intestinal motility and gastrointestinal mucosal blood flow, we have investigated the effects of different beta-adrenergic agonists on nutrient absorption by the rat jejunum in-vitro. When intestinal everted sacs were used the beta2-agonist salbutamol had no effect either on galactose uptake by the tissue or mucosal-to-serosal flux whereas mixed beta1- and beta2-agonists (isoproterenol and orciprenaline) and beta3-agonists (BRL 35135, Trecadrine, ICI 198157 and ZD 7114) inhibited galactose uptake and transfer of D-galactose from the mucosal-to-serosal media across the intestinal wall (although the inhibiting effects of isoproterenol and Trecadrine were not statistically significant). In intestinal everted rings both Trecadrine and BRL 35135 clearly reduced galactose uptake, the effect being a result of inhibition of the phlorizin-sensitive component. Total uptake of phenylalanine by the intestinal rings was also reduced by those beta3-adrenergic agonists. These results suggest that beta1- and beta3-adrenergic receptors could be involved in the regulation of intestinal active transport of sugars and amino acids.

Adrenergic beta-Agonists↗

Functional expression of the rabbit intestinal Na+/L-proline cotransporter (IMINO system) in Xenopus laevis oocytes.

Proline absorption across small intestine takes place mainly through a Na+-dependent cotransporter localized at the brush border membrane of the enterocyte named IMINO system. It transports L-proline and 4-OH-proline but not L-alanine, neither cationic nor anionic amino acids. The present work demonstrates the functional expression of this transporter in Xenopus laevis oocytes by mRNA microinjection and radiotracer uptake techniques. Poly (A)+-RNA was isolated from rabbit jejunal mucosa and injected into oocytes. Five days after the injection, results showed 1.5 fold stimulation of 50 microM 3H-proline uptake by the injected oocytes when compared to the non injected oocytes uptake. Poly (A)+-RNA was sized fractionated and fractions were injected again. Increase on Na+-dependent L-proline uptake was obtained with a mRNA fraction between 2,4 and 4,4 kb, which was used to construct a cDNA library. The library was sequentially divided and cRNAs injected into oocytes in order to screen for an increment on the signal. A subdivision containing around 2,000 colonies was found to augment L-proline uptake 25 fold over the non injected oocytes uptake. This cRNA pool was used to further characterize the transporter. Results showed that in the absence of Na+ there was no L-proline uptake, 2 mM 4-OH-L-proline completely inhibited 50 microM proline uptake and there was no 50 microM alanine uptake. In summary, these results demonstrate the expression of the rabbit small intestine IMINO transporter in Xenopus laevis oocytes and support the next steps in the isolation of the clone.

Alanine↗

Synthesis and stereochemical structure-activity relationships of 1,3-dioxoperhydropyrido[1,2-c]pyrimidine derivatives: potent and selective cholecystokinin-A receptor antagonists.

The synthesis and stereochemical structure--activity relationships of a new class of potent and selective non-peptide cholecystokinin-A (CCK-A) receptor antagonists based on the 1,3-dioxoperhydropyrido[1,2-c]pyrimidine skeleton are described. The most potent member of this series of eight diastereoisomers, (4aS,5R)-2-benzyl-5-[N-[(tert-butoxycarbonyl)-L-tryptophyl]-amino] - 1,3-dioxoperhydropyrido[1,2-c]pyrimidine, displays nanomolar CCK-A receptor affinity and higher than 8000-fold potency at the CCK-A than at the CCK-B receptor. As CCK-A antagonist, this compound inhibits the CCK-8-evoked amylase release from pancreatic acinar cells at a low concentration, similar to that of the typical antagonist Devazepide. Highly strict stereochemical requirements for CCK-A receptor binding and selectivity have been found. The L-Trp and the 4a,5-trans disposition of the bicyclic perhydropyrido[1,2-c]pyrimidine are essential for binding potency and selectivity.

Amylases↗

Pharmacological evaluation of IQM-95,333, a highly selective CCKA receptor antagonist with anxiolytic-like activity in animal models.

1. The pyridopyrimidine derivative IQM-95,333 ((4aS,5R)-2-benzyl-5-[N alpha-tert-butoxicarbonyl)L-tryptophyl] amino-1,3dioxoperhydropyrido[1,2-c]pyrimidine), a new non-peptide antagonist of cholecystokinin type A (CCKA) receptors, has been evaluated in vitro and in vivo in comparison with typical CCKA and CCKB receptor antagonists, such as devazepide, lorglumide, L-365,260 and PD-135,158. 2. IQM-95,333 displaced [3H]-CCK-8S binding to CCKA receptors from rat pancreas with a high potency in the nanomolar range. Conversely, the affinity of this new compound at brain CCKB receptors was negligible (IC50 > 10 microM). IQM-95,333 was a more selective CCKA receptor ligand than devazepide and other CCKA receptor antagonists. 3. Like devazepide, IQM-95,333 was a more potent antagonist of CCK-8S- than of CCK-4-induced contraction of the longitudinal muscle from guinea-pig ileum, suggesting selective antagonism at CCKA receptors. 4. IQM-95,333 and devazepide were also potent inhibitors of CCK-8S-stimulated amylase release from isolated pancreatic acini, a CCKA receptor-mediated effect. The drug concentrations required (IC50s around 20 nM) were higher than in binding studies to pancreas homogenates. 5. Low doses (50-100 micrograms kg-1, i.p.) of IQM-95,333 and devazepide, without any intrinsic effect on food intake or locomotion, blocked the hypophagia and the hypolocomotion induced by systemic administration of CCK-8S, two effects associated with stimulation of peripheral CCKA receptors. 6. IQM-95,333 showed an anxiolytic-like profile in the light/dark exploration test in mice over a wide dose range (10-5,000 micrograms kg-1). Typical CCKA and CCKB antagonists, devazepide and L-365,260 respectively, were only effective within a more limited dose range. 7. In a classical conflict paradigm for the study of anxiolytic drugs, the punished-drinking test, IQM-95,333, devazepide and L-365,260 were effective within a narrow dose range. The dose-response curve for the three drugs was biphasic, suggesting that other mechanisms are operative at higher doses. 8. In conclusion, IQM-95,333 is a potent and selective CCKA receptor antagonist both in vitro and in vivo with an anxiolytic-like activity in two different animal models, which can only be attributed to blockade of this CCK receptor subtype.

Amylases↗

Effects of trecadrine, a beta 3-adrenergic agonist, on intestinal absorption of D-galactose and disaccharidase activities in three physiopathological models.

Impairments in intestinal absorptive and digestive processes have been described in several pathophysiological situations, such as in drug-induced diabetes, obesity and hypercholesterolaemia. Furthermore, there is evidence for the occurrence of beta 3-adrenoceptors in multiple regions of the gastrointestinal tract, but there are no data concerning their possible involvement on jejunal and ileal digestive and absorptive functions. In this work, we have measured the modifications of selective intestinal absorption and disaccharidase activities in alloxan-induced diabetic and in diet-induced obese and hypercholesterolaemic Wistar rats. The action of a beta 3-adrenergic agonist (Trecadrine) with hypoglycaemic and lipolytic properties on those gastrointestinal functions has been studied. Increases in the galactose uptake by intestinal rings and in both sucrase and maltase activities were found in diabetic rats. The results obtained after Trecadrine administration to diabetic rats led to an improvement of the altered values. On the other hand, our data show a decrease in sugar absorption and in disaccharidase activities in both obese and hypercholesterolaemic groups, probably related to the low carbohydrate and high fat content of these diets. An amelioration in sucrase activity was observed after treatment with Trecadrine. Finally, Trecadrine administration to control animals significantly inhibited galactose intestinal absorption, which was independently confirmed by additional in-vitro studies. Overall, these results could be attributed not only to an improvement in the pathophysiological condition (diabetes, obesity and hypercholesterolaemia), but also to a direct effect of the beta 3-adrenergic agonist on the intestinal absorption processes.

Adrenergic beta-Agonists↗

Novel developments with selective, non-peptidic kappa-opioid receptor agonists.

Despite the recent introduction of a number of new compounds, there has of late been a cooling of interest by pharmaceutical companies in the development of centrally-active, selective kappa opioid agonists for therapeutic purposes. This is reflected in the discontinuation of a number of clinical trials, for reasons that are often not completely clear to outside observers. Spiradoline and enadoline have apparently been abandoned as potential analgesics because they induce dose-limiting central side-effects (i.e., dysphoria) in models of post-surgical pain. The development of niravoline as an aquaretic for the treatment of cirrhosis with ascites and other hyponatraemic disorders has also been halted. Enadoline may yet find some application against ischaemic stroke and severe head injury, presumably in comatose patients in whom psychiatric side-effects are taken to be immaterial, while apadoline and TRK 820 remain in Phase II clinical testing against cancer pain. The peripherally-selective kappa agonists, asimadoline, and the atypical compound, fedotozine, are well-tolerated in man. Results of Phase III trials of fedotozine against irritable bowel syndrome and dyspepsia have, however, ultimately been disappointing, whereas asimadoline is currently in Phase II clinical trials against pain of rheumatic and osteoarthritic origin. The results of these trials are eagerly awaited.

Journal Article↗

Modulation of intestinal paracellular permeability by intracellular mediators and cytoskeleton.

The influence of cytoskeletal inhibitors (cytochalasin E and colchicine) and intracellular mediators (cAMP, Ca2+, and protein kinase C) in the control of paracellular permeability to mannitol has been examined in rat jejunum in Ussing-type chambers. Cytoskeletal inhibitors, cytochalasin E (20 mumol.L-1) or colchicine (0.5 mmol.L-1), when present in mucosal, serosal, or in both mediums, significantly increase unidirectional mannitol fluxes. Exposure of mucosal and serosal intestinal surface to 10 mmol.L-1 theophylline or 1 mmol.L-1 cyclic AMP analogue for raising the intracellular cAMP enhances paracellular permeability. In Ca(2+)-free physiological medium passive permeability strongly increases. Alterations of cytosolic Ca2+ levels induced by the Ca2+ ionophore A23187 (20 mumol.L-1) or by 0.3 mmol.L-1 TMB-8, a Ca2+ releasing inhibitor from the intracellular stores, enhance mannitol flux. Addition of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate, which activates protein kinase C (PKC), also induces a large increase in the intestinal permeability to mannitol. These results provide evidence that tight junctions and consequently epithelial paracellular permeability can be physiologically controlled by intracellular mediators (Ca2+, cAMP, and PKC) probably through modulation of the cytoskeleton activity.

Animals↗

Some technical precisions to a method for in vivo intestinal absorption studies.

Some modifications to the method of PONZ et al. for in vivo intestinal absorption studies using an in situ perfused segment of small intestine, under anesthesia, are described. They improve its accuracy and applicability, especially when slowly absorbed substrates are used or when volume flux measurements are desired. Calculations for the absorbed substrate and net fluid volume change determinations are reported. Several aspects of the use of the method under a single pass or a recirculation perfusion system are discussed.

Animals↗

Acute mediastinitis secondary to leakage of parenteral nutrition from a migrated central venous catheter in a patient undergoing autologous bone marrow transplant.

We describe an unusual case of pyrexia of unknown origin in a patient undergoing autologous bone marrow transplantation for metastatic breast cancer. The fever was due to extravasation of lipid-containing hyperalimentation fluid from a migrated central venous catheter into the mediastinum, resulting in mediastinitis and pleurisy. The fever persisted despite broad-spectrum antibiotics and amphotericin B, and finally responded to steroids.

Acute Disease↗