Biomedical subjects
E Beubler
Publications and source records attributed to E Beubler.
Cholera toxin induces prostaglandin synthesis via post-transcriptional activation of cyclooxygenase-2 in the rat jejunum.
The mechanisms of diarrhea in Asiatic cholera have been studied extensively. Cyclic AMP, 5-hydroxytryptamine, prostaglandins, and the function of neuronal structures have been implicated in the pathogenesis of cholera. To elucidate the role of the different isoforms (COX-1 and COX-2) of cyclooxygenase in cholera toxin (CT)-induced fluid secretion and intraluminal prostaglandin E(2) (PGE(2)) release in the rat jejunum in vivo, the effects of the COX-2 inhibitors NS-398 ([N-(2-cyclohexaloxy-4-nitrophenyl)methanesulfonamide]) and DFU [5,5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulfonyl)phenyl-2(5H)-furanone], and of the COX-1 inhibitor SC-560, were studied. Net fluid transport was measured gravimetrically and PGE(2) by radioimmunoassay. COX-1 and COX-2 mRNA expression were determined by reverse transcription-polymerase chain reaction (RT-PCR) and COX-2 protein by Western blot analysis in mucosal scrapings. CT caused profuse net fluid secretion in all control rats. The COX-2 inhibitors NS-398 and DFU, but not the COX-1 inhibitor SC-560 or dexamethasone, dose-dependently inhibited CT-induced fluid secretion and PGE(2) release. RT-PCR showed expression of COX-1 and of COX-2 mRNA in control rats. CT did not induce an increase and dexamethasone did not reduce COX-2 mRNA, whereas lipopolysaccharide caused a marked induction of COX-2 mRNA, which was inhibited by dexamethasone. A weak band of COX-2 protein was observed in controls; however, CT enhanced COX-2 levels, which remained unaffected by dexamethasone. It can be assumed that post-transcriptional modulation is responsible for CT-induced increase in COX-2 protein. COX-1 does not seem to be involved. Therefore, PGE(2) produced by COX-2 seems to be responsible for the profuse fluid secretion induced by CT, and COX-2 appears to be a specific target for the treatment of Asiatic cholera.
Mechanisms of cholera toxin-induced diarrhea.
In the pathogenesis of cholera, cyclic adenosine monophosphate, 5-hydroxytryptamine, prostaglandins, and the function of neuronal structures have been implicated. To elucidate the role of different isoforms of cyclooxygenase (COX)-1 and COX-2, selective COX-2 inhibitors were used. The selective COX-2 inhibitors NS-398 and DFU completely suppressed cholera toxin-induced prostaglandin E2 biosynthesis and caused a dose-dependent inhibition of cholera toxin-induced fluid secretion in the rat jejunum in vivo. Constitutive expression of COX-1 but also of COX-2 mRNA was found in mucosal scrapings of the rat jejunum. Cholera toxin had no effect on COX-1 as well as COX-2 mRNA expression. Treatment of rats with dexamethasone did not effect cholera toxin-induced prostaglandin E2 biosynthesis and did not influence the expression of COX-2 mRNA, further substantiating that cholera toxin does not cause an induction of COX-2 mRNA. Treatment of rats with E. coli lipopolysaccharide caused a marked increase in COX-2 mRNA expression that was inhibited by dexamethasone. In conclusion, the results provide evidence that cholera toxin, in addition to other mediators, uses prostaglandin E2 to exert its secretory effect and that in the case of cholera toxin prostaglandins are metabolized via COX-2.
[Pain can and must be treated].
Explore the source record for details and available documents.
Nitric oxide counteracts 5-hydroxytryptamine- and cholera toxin-induced fluid secretion and enhances the effect of oral rehydration solution.
The effects of pharmacological modulation of the nitric oxide (NO) pathway on intestinal fluid transport were studied in a model of ligated jejunal loops of anaesthetized rats in vivo. Close intraarterial infusion of 5-hydroxytryptamine (5-HT) (0.16 microg/min) induced net fluid secretion. Intravenous infusion of the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) (0.55 mg/kg per min) reversed net fluid absorption in controls to net secretion and significantly enhanced 5-HT-induced fluid secretion. 5-HT-induced net fluid secretion was inhibited by intravenous infusion of L-arginine (8.88 mg/kg per min), sodium nitroprusside (22.2 microg/kg per min), or 3-morpholino sydnonimine (SIN-1) (22.2 microg/kg per min). Intraluminal instillation of cholera toxin (0.5 microg/ml) induced net secretion, which was significantly enhanced by L-NAME and reduced by L-arginine. Another series of experiments was performed using a model of luminally perfused jejunal loops. Cholera toxin (10 microg/ml) induced profuse net fluid secretion also in this model. L-Arginine and sodium nitroprusside significantly enhanced net fluid absorption compared to controls and abolished the secretory effect of cholera toxin. Luminal perfusion with oral rehydration solution enhanced net absorption of fluid in controls and reversed cholera toxin-induced secretion to absorption. Intravenous infusion, but not intraluminal administration, of L-arginine significantly enhanced the antisecretory effect of oral rehydration solution. These results give further support to the existence of an intestinal NO-mediated proabsorptive tone, which also downregulates fluid secretion elicited by different enterotoxins or mediators of secretion. Intravenous administration of exogenous sources of NO counteracts intestinal fluid accumulation and augments the antisecretory effect of oral rehydration solution, findings which may lead to therapeutic consequences.
Involvement of K+ channel modulation in the proabsorptive effect of nitric oxide in the rat jejunum in vivo.
The role of K+ channels in the mediation of the nitric oxide(NO)-induced proabsorptive effect in intestinal fluid transport was investigated in a functional study, using a model of ligated jejunal loops of anaesthetized rats in vivo. The K+ channel opener cromakalim and the K+ channel blocker glibenclamide were administered under basal conditions as well as under conditions, when fluid secretion was influenced by N omega-nitro-L-arginine methyl ester (L-NAME), prostaglandin E2, Escherichia coli heat stable enterotoxin a (E. coli STa) or L-arginine. Intravenous infusion of cromakalim (63.5 micrograms/kg per min) significantly enhanced net fluid absorption compared to controls, totally abolished net fluid secretion induced by L-NAME (0.55 mg/kg per min), reversed net fluid secretion induced by intraluminal instillation of E. coli STa (10 units/ml) to absorption, but did not influence fluid secretion elicited by close i.a. infusion of prostaglandin E2 (79 ng/min). Close i.a. infusion of glibenclamide (0.16 mg/kg per min) reversed net fluid absorption to net secretion, blocked the absorptive effect of L-arginine (8.88 mg/kg per min) and reduced the proabsorptive effect of cromakalim. The secretory effect of L-NAME was not further enhanced by glibenclamide. These results suggest that modulation of basolateral K+ channels by NO is involved in the mediation of its proabsorptive effect, since opening and closure of K+ channels mimicked, respectively counteracted, the action of NO-donors and inhibitors of NO-synthesis on intestinal fluid transport. The role of prostaglandins in the proabsorptive effect of NO remains to be elucidated. These results furthermore support the role of K+ channel openers as potential new antidiarrheal drugs.
The effect of alpha-trinositol on cholera toxin-induced hypersecretion and morphological changes in pig jejunum.
alpha-Trinositol (D-myo-inositol 1,2,6-trisphosphate, PP56) is a novel antiinflammatory drug. This study elucidates the effect of intravenous alpha-trinositol on basal and acute fluid transport and morphological changes following cholera toxin administration in pig jejunum in vivo. Using isolated jejunal tied-off loops, the fluid hypersecretory (accumulation) effect of different doses of cholera toxin was studied in pigs treated intravenously with saline added different doses (0, 4, 8, 16 and 32 mg x kg-1 x hr-1) of alpha-trinositol. Levels of alpha-trinositol, as well as stereomicroscopical, light microscopical and scanning electron microscopical morphological studies were performed. Cholera toxin evoked a dose-dependent fluid hypersecretion. Treatment with alpha-trinositol caused a dose-dependent inhibition of the cholera toxin-induced fluid hypersecretion and did not affect basal fluid absorption. The 16 mg x kg-1 x hr-1 alpha-trinositol dose gave a maximal inhibition of 36%. Morphological studies showed only minor changes following 6 hr of exposure to 20 micrograms x loop-1 cholera toxin. These changes consisted of dilation of the villus capillaries, an increase of apical membrane blebbing and a reduction of the intercellular space. Treatment with 16 mg x kg-1 x hr-1 alpha-trinositol alone did not induce any morphological changes, and did not alter the morphological changes induced by cholera toxin, which caused fluid hypersecretion and only minor acute morphological changes. In conclusion, alpha-trinositol treatment reduced cholera toxin-induced fluid hypersecretion without altering basal fluid absorption, basal morphology, or cholera toxin-induced morphological changes in pig jejunum in vivo.
[Bioavailability of morphine after oral administration as retard tablets].
The oral bioavailability of morphine following administration of a single dose of 30 mg morphine hydrochloride as Vendal retard film tablets (Lannacher Heilmittel) was investigated and compared with the bioavailability of morphine following administration of 30 mg morphine sulphate as Mundidol retard film tablets (Mundipharma). A randomized crossover study was conducted in 24 male, healthy volunteers. In 6 of them a pilot study with formulations containing 60 mg was conducted. Morphine and its metabolites were quantitated with an immunofluorimetric solid-phase assay (DELFIA). With regard to the following parameters the novel controlled-release formulation was statistically different from the reference formulation: area under the concentration-time curve, time to maximum and half value duration. After a single dose of the test formulation analgesic serum levels were maintained over a longer lasting period of time than after administration of the reference formulation. The maximal levels in serum and the elimination half life were not different. From the improved pharmacokinetic parameters of the novel controlled-release formulation an improved clinical efficacy can be expected.
Significance of nitric oxide in the stimulation of intestinal fluid absorption in the rat jejunum in vivo.
1. The effects of inhibiting nitric oxide (NO)-synthase on fluid transport, mucosal cyclic GMP and cyclic AMP levels and intraluminal prostaglandin E2 (PGE2)-release were studied in a model of ligated jejunal loops of anaesthetized rats in vivo. Experiments were performed under basal conditions as well as under conditions, when net fluid secretion was induced by Escherichia coli heat stable enterotoxin a (E. coli STa) or PGE2. 2. Intravenous infusion of the NO-synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME, 0.25-50 mg kg-1, 45 min) dose-dependently reversed net fluid absorption to net secretion, whereas infusion of D-NAME, the inactive enantiomer of L-NAME, in corresponding doses did not influence net fluid transport. N omega-nitro-L-arginine (L-NOARG, 25 mg kg-1), another NO-synthase inhibitor, also elicited net secretion of fluid. 3. L-NAME (25 mg kg-1)-induced net fluid secretion was reversed to net absorption by infusion of L-arginine (400 mg kg-1) or sodium nitroprusside (1 mg kg-1) and s.c. administration of indomethacin (10 mg kg-1). Hexamethonium (1 mg kg-1, s.c.), a ganglionic blocker and granisetron (100 micrograms kg-1, s.c.), a 5-HT3-receptor antagonist, did not influence L-NAME-induced net secretion. 4. Net fluid secretion induced by intraluminal instillation of E. coli STa (10 units ml-1) was enhanced by infusion of L-NAME (25 mg kg-1) and was inhibited by infusion of L-arginine (400 mg kg-1) and sodium nitroprusside (1 mg kg-1). D-Arginine (400 mg kg-1) did not influence E. coli STa-induced fluid secretion. Likewise, net fluid secretion induced by i.a. infusion of PGE2 (79 ng ml-1, 30 min) was enhanced by infusion of L-NAME and was inhibited by L-arginine and sodium nitroprusside. D-Arginine(400 mg kg-1) did not influence PGE2-induced fluid secretion.5. PGE2 levels in intraluminal fluid were not elevated after infusion of L-NAME (25mgkg-1) compared to controls.6. Mucosal cyclic GMP and cyclic AMP levels after L-NAME-treatment were not different from control values.7. These results indicate that nitric oxide plays an important role in the regulation of intestinal fluid transport. The data suggest a nitric oxide-dependent proabsorptive tone in the intestine, which possibly involves the enteric nervous system and suppression of prostaglandin formation. This proabsorptive tone also may downregulate fluid secretion induced by E. coli STa or PGE2.
[Migraine: dihydroergotamine nasal spray--an alternative].
Dihydroergotamine (DHE) formerly had to be administered intramuscularly or intravenously to cope with the migraine attack. The introduction of a new regimen, the DHE nasal spray, a new era in the treatment of the migraine attack has started. The patient is independent of his physician and may avoid the painful attack by taking the treatment already during the aura. The speed and thoroughness of the relief from pain are directly proportional to the promptness with which medication is started after the onset of an attack. The recommended dose of intranasally administered DHE is 2 mg, which means two times 0.5 mg into each nostril. The effect of DHE is mediated by its affinity to the 5-HT1D-receptor. DHE furthermore reacts with other 5-HT receptors and with alpha adrenergic receptors. The side effects of DHE given by nasal route are generally mild to moderate and are primarily local ones like nose or throat problems and a bitter or abnormal taste. Nausea and vomiting rarely occur. Side effect of nasal administered DHE may not be mixed up with side effects caused by ergotamine, another ergotalkaloide with a distinct profile of effects.
Effect of 5-hydroxytryptamine antagonists on cholera toxin-induced secretion in the human jejunum.
In rats, the combined administration of the 5-HT2 antagonist ketanserin and the 5-HT3 antagonist tropisetron inhibits cholera toxin-induced intestinal secretion. We investigated whether these agents and the 5-HT3 antagonist ondansetron can inhibit cholera toxin-induced secretion in the human jejunum using a segmental perfusion technique. In a first control period the subjects' jejunums were perfused continuously with a plasma-like electrolyte solution. In a second control period they either received a combination of tropisetron plus ketanserin, or tropisetron or ondansetron alone. Cholera toxin 6.25 micrograms was then administered intrajejunally and the experiments were continued for 4 h. Net water movements during the 4th hour after CT administration minus net water movement during the first control period was used for further calculation and was referred to as net luminal gain. In perfusion studies with tropisetron plus ketanserin resp. ondansetron the net luminal gain of water (+ 161 +/- 26 resp. 189 +/- 28 ml 30 cm-1 h-1, mean +/- SEM) was significantly higher compared to perfusion studies with cholera toxin alone (+ 94 +/- 30). Treatment with tropisetron did not change the CT-induced net luminal gain of water (+ 108 +/- 41). Movements of sodium, chloride, bicarbonate and potassium paralleled the movement of water. In agreement with these observations we found a deterioration of clinical parameters after the end of the perfusion studies in four of five subjects treated with CT 25 micrograms plus ketanserin and tropisetron.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of indomethacin, renzapride, methysergide, ketanserin, granisetron and citalopram on serotonin-induced fluid accumulation in pig jejunum.
The purpose of this study was to elucidate the intestinal serotonin (5-HT) receptor subtypes involved in fluid transport in the pig jejunum in vivo. The fluid accumulating effect of intraluminally administered 5-HT, renzapride, methysergide, ketanserin, granisetron, citalopram and intravenous indomethacin, was tested in tied-off loops in vivo. 5-HT caused a dose-dependent fluid accumulation, which was reduced by indomethacin by about 30%. Renzapride, methysergide, ketanserin, granisetron and citalopram all caused fluid accumulation. Taking into account these fluid accumulating effects, renzapride, methysergide, ketanserin and granisetron reduced the fluid accumulating effect of 5-HT, giving a maximal reduction of 70, 46, 76, and 80%, respectively. These data suggest the existence of intestinal 5-HT receptor subtypes involved in fluid transport in the pig jejunum. The antagonistic effects of indomethacin, ketanserin and granisetron, suggest the involvement of prostaglandins, as well as the 5-HT2 and the 5-HT3 receptor subtypes in the fluid accumulating response of 5-HT.
[Pharmacotherapy of headache with special reference to migraine].
Drug therapy is only one possibility to treat headache or migraine. In a migraine attack aspirin, acetaminophen, non-steroidal antiinflammatory drugs like ibuprofen, naproxen and mefenamic acid are used. Further more weak opiates, caffeine, metoclopramide and the new 5-HT1-receptor agonist sumatriptan are effective in the attack. Ergotamine and dihydroergotamine are probably the most effective though their side effects are troublesome. For prophylactic treatment, the beta-adrenergic receptor blockers propranolol, metoprolol and atenolol are the drugs of first choice. Also calcium channel antagonists like flunaricine and antidepressant drugs like amitryptiline and doxepine are used.
Inhibition of 5-hydroxytryptamine- and enterotoxin-induced fluid secretion by 5-HT receptor antagonists in the rat jejunum.
The effects of cholera toxin and heat stable Escherichia coli (E. coli) enterotoxin on intestinal fluid secretion are commonly considered to be mediated by cyclic nucleotides. It was demonstrated recently, by using the 5-hydroxytryptamine (5-HT)2 receptor antagonist ketanserin and the 5-HT3 receptor antagonist tropisetron, that 5-HT acts as an important mediator in cholera toxin- and heat stable E. coli enterotoxin-induced fluid secretion. In the present investigation ketanserin and tropisetron were compared with the newer 5-HT3 receptor antagonists ondansetron and granisetron versus 5-HT-, cholera toxin- and heat stable E. coli enterotoxin-induced fluid secretion in the rat jejunum in vivo. Both ondansetron and granisetron dose-dependently inhibited 5-HT- and enterotoxin-induced fluid secretion. Ketanserin blocked 5-HT-induced fluid secretion, but only diminished enterotoxin-induced effects even at higher doses. Tropisetron inhibited 5-HT- and cholera toxin-induced effects at high dose but only diminished heat stable E. coli enterotoxin-induced effects. We conclude that 5-HT3 receptors, located on enterochromaffin cells and nervous structures, are more important in mediating fluid secretion than 5-HT2 receptors, located on the epithelial cells.
Effects of purified Clostridium difficile toxin A in the small intestine of the rat in vivo.
The action of highly purified Clostridium difficile toxin A was studied in the jejunum of rats in vivo. C. difficile toxin A reversed dose-dependently net fluid absorption into net fluid secretion, accompanied by an increase in prostaglandin E2 but not 5-hydroxytryptamine output into the gut lumen. Accordingly, indomethacin but not the 5-hydroxytryptamine receptor antagonists ketanserin plus tropisetron were able to inhibit toxin A-induced fluid secretion. Atropine and hexamethonium were without effect on the action of toxin A, such excluding a nervous mechanism. The cyclic nucleotides cyclic AMP and cyclic GMP appear not to be involved in the mediation of the secretory response. The reduced cyclic GMP levels are most likely the result of a complete destruction of the villus membranes, where the guanylate cyclase is located. Histological studies revealed massive damage to intestinal villi, whereas the majority of the crypts seem to be unaffected. In conclusion, toxin A-induced intestinal fluid secretion appears to be caused mainly by severe mucosal damage. PGE2-release may be the consequence of the inflammation accompanying this damage. The mechanism seems to be completely different to those of cholera toxin or Escherichia coli heat stable enterotoxin.
Stimulation of enterocyte protein kinase C by laxatives in-vitro.
To elucidate the role of protein kinase C in the mechanism of action of stimulatory laxatives, experiments were performed with preparations of rat lysed enterocytes. The phorbol ester 4-beta-phorbol 12-myristate 13-acetate (PMA) concentration-dependently (2-200 micrograms mL-1) stimulated the activity of protein kinase C in this preparation. Ricinoleic acid, the active principle of castor oil, deacetylbisacodyl, the active principle of bisacodyl, and deoxycholic acid exerted the same effect, although less efficiently. This reflects their potency for inducing intestinal fluid secretion and prostaglandin release, effects that are also induced more potently by PMA. Accordingly, the potency of the three C18 fatty acids, ricinoleic acid, stearic acid and oleic acid on protein kinase C activity in-vitro, on prostaglandin E2 release and on net fluid secretion in-vivo runs in parallel. It is therefore concluded that stimulatory laxatives activate protein kinase C, leading to prostaglandin E2 release, thus resulting in net fluid secretion.
Antisecretory activities of orally administered loperamide and loperamide oxide on intestinal secretion in rats.
In-vivo experiments in the rat jejunum have been performed to compare the antisecretory effect of orally administered loperamide with the effect of its pro-drug, loperamide oxide. Both loperamide and loperamide oxide, administered orally, reduced the secretory effect of prostaglandin E2 (32 ng min-1, intra-arterially) in the jejunum and the colon. Differences between the two drugs as to time course and dose response can be seen. Loperamide oxide shows its antisecretory effect in the jejunum, and at a dose of 2 mg kg-1 also shows its effect in the colon 1 h after administration. The effect was maximal after 2 h and decreased after 4 h. A dose-response relationship was demonstrated at 2 h in the jejunum and the colon. In comparison, the effect of loperamide started later, and a good dose-response relationship was not observed in the jejunum or in the colon, higher doses always appearing less effective than lower doses.
Serotonin antagonists inhibit sennoside-induced fluid secretion and diarrhea.
The aim of this study was to investigate whether 5-hydroxytryptamine (serotonin, 5-HT) is involved in the mediation of sennoside-induced colonic fluid secretion and diarrhea. Oral administration of purified sennosides (25, 40 and 64 mg/kg) dose-dependently reversed net fluid absorption to net fluid secretion, enhanced the incidence of diarrhea and stimulated the release of 5-HT into the colonic lumen from 7.1 to 17.3 ng/g wet weight. The 5-HT2 antagonist ketanserin and the 5-HT3 antagonist tropisetron dose-dependently but only partially reduced sennoside (40 mg/kg)-induced fluid secretion whereas the 5-HT3 antagonist granisetron dose-dependently reduced and at 300 micrograms/kg totally abolished sennoside-induced secretion. Granisetron, but not ketanserin and tropisetron, reduced the incidence of diarrhea in sennoside-treated rats, indicating the involvement of 5-HT also in acceleration of large intestinal transit. It is concluded that 5-HT is an important mediator both of sennoside-induced fluid secretion in the rat colon and of diarrhea.