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Biomedical subjects

J Rask-Madsen

Publications and source records attributed to J Rask-Madsen.

At least 37 records · Page 2Linked to original sources

From basic science to future medical options for treatment of ulcerative colitis.

Both ulcerative colitis (UC) and Crohn's disease are considered the result of an unrestrained inflammatory reaction, but an explanation for the aetiopathogenesis has still not emerged. Until the predisposing and trigger factors have been clearly defined, therapeutic and preventive strategies for these disorders must, therefore, rely on interrupting or inhibiting the immunopathogenic mechanisms involved. Current therapies, such as glucocorticoids and 5-aminosalicylic acid, inhibit raised concentrations of interdependent, soluble mediators of inflammation, which may amplify one another or have parallel effects. Future medical options for treatment of UC aim at removing perpetuating antigens, blocking entry of inflammatory cells by manipulating adhesion molecules, targeting soluble mediators of inflammation by blocking proinflammatory molecules or by preserving endogenous suppressive molecules, or correcting genetic defects. It remains, however, to be determined whether targeting multi-inflammatory actions or a single key pivotal process is the better therapeutic strategy and whether subgroups of UC with different clinical courses will require different treatment approaches.

Antibody Formation↗

Reappraisal of bicarbonate secretion by the human oesophagus.

BACKGROUND AND AIMS: Administration of omeprazole to healthy volunteers was recently reported to increase proximal duodenal mucosal bicarbonate secretion. As human oesophagus also secretes bicarbonate, the hypothesis was tested that omeprazole may stimulate oesophageal bicarbonate secretion and thus contribute to the therapeutic efficacy of the drug in gastro-oesophageal reflux disease. SUBJECTS AND METHODS: In nine healthy volunteers, oesophageal "steady state" perfusion of a 10 cm open segment of distal oesophagus was performed twice in random order. The volunteers were pretreated with either 60 mg/day omeprazole for three days and 80 mg intravenous omeprazole before perfusion or 600 mg/day ranitidine for three days and 50 mg/h intravenously during the perfusion. Saliva and samples of aspirate from the perfused oesophagus and stomach were collected and bicarbonate concentrations were measured. RESULTS: The median rates (95% confidence intervals) of intrinsic oesophageal bicarbonate secretion, corrected for contaminating salivary and gastric bicarbonate, were 89 (33-150) and 121 (63-203) mumol/h/10 cm (p > 0.5) in omeprazole and ranitidine treated subjects respectively. Salivary and gastric bicarbonate contaminating the oesophagus accounted for 14% and 3%, respectively, of total oesophageal bicarbonate output. CONCLUSIONS: Bicarbonate secretory capacity of the human oesophagus is less than previously assumed, and the clinical relevance of intrinsic oesophageal bicarbonate for mucosal defence may be overestimated. As omeprazole and ranitidine did not affect bicarbonate secretion differently there was no evidence that omeprazole acts on bicarbonate secretory cells in the oesophageal mucosa.

Adult↗

Omeprazole promotes proximal duodenal mucosal bicarbonate secretion in humans.

The proton pump inhibitor, omeprazole, surprisingly resulted in higher rates of proximal duodenal mucosal bicarbonate secretion than previously reported using an H2 receptor antagonist for gastric acid inhibition. Gastroduodenal perfusions were performed in healthy volunteers to evaluate whether this incidental finding is explained by more potent gastric acid inhibition by omeprazole or might be caused by the different mode of drug action. Basal and stimulated gastric and duodenal bicarbonate secretion rates were measured in the same subjects in control experiments (n = 17) and after pretreatment with high dose omeprazole (n = 17) and ranitidine (n = 9), respectively, by use of a technique permitting simultaneous measurements. Concentrations of bicarbonate were measured in the respective effluents by the method of back titration. Both omeprazole and ranitidine completely inhibited gastric acid secretion (pH 6.9 v 6.8; p > 0.05). Omeprazole caused higher rates of basal (mean (SEM)) (597 (48) v 351 (39) mumol/h; p < 0.02) and vagally stimulated (834 (72) v 474 (66) mumol/h; p < 0.02), but not acid stimulated (3351 (678) v 2550 (456) mumol/h; p > 0.05) duodenal bicarbonate secretion compared with control experiments. Also the combination of omeprazole and ranitidine increased (p = 0.05) duodenal bicarbonate secretion, while ranitidine alone caused no change in either basal or stimulated secretion. In the stomach basal as well as vagally stimulated bicarbonate secretion was independent of the means of acid inhibition. These results show that the proton pump inhibitor, omeprazole, promotes proximal duodenal mucosal bicarbonate secretion apparently independent of its gastric acid inhibitory effect. The mechanism of action remains speculative.

Adult↗

Gastric bicarbonate secretion and release of prostaglandin E2 are increased in duodenal ulcer patients but not in Helicobacter pylori-positive healthy subjects.

BACKGROUND: Duodenal ulcer (DU) patients have impaired proximal duodenal mucosal bicarbonate secretion at rest and in response to luminal acid with higher acid-stimulated mucosal release of prostaglandin (PG) E2 than healthy subjects. Our purpose was to determine whether this abnormality was present also in the stomach of DU patients. METHODS: Simultaneous determinations of gastric and duodenal bicarbonate secretion and luminal release of PGE2 were performed in 16 healthy volunteers (5 Helicobacter pylori-positive) and 8 inactive DU patients (all H. pylori-positive). RESULTS: In healthy volunteers the rates of gastroduodenal bicarbonate secretion and the release of PGE2 were not influenced by H. pylori status. In inactive DU patients the rates of basal (704 +/- 84 versus 356 +/- 40 mumol/h; mean +/- SEM) and vagally stimulated (modified sham feeding) (1724 +/- 376 versus 592 +/- 52 mumol/h) gastric bicarbonate secretion were higher (p < 0.05) than in the health, whereas the corresponding rates (339 +/- 42 versus 591 +/- 51 mumol/h and 543 +/- 99 versus 778 +/- 69 mumol/h) in duodenal bicarbonate secretion were lower (p < 0.05). In addition, inactive DU patients had higher basal (148 +/- 32 versus 53 +/- 5 ng/h) and stimulated (291 +/- 84 versus 131 +/- 25 ng/h) gastric release of PGE2, but only the basal release of PGE2 into the duodenum was significantly increased (20 +/- 3 versus 5 +/- 1 ng/h; p < 0.05). CONCLUSION: Increased mucosal production of PGE2 may be responsible for the abnormally high gastric secretion of bicarbonate in inactive DU patients. The defective duodenal secretion of bicarbonate observed in these patients may be a consequence of previous ulceration rather than the mere presence of H. pylori infection.

Adult↗

Mediators of inflammation in chronic inflammatory bowel disease.

A distinguishing feature of inflammatory bowel disease (IBD) is its apparently spontaneous, chronic relapsing course. Despite extensive research over several decades the etiology of IBD remains unknown, but evidence has accumulated to suggest that the mucosal inflammatory response may be caused by (i) a defective mucosal barrier function resulting in an abnormally increased exposure to luminal antigens and toxins, (ii) an appropriate immunologic response to an unusual infection, antigen or toxin, or (iii) an inappropriate immunological response to ubiquitous antigens or stimuli. In recent years, the identification of established and potential mediators of inflammation has expanded to include eicosanoids, platelet activating factor, biogenic amines, kinins, complement-derived peptides, chemotactic peptides, cytokines, neuropeptides, and reactive metabolites of oxygen and nitrogen. Thus, the study of the inflammatory process has become ever more complex. Until the predisposing and trigger factors have been identified the achievement of a more rational and effective approach to therapy in IBD relies on interruption of the mechanisms responsible for excess mediator formation. As summarized in this review on the role of soluble mediators of inflammation, several Danish gastroenterologists have been profoundly engaged in basic and clinical research in the past 25 years to place some pieces of the confusing puzzle of IBD.

Colitis, Ulcerative↗

Selective blockade of leukotriene production by a single dose of the FPL 64170XX 0.5% enema in active ulcerative colitis.

5-Lipoxygenase products of arachidonic acid metabolism are thought to play a central role in the secondary amplification of the inflammatory response of several inflammatory diseases, including ulcerative colitis. FPL 64170XX is a selective inhibitor of the enzyme 5-lipoxygenase. Concentrations of leukotriene B4 and prostaglanding E2 in rectal dialysis fluid from 23 males with clinically and sigmoidoscopically active, distally located ulcerative colitis were measured by radioimmunoassays in a double-blind, placebo-controlled, parallel design study before and after rectal administration of an enema containing 0.5% of FPL 64170XX. Repeated measures analysis of leukotriene B4, after adjusting for baseline, showed a significant treatment effect (P = 0.0014). The concentration of leukotriene B4 from rectal dialysates in patients receiving the active drug dropped to 15% (95% confidence interval 5-40%) of the placebo level in the second dialysis following administration of FPL 64170XX 0.5%. By contrast, prostaglanding E2 concentrations doubled (P = 0.0068) in patients receiving FPL 64170XX 0.5% with no change in the placebo group. These findings demonstrate that a single dose of FPL 64170XX 0.5% enema selectively blocks the generation of the 5-lipoxygenase product, leukotriene B4, to a mean of 85% in the target tissue of inflammation. Topical administration of this new leukotriene synthesis inhibitor may prove to be a clinically useful approach to the treatment of active, distally located ulcerative colitis.

Adult↗

Misoprostol inhibits gastric mucosal release of endogenous prostaglandin E2 and thromboxane B2 in healthy volunteers.

Prostaglandin analogues of the E-series theoretically offer the ideal antiulcer drugs. Peptic ulcer healing with prostaglandin analogues is, however, no better than would be predicted from their ability to inhibit gastric acid secretion and they are less effective than histamine H2 receptor antagonists in preventing ulcer relapse. It could be that prostaglandin analogues inhibit gastric mucosal synthesis or release of endogenous eicosanoids, thereby abrogating their own effects. This study, therefore, examined how a single therapeutic dose (200 micrograms) of misoprostol, a synthetic analogue of prostaglandin E1, influences gastric mucosal release of endogenous prostaglandin E2 (PGE2), thromboxane B2 (TXB2), and chemotactic leukotriene B4 (LTB4) during basal conditions and in response to gastric luminal acidification (0.1 M HCl; 5 ml/min for 10 minutes). Nine healthy volunteers were studied in a single blind, cross over design. In each subject misoprostol or placebo was instilled in randomised order into the stomach, which was subsequently perfused with isotonic mannitol. Misoprostol significantly decreased basal as well as acid stimulated output of PGE2 and TXB2, without affecting output of LTB4. These data show that misoprostol inhibits gastric mucosal synthesis of prostanoids. Decreased concentrations, or even a changed profile, of native eicosanoids modulating the release of inflammatory mediators from immune cells might explain why prostaglandin analogues have a comparatively poor clinical performance in ulcer healing and prevention.

Adult↗

Muscarinic M1 receptor inhibition reduces gastroduodenal bicarbonate secretion and promotes gastric prostaglandin E2 synthesis in healthy volunteers.

The selective muscarinic M1 receptor antagonist, pirenzepine, considerably stimulates duodenal mucosal bicarbonate secretion in the rat and increases gastric luminal release of prostaglandin E2 (PGE2) in humans. This study, therefore, looked at the effect of pirenzepine on bicarbonate secretion and luminal output of PGE2 into the stomach and the duodenum of nine healthy volunteers using a new technique permitting simultaneous measurements. In the stomach modified sham feeding increased bicarbonate secretion from 382 (62) mumol/h (mean (SEM)) to 959 (224) mumol/h (p < 0.02). In the duodenum modified sham feeding and acid exposure (HCl 0.1 M; 20 ml; 5 min) of the duodenal bulb increased mucosal bicarbonate secretion from 191 (14) mumol/cm x h to 266 (27) mumol/cm x h (p < 0.02) and 634 (157) mumol/cm x h (p < 0.01), respectively. Pirenzepine (10 mg/h intravenously) reduced basal and vagally stimulated gastric and basal duodenal bicarbonate secretion by about 50% (p < 0.03). In the stomach, but not the duodenum, basal and vagally stimulated PGE2 output increased significantly (p < 0.05) in response to pirenzepine. In conclusion, human gastroduodenal mucosal bicarbonate secretion is regulated by a pirenzepine sensitive mechanism, which is probably cholinergic. The rise in gastric PGE2 output seen in response to M1 receptor inhibition by pirenzepine suggests the existence of a feed back loop secondary to the decrease seen in bicarbonate secretion.

Adult↗

Indomethacin decreases gastroduodenal mucosal bicarbonate secretion in humans.

BACKGROUND: Cyclooxygenase inhibitors reduce mucosal bicarbonate secretion in the duodenum, but the evidence for their effect on bicarbonate secretion in the stomach remains controversial. We have, therefore, studied how indomethacin influences gastroduodenal bicarbonate secretion and luminal release of prostaglandin (PG) E2 by means of a method that enables simultaneous measurements in the stomach and the duodenum. METHODS: Gastric and duodenal perfusions were performed twice in random order during control conditions or after pretreatment with indomethacin (100 mg intravenously) in eight healthy volunteers. Bicarbonate and PGE2 were measured in the gastroduodenal effluents by back-titration and radioimmunoassay, respectively. RESULTS: Vagal stimulation and duodenal luminal acidification (0.1 M HCl; 20 ml; 5 min) increased gastroduodenal bicarbonate secretion (p < 0.05). Indomethacin markedly inhibited both basal and stimulated gastric and duodenal mucosal bicarbonate secretion, and this reduction was similar to the degree of cyclooxygenase inhibition estimated by the luminal release of PGE2 (p < 0.05). CONCLUSION: These results unequivocally demonstrate that endogenous PG modulates basal and stimulated bicarbonate secretion, both in the stomach and in the duodenum.

Adult↗

Failure of tropisetron to inhibit jejunal water and electrolyte secretion induced by 5-hydroxytryptamine in healthy volunteers.

The effects of the 5-hydroxytryptamine (5-HT3) receptor antagonist, ICS 205-930 (tropisetron), on basal and 5-HT induced jejunal secretion of water and electrolytes were examined using a double blind, randomised crossover design. In seven healthy volunteers steady state perfusions of the proximal jejunum were performed twice with the Loc-I-Gut tube after 5+5 mg ICS 205-930 or placebo capsules were given. After equilibration for 60 minutes and completion of a 120 minute basal period 5-HT (10 micrograms/kg x min intravenously) was infused for 120 minutes. Net water absorption (mean (SEM)) in the basal period was 0.55 (0.84) ml/cm x h and 0.74 (0.72) ml/cm x h after placebo and ICS 205-930, respectively (p > 0.05). Infusion of 5-HT caused significant net secretion of water after placebo (2.05 (0.58) ml/cm x h; p < 0.02) as well as ICS 205-930 (2.60 (0.89) ml/cm x h; p < 0.05). As ICS 205-930 excerted no effects on either basal or 5-HT induced water and electrolyte transport in the intact human jejunum the compound is probably not efficacious as an anti-secretory drug in patients with 5-HT induced diarrhoea.

Adult↗

Indomethacin decreases jejunal fluid secretion in addition to luminal release of prostaglandin E2 in patients with acute cholera.

Human cholera is associated with an increased luminal release of prostaglandin E2 (PGE2), but whether inhibition of increased PGE2 synthesis will reduce or control intestinal secretion is uncertain. 'Steady state' perfusions (10 ml/minute) in 12 patients with acute cholera, and repeat perfusions in nine of these patients during the convalescent phase were therefore performed using the triple lumen technique. The proximal jejunum was perfused with isotonic saline containing sodium-sulphobromophthalein as a non-absorbable marker. After intravenous administration of indomethacin (1.0 mg/kg) the jejunal net transfer of fluid and the jejunal flow rate of PGE2 were determined in 30 minute periods for 120 minutes after a 120 minute control period. Indomethacin decreased net fluid secretion (2.1 (0.3-4.2) v 4.5 (2.5-8.4) ml/hour x cm; medians, Q50 ranges, p less than 0.01) and the jejunal flow rate of PGE2 (1.5 (1.2-2.7) v 2.2 (1.4-4.9) ng/minute, p less than 0.05). The results of similar perfusion studies in 22 patients with acute cholera, used to establish the spontaneous time related change in fluid secretion, showed no significant change in net fluid transfer (3.5 (2.2-6.2) to 3.5 (2.6-11.6) ml/hour x cm, p greater than 0.25) over 240 minutes. These data provide further evidence in favour of the hypothesis that prostaglandins have a role in the cholera toxin induced intestinal fluid secretion in man.

Adult↗

5-Lipoxygenase inhibitors for the treatment of inflammatory bowel disease.

The unique role of the enzyme 5-lipoxygenase (5-LO) in the production of leukotrienes (LTs) makes it a likely target for biochemical manipulation. The rationale for using 5-LO inhibitors for the treatment of inflammatory bowel disease (IBD) is based on the increased generation of LTs in the inflamed mucosa, LTB4 being the most potent chemotactic and chemokinetic metabolite of arachidonic acid. Furthermore, conventional drugs, such as corticosteroids, sulphasalazine, and 5-aminosalicylic acid, inhibit LT production and specific 5-LO inhibition accelerates healing in animal models of acute colitis. The compounds identified as 5-LO inhibitors can be divided into antioxidants, substrate-analogous, and a large miscellaneous group of inhibitors, where hydroxamic acids are potent and more selective inhibitors of 5-LO. The benzothiophene hydroxyurea, zileuton, is the first selective 5-LO inhibitor evaluated for the treatment of patients with IBD. An 800-mg oral dose of zileuton was shown to reduce LTB4, but not prostaglandin E2, concentrations by 75-85% in rectal dialysates from patients with active ulcerative colitis. The clinical efficacy of zileuton 800 mg b.i.d. has also been tested in a randomized, double-blind, placebo-controlled trial in similar patients. Zileuton significantly improved the symptom scores and the histology score, but not the sigmoidoscopy score, compared to pretreatment conditions and with response to placebo, the beneficial effects being most pronounced in patients not receiving concomitant sulphasalazine treatment. The mean inhibition of LTB4 in the target tissue of inflammation was 70%. The proof that any putative 5-LO inhibitor is blocking LT production is an important stage in assessing any such drug. The main disadvantage of existing new LT inhibitors relates to the high potency of LTs, and unless a higher level of inhibition can be achieved, endogenous LTs may still be present in sufficient amounts to produce their effects.

Adrenal Cortex Hormones↗

Omeprazole 20 mg three days a week and 10 mg daily in prevention of duodenal ulcer relapse. Double-blind comparative trial.

In a double-blind, parallel-group clinical trial of 195 patients with duodenal ulcers who after a short-term study had relief of pain and healed ulcers proved endoscopically, 65 were randomized to receive 20 mg omeprazole 3 days a week (once in the morning from Friday to Sunday), 64 to receive 10 mg omeprazole once daily in the morning, and 66 to receive placebo for up to 6 months. The patients underwent repeat endoscopy with biopsy of the gastric fundic mucosa (qualitative assessment of argyrophilic cell population), assessment of symptoms, and laboratory screening with measurement of basal serum gastrin concentrations at 3 and 6 months or more often if indicated by recurrence of symptoms. At 3 months, endoscopically proved ulcer relapse occurred in 16% receiving 20 mg omeprazole 3 days a week; 21% receiving 10 mg omeprazole daily; and 50% receiving placebo. At 6 months, corresponding rates were 23%, 27%, and 67% with 95% confidence intervals of difference between the placebo group and omeprazole groups of 28%-60% and 24%-56% (P less than 0.00001), respectively, and between omeprazole groups of -19%-11% (NS). No major clinical or laboratory side effects were noted. Thus both omeprazole regimens are effective and safe in preventing duodenal ulcer relapse.

Adolescent↗

Colloidal bismuth subcitrate causes sustained release of gastric mucosal prostaglandin E2.

Gastric application of high doses of colloidal bismuth subcitrate (CBS) stimulates mucosal prostaglandin E2 (PGE2) production, which is considered part of the mechanism by which the drug accelerates peptic ulcer healing. Whether therapeutic, orally administered, doses of CBS cause a sustained stimulation of prostaglandin production is not known. We have, therefore, determined gastric luminal release of PGE2 during 'steady-state' perfusion of the stomach with CBS (10 mg/ml; isotonic mannitol 5 ml/min) and 4 h after the last oral dose of the drug (240 mg b.d.) for 2 weeks (isotonic mannitol 5 ml/min) in 8 healthy volunteers. A significant increase in PGE2 concentrations (712 (409-1076) vs. control 334 (252-655) pg/ml; medians with Q50 ranges; P less than 0.02) and PGE2 output (12.5 (7.3-14.3) vs. control 4.8 (4.1-7.3) ng/15 min; P less than 0.02) occurred during gastric perfusion with CBS. A similar increase in PGE2 concentrations (630 (297-1429) pg/ml; P less than 0.02) and PGE2 output (12.6 (6.4-22.2) ng/15 min; P less than 0.02) was observed following treatment with CBS for 2 weeks. These results suggest that therapeutic doses of CBS cause a sustained stimulation of gastric mucosal PGE2 formation.

Adult↗