Complete genome sequence of Methanobacterium thermoautotrophicum deltaH: functional analysis and comparative genomics

The complete 1,751,377-bp sequence of the genome of the thermophilic archaeon Methanobacterium thermoautotrophicum deltaH has been determined by a whole-genome shotgun sequencing approach. A total of 1,855 open reading frames (ORFs) have been identified that appear to encode polypeptides, 844 (46%) of which have been assigned putative functions based on their similarities to database sequences with assigned functions. A total of 514 (28%) of the ORF-encoded polypeptides are related to sequences with unknown functions, and 496 (27%) have little or no homology to sequences in public databases. Comparisons with Eucarya-, Bacteria-, and Archaea-specific databases reveal that 1,013 of the putative gene products (54%) are most similar to polypeptide sequences described previously for other organisms in the domain Archaea. Comparisons with the Methanococcus jannaschii genome data underline the extensive divergence that has occurred between these two methanogens; only 352 (19%) of M. thermoautotrophicum ORFs encode sequences that are >50% identical to M. jannaschii polypeptides, and there is little conservation in the relative locations of orthologous genes. When the M. thermoautotrophicum ORFs are compared to sequences from only the eucaryal and bacterial domains, 786 (42%) are more similar to bacterial sequences and 241 (13%) are more similar to eucaryal sequences. The bacterial domain-like gene products include the majority of those predicted to be involved in cofactor and small molecule biosyntheses, intermediary metabolism, transport, nitrogen fixation, regulatory functions, and interactions with the environment. Most proteins predicted to be involved in DNA metabolism, transcription, and translation are more similar to eucaryal sequences. Gene structure and organization have features that are typical of the Bacteria, including genes that encode polypeptides closely related to eucaryal proteins. There are 24 polypeptides that could form two-component sensor kinase-response regulator systems and homologs of the bacterial Hsp70-response proteins DnaK and DnaJ, which are notably absent in M. jannaschii. DNA replication initiation and chromosome packaging in M. thermoautotrophicum are predicted to have eucaryal features, based on the presence of two Cdc6 homologs and three histones; however, the presence of an ftsZ gene indicates a bacterial type of cell division initiation. The DNA polymerases include an X-family repair type and an unusual archaeal B type formed by two separate polypeptides. The DNA-dependent RNA polymerase (RNAP) subunits A', A", B', B" and H are encoded in a typical archaeal RNAP operon, although a second A' subunit-encoding gene is present at a remote location. There are two rRNA operons, and 39 tRNA genes are dispersed around the genome, although most of these occur in clusters. Three of the tRNA genes have introns, including the tRNAPro (GGG) gene, which contains a second intron at an unprecedented location. There is no selenocysteinyl-tRNA gene nor evidence for classically organized IS elements, prophages, or plasmids. The genome contains one intein and two extended repeats (3.6 and 8.6 kb) that are members of a family with 18 representatives in the M. jannaschii genome.

Gastric response to increased meal viscosity assessed by echo-planar magnetic resonance imaging in humans

Normal meals are highly viscous, and viscosity is a key factor in influencing gastric emptying of food. However, the process of meal dilution and mixing is difficult to assess with the use of conventional methods. The aim of this study was to validate an in vivo, novel, noninvasive, echo-planar magnetic resonance imaging (EPI) technique, capable of monitoring the viscosity of a model meal, and to use this to investigate the effects of viscosity on gastric emptying, meal dilution and satiety. Healthy volunteers (n = 8) ingested 500 mL of locust bean gum (0.25, 0.5, 1.0 or 1.5 g/100 g), nonnutrient, liquid meals of varying viscosities, and labeled with a nonabsorbable marker, phenol red. Meal viscosity was calibrated against the water proton transverse relaxation rate (T(2)(-1)) in vitro before ingestion, thus viscosity was measured in vivo via EPI measurements of T(2)(-1). Viscosity and dilution were also measured directly using nasogastric aspirates. Gastric volumes as measured by EPI, fullness, appetite and hunger were also assessed serially. Before ingestion, the log of initial meal viscosity was linearly related to T(2)(-1) (n = 8, r(2) = 0.95). Similarly, T(2)(-1) measured in vivo was also linearly related to the viscosity of the aspirates (r(2) = 0.88). All meals underwent rapid dilution, leading to a reduction in viscosity, which was greatest for the most viscous meal (P < 0.01). Surprisingly, despite the fact that the initial meal viscosity varied 1000-fold, there was only a small delay in gastric emptying (P for trend < 0.05). The area under the curve for satiety increased with initial meal viscosity, whereas that for hunger decreased (P < 0.05). In conclusion, the viscosity of a meal in vivo can be measured noninvasively using EPI. The stomach responds to meal ingestion by rapid intragastric dilution, causing a reduction of meal viscosity, and gastric emptying is minimally delayed. However, increased viscosity is associated with more prolonged satiety.

A nested case-control study of non-Hodgkin lymphoma and serum organochlorine residues

BACKGROUND

The steady worldwide increase in the incidence of non-Hodgkin lymphoma during the past few decades remains mostly unexplained. Several studies suggest that there may be an association between the agricultural use of the organochlorine 1,1,1-trichloro-2,2'bis(p-chlorophenyl)ethane (DDT) and increased risk of non-Hodgkin lymphoma. We have investigated the association between risk of non-Hodgkin lymphoma and body burden of selected organochlorines in the general population in a nested case-control study.

METHODS

We measured prediagnostic serum concentrations of DDT, its metabolites, and other organochlorines, including polychlorinated biphenyls (PCBs), in 74 cases of non-Hodgkin lymphoma and 147 matched controls identified from a prospective cohort of 25,802 adults, established in 1974 in Washington County, Maryland, USA. We report results for total lipid-corrected serum concentrations of DDT and total PCBs.

FINDINGS

There was a strong dose-response relation between quartiles of total lipid-corrected serum PCB concentrations and risk of non-Hodgkin lymphoma overall (odds ratios by quartile: 1.0; 1.3 [95% CI 0.5-3.3]; 2.8 [1.1-7.6]); and 4.5 [1.7-12.0]; p for trend = 0.0008) and separately in men and in women. There was also evidence suggesting that seropositivity for the Epstein-Barr virus early antigen potentiated the effects of serum PCBs. By contrast, total lipid-corrected serum concentrations of DDT were not associated with risk of non-Hodgkin lymphoma.

INTERPRETATION

These results should be regarded as hypothesis-generating. Before causal inferences can be made about exposure to PCBs and increased risk of non-Hodgkin lymphoma, our findings require replication and the biological plausibility of the association needs further investigation.

Determination of baseline human nasal pH and the effect of intranasally administered buffers

The nose is becoming a common route of drug administration, however, little is known about the pH of the human nasal cavity. Local pH may have a direct effect on the rate and extent of absorption of ionizable compounds and hence this study was performed to investigate normal pH values and whether pH could be manipulated by various buffers. Twelve healthy volunteers participated in a study to measure pH in the anterior and posterior sites of the nasal cavity. Miniature pH electrodes were placed 3 cm apart in the nasal cavity and a baseline was recorded for 30 min once the pH had stabilized. One hundred microlitres of isotonic solution was sprayed into the nostril and the pH was measured for 4 h post-dose. The following five formulations were tested: formulation A--sodium chloride (0.9%) at pH 7.2; formulation B--sodium chloride (0.9%) at pH 5.8; formulation C--Sorensens phosphate buffer (0.06 M) at pH 5. 8; formulation D--Sorensens phosphate buffer (0.13 M) at pH 5.8 and formulation E--formulation as (c) but adjusted to pH 5.0. Each formulation also contained saccharin sodium (0.5%) as a taste marker for nasal clearance. The time at which each subject detected the taste of saccharin was noted. The 30-minute baseline recording prior to administration of the nasal spray formulation demonstrates that there was both considerable intersubject and intrasubject variation in nasal pH. The average pH in the anterior of the nose was 6.40 (+0. 11, -0.15 S.D.) when calculated from H(+) values. The pH in the posterior of the nasal cavity was 6.27 (+0.13, -0.18 S.D.). The overall range in pH was 5.17-8.13 for anterior pH and 5.20-8.00 for posterior pH. Formulation A caused the pH in the anterior part of the nasal cavity to reach a maximum of 7.06 in 11.25 min from the baseline of pH 6.14 (P<0.05). The mean baseline pH was 6.5 for the posterior part of the nose which did not change over the recording period. Formulation B caused the anterior pH to increase from pH 6. 60 to 7.25 within the first minute. This fell back to a mean pH of 7.07 over the first hour which was still significantly above the baseline. It remained at this value for the remainder of the recording period. The initial average posterior pH was 6.32 and again this did not significantly change over the recording period. Formulation C produced a sustained increase in anterior nasal pH from a baseline pH of 6.57-7.12. A small transient decrease was observed in the pH in the posterior of the nose but baseline pH of 6. 6 was re-established within 15 min post dose. Formulation D significantly reduced anterior nasal pH from 6.30 to 5.87 by 30 min reaching a pH of 5.95 by 90 min where it remained for the remainder of the recording period. The posterior baseline pH was 6.3 and introduction of the pH 5.8 buffer caused a slow increase over 90 min to pH 6.6. Formulation E increased anterior pH from 6.1 to 6.7 for the remainder of the recording period. It had an insignificant effect on posterior nasal pH. The mean (+/-S.D.) time to taste saccharin for formulations A to E was 13.42+/-10.21, 14.67+/-8.37, 11.67+/-8.08, 10.08+/-7.6, 9.80+/-6.73 min, respectively. There was no significant difference between the clearance times for the different formulations. In conclusion, average baseline human nasal pH is approximately 6.3. Nasal anterior pH can be decreased when buffers of 0.13 M and above are used. Mildly acidic solutions produce an increase in pH presumably due to reflux bicarbonate secretion. Posterior nasal pH was not altered by administration of any buffer except the 0.13 M buffer at pH 5.8. This produced a rise in posterior pH.

Transient atrial dysfunction after conversion of chronic atrial fibrillation to sinus rhythm

Although conversion of atrial fibrillation (AF) to sinus rhythm can usually be accomplished by electrical or drug therapy, effective atrial systole may not be restored. To investigate the return of atrial transport function and its relation to the duration of the arrhythmia, Doppler echocardiography was performed after conversion in 18 patients with acute AF (less than or equal to 1 week duration), 14 patients with chronic AF (greater than 1 week duration) and 15 control patients. Flow velocities during rapid filling (E wave) and atrial systole (A wave) were measured in both left and right ventricles. Patients in the acute AF group had left ventricular A waves (49 +/- 4 cm/s) and A/E ratios (0.97 +/- 0.1) similar to those of the control patients (55 +/- 7 cm/s, 0.87 +/- 0.08, respectively). In contrast, patients in the chronic AF group had much smaller A waves (19 +/- 5 cm/s) and A/E ratios (0.30 +/- 0.08) than those in the other 2 groups (p less than 0.001). Five patients with chronic AF (36%) had complete left atrial paralysis (A/E = 0) despite normal sinus P waves. Measurements in the right ventricle showed similar differences among the groups. Patients with chronic AF who maintained sinus rhythm showed an increase in A/E ratio to control levels, from 0.45 +/- 0.1 to 0.93 +/- 0.1 (p = 0.003) at 48 days (average) after conversion. Thus, atrial transport function is normal after brief periods of AF, but reduced or absent when conversion is achieved after the arrhythmia has been sustained greater than 1 week.(ABSTRACT TRUNCATED AT 250 WORDS)

Visceral hypersensitivity in symptomatic diverticular disease and the role of neuropeptides and low grade inflammation

BACKGROUND

  Recurrent abdominal pain is reported by a third of patients with diverticulosis, particularly those with previous episodes of acute diverticulitis. The current understanding of the etiology of this pain is poor. Our aim was to assess visceral sensitivity in patients with diverticular disease and its association with markers of previous inflammation and neuropeptides.

METHODS

  Patients with asymptomatic and symptomatic diverticular disease underwent a flexible sigmoidoscopy and biopsy followed 5-10 days later by visceral sensitivity testing with barostat-mediated rectal distension. Inflammation was assessed by staining of serotonin (5HT) and CD3 positive cells. mRNA levels of tumor necrosis factor alpha (TNF α) and interleukin-6 (IL-6) were quantitated using RT-PCR. Neuropeptide expression was assessed from percentage area staining with substance P (SP) and mRNA levels of the neurokinin 1 & 2 receptors (NK1 & NK2), and galanin 1 receptor (GALR1).

KEY RESULTS

  Thirteen asymptomatic and 12 symptomatic patients were recruited. The symptomatic patients had a lower first reported threshold to pain (28.4 mmHg i.q.r 25.0-36.0) than the asymptomatic patients (47 mmHg i.q.r 36.0-52.5, P < 0.001). Symptomatic patients had a higher median overall pain rating for the stimuli than the asymptomatic patients (P < 0.02). Symptomatic patients had greater median relative expression of NK1 and TNF alpha mRNA compared with asymptomatic patients. There was a significant correlation between barostat VAS pain scores and NK 1 expression (Figure 4, r(2) 0.54, P < 0.02).

CONCLUSIONS & INFERENCES

  Patients with symptomatic diverticular disease exhibit visceral hypersensitivity, and this may be mediated by ongoing low grade inflammation and upregulation of tachykinins.

Polyprenylphosphate-pentoses in mycobacteria are synthesized from 5-phosphoribose pyrophosphate

Polyprenylphosphate-arabinose (in which the polyprenyl unit is found both as decaprenyl and octahydroheptaprenyl) is a donor of mycobacterial cell wall arabinosyl residues. Because of this important role, its biosynthetic pathway, and that of the related lipid, polyprenylphosphate-D-ribose, was investigated. Surprisingly, phosphoribose pyrophosphate was shown to be a key intermediate on the pathway to both polyprenylphosphate-D-pentoses. Thus, incubation of 5-phospho-D-[14C]ribose pyrophosphate with membranes prepared from Mycobacterium smegmatis resulted in the presence of organic-soluble radioactivity that was shown to be, in part, polyprenylphosphate-[14C]arabinose and polyprenylphosphate-[14C]ribose. Two additional intermediates, polyprenylphosphate-5-phospho[14C]ribose and polyprenylphosphate-5-phospho[14C]arabinose, were identified. Further experiments showed that the mature polyprenylphosphate-ribose is formed from phosphoribose pyrophosphate via a two-step pathway involving a transferase to form polyprenylphosphate-5-phosphoribose and then a phosphatase to form the final polyprenylphosphateribose. Polyprenylphosphate-arabinose is formed by a similar pathway with an additional step being the epimerization at C-2 of the ribosyl residue. This epimerization occurs at either the level of phosphoribose pyrophosphate or at the level of polyprenylphosphate-5-phosphoribose.

Analysis of amino acids and catecholamines, 5-hydroxytryptamine and their metabolites in brain areas in the rat using in vivo microdialysis

In vivo microdialysis, using dialysis probes inserted into discrete brain areas and subsequent analysis of neurotransmitters and related substances in the dialysates (usually with HPLC), has yielded a great deal of important information about the actions of psychotropic drugs and endogenous neurotransmitter systems and about the functional interactions between various brain areas. This paper reviews the principles involved in in vivo microdialysis, its advantages and disadvantages, and recent innovations in methodology and applications. The first section includes brief discussions of principles and applications of dialysis, use of anesthetized versus conscious freely moving animals, and methods used to determine the neural origin of neurotransmitters in the dialysate. The subsequent sections provide detailed descriptions, based largely on our own studies in rats, of stereotaxic surgery, in vivo microdialysis, and dialysate analysis, with an emphasis on amino acids and biogenic amines and their metabolites. A discussion of methodological problems which may be encountered in the analysis of amino acids and biogenic amines is also included.

Dual pH probe monitoring versus single pH probe monitoring in infants on milk feeds: the impact on diagnosis

OBJECTIVES

Oesophageal pH monitoring is the gold standard technique for the detection of gastro-oesophageal reflux in adults and children. A standard parameter used to define "abnormal" reflux is the percentage of recording time for which the gastric pH is < 4. This study investigated the relevance of this measure in infants on regular milk feeds whose gastric contents and refluxate will be neutral for most of the recording time.

METHODS

Simultaneous oesophageal and gastric pH monitoring was carried out on all infants who were milk fed exclusively and admitted to hospital for suspected gastro-oesophageal reflux. In vitro studies were performed to establish the buffering capacities of the fruit juice, Dioralyte (a glucose electrolyte solution), breast milk, and milk formula feeds available on the paediatric wards.

RESULTS

Complete sets of data were obtained from 30 babies with a mean age of 4 months. Gastric pH was </= 4 for a mean (SEM) of 42.4 (4.9)% of the recording time. The mean (SEM) percentage time that oesophageal pH was < 4 for the total recording period was 6.89 (0.92)%. Recalculation of the percentage of time that the gastric pH was > 4 increased this value to 17.81 (2. 46)%. Using a cut off point of 10%, 11 of the 30 babies would have been diagnosed positive for reflux using the conventional method; however, recalculation by ignoring the time for which gastric pH was high doubled this to 22 positive for reflux.

CONCLUSION

Combined oesophageal and gastric pH monitoring greatly increases the number of positive results from tests in infants on regular milk feeds.

Effects of proton and combined proton/photon beam radiation on pulmonary function in patients with resectable but medically inoperable non-small cell lung cancer

STUDY OBJECTIVES

We evaluated the effects on pulmonary function of irradiating lung cancer with protons alone or protons combined with photons.

DESIGN

Prospective phase I/II study.

SETTING

University medical center.

PATIENTS AND INTERVENTIONS

Ten patients with stage I-II non-small cell lung cancer (NSCLC) and FEV(1) < or = 1.0 L were irradiated with protons to areas of gross disease only, using 51 cobalt gray equivalents (CGE) in 10 fractions (protocol 1). Fifteen patients with stage I-IIIA NSCLC and FEV(1) > 1.0 L received 45-Gy photon irradiation to the primary lung tumor and the mediastinum, plus a 28.8-CGE proton boost to the gross tumor volume (protocol 2).

MEASUREMENTS

Pulmonary function was evaluated prior to treatment and 1 month, 3 months, and 6 to 12 months following irradiation.

RESULTS

In patients receiving protocol 1, no significant changes in pulmonary function occurred. In patients receiving protocol 2, at 6 to 12 months, the diffusion capacity of the lung for carbon monoxide had declined from 61% of predicted to 45% of predicted (p < 0.05), total lung capacity had declined from 114% of predicted to 95% of predicted (p < 0.05), and residual volume had declined from 160% of predicted to 132% of predicted (p < 0.05). Airway resistance increased from 3.8 to 5.2 cm H(2)O/L/s (p < 0.05). No statistically significant changes occurred in vital capacity, FEV(1), or PaO(2).

CONCLUSIONS

Our observations indicate that it is feasible to apply higher-than-conventional doses of radiation at a higher-than-conventional dose per fraction without excess pulmonary toxicity when conformal radiation techniques with protons are used.

Patterns of food and acid reflux in patients with low-grade oesophagitis--the role of an anti-reflux agent

BACKGROUND

Food and acid have been shown to be refluxed independently of each other in healthy volunteers, and anti-reflux agents decrease the reflux of both parameters. Until now this phenomenon had not been studied in patients with low-grade oesophagitis, who are the group most likely to use anti-reflux medication.

AIM

To assess patterns of gastro-oesophageal reflux of acid and food in 12 ambulant patients with endoscopically proven oesophagitis of between grades I and II, but who were otherwise healthy. Also to assess the effectiveness of a single dose of an alginate-containing anti-reflux agent in controlling food and acid reflux in this patient group.

METHODS

Oesophageal pH monitoring and external ambulatory gamma detection were used to study food and acid reflux. A pH electrode was positioned 5 cm above the cardia and the gamma detector was positioned externally over the pH electrode. The patients then received a technetium-99m labelled meal designed to provoke reflux. Thirty minutes later the patients were given a 20 ml dose of alginate (Liquid Gaviscon), or 20 ml of tap water. Incidence of reflux was monitored for approximately 4 h from the end of the meal. Allocation to treatment group was randomized, with patients receiving the alternative treatment on the second study day after approximately a 7-day washout period.

RESULTS

The mean percentage time oesophageal pH remained below 4 was 16.3 min for the control group and 5.4 min for the treatment group (P = 0.03). Food reflux was detected 23.7% of the time in the control group compared to 12% of the time in the treatment group (P = 0.02). The anti-reflux agent was also successful in decreasing the number of events, but the duration of the reflux events was not significantly different.

CONCLUSIONS

Patients with grades I and II oesophagitis reflux food and acid independently, and are predominantly either food refluxers or acid refluxers, but not both. Liquid alginate decreases the number of both food and acid reflux events, but does not change their duration.

Treatment of heterotopic cervical and intrauterine pregnancy

OBJECTIVE

To find a suitable technique to selectively terminate a cervically implanted embryo while maintaining viability of a concomitant intrauterine pregnancy.

METHODS

A 34-year-old patient achieved a twin pregnancy after 4 IVF attempts. Ultrasound revealed a viable intrauterine and cervical pregnancy. Given our experience with KCl injection for fetal reduction, we offered the patient an attempt to reduce the cervical pregnancy.

RESULTS

Best visualization in this case was obtained by transabdominal scanning. A 6-inch 20-gauge spinal needle was inserted transcervically and maneuvered into the thorax of the embryo. Fetal heart rate ceased even before KCl could be injected. Then 3 cm(3) of saline were injected to provide better visualization of the cervical fetus, and to confirm absence of heart beat. The patient had minor vaginal bleeding for several days. The intrauterine pregnancy progressed uneventfully through 36(1)/(2) weeks with delivery of a healthy, 2, 700-gram newborn.

CONCLUSION

Cervical pregnancy is usually considered a life-threatening event. Other factors such as concomitant intrauterine pregnancy and the patient's infertility history generally would be secondary concerns. In this case, we were able to selectively terminate the cervical pregnancy, while preserving the intrauterine one, allowing this couple to have a healthy newborn. Further cases will be necessary to appropriately define risk rates for such an approach.

Twenty-four hour ambulatory nasal pH monitoring

The nasal delivery of drugs, both for systemic and local use, is an expanding field with many drugs being delivered by this route. It is known that changes in pH can affect drug absorption but there is no data regarding intranasal pH over time. We present the results of 24-h ambulatory nasal pH monitoring in four subjects, each of whom had monitoring on two separate occasions. The apparatus consisted of a pH monitor with two electrodes, thus enabling us to take readings from 1 and 4 cm behind the anterior end of the inferior turbinate. Measurements were recorded every 6 s by the posterior electrode and every 30 s by the anterior electrode. The recording apparatus was worn around the subjects waist. Analysis of the results showed that there was no diurnal variation and no significant differences between the subjects. The mean pH from the anterior electrode was higher than that from the posterior (7.1 versus 6.6). The pH did not fluctuate with daily activities such as eating, drinking or sleeping. The results are interesting and may be of importance with regard to the design of formulations for nasal drug delivery systems.

fMRI and MEG analysis of visceral pain in healthy volunteers

BACKGROUND

Although many studies of painful rectal stimulation have found activation in the insula, cingulate, somatosensory, prefrontal cortices and thalamus, there is considerable variability when comparing functional magnetic resonance imaging (fMRI) results. Multiple factors may be responsible, including the model used in fMRI data analysis. Here, we assess the temporal response of activity to rectal barostat distension using novel fMRI and magnetoencephalography (MEG) analysis.

METHODS

Liminal and painful rectal barostat balloon inflation thresholds were assessed in 14 female healthy volunteers. Subliminal, liminal and painful 40s periods of distension were applied in a pseudo-randomized paradigm during fMRI and MEG neuroimaging. Functional MRI data analysis was performed comparing standard box-car models of the full 40s of stimulus (Block) with models of the inflation (Ramp-On) and deflation (Ramp-Off) of the barostat. Similar models were used in MEG analysis of oscillatory activity.

KEY RESULTS

Modeling the data using a standard Block analysis failed to detect areas of interest found to be active using Ramp-On and Ramp-Off models. Ramp-On generated activity in anterior insula and cingulate regions and other pain-matrix associated areas. Ramp-Off demonstrated activity of a network of posterior insula, SII and posterior cingulate. Active areas were consistent with those identified from MEG data.

CONCLUSIONS & INFERENCES

In studies of visceral pain, fMRI model design strongly influences the detected activity and must be accounted for to effectively explore the fMRI data in healthy subjects and within patient groups. In particular a strong cortical response is detected to inflation and deflation of the barostat, rather than to its absolute volume.

Comparative scintigraphic assessment of the intragastric distribution and residence of cholestyramine, Carbopol 934P and sucralfate

It has been demonstrated that orally administered cholestyramine is distributed throughout the stomach and provides prolonged gastric residence via mucoadhesion. Gamma scintigraphy was used to compare the gastric emptying and residence of this resin with two formulations known to exhibit retentive or bioadhesive properties, Carbopol 934P and sucralfate. Fasted normal subjects received a single radiolabelled dose and gastrointestinal transit was monitored for 6 h. The subjects were fed after 4 h to determine the effects of inducing a fed pattern of motility on the retention of the formulations. Initial gastric emptying was similar (Mean T50+/-S.E.M.: cholestyramine=66.93+/-9.39 min; Carbopol=56.57+/-11.96 min; sucralfate=48.33+/-11.07 min; P=0.548: n=10), however, the emptying of cholestyramine slowed beyond 2 h. This resulted in greater residence for cholestyramine (Mean AUC0-6+/-S.E.M. (relative units)=11516+/-686 versus 7657+/-1170 versus 6170+/-998; cholestyramine versus Carbopol versus sucralfate; P=0.004: n=10), with approximately 25% remaining in the stomach at 6 h compared to 3.84 and 2.65% of Carbopol and sucralfate, respectively. Cholestyramine was also distributed widely throughout the stomach whereas Carbopol and sucralfate were concentrated in the body and antrum. Thus, as cholestyramine had a comparable emptying time to Carbopol and sucralfate but greater gastric residence and wider distribution, it could provide a potential mucoadhesive drug delivery system targeting the gastric mucosa for treatment of conditions such as Helicobacter pylori infection.

Effects of a 5-HT(3) antagonist, ondansetron, on fasting and postprandial small bowel water content assessed by magnetic resonance imaging

BACKGROUND

5-HT(3) antagonists have been shown to be effective in relieving the symptoms of irritable bowel syndrome with diarrhoea (IBS-D). Using a recently validated magnetic resonance imaging (MRI) method, we have demonstrated reduced fasting small bowel water content (SBWC) in IBS-D associated with accelerated small bowel transit. We hypothesized that slowing of transit with ondansetron would lead to an increase in SBWC by inhibiting fasting motility.

AIM

To assess the effects of ondansetron compared with placebo in healthy volunteers on SBWC and motility in two different groups of subjects, one studied using MRI and another using manometry.

METHODS

Healthy volunteers were given either a placebo or ondansetron on the day prior to and on the study day. Sixteen volunteers underwent baseline fasting and postprandial MRI scans for 270 min. In a second study, a separate group of n = 18 volunteers were intubated and overnight migrating motor complex (MMC) recorded. Baseline MRI scans were carried out after the tube was removed.

RESULTS

Fasting SBWC was markedly increased by ondansetron (P < 0.0007). Ondansetron reduced the overall antroduodenal Motility Index (P < 0.04). The subjects who were intubated had significantly lower fasting SBWC (P < 0.0002) compared with the group of subjects who were not intubated.

CONCLUSIONS

The 5-HT(3) receptor antagonism increased fasting small bowel water. This was associated with reduced fasting antroduodenal Motility Index which may explain the clinical benefit of such drugs.