Effect of obesity on gastrointestinal transit, pressure and pH using a wireless motility capsule.

BACKGROUND: Despite the increasing prevalence and medical burden of obesity, the understanding of gastrointestinal physiology in obesity is scarce, which hampers drug development. AIM: To investigate the effect of obesity and food intake on gastrointestinal transit, pressure and pH. MATERIAL AND METHODS: An exploratory cross-sectional study using a wireless motility capsule (SmartPill©) was performed in 11 participants with obesity and 11 age- and gender-matched participants with normal weight (group) in fasted and fed state (visit). During the first visit, the capsule was ingested after an overnight fast. During a second visit, the capsule was ingested after a nutritional drink to simulate fed state. Linear mixed models were constructed to compare segmental gastrointestinal transit, pressure and pH between groups (obesity or control) and within every group (fasted or fed). RESULTS: Food intake slowed gastric emptying in both groups (both P < 0.0001), though food-induced gastric contractility was higher in participants with obesity compared to controls (P = 0.02). In the small intestine, a higher contractility (P = 0.001), shorter transit (P = 0.04) and lower median pH (P = 0.002) was observed in participants with obesity compared to controls. No differences were observed for colonic measurements. CONCLUSION: Obesity has a profound impact on gastrointestinal physiology, which should be taken into account for drug development.

Randomized clinical trial: a controlled pilot trial of the 5-HT4 receptor agonist revexepride in patients with symptoms suggestive of gastroparesis.

BACKGROUND: Gastroparesis is a chronic gastric disorder characterized by delayed gastric emptying without mechanical obstruction, and clinical symptoms as postprandial fullness, early satiety, bloating, nausea, vomiting, and abdominal pain. Prokinetic agents are used for the treatment of gastroparesis. Revexepride, a 5-hydroxytryptamine (serotonin) receptor (5-HT4 R) agonist, could be a good candidate drug for the gastroparesis treatment. AIM: In the current phase II, exploratory, double-blind, randomized, stratified, placebo-controlled, repeated dose trial (EudraCT number 2007-004997-23), the efficacy on gastrointestinal symptoms and gastric emptying rate, safety, and pharmacokinetic profile of three oral doses of revexepride (0.02, 0.1, and 0.5 mg administered orally t.i.d. for 4 weeks) was evaluated in trial participants (diabetic and non-diabetic) with upper gastrointestinal tract symptoms suggestive for gastroparesis. METHODS: Eighty participants, enrolled in four parallel treatment groups, were asked to score their symptom diary data, gastroparesis cardinal symptom index (GCSI), patient assessment of upper gastrointestinal disorders-symptom severity index (PAGI-SYM), quality of life questionnaires, and meal-related symptom score. Gastric emptying rate was evaluated by (13) C-octanoic acid breath test. KEY RESULTS: The severity of the symptoms assessed by means of GCSI and PAGI-SYM decreased at Week 2 and decreased further at Week 4 in all treatment groups including placebo, with similar trends in all treatment groups. Quality of life improved in all treatment groups after 4 weeks of treatment. No differences on gastric emptying rate were shown between any of the active treatment groups and placebo. Revexepride was generally safe and well-tolerated. CONCLUSIONS & INFERENCES: Four weeks of revexepride treatment did not improve symptoms or gastric emptying over placebo in patients with symptoms suggestive of gastroparesis.

A semi-blinded study comparing 2 methods of measuring nasal potential difference: Subcutaneous needle versus dermal abrasion.

BACKGROUND: According to European and US protocols, two nasal potential difference (NPD) measurement methods are considered acceptable, although they have not been formally compared: subcutaneous agar-filled needle with calomel (Ndl) and dermal abrasion with conducting cream and Ag/AgCl electrodes (Abr). We compared both in CF and healthy volunteers (HV), assessing their discriminative value and subject's preference. METHODS: Twelve classic CF and 17 HV underwent both NPD methods, performed by one operator in random order. A written questionnaire, assessing preference, was completed after each test. Tracings were coded, scored in a semi-blinded fashion and categorised as CF/non-CF. RESULTS: 110 tracings (56 Ndl/54 Abr) were collected: 42/110 scored CF and 68/110 non-CF, showing a good correlation. No significant preference for either method was reported. CONCLUSION: Both NPD methods are similar in terms of discriminative value and subject's preference, comparing classical CF and HV. For diagnosing CF, the operator's preferred NPD-method may be used.

Randomised clinical trial: the 5-HT4 agonist revexepride in patients with gastro-oesophageal reflux disease who have persistent symptoms despite PPI therapy.

BACKGROUND: A substantial proportion of patients with gastro-oesophageal reflux disease (GERD) have only a partial response to proton pump inhibitor (PPI) therapy. Prokinetic drugs may improve reflux symptoms by enhancing oesophageal motility and gastric emptying. AIM: To evaluate the effect of revexepride, a novel prokinetic 5-hydroxytryptamine type 4 (5-HT4 ) receptor agonist, compared with placebo, in patients with GERD who have a partial response to PPIs. METHODS: A phase 2b, double-blind, parallel-group study was conducted, in which patients were randomised to one of three revexepride treatment groups (0.1, 0.5 and 2.0 mg three times daily) or placebo (1:1:1:1 ratio). Daily e-diary data captured patients' symptoms over an 8-week treatment period. The primary efficacy outcome was the weekly percentage of regurgitation-free days in the second half of the study (weeks 5-8). RESULTS: In total, 480 patients were randomised and 477 received treatment (mean age 47.9 years; 61% women). The mean percentage of regurgitation-free days increased from baseline (range, 15.0-18.8%) to week 8 (62.3-70.5%) in all four study arms; however, there were no statistically significant differences in this change between placebo and the three treatment arms. No dose-dependent relationship in treatment effect was observed for any of the study endpoints. The incidence of treatment-emergent adverse events (TEAEs) was revexepride dose-dependent. Only one serious TEAE occurred and none resulted in death. CONCLUSIONS: Revexepride was no more effective than placebo in controlling regurgitation in patients with GERD symptoms partially responsive to PPIs. Revexepride was well tolerated. ClinicalTrials.gov Identifier: NCT01472939.

Randomized clinical trial: effect of the 5-HT4 receptor agonist revexepride on reflux parameters in patients with persistent reflux symptoms despite PPI treatment.

BACKGROUND: Approximately, 20-30% of patients with gastro-esophageal reflux disease (GERD) experience persistent symptoms despite treatment with proton pump inhibitors (PPIs). These patients may have underlying dysmotility; therefore, targeting gastric motor dysfunction in addition to acid inhibition may represent a new therapeutic avenue. The aim of this study was to assess the pharmacodynamic effect of the prokinetic agent revexepride (a 5-HT4 receptor agonist) in patients with GERD who have persistent symptoms despite treatment with a PPI. METHODS: This was a phase II, exploratory, multicenter, randomized, placebo-controlled, double-blind, parallel-group study in patients with GERD who experienced persistent symptoms while taking a stable dose of PPIs (ClinicalTrials.gov identifier: NCT01370863). Patients were randomized to either revexepride (0.5 mg, three times daily) or matching placebo for 4 weeks. Reflux events and associated characteristics were assessed by pH/impedance monitoring and disease symptoms were assessed using electronic diaries and questionnaires. KEY RESULTS: In total, 67 patients were enrolled in the study. There were no significant differences between study arms in the number, the mean proximal extent or the bolus clearance times of liquid-containing reflux events. Changes from baseline in the number of heartburn, regurgitation, and other symptom events were minimal for each treatment group and no clear trends were observed. CONCLUSIONS & INFERENCES: No clear differences were seen in reflux parameters between the placebo and revexepride groups.

Risk factors for elevated levels of 17-hydroxyprogesterone during neonatal intensive care unit admission.

INTRODUCTION: Screening for congenital adrenal hyperplasia (CAH) by measurement of 17-hydroxyprogesterone (17-OHP) in dried blood spots results in a high false positive rate among preterm newborns admitted in a neonatal intensive care unit (NICU). We searched for risk factors of this population for raised 17-OHP levels. METHODS: We retrospectively collected clinical characteristics (prenatal, at birth, postnatal) in newborns with an increased 17-OHP level at initial screening (> 30 nmol/L for a birth weight > 2000 g and > or = 60 nmol/L for a birth weight < or = 2000 g), that turned out to be false positive (no CAH). The correlation of these characteristics with individual 17-OHP levels was evaluated. We also performed a case-control study matched for gestational age (GA). RESULTS: In 94 screened newborns 17-OHP levels were raised at initial screening. Negative correlations were found between 17-OHP levels and GA and birth weight, positive correlations with prenatal betamethasone administration and several parameters of respiratory disease. In a multiple regression model GA was the dominant variable. In the case control study with 91 index patients admitted to the NICU (91/1275 newborns admitted to the NICU, 7.1%) a positive correlation with respiratory disease was confirmed and cases had a significant higher birth weight and a significant lower incidence of prenatal betamethasone administration. Application of new cutoff tables adjusted by GA and/or day of sampling would have resulted in a reduction in false positive rate. CONCLUSION: The dominant risk factor for a false positive screening during NICU admission is GA. Prenatal administration of betamethasone and birth weight are more complex risk factors. These observations support the use of new cut-off values based on GA to reduce the problem of false positive screening.

Pregnancy during nitisinone treatment for tyrosinaemia type I: first human experience.

A 19 year old woman with tyrosinaemia type 1 gave birth to a healthy girl after 41 weeks of gestation. Nitisinone was continued throughout the pregnancy (maternal levels 68-96 µmol/l, target level 30-60 µmol/l). Tyrosine levels during pregnancy were between 500 and 693 µmol/l (normal values 20-120 µmol/l) and phenylalanine levels between 8 and 39 µmol/l (normal values 30-100 µmol/l). Nitisinone was measurable in neonatal blood immediately after birth, at a level comparable to the simultaneous level in the mother. Nitisinone half-life in the neonate was estimated to be 90 h. Tyrosine levels in the neonate decreased from 1,157 µmol/l at birth (cord blood) to normal levels within 4 weeks. Phenylalanine levels in the neonate were normal from birth on. The child had a normal psychomotor development as assessed throughout the first year of life.This is the first report worldwide of a pregnancy during treatment with nitisinone.In this case, no adverse effects of nitisinone, maternal high tyrosine or low phenylalanine were detected in the child, so far. Long-term results in a larger cohort of pregnancies and births are needed to determine whether nitisinone can be administered safely during pregnancy.

The use of technetium-99m radiolabeled human antimicrobial peptides for infection specific imaging.

Bacterial resistance to conventional antibiotics poses a challenge medicine to search for alternatives. Cationic antimicrobial peptides (AMPs) are promising for the development of a new class of antibiotics. This review focuses on the use of technetium-99m labeled synthetic AMPs, derived from human natural cationic AMPs, for target-delivery to and in vivo detection of infection sites caused by (drug-resistant) micro-organisms. The scintigraphic approach has proven to be a reliable method for evaluating AMPs in pharmacological studies and for optimizing target-delivery of radiolabeled AMPs to pathological sites in animals and humans. In addition, the effect of alterations in amphipathicity, amino acid substitution, and dimerization on the biological performance of AMPs is reported. Radiolabeled AMPs offer good perspectives for diagnosis of infections, for monitoring therapy, and, most importantly, for the ability to discriminate between infections and sterile inflammatory processes.

Tolerance of adjuvant letrozole outside of clinical trials.

Recently aromatase inhibitors have become a standard care as an adjuvant treatment for many postmenopausal patients with hormone receptor positive early breast cancer. Adjuvant letrozole was made available either immediately postoperative, after 2-3 years of tamoxifen, or as an extended treatment after 5 years of tamoxifen. Between October 2003 and October 2005, we analyzed the subjective tolerance in 185 postoperative early breast cancer patients receiving letrozole outside of a clinical trial. The most prominent toxicity was musculoskeletal pain. In addition hot flushes, increased fatigue, nausea, vomiting, anorexia, mood disturbances, vaginal dryness, hair loss and rash were also recorded. In contrast to the prospective randomized clinical trials, a high drop-out rate of 20% was documented, mainly due to aromatase inhibitor-associated arthralgia syndrome interfering significantly with the daily life of our patients. Although adjuvant aromatase inhibitors have proven to be generally superior to tamoxifen in the adjuvant setting, it is important to focus attention on the tolerance during the adjuvant therapy and to balance this against the potential benefit in individual patients. Alternative options including switching to tamoxifen remain available.

Topology of the fibrinolytic system within the mural thrombus of human abdominal aortic aneurysms.

Development and progression of acquired abdominal aortic aneurysms (AAAs) involve proteolytic activity. In the present study, we investigate the distribution of fibrinolytic system components within mural thrombi of human AAAs. 20 mural thrombi and the remaining AAA walls were dissected. The luminal, intermediate and abluminal thrombus layers, and media and adventitia were separately incubated in cell culture medium. Conditioned media were then analysed for plasminogen activators (PAs), plasminogen activator inhibitor-1 (PAI-1), free-plasmin, plasmin alpha(2)-antiplasmin complexes (PAPs) and D-dimers release. In parallel, PA and PAI-1 mRNA expression analysis was performed by RT-PCR. The study was completed by immunohistochemical localization of these components in AAA, ex vivo functional imaging using (99m)Tc-aprotinin as a ligand and measurement of PAP and D-dimer plasma levels. All fibrinolytic system components were present in each aneurysmal layer. However, the mural thrombus was the main source of active serine-protease release. Interestingly, the luminal layer of the thrombus released greater amounts of PAPs and D-dimers. This paralleled the preferential immunolocalization of plasminogen and PAs, and the (99m)Tc-aprotinin scintigraphic signal observed in the luminal pole of the thrombus. In contrast, mRNA expression analysis showed an exclusive synthesis of tPA and PAI-1 within the wall, whereas uPA mRNA was also expressed within the thrombus. Taken together, these results suggest that the increased plasma concentrations of PAPs and D-dimers found in AAA patients are related to mural thrombus proteolytic activity, thus explaining their known link with AAA progression. Components of the fibrinolytic system could also represent a target for functional imaging of thrombus activities in AAA.

The influence of the novel 5-HT1A agonist R137696 on the proximal stomach function in healthy volunteers.

As fundic dysaccommodation represents one of the pathophysiological mechanisms underlying functional dyspepsia, gastric relaxant agents may serve as a new treatment of this disorder. Previous studies have suggested the involvement of 5HT1 receptors in the control of gastric tone. Our aim was to study the effect of R137696, a novel 5HT1A agonist, on fundus sensorimotor function in healthy volunteers. The effect of single oral doses (1-2 mg) R137696 was evaluated in a double-blind, placebo-controlled manner on fasting fundic volume, visceral perception, distension-evoked symptoms and fundic compliance in 21 healthy male subjects. R137696 increased the proximal stomach volumes in a dose-dependent manner. Distention-evoked symptoms or distention and discomfort threshold were not altered by R137696. A logistic regression model, characterizing the relationships between the volume and the visual analogue scale score for dyspeptic symptoms (nausea, fullness, discomfort, pain and satiety) as a sigmoidal curve, revealed that R137696 had no effect on distension-induced discomfort, fullness, pain and satiety compared to placebo. R137696 relaxes the gastric fundus in fasting conditions but has no effect on distension-evoked dyspeptic symptoms in healthy volunteers.

Influence of ghrelin on interdigestive gastrointestinal motility in humans.

BACKGROUND: Recent studies in animals have shown that ghrelin stimulates upper gastrointestinal motility through the vagus and enteric nervous system. The aim of the present study therefore was to simultaneously investigate the effect of administration of ghrelin on upper gastrointestinal motility and to elucidate its mode of action by measuring plasma levels of gastrointestinal hormones in humans. MATERIALS AND METHODS: Nine healthy volunteers (four males; aged 22-35 years) underwent combined antroduodenal manometry and proximal stomach barostat study on two separate occasions at least one week apart. Twenty minutes after the occurrence of phase III of the migrating motor complex (MMC), saline or ghrelin 40 mug was administered intravenously over 30 minutes in a double blind, randomised, crossover fashion. Ghrelin, motilin, pancreatic polypeptide, glucagon, and somatostatin were measured by radioimmunoassay in blood samples obtained at 15-30 minute intervals. The influence of ghrelin or saline on MMC phases, hormone levels, and intraballoon volume was compared using paired t test, ANOVA, and chi(2) testing. RESULTS: Spontaneous phase III occurred in all subjects, with a gastric origin in four. Administration of ghrelin induced a premature phase III (12 (3) minutes, p<0.001; gastric origin in nine, p<0.05), compared with saline (95 (13) minutes, gastric origin in two). Intraballoon volumes before infusion were similar (135 (13) v 119 (13) ml; NS) but ghrelin induced a longlasting decrease in intraballoon volume (184 (31) v 126 (21) ml in the first 60 minutes; p<0.05). Administration of ghrelin increased plasma levels of pancreatic polypeptide and ghrelin but motilin, somatostatin, and glucagon levels were not altered. CONCLUSIONS: In humans, administration of ghrelin induces a premature gastric phase III of the MMC, which is not mediated through release of motilin. This is accompanied by prolonged increased tone of the proximal stomach.

Divergent role for CRF1 and CRF2 receptors in the modulation of visceral pain.

Both anti- and pro-nociceptive effects of corticotropin-releasing factor (CRF) treatment on visceral pain have been reported. Here, this dual action of CRF was differentiated by selective (in)activation of the CRF1 and CRF2 receptor prior to a visceral pain stimulus. Visceral pain was evaluated out of behavioural and visceromotor (abdominal electromyogram) responses to duodenal distension in the freely moving rat. Intraperitoneal (i.p.) CRF (50 microg kg-1) increased the distension-induced visceromotor and behavioural pain response. The pro-nociceptive effects of CRF on the behavioural response were attenuated by a selective CRF1 (CP-154526; 20 mg kg-1) but not a selective CRF2 [antiSauvagine30 (aSVG30); 100 microg kg-1] antagonist. Selective activation of the CRF2 receptor by stresscopin-related peptide (SRP; i.p. 25 microg kg-1) reduced the distension-induced visceromotor and behavioural response. Intrathecal injection of CRF (2 microg 10 microL-1) or SRP (20 microg 10 microL-1) decreased the distension-induced visceromotor and behavioural response. The antinociceptive effects of intrathecal CRF on the behavioural response were attenuated by aSVG30 (20 microg 10 microL-1) but not with CP-154526 (10 microg 10 microL-1). These findings indicate that the CRF1 receptor is involved in pro-nociception of visceral pain, whereas the CRF2 receptor is mainly involved in antinociception. This divergent role of the CRF subreceptors may explain the bimodal effects of CRF treatment on visceral nociception.

In vivo characterization of 5-HT1A receptor-mediated gastric relaxation in conscious dogs.

Accumulating data have been published emphasizing the important role of 5-hydroxytryptamine (5-HT) receptors in proximal stomach relaxation. However, a proper in vivo characterization of 5-HT receptors mediating gastric relaxation is still missing. In the current study, we focus on the in vivo characterization of 5-HT1A receptors mediating relaxation of the proximal stomach in conscious dogs. Beagle dogs were equipped with a gastric fistula. In the conscious state, volume changes within an intragastric bag were measured at constant pressure by means of a barostat. Results are presented as the maximum volume increase after treatment (mean+/-s.e.m.). All drugs were injected intravenously. The 5-HT1A receptor agonist flesinoxan (10, 50, 100 and 150 microg kg-1) induced a dose-dependent relaxation of the canine proximal stomach (50+/-10, 230+/-51, 290+/-38 and 275+/-33 ml, respectively; n=9-11). The selective 5-HT1A receptor antagonist WAY-100635 dose-dependently inhibited the flesinoxan-induced relaxation. NG-nitro-l-arginine methyl ester did not affect this relaxation, suggesting that nitrergic nerves are not involved. After supradiaphragmatic vagotomy, the baseline of the intragastric volume was larger compared to that before vagotomy (317+/-50 vs 142+/-28 ml, respectively; n=5). Compensation for this by either reduction of the intraballoon pressure or infusion of a contractile dose of bethanechol did not establish a condition in which flesinoxan was able to relax the stomach. In contrast, nitroprusside induced a significant gastric relaxation when tone was increased by bethanechol. It is concluded that flesinoxan induces proximal gastric relaxation in conscious dogs via 5-HT1A receptors. The response is mediated through a vagal pathway without involvement of nitrergic nerves.

Telemetric animal model to evaluate visceral pain in the freely moving rat.

Several research groups have measured the visceromotor response to visceral distension by electromyography (EMG) in the conscious restraint, wrapped or lightly anaesthetized rat. Our aim was to develop a more physiological and stress-free technique that enables the simultaneous measurement of duodenal distension-induced visceromotor and cardiovascular responses in the conscious, freely moving rat. A telemetry transmitter, consisting of a bipolar electrode pair and arterial catheter, was chronically implanted into the rat to measure abdominal EMG, mean arterial pressure (MAP) and heart rate (HR). Furthermore, a balloon catheter was chronically implanted in the duodenum to deliver volume-fixed staircase (0.1-0.6 ml) or phasic (0.1, 0.3, 0.5 ml) distensions. The area under the curve (AUC; mVs) and maximal amplitude (EMG(max); mV) during distension were analyzed. The model was validated by pre-treatment with morphine (0.3, 1.5 and 3 mg/kg, intraperitoneally). Staircase and phasic distension produced a volume-dependent increase in AUC and EMG(max), HR and MAP. Pre-treatment with morphine inhibited the distension-induced visceromotor response, i.e. abdominal contractions, increase in AUC and EMG(max). These findings indicate that telemetry is an adequate tool to measure visceromotor and cardiovascular responses to averse, noxious duodenal distension continuously and simultaneously in the rats home cage, without additional handling-related or restraint-induced stress. The presented animal visceral model is intended for studying acute and chronic analgesic properties of new pharmaceutical compounds.

Modulation of NA-synthase activity in rat cortex using NA measurement with ultramicro carbon electrode following topical applications of pharmacological agents.

The aim of the study was to document NA, the active product of brain NA-synthase known as NO-synthase in rat cortex. NA measurements in brain extracellular fluid were performed using an ultramicro carbon electrode (0.5-2 microm) with differential pulse voltammetry. The ultramicro carbon electrode was inserted at a fixed depth (125 microm) into the frontal cortex. A constant level of neuronal NA (0.66 mM) was found in rat cortex during a few hours in the basal state. Topical applications of competitive inhibitors of brain NO-synthase (L-NNA, L-NMA, D-arginine, 1 mg ml(-1)) and a NO-donor (SNAP, 1 mg ml(-1)) resulted in a complete disappearance of NA. Simultaneous in vivo measurements of L-NNA, an electroactive inhibitor (-1.2 V vs. Ag/AgCl), and NA (-1.66 V vs. Ag/AgCl) allowed the following of the diffusion of this neuronal specific inhibitor and the simultaneous inhibition of NA synthesis. Topical addition of acetylcholine (10 microM) produced a NA increase, while bradykinin, adenosine, and hydrogen peroxide (10 microM each) resulted in the disappearance of NA. Topical addition of radical oxygen species (ROS) scavengers (oxy-hemoglobin, methylen blue, ascorbic acid and cystein, l mg ml(-1)) had no influence on NA concentrations which remained at a constant level in brain cortex. These preliminary results indicated that NA is continuously produced at a high level by neurons. Acetylcholine and vasodilatators modulated neuronal NA synthesis after topical application, but ROS had no effect.

The effect of mechanical cleaning and thermal disinfection on light intensity provided by fibrelight Macintosh laryngoscopes.

The increased use of thermal decontamination procedures for fibrelight laryngoscope blades, to comply with international guidelines, will have considerable economical effects. We evaluated the effect of mechanical cleaning plus thermal disinfection at 90 degrees C, with or without subsequent steam sterilisation at 134 degrees C, on light intensity provided by fibrelight laryngoscopes. After mounting the blades in a special frame with a built-in light source, light intensity was measured using radiometer/photometer. In total, 14 blades provided by 11 companies were tested. The majority of fibrelight laryngoscope blades were fairly resistant to the damaging effects of machine washing plus disinfection at 90 degrees C (mean [range] reduction in light intensity 34.6%[2.1-78.3%]). However, when exposed to an additional sterilisation procedure at 134 degrees C, the majority of blades were unable to withstand the combined treatment for 300 cycles (mean [range] reduction in light intensity 86.5%[32.0-98.7%]). This study stresses the need for fibrelight laryngoscope blades which are more resistant to thermal decontamination procedures than those available at present.

Smooth muscle 5-HT2A receptors mediating contraction of porcine isolated proximal stomach strips.

1. The aim of this study was to characterize the 5-HT receptors involved in the 5-HT-induced contraction of longitudinal muscle (LM) strips of porcine proximal stomach. This was done in a classical organ bath set-up for isotonic measurement. 2. The concentration-contraction curve to 5-HT was not modified by 5-HT(3) and 5-HT(4) receptor antagonism. Methysergide, ketanserin and mesulergine antagonized the curve to 5-HT. Concomitantly, increasing concentrations of ketanserin and mesulergine progressively revealed a biphasic nature of the 5-HT curve. Ketanserin antagonized the low-affinity receptor while it did not modify the high-affinity receptor. 3. Tetrodotoxin did not influence the concentration-contraction curve to 5-HT neither in the absence nor presence of ketanserin, indicating that nerves are not involved. 4. Ketanserin competitively antagonized the monophasic concentration-response curve to alpha-Methyl-5-HT, yielding a Schild slope that was not significantly different from unity. After constraining the Schild slope to unity, a pK(B) estimate of 8.23+/-0.90 was obtained. This affinity estimate of ketanserin closely approximates previously reported affinities at 5-HT(2A) receptors. 5. In the presence of ketanserin (0.1 microM; exposing the high-affinity receptor), a wide range of 5-HT receptor antagonists covering all 5-HT receptors known, was tested. Only methysergide and ritanserin inhibited the response to 5-HT, thus expressing affinity for the high-affinity receptor. This did not reveal the identity of the receptor involved. 6 It can be concluded that 5-HT induces pig proximal stomach (LM) contraction via 5-HT(2A) receptors located on smooth muscle. A ketanserin-insensitive phase of contractions could not be characterized between the actually known classes of 5-HT receptors with the pharmacological tools that were used.