The duodenal motility response to HCl is influenced by NO and prostaglandins

The NO/cGMP pathway in duodenal motor, mechano- and chemosensory responses to acid: A randomized, placebo-controlled study with sildenafil in healthy volunteers

BACKGROUND

Altered duodenal sensorimotor responses to acid have been reported in a subset of patients with functional dyspepsia. To investigate whether NO is involved in these abnormalities, the effect of sildenafil (activates the NO pathway) on duodenal motor and sensory responses to acid in healthy humans was evaluated.

METHODS

A barostat-manometry catheter including an infusion tube was positioned in the duodenum of 12 healthy volunteers. Duodenal motility and dyspeptic symptoms were evaluated during the whole study. A first series of stepwise isobaric distensions was performed while participants scored their perception of upper abdominal sensations at the end of every distension step. Next, the duodenum was infused with sildenafil 50 mg or saline, followed by duodenal acid infusion. During duodenal acidification, a second sequence of stepwise isobaric distensions with the assessment of sensations was repeated.

KEY RESULTS

Acid infusion did not induce dyspeptic symptoms with both placebo and sildenafil pretreatment. Duodenal motility decreased after sildenafil infusion, whereas it was not affected by placebo. Acid-induced increase in motility was, however, observed in both conditions, and no difference between the conditions was found. Duodenal acidification decreased thresholds for discomfort and increased perception scores during duodenal distensions in both groups, but again no difference was observed between placebo and sildenafil pretreatment.

CONCLUSIONS AND INFERENCES

Sildenafil does not affect duodenal motor, mechanosensory, and chemosensory responses to acid in healthy controls. Therefore, it is less likely that the NO pathway plays a role in the altered response to acid in functional dyspepsia patients.

A pilot study on duodenal acid exposure and its relationship to symptoms in functional dyspepsia with prominent nausea

BACKGROUND

Duodenal hypersensitivity to acid and decreased duodenal clearance of exogenous acid have been reported in functional dyspepsia (FD). However, the relevance of these abnormalities to spontaneous duodenal acid exposure and dyspeptic symptoms in FD is unknown.

AIMS

To determine spontaneous duodenal acid exposure and its relationship with symptoms, duodenal sensitivity to acid, and the effects of a 5-HT(3) receptor antagonist on duodenal responses to acid in FD.

METHODS

Eleven FD patients with prominent nausea and 11 healthy controls underwent 24-h ambulatory duodenal pH monitoring with assessment of dyspeptic symptoms. On the next day, duodenal bolus infusions of 5 ml of acid and normal saline were given in a randomized double-blind manner and repeated after ondansetron or a placebo.

RESULTS

Nighttime duodenal acid exposure was similar, but FD patients had lower duodenal pH and higher duodenal % time (pH < 4) than controls during the daytime and in the second postprandial 2 h (p < 0.05). Seven patients (64%) with duodenal acid exposure above the normal range had higher severity scores for several dyspeptic symptoms including nausea. However, the symptom severity was poorly or weakly correlated to duodenal pH, and brief duodenal acid infusion did not affect any symptoms. Duodenal responses to exogenous acid were unaffected by 5-HT(3) receptor antagonism.

CONCLUSIONS

Spontaneous duodenal acid exposure is increased in a subset of FD patients with prominent nausea, and this is associated with more severe dyspeptic symptoms. However, a direct relationship between duodenal acid exposure and symptom severity is lacking.

Nitric oxide prevents rat duodenal contractions induced by potentially noxious agents

After abdominal surgery, luminal HCl fails to induce duodenal contractions in anaesthetized rats. Elevated tissue levels of nitric oxide (NO) and prostaglandins possibly contribute to this observation. The aim of this study was to compare the effects of luminal capsaicin (1.2 mg mL-1), ethanol (15%) and high partial pressure of CO2 (>250 mmHg) with those of HCl (10 mM) in anaesthetized rats. Motility (intraluminal pressure), mucosal permeability [blood-to-lumen clearance of 51Cr-EDTA (51Chromium-labelled ethylenediaminetetraacetate)] and duodenal mucosal bicarbonate secretion (DMBS) were recorded. Three groups of animals were studied: (1) controls, (2) pretreatment with the NO synthase inhibitor N-nitro-L-arginine-methyl-ester (L-NAME) and (3) pretreatment with the cyclo-oxygenase inhibitor indomethacin. Neither capsaicin, ethanol, CO2 nor HCl induced duodenal contractions or affected DMBS in control rats. However, L-NAME induced duodenal contractions that were augmented by capsaicin, ethanol and HCl, but not by CO2. Indomethacin also induced contractions that were reversibly diminished by capsaicin and HCl, but not by ethanol or CO2. Significant increases in mucosal permeability occurred during ethanol perfusion in indomethacin- and L-NAME pretreated rats. In conclusion, NO probably plays a key role in preventing duodenal contractions in response to luminally HCl, capsaicin and ethanol. The HCl-induced effect on motility appears to be independent of CO2 and is not caused by alteration in mucosal integrity.