Preliminary report: modulation of parasympathetic nervous system tone influences oesophageal pain hypersensitivity

OBJECTIVES

Autonomic nervous system dysfunction has been implicated in visceral hypersensitivity. However, the specific contribution of the parasympathetic nervous system (PNS) is unclear. We aimed to determine whether physiological and pharmacological manipulation of parasympathetic tone influences the development of hypersensitivity in a validated model of acid-induced oesophageal pain.

DESIGN

Prior to, and following, a 30-min distal oesophageal infusion of 0.15 M hydrochloric acid, pain thresholds to electrical stimulation were determined in the proximal non-acid exposed oesophagus in healthy subjects. Validated sympathetic (skin conductance response) and parasympathetic (cardiac vagal tone) parameters were measured at baseline and continuously thereafter. In study 1, 55 subjects were randomised in a pragmatic blinded crossover design to receive deep breathing or un-paced breathing during acid infusion. In study 2, 32 subjects were randomised in a blinded, crossover design to receive intravenous atropine or placebo (saline) with deep breathing during acid infusion.

RESULTS

Study 1: Deep breathing increased cardiac vagal tone (2.1±2.3 vs -0.3±2.3, p=0.0006) with concomitant withdrawal of skin conductance response (-0.6±4.9 vs 3±4.8, p=0.03) in comparison with un-paced breathing. Deep breathing prevented the development of acid-induced oesophageal hypersensitivity in comparison with sham breathing (p=0.0001). Study 2: Atropine, in comparison with placebo, blocked the attenuating effect of deep breathing on the development of acid-induced oesophageal hypersensitivity (p=0.046).

CONCLUSIONS

The development of oesophageal hyperalgesia is prevented by physiologically increasing parasympathetic tone. This effect is pharmacologically blocked with atropine, providing evidence that the PNS influences the development of oesophageal pain hypersensitivity.

Anal gas evacuation and colonic microbiota in patients with flatulence: effect of diet

OBJECTIVE

To characterise the influence of diet on abdominal symptoms, anal gas evacuation, intestinal gas distribution and colonic microbiota in patients complaining of flatulence.

DESIGN

Patients complaining of flatulence (n=30) and healthy subjects (n=20) were instructed to follow their usual diet for 3 days (basal phase) and to consume a high-flatulogenic diet for another 3 days (challenge phase).

RESULTS

During basal phase, patients recorded more abdominal symptoms than healthy subjects in daily questionnaires (5.8±0.3 vs 0.4±0.2 mean discomfort/pain score, respectively; p=<0.0001) and more gas evacuations by an event marker (21.9±2.8 vs 7.4±1.0 daytime evacuations, respectively; p=0.0001), without differences in the volume of gas evacuated after a standard meal (262±22 and 265±25 mL, respectively). On flatulogenic diet, both groups recorded more abdominal symptoms (7.9±0.3 and 2.8±0.4 discomfort/pain, respectively), number of gas evacuations (44.4±5.3 and 21.7±2.9 daytime evacuations, respectively) and had more gas production (656±52 and 673±78 mL, respectively; p<0.05 vs basal diet for all). When challenged with flatulogenic diet, patients' microbiota developed instability in composition, exhibiting variations in the main phyla and reduction of microbial diversity, whereas healthy subjects' microbiota were stable. Taxa from Bacteroides fragilis or Bilophila wadsworthia correlated with number of gas evacuations or volume of gas evacuated, respectively.

CONCLUSIONS

Patients complaining of flatulence have a poor tolerance of intestinal gas, which is associated with instability of the microbial ecosystem.

Endogenous regulation of visceral pain via production of opioids by colitogenic CD4(+) T cells in mice

BACKGROUND & AIMS

A dysregulated response of CD4(+) T cells against the microbiota contributes to the development of inflammatory bowel disease. Effector CD4(+) T cells, generated in response to microbe-derived antigens, can reduce somatic inflammatory pain through the local release of opioids. We investigated whether colitogenic CD4(+) T cells that accumulate in the inflamed colon also produce opioids and are able to counteract inflammation-induced visceral pain in mice.

METHODS

Colitis was induced via transfer of naive CD4(+)CD45RB(high) T cells to immune-deficient mice or by administration of dextran sulfate sodium. Mice without colitis were used as controls. Samples of colon tissue were collected, and production of opioids by immune cells from inflamed intestine was assessed by quantitative polymerase chain reaction and cytofluorometry analyses. The role of intestinal opioid tone in inflammation-induced visceral hypersensitivity was assessed by colorectal distention.

RESULTS

In mice with T cell- or dextran sulfate sodium-induced colitis, colitogenic CD4(+) T cells (T-helper 1 and Th17 cells) accumulated in the inflamed intestine and expressed a high level of endogenous opioids. In contrast, macrophages and epithelial cells did not express opioids; opioid synthesis in the myenteric plexus was not altered on induction of inflammation. In mice with colitis, the local release of opioids by colitogenic CD4(+) T cells led to significant reduction of inflammation-associated visceral hypersensitivity.

CONCLUSIONS

In mice, colitogenic Th1 and Th17 cells promote intestinal inflammation and colonic tissue damage but have simultaneous opioid-mediated analgesic activity, thereby reducing abdominal pain.

Rome III functional constipation and irritable bowel syndrome with constipation are similar disorders within a spectrum of sensitization, regulated by serotonin

BACKGROUND & AIMS

Patients with irritable bowel syndrome with constipation (IBS-C) and patients with functional constipation (FC) have similar symptoms, and these disorders overlap in their diagnostic features. Little is known about their overlap in physiology or the involvement of serotonin signaling. We investigated relationships between platelet-depleted plasma concentrations of serotonin, gastrointestinal symptoms, and motor-sensory function in patients with FC or IBS-C compared with healthy volunteers (controls).

METHODS

We measured platelet-depleted plasma concentrations of serotonin in fasting and fed individuals with IBS-C (n = 23; 19-50 years old), FC (n = 11; 25-46 years old), and controls (n = 23; 20-49 years old) recruited in Manchester, UK. We also quantified abdominal and bowel-related symptoms, rectal sensitivity, oro-cecal transit, and colonic (whole intestine) transit.

RESULTS

Patients with IBS-C or FC had similar baseline symptoms, bowel habits, oro-cecal and colonic transit, and fasting concentrations of serotonin and response to meal ingestion. Only patients with IBS-C had increased symptoms after ingestion of a meal (P < .001)-these patients tended to have lower sensory thresholds than patients with FC. Defecation frequency in the combined group of patients with IBS-C or FC correlated inversely with serotonin concentration (r = -0.4; P = .03). Serotonin concentration also correlated with pain threshold (r = 0.4; P = .02) and stool threshold (r = 0.5; P = .06), which correlated inversely with defecation frequency (r = -0.3; P = .10).

CONCLUSIONS

FC and IBS-C, based on Rome III criteria, are not distinct disorders, symptomatically or physiologically. Instead, they appear to lie in a spectrum of visceral sensitivity modulated by serotonin signaling. Symptom response to meal ingestion should be considered in patient classification.