Red chili induces rectal hypersensitivity in healthy humans: possible role of 5HT-3 receptors on capsaicin-sensitive visceral nociceptive pathways.
BACKGROUND
Red chili has been reported to modulate visceral hypersensitivity, probably by the action of its active ingredient, capsaicin. The role of 5HT-3 receptors on capsaicin-sensitive visceral nociceptive pathways is unknown.


OBJECTIVE
To test the hypothesis that capsaicin-containing red chili induces rectal hypersensitivity in healthy humans and 5HT-3 receptors participate in this effect.


METHODS
Eighteen healthy volunteers, each underwent three rectal barostat studies under three conditions: (i) oral placebo; (ii) oral chili (5 g daily x 3 days); and (iii) oral chili with 1-mg intravenous (i.v.) granisetron, in randomized, double-blinded, cross-over fashions. Rectal sensation was evaluated by using a 5-point Likert scale.


RESULTS
Chili ingestion significantly decreased rectal threshold for first, moderate and severe urgency (18 +/- 0.9, 24 +/- 1.2, and 38 +/- 1.5 mmHg, respectively) compared with placebo (22 +/- 0.9, 31 +/- 1.3, and 45 +/- 1.4 mmHg, respectively, P < 0.01). The threshold for first, moderate and severe urgency after chili with i.v. granisetron was 20 +/- 0.9, 28 +/- 1.2 and 44 +/- 1.3 mmHg, respectively. This is a significant increase compared with chili ingestion without granisetron (P < 0.05). After placebo ingestion, i.v. granisetron produced no effect on rectal sensation compared with i.v. placebo in 10 healthy volunteers (P > 0.05).


CONCLUSIONS
Low-dose granisetron, a 5HT-3 receptor antagonist, partially reversed chili-induced rectal hypersensitivity but had no effect on rectal perception induced only by mechanical balloon distention. This study suggests that 5HT-3 receptors may be involved in chili-induced rectal hypersensitivity and potentially participate in the capsaicin-sensitive nociceptive pathways of the human gut.
GI Motility Research Unit, Division of Gastroenterology, Department of Internal Medicine, Chulalongkorn University, Rama 4 Road, Bangkok 10330, Thailand. gsutep@hotmail.com
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Gonlachanvit
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Fongkam
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Wittayalertpanya
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Kullavanijaya
D000328:Adult; D018712:Analgesics, Non-Narcotic / Q000008:administration & dosage* / Q000009:adverse effects / Q000494:pharmacology; D002211:Capsaicin / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*; D002212:Capsicum / Q000009:adverse effects / Q000502:physiology*; D018592:Cross-Over Studies; D005260:Female; D005772:Gastrointestinal Transit / Q000187:drug effects; D017829:Granisetron / Q000494:pharmacology; D006801:Humans; D007262:Infusions, Intravenous; D008297:Male; D008365:Manometry / Q000379:methods; D008875:Middle Aged; D011312:Pressure; D044406:Receptors, Serotonin, 5-HT3 / Q000502:physiology*; D012007:Rectum / Q000187:drug effects* / Q000502:physiology; D012677:Sensation / Q000187:drug effects*; D012684:Sensory Thresholds / Q000187:drug effects; D058831:Serotonin 5-HT3 Receptor Antagonists; D012702:Serotonin Antagonists / Q000494:pharmacology
D018712:Analgesics, Non-Narcotic; D002211:Capsaicin; D017829:Granisetron; D044406:Receptors, Serotonin, 5-HT3; D058831:Serotonin 5-HT3 Receptor Antagonists; D012702:Serotonin Antagonists