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. AIM: 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.

RCT Entities:   Population Interventions Outcomes