Referenced in: none

Automatically associated channels: TRP , TRPV , TRPV1

Title: Inhibitory effect of Iboga-type indole alkaloids on capsaicin-induced contraction in isolated mouse rectum.

Authors: Mee Wah Lo, Kenjiro Matsumoto, Masumi Iwai, Kimihito Tashima, Mariko Kitajima, Syunji Horie, Hiromitsu Takayama

Journal, date & volume: J Nat Med, 2011 Jan , 65, 157-65

PubMed link: http://www.ncbi.nlm.nih.gov/pubmed/21042867

Abstract
Voacanga africana (Apocynaceae) is used as an anti-diarrheal medicine in West Africa. In the present study, we investigated the effect of an extract of V. africana and its constituents on smooth muscle contraction induced by capsaicin in mouse rectum, where transient receptor potential vanilloid type 1 (TRPV1)-immunoreactive fibers are abundant. Methanol and alkaloid extracts of the root bark of V. africana were found to inhibit capsaicin-induced contraction in a dose-dependent manner (30-300 μg/ml). Major constituents isolated from the alkaloid extract were then studied for their effects on the capsaicin-induced contraction. The main active constituents were found to be Iboga-type alkaloids, including voacangine (1), 3-oxovoacangine (2), voacristine (3), and (7α)-voacangine hydroxyindolenine (4). The voacangine concentration dependently (3-100 μM) inhibited the capsaicin-induced contraction. The capsaicin-induced contraction was almost completely inhibited by the TRPV1 antagonist, N-(4-tertiarybutylphenyl)-4-(3-chloropyridin-2-yl)tetrahydropyrazine-1(2H)-carbox-amide (BCTC). On the other hand, the Iboga-type alkaloids did not inhibit the contractions induced by 3 μM acetylcholine and 300 μM nicotine. These results suggest that Iboga-type alkaloids isolated from V. africana inhibit capsaicin-induced contraction in the mouse rectum, possibly via the inhibition of a TRPV1-mediated pathway. This inhibition may be involved in the anti-diarrheal effect of V. africana.