Possible involvement of muscarinic mechanisms in contractile response of guinea pig ileum by Erythrina velutina

The plant Erythrina velutina Willd (Fabaceae) is popularly used to combat pain and anxiety in Brazil [1]. We have recently reported that E. velutina (AEEV) produces an opioid-like antinociceptive effect in mice [2]. In the present study, we investigated the mechanism of action of AEEV in the guinea pig ileum. E. velutina leaves, collected in Brazil (10€56'S, 37€05'W), were infused and lyophilized (8.32%). Terminal segments of guinea pig ileum (n=5–8) were mounted in an organ bath and isotonic contractions were recorded. AEEV (0.05–2.5mg/mL) contracted the guinea pig ileum (0.86±0.31g –1.45±0.16g) and increased neurogenic contractions (0.1Hz; 0.5 ms; 40 V) by a maximum of 57.7±9.1% (p<0.01). Tetrodotoxine (1µM; p<0.01; 38.2±2.5%), a neuronal sodium channel blocker, and the muscarinic receptor antagonist atropine (10µM; p<0.01; 38.7±13.2%) reduced contractile response induced by aqueous extract (1.5mg/mL). Verapamil (10 nM; 52.4±9.8%; p<0.01), an L-type Ca⁺² channel blocker, or low Ca⁺² concentration (76.0±6.1%; p<0.05) also reduced the contractile response to AEEV. Atropine (10µM) along with verapamil (10 nM) abolished AEEV-induced contractile response (p<0.001; 98.1±1.4%). In conclusion, an opioid-like response could not be detected in the guinea pig ileum. Indeed, these results suggest that the contractile response of the aqueous extract of Erythrina velutina involves a neurotransmitter release, possibly acetylcholine, muscarinic receptor activation, augmentation of Ca⁺² entry through L-type calcium channels and calcium release from the intracellular stores.

Acknowledgments: CNPq.

References: 1. Dantas, M.C. et al. (2004), J. Ethnopharmacol. 94: 12. 2. Marchioro, M. et al. (2005), Fitoterapia 76: 637.