Spasmolytic effect of Alternanthera repens on isolated rat ileum

Context: Alternanthera repens (L.) Kuntze (Amaranthaceae) is widely used in Mexican traditional medicine for the treatment of gastrointestinal disorders that are mainly related to diarrhea. Objective: The aim of the present study was to investigate the spasmolytic effect of hexane (Hx), methanol (Me) and aqueous (Aq) extracts as well as chromatographic Me fractions (F1-F6) of A. repens in rat ileum. Materials and methods: Dried and powdered aerial parts were used to obtain the extracts. The rat ileum preparations were incubated in Tyrode's solution gassed (95% O₂-5% CO₂) at 37 °C. The effect on the contractile response of isolated ileum was evaluated by obtaining cumulative concentration-response curves to CaCl₂, KCl, 5-HT and acetylcholine in the absence and presence of different doses of Aq (0.56-2.09 mg/mL), Me (0.24-0.91 mg/mL) and Hx (0.24-0.91 mg/mL) extracts, as well as six Me fractions of 0.66 mg/mL (F1 to F6). Results: The A. repens Me (0.24-mg/mL) caused an inhibitory response of the Ca²⁺-induced contractions, with IC₅₀ values of 0.18 ± 0.061 and 0.67 ± 0.061 mM in the presence and absence of the Me, respectively. Me fractions F2 to F4 presented a significant inhibitory effect (F_(3,8) = 60.17, p = 0.0001), causing a reduction in the CaCl₂-induced contractions and shifting the Ca²⁺ (0.39 to 1.81 mM) concentration-response curves to the right. With respect to the effect on 5-HT-induced contractions, IC₅₀ values Hx extract (0.24 mg/mL) were 5.44 ± 0.08 × 10^-6 M and 3.38 ± 0.07 × 10^-6 M in the presence and absence of the Hx, respectively. Discussion and conclusion: The spasmolytic effects induced by Me and Me fractions of A. repens may involve a serotonergic and Ca²⁺ influx blockade mechanisms, which may justify the use of A. repens extracts as an effective traditional treatment against diarrhea.