Pharmacological evidence of the mechanisms of action of Phoradendron piperoides Kunth (Viscaceae) aqueous extract

The infusion from the leaves of Phoradendron piperoides is commonly used to soothe abdominal pain in Brazil [1]. We have recently reported that the lyophilized extract from the leaves of P. piperoides (AE) did not produce an antinociceptive effect in mice, whereas it produced relaxing responses in the guinea-pig intestinal smooth muscle [1]. Here, we have investigated the effect of the AE on normal intestinal transit in mice and the mechanisms of action in the isolated guinea-pig ileum. AE (200–500mg/kg, p.o.; p<0.05) significantly reduced the intestinal transit in the charcoal meal test when compared to atropine (2mg/kg; p.o.). In the guinea-pig ileum, the contractions induced by histamine (2µM), carbachol (2µM) and BaCl₂ (0.03M) were significantly (p<0.01) reduced in the presence of the AE (1.5mg/ml). AE (0.05–2.0mg/ml) reduced, in a concentration-dependent fashion, the contractions induced by KCl (60 mM). This effect is probably due to inhibition of calcium influx through voltage-operated calcium (Ca(v)) channels. To confirm this hypothesis, we evaluated their effect on cumulative CaCl₂ curves in depolarizing medium nominally without Ca²⁺. The CE₅₀ of CaCl₂ concentration-response curves did not change in the presence of AE (1.5mg/ml)_. However, AE (1.5 and 3.0mg/ml) reduced, in a nonreversible fashion, the E(max) of CaCl₂ concentration-response curves. Finally, propranolol (5µM) along with yohimbine (1µM) and prazocin (1µM) antagonized norepinephrine (0.3µM) and AE (1.5mg/ml) relaxing responses. In brief, the effect of AE is probably due to a blockade of calcium influx through Ca(v) channels and adrenergic receptor activation.

Acknowledgements: CNPq, FINEP

References: [1] Dias, K.S. et al. (2007) Braz. J. Pharmacognosy, [accepted].