Abstract
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.
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