Action of polygodial on agonist-induced contractions of the rat portal vein in vitro.

This study investigated the vasorelaxant action of the sesquiterpene polygodial, isolated from the bark of Drymis winteri, on rat portal vein in vitro, contracted by various agonists. Polygodial (21-342 microM) preincubated 20 min before, produced graded antagonism of the contractile responses caused by bradykinin, endothelin-1, noradrenaline, the stable analogue of thromboxane A2 U46619, substance P, neurokinin B, and senktide (an NK3-selective agonist). Polygodial, at the same concentration, also produced graded inhibition of the contractile response induced by potassium chloride and by phorbol ester. At the median inhibitory concentration (IC50) level, polygodial was approximately 114- to 177-fold more active in inhibiting mediated contractions to senktide and phorbol ester. When assessed in the tonic contraction induced by endothelin-1 (0.5 nM) or by phorbol (3 microM), polygodial (0.1-100 microM) produced concentration-dependent relaxation, with maximal inhibition (E(max)) of 62 +/- 2% and 100%, respectively. Finally, polygodial (0.1-100 microM) inhibited the rhythmic spontaneous contractions of the rat portal vein (E(max) of 75 +/- 2%). Taken together, these results suggest that the vasorelaxant actions caused by polygodial in rat portal vein are, at least in part, associated with inhibition of calcium influx through voltage-sensitive channels and interaction with protein kinase C-dependent mechanisms. In addition, these data confirm and extend our previous suggestion that polygodial preferentially antagonizes tachykinin-mediated contraction, especially the NK3-mediated responses.

In vitro effect of the extract and the 1,7-dihydroxy-2,3-dimethoxy xanthone from Polygala cyparissias on the contractions induced by inflammatory mediators and ovalbumin in normal and actively sensitised trachea from guinea pig.

OBJECTIVE: This study describes the in vitro action of the hydroalcoholic extract and the 1,7-dihydroxy-2,3-dimethoxy xanthone isolated from P. cyparissias on agonist and ovalbumin induced contractions in trachea, from normal and actively sensitised guinea pigs. RESULTS: The hydroalcoholic extract of P. cyparissias (0.125 to 1 mg/ml), incubated with the guinea-pig trachea for 20 min, had no effect on the resting tone of the preparations, but caused a concentration-dependent, reversible and non competitive inhibition of contractions induced by acetylcholine, histamine, compound 48/80, bradykinin, substance P, prostaglandin E2 and the stable analogue of thromboxane A2 mimetic U 46619. The calculated mean IC50 values for the hydroalcoholic extract were: 0.37, 0.51, 0.06, 0.32, 0.48, 0.3 and 0.17 mg/ml, respectively. Also, the extract of P. cyparissias (0.125 to 0.5 mg/ml) antagonised, in a graded manner (IC50 of 0.46 mg/ml) ovalbumin-induced contractions in guinea-pig trachea obtained from animals which had been actively sensitised to this antigen. Pre-incubation of the preparations with the purifed xanthone isolated from P. cyparssias (2.5 to 80 microg/ml; 10.0 to 310.0 microM) caused significant and concentration-dependent, reversible and noncompetitive inhibition of the contractile responses elicited by acetylcholine, histamine, bradykinin, substance P, U 46619 and prostaglandin E2. The calculated mean IC50 values for these effects were: 132.0, 73.0, 9.2, 32.0, 110.6 and 66.0 microM, respectively. At very high concentrations (I55.0-620.0 microM) the xanthone also antagonised contraction induced by KCl in guinea-pig trachea (IC50 of 190.0 microM). CONCLUSIONS: Taken together these and our previous in vivo results are consistent with the view that the active principles present in P. cyparissias, including the 1,7-dihydroxy-2,3-dimethoxy xanthone, antagonise, in a non competitive but, reversible manner the contractions induced by chemical inflammatory mediators in the guinea pig trachea in vitro. Thus, these results might explain at least in part, the medicinal use of this plant in the management of inflammation, asthma and allergy.

Action of polygodial, a sesquiterpene isolated from Drymis winteri, in the guinea-pig ileum and trachea 'in vitro'.

This study describes the action of the sesquiterpene polygodial, the major constituent isolated from the bark of Drymis winteri in the guinea pig ileum and trachea in vitro. Polygodial (5 to 128 microM), added for 20 min, did not affect the resting tone of the preparations, but caused graded inhibition, associated in some cases with rightward displacement of the acetylcholine, histamine (1 nM to 10 microM), bradykinin (0.1 nM to 1 microM) and KCl (1 to 100 mM)-contraction response curves. When assessed in the guinea-pig trachea, polygodial (5 to 342 microM) caused significant inhibition of bradykinin (10 pM to 1 microM), 9,11-dideoxy-9alpha,11alpha-methano-epoxy prostaglandin F2alpha (0.1 to 1000 nM) and KCl (1 to 100 mM)-induced contractions, although the action against bradykinin was not concentration-dependent. Polygodial (5 to 80 microM) caused a small but significant shift to the right of substance P and also the selective agonist of tachykinin NK2 receptor [beta-Ala8]neurokinin A-(4-10)-induced contractions in guinea pig trachea. This action of polygodial seems to be quite selective towards tachykinin NK2 receptors since up to 432 microM, polygodial had no effect against contraction caused by tachykinin NK1 receptor agonist, substance P methyl ester. When tested in the guinea-pig trachea from animals which had been actively sensitised to ovalbumin, polygodial (30 to 40 microM) caused time and concentration-dependent inhibition of ovalbumin-mediated contraction. In addition, polygodial (85 to 342 microM) inhibited contraction induced by compound 48/80 (1 to 1000 microg/ml), in the guinea-pig trachea from non-sensitised animals. These findings and those from our previous study are consistent with the notion that the main sesquiterpene polygodial isolated from the bark of D. winteri is responsible for most, if not all, of the relevant pharmacological action reported previously for the extract of this plant. Thus, polygodial could be of potential value in the development of a new drug for the treatment of asthma, allergy and other inflammatory processes.