Abstract
Background:
To examine one possible mechanism for the observed relaxant effect of Viola odorata, in the present study the inhibitory effect of the extract of this plant on muscarinic receptors was examined.
Methods:
The effects of three concentrations of ethanolic extract, 10 nM atropine, and saline on muscarinic receptors were tested in three conditions: In non incubated tracheal smooth muscle (group I), tracheal chain incubated with propranolol and chlorpheniramine (group II), and the one incubated with propranolol (group III). The anticholinergic effect of Viola odorata was examined by producing the cumulative log concentration-response curve of methacholine hydrochloride (Sigma Chemical Ltd, Ltd UK) induced contraction of tracheal chains 10 min after exposure of the tissue to one solution of 10 nM atropine maleate (Sigma Chemical, UK) as well as three concentrations of ethanolic extract of Viola odorata (0.4, 0.8 and 1.2 mg/mL). The consecutive concentrations of methacholine were added every 2 min (range 0.1 - 1000 M); and the percentage of contraction (each concentration in proportion to the maximum contraction) obtained in the presence of saline, was plotted against log concentration of methacholine. The effective concentration of methacholine causing 50% of maximum response (EC50) in each experiment was measured using the log concentration-response curve of the corresponding experiment. Result: The EC50 obtained in the presence of all three concentrations of the extract were significantly higher compared to saline in groups II and III (P < 0.001and P < 0.01 in group II and III respectively). The EC50 obtained in the presence of all concentrations of the extract in group II were significantly improved compared to groups I and III (P < 0.05 to P < 0.001). The maximum responses to methacholine in presence of only the higher concentration of the extract (1.2 mg/mL) was significantly lower than that of saline in groups I (P < 0.05). There was neither significant difference between slopes of methacholine response curves obtained in the presence of different concentrations of the extract and that of saline nor between the three groups.
Conclusions:
The results of this study suggested a competitive antagonistic effect of Viola odorata at muscarinic receptors. The results also indicated a stimulatory effect for the extract at beta-adrenergic receptors and suggested a small inhibitory effect on histamine (H1) receptors.
Table 1: The maximum responses to methacholine obtained in the presence of only higher concentration of the extract in groups I (1.2 mg/ml) was significantly lower than that of saline (p < 0.05) . There was not statistical difference in maximum response between three groups.
Solutions
Concentration
Group I
Group II
Group III
Saline
100.00±0.00
100.00±0.00
100.00±0.00
Viola odorata
0.4 mg/mL
94.11±4.70
97.08±1.64
100.00±0.00
0.8 mg/mL
78.22±10.92
97.94±0.79
94.69±4.52
1.2 mg/mL
67.68±8.93*
93.76±4.80
85.79±8.02
Atropine
95.24±2.55
99.30±0.50
95.48±1.67
Get full access to this article
View all access options for this article.