Calcium antagonistic activity of Bacopa monniera on vascular and intestinal smooth muscles of rabbit and guinea-pig

Abstract

The present study demonstrates the calcium antagonistic activity in ethanol extract of Bacopa monniera. The plant extract inhibited the spontaneous movements of both guinea-pig ileum (IC₅₀=24±4 μg/ml) and rabbit jejunum (IC₅₀=136±9 μg/ml). A marked reduction in acetylcholine- and histamine-induced responses (0.0001–10 μM) in the ileum was evident in the presence of extract (260 μg/ml). The acetylcholine (1 μM)-induced contraction in the ileum was also inhibited by the extract (100–700 μg/ml) in a concentration dependent way (IC₅₀=285±56 μg/ml). All these results indicate a direct action of the extract on smooth muscles. Calcium chloride-induced responses in the rabbit blood vessels and jejunum were attenuated in the presence of plant extract (10–700 μg/ml) implying a direct interference of plant extract with influx of calcium ions in the cells. However, the lack of modification of either noradrenaline- or caffeine-induced contractions in the presence of extract suggests that extract has no detectable effect on mobilization of intracellular calcium. These results indicate that spasmolytic effect of the B. monniera extract in smooth muscles is predominantly due to inhibition of calcium influx via both voltage and receptor operated calcium channels of the cell membrane.

Introduction

Bacopa monniera syn. Herpestis monniera, Linn. (Scrophulariaceae), herbaceous plant is widely distributed throughout the Indo-Pakistan subcontinent (Nadkarni, 1976). It is found in wet and marshy areas and is locally called ‘Brahmi’.

Plant constituents that have been identified include compounds like saponins: bacoside A and B (Chatterji et al., 1963; Chatterji et al., 1965), stigmasterol (Banerjee and Chakravarti, 1963), sapogenins: bacogenin A₁, A₂ and A₃ (Basu et al., 1967), and flavonoides: luteolin and luteolin-7 glucoside (Schulte et al., 1972). Other compounds like triterpenoid saponins (Garai et al., 1996) and different alkaloids: nicotine, brahmine and herpestine (Chopra et al., 1956; Schulte et al., 1972) have also been reported.

Recently, we demonstrated that the ethanol extract of B. monniera plant possessed smooth muscle relaxant properties with a partial contribution by β-adrenoceptors and prostaglandins (Dar and Channa, 1997a). B. monniera also produced bronchodilation in anaesthetized rats (Dar and Channa, 1997b) which not only supported our earlier findings but also the traditional use of this plant in folklore medicine for various respiratory ailments (Chopra et al., 1956; Nadkarni, 1976). Consequently, the present study was performed with the aim of evaluating the action of ethanol extract of B. monniera on smooth muscle preparations, in particular to define its role in the calcium mobilization.