PHYTOTHERAPY RESEARCH, VOL.

11, 323–325 (1997)

SHORT COMMUNICATION
Relaxant Effect of Ethanol Extract of Bacopa
monniera on Trachea, Pulmonary Artery and
Aorta from Rabbit and Guinea-pig

Ahsana Darw and Shabana Channa

Pharmacology Section, HEJ Research Institute of Chemistry, University of Karachi, Karachi-75270, Pakistan

The relaxant action of an ethanol extract of Bacopa monniera was examined on ring segments of pulmonary
arteries (guinea-pig and rabbit), aorta (rabbit) and tracheal preparations (guinea-pig). The plant extract induced
relaxation in all the tissues in a dose-dependent manner. Guinea-pig main pulmonary artery was found to be the
most responsive to the plant extract, however, complete relaxation was obtained in the tracheal preparations. The
relaxant response to the plant extract was unaffected by pretreatment of the blood vessels with either atropine
or propranolol, whereas in the tracheal preparations propranolol partially blocked the response. Indomethacin
reduced the plant extract-induced relaxation in all the tissues. In blood vessels relaxation induced by the plant
extract was not modified in the presence or absence of the endothelial layer. These results suggest that relaxation
induced by Bacopa monniera possibly involves prostacyclin compounds (in all the tissues) and b-adrenoceptors
(in tracheal preparations). Furthermore, this relaxation is independent of endothelium and muscarinic receptors
activation. © 1997 by John Wiley & Sons, Ltd.

Phytother. Res. 11, 323–325 (1997)

No. of Figures: 0. No. of Tables: 2. No. of References: 11

Keywords: Bacopa monniera; relaxant effect; tracheal chain; pulmonary arteries; aorta.

INTRODUCTION MATERIALS AND METHODS

Plant material and extraction procedure. Leaves and stalks of

Bacopa monniera (L) syn. Herpestis monniera Linn (N.O. Bacopa monniera (330 g) were extracted in 95% ethanol to
scrophulariaceae) is a herbaceous plant and is widely obtain a plant extract (30 g).
distributed throughout the Indo-Pakistan subcontinent. In
folklore medicine it is used for the cure of various ailments Animals. Rabbits (1.04 ± 0.04 kg) and guinea-pigs
including bronchitis, inflammation and asthma (Nadkarni, (444 ± 17 g) of either sex were used. Main pulmonary artery
1976). An alcohol extract of Bacopa monniera had a (MPA), aorta (AO) and trachea (TRA) were kept in
sedative effect on frogs, dogs, rats and guinea-pigs (Malho- modified Krebs’–Henseleit solution with the following
tra and Das, 1959). Histamine-induced contraction was composition (mM): NaCl, 118; KCl, 4.57; CaCl2, 1.27;
reduced by the extract in the guinea-pig tracheal chain MgSO4, 1.19; KH2PO4, 1.19; NaHCO3, 25 and glucose,
(Aithal and Sirsi, 1961). 5.55.
Chemical constituents that have been identified from this
plant include alkaloids, brahmine and herpestine as well as
Drugs used. Acetylcholine chloride, atropine sulphate,
glycoside saponins, bacoside A and B (Dutta and Basu,
histamine dihydrochloride, indomethacin, phenylephrine
1963; 1968). Total alkaloidal fractions of Bacopa monniera
hydrochloride and propranolol hydrochloride were obtained
produced spasm of the skeletal muscle and initial stimula-
from Sigma Chemicals, USA. BM was suspended in 5%
tion of respiration followed by depression (Das et al., 1961).
dimethylsulphoxide (DMSO).
Despite its use in folklore medicine for curing various
The BM extract was evaluated for its relaxant effect on
respiratory ailments the relaxant action of Bacopa monniera
the blood vessels (MPA, guinea-pig and rabbit and AO,
has not been reported so far on isolated systemic and
rabbit) and trachea (guinea-pig).
pulmonary blood vessels. We have made an attempt to
elucidate the activity of the ethanol extract of Bacopa
Blood vessels and tracheal chain. The MPA and AO ring
monniera (BM) on isolated tissues from different animal
segments (2–3 mm) or tracheal chain (Grover, 1990)
species, i.e. rabbit and guinea-pig.
comprising four rings (3–4 mm) were excised and mounted
on a stainless steel hook connected to a FTO3 force-
displacement transducer attached to 7 D Grass polygraph
w
Correspondence to: A. Dar, Pharmacology Section, HEJ Research and the other end of the ring was attached to the gas tubing.
Institute of Chemistry, University of Karachi, Karachi-75270, Pakistan. The organ baths were filled with 10 or 20 mL of Kreb’s
Contract grant sponsor: Wellcome Pakistan Ltd. solution, maintained at 37°C and bubbled continuously with

CCC 0951–418X/97/040323–03 $17.50 Accepted (revised) 6 November 1996

© 1997 by John Wiley & Sons, Ltd.
324 A. DAR AND S. CHANNA

5% CO2 in O2 at a pH of 7.4. A resting tension of 1.5 g Table 2. EC50 values of Bacopa monniera in blood vessels and
(MPA), 2 g (AO) and 1 g (TRA) was applied and the tissues trachea from guinea-pig and rabbit
were allowed to equilibrate for 1 h. EC50
Animal Tissue n (mg/mL)
MPA 4 312.5 ± 31
Relaxation experiments. Prior to the addition of BM to the
Guinea-pig
various tissues a stable response was monitored for TRA 4 500.0 ± 25b
15–30 min followed by a change of Kreb’s solution. The MPA 3 b
443.0 ± 38a
reduction in the tension induced by BM was noted. Rabbit
Relaxation was expressed as the percent decline of the AO 4 a
309.0 ± 23
tension induced by phenylephrine (Phe) or histamine (Hist)
MPA, main pulmonary artery; TRA, tracheal chain; AO, aorta. n
in blood vessels or tracheal chain, respectively. is the number of animals used in experiments. Values shown are
mean ± SEM.
Statistical analysis. The results presented are mean ± SEM. Significant differences (ap < 0.05 and bp < 0.005) with the respec-
The statistical significance of differences between two tive values showing arrows.
means (p < 0.05) were estimated by Student’s t-test for
paired data.
physiological solvent and may have allowed various
compounds to be solubilized and to exert their effect, hence
complete relaxation was seen.
RESULTS AND DISCUSSION Table 2 depicts EC50 values obtained for BM responsible
for relaxation of blood vessels and tracheal preparations.
The toxicity of BM (10–3000 mg/kg) was determined in Based on EC50 values the order of potency of BM as the
mice (NMRI, 24.7 ± 0.23 g). BM (10–200 mg/kg) produced relaxant agent for various tissues is MPA (guinea-pig)
no change in the behavioural response of mice with a LD50 = AO > MPA (rabbit) > TRA. It is clear that both MPA
of 520 mg/kg. (guinea-pig) and AO are equally, as well as most, sensitive
Bacopa monniera did not exert any effect on the basal to the relaxation elicited by BM and that TRA is least
tone of either blood vessels or tracheal but when basal tone sensitive of all the tissues tested and these differences were
was raised by contractile agents, i.e. Phe (blood vessels) or significant. Clearly significant species differences were
Hist (trachea), a dose-dependent relaxant effect was evident evident between the guinea-pig and rabbit regarding the
(Table 1). Addition of BM at 100–200 mg/mL (in rabbit) EC50 values. Although BM for MPA had a lower EC50 than
and 100–300 mg/mL (in guinea-pig) caused a non-sign- the tracheal preparations from guinea-pig, the trachea
ificant reduction. However, significant dose-dependent showed complete relaxation (Table 1) in the presence of BM
reductions in Phe or Hist-induced contractions were possibly due to functional intrinsic differences between
observed at doses above 200 (rabbit) or 300 mg/mL (guinea- vascular and airway smooth muscles, resulting in the
pig) of BM. The vasorelaxant action of BM is reported for inability of the blood vessels to be completely relaxed at
the first time here. However, Aithal and Sirsi (1961) higher doses. Furthermore, the BM-induced relaxant effect
reported a 75% relaxation of the guinea-pig tracheal chain at was long lasting up to 2 h in the tracheal preparations
3.5 mg/mL of Bacopa monniera extract. Whereas complete compared with the blood vessels. This property of BM may
relaxation of the tracheal chain at comparatively lower partially account for the use of this plant as an antiasthmatic
doses of BM (700 mg/mL) was obtained in the present agent in traditional medicine.
investigation. This discrepancy may be due to various Preliminary experiments to understand the mechanism of
reasons, possibly due to the differences in the extraction the relaxant action of BM in the presence of various
procedure employed in the different laboratories or different antagonists such as atropine, propranolol and indomethacin
solvents used to solubilize the plant extract. It is important were investigated. These experiments were conducted in the
to mention that we used DMSO (5%) which is an excellent presence of different antagonists using an , ED70 concen-
tration of BM and of contractile agent for the respective
tissue.
Table 1. Percent relaxation induced by different doses of Blood vessels have been shown to be relaxed in response
ethanol extract of Bacopa monniera on blood vessels to acetylcholine via the release of endothelium-derived
and trachea from guinea-pig and rabbit
Percent relaxation
relaxing factor(s), (EDRF, Furchgott and Zawadzki, 1980).
Dose Guinea-pig Rabbit In the present work it was used as an important criterion for
(mg/mL) MPA TRA MPA AO
judging the integrity of the endothelium. However, BM
100 1.3 ± 1 3.3 ± 1 4 ± 2.5 8±2 produced relaxation in both endothelium intact and denuded
200 33 ± 2 9 24 ± 6 9±3
blood vessels. Thus it can be said with certainty that the
300 37 ± 8 12 ± 5 30 ± 10a 26 ± 9a
400 57 ± 4c 23 ± 6a 40 ± 11a 44 ± 6a
BM-induced relaxation is independent of endothelial
500 62 ± 8c 66 ± 10b 50 ± 6c 62 ± 8a released substances, thereby ruling out the involvement of
600 69 ± 3c 78 ± 9c 75 ± 10c 51 ± 4b EDRF.
700 74 ± 13b 100 ± 0c 90 ± 8c 48 ± 12a Atropine is a known competitive antagonist of muscarinic
Control 899 ± 97 423.5 ± 26 1458 ± 97 1330 ± 125 receptors (Arunlakshana and Schild, 1959). Pretreatment of
(mg tension) the blood vessels from rabbit and guinea-pig remained
MPA, main pulmonary artery; TRA, tracheal chain; AO, aorta. unaltered in the presence of atropine (0.1 mM) suggesting
The contractile agent in the blood vessels and trachea was that the BM mediates its relaxant action through a
phenylephrine and histamine, respectively. mechanism independent of muscarinic receptor activation.
Values are mean ± SEM. Propranolol is a non-specific b-adrenoceptor blocking
Asterisks indicate significant percent relaxation (ap < 0.05,
b
p < 0.01 and cp < 0.005) compared with the control. agent (Hoffman and Lefkowitz, 1990) and abolished the
effect of isoprenaline in the blood vessels from guinea-pig

Phytother. Res. VOL. 11, 323–325 (1997) © 1997 by John Wiley & Sons, Ltd.
 RELAXANT EFFECT OF B. MONNIERA 325

and rabbit. The BM-induced relaxation in the presence of prostaglandin compounds. This important information
propranolol (0.1 mM) remained unchanged in blood vessels, needs to be further investigated.
thus ruling out the relaxant effect through the stimulation of Considering the fact that the plant extract used is still in
b-adrenoceptors. However, the situation for the tracheal its crude form and possibly contains many compounds with
preparations was different as the propranolol partially perhaps one or two active principle(s), bioassay directed
reduced (24%) the BM-induced relaxation implying that the fractionation is in progress which may elucidate the active
BM in the trachea may activate b2-adrenoceptors. compounds responsible for the relaxant action of Bacopa
Interestingly in all the tissues studied BM-induced monniera.
relaxation was inhibited by indomethacin (0.1 mM) (a
cyclooxygenase inhibitor, Rang and Dale, 1987) so it may
be inferred that the BM may stimulate the cyclooxygenase Acknowledgements
pathway. Despite the different species and tissues used in This study was partly supported by the Wellcome Pakistan Limited.
the present work, BM-induced relaxation was consistently Professor Atta-ur-Rahman’s group prepared the ethanol extract of the
inhibited by indomethacin indicating a universality of the plant.

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© 1997 by John Wiley & Sons, Ltd. Phytother. Res. VOL. 11, 323–325 (1997)