CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 1, February 2012
12
AFRICA
Contractile effect of
Sclerocarya birrea
(A Rich) Hochst
(Anacardiaceae) (Marula) leaf aqueous extract on rat and
rabbit isolated vascular smooth muscles
TARIRO MAWOZA, JOHN AO OJEWOLE, PETER MO OWIRA
Abstract
Background: Sclerocarya birrea
(Anacardiaceae) is tradition-
ally used for treating hypertension. The pharmacological
effects of
S birrea
leaf aqueous extract (SBE) on rabbit and
rat vascular smooth muscles were investigated in this study.
Methods:
Fresh
S birrea
leaves (1 kg) were air dried at 26
±
1°C, milled, macerated in 2.5 l of distilled water for 48
hours, filtered, and the filtrate was concentrated in a rotary
evaporator. Rat isolated portal vein preparations, as well
as rabbit isolated endothelium-denuded and endothelium-
intact descending thoracic aortic ring preparations were
mounted in 30-ml Ugo Basile organ baths under physiologi-
cal conditions, and challenged with SBE (50–400 mg/ml). The
contractile effects of SBE and/or other reference drugs on the
isolated vascular smooth muscle preparations were recorded
by means of Ugo Basile’s force–displacement transducers
and Gemini recorders.
Results:
SBE (50–400 mg/ml) caused a significant, concen-
tration-dependent upward shift in baseline tone in the
aortic ring preparations (
p
<
0.01–0.001). Indomethacin
(20
µ
M) markedly attenuated the contractile effects of SBE
in both the endothelium-intact and -denuded aortic rings,
while N
G
-nitro-
L
-arginine methyl ester (L-NAME, 100
µ
M)
significantly (
p
<
0.05) increased the contractile tension of
the endothelium-intact aortic rings. Verapamil (1–3
µ
g/ml)
partially inhibited the contractile effects of SBE. SBE also
elicited significant (
p
<
0.05–0.01) increases in the ampli-
tude of the myogenic contractions of the portal veins. These
contractions were abolished by verapamil (1–3
μ
g/ml) in a
concentration-dependent manner, while prazosin (1–3
μ
g/ml)
did not affect the SBE-induced contractions.
Conclusion:
SBE possessed spasmogenic effects on vascular
smooth muscle preparations
in vitro
. It may induce and/or
exacerbate hypertension, contrary to the folkloric, ethno-
medical use of
S birrea
.
Keywords:
Sclerocarya birrea
, contraction, vascular smooth
muscles
Submitted 29/6/10, accepted 26/11/10
Cardiovasc J Afr
2012;
23
: 12–17
DOI: 10.5830/CVJA-2010-098
Sclerocarya birrea
(A Rich) Hochst (family: Anacardiaceae),
popularly known as the cider or marula tree in English,
maroele
in Afrikaans, or
umganu
in IsiZulu, is a medium-sized, single-
stemmed, perennial, deciduous tree with grey-fissured bark,
stout branchlets and pale foliage.
1
The tree is native to sub-
Saharan Africa,
2
with different species distributed from Ethiopia
to KwaZulu-Natal Province in South Africa,
3
where it is widely
used by local communities as a source of food and for ethno-
medical as well as cultural practices.
4-6
In South Africa, the stem bark, roots and leaves of
S birrea
have traditionally been used to treat human ailments such as
infections (malaria, fever, diarrhoea, dysentery, schistosomia-
sis) and degenerative diseases (stomach disorders, headaches,
toothache, high blood pressure, backache, dysmenorrhoea,
body pains, diabetes mellitus, arthritis).
7-10
The Zulus of South
Africa have also used decoctions of
S birrea
stem bark and
leaf aqueous extracts
as enemas for diarrhoea and for prophy-
laxis against gangrenous rectitis,
8,11
dysentery, fevers, stomach
ailments, ulcers and bacterial-related diseases.
11
The Vhavenda of
Limpopo Province in South Africa reportedly use the stem bark
of
S birrea
for treating fevers, stomach ailments and ulcers.
12
In other rural African communities, chewing fresh leaves of
S
birrea
and swallowing the astringent juice has been reported to
help with indigestion.
9
Ethnomedicinal use of the extracts of
S birrea
in the treatment
of stomach ailments and high blood pressure, among others,
suggests that certain chemical constituents in these extracts may
affect smooth muscle contractility. In an attempt to provide a
pharmacological rationale (or otherwise) for the folkloric and
ethnomedicinal uses of the extracts of this plant in the treatment
of diseases affecting vascular smooth muscles, the present study
was undertaken to investigate the contractile effects of
S birrea
leaf aqueous extract (SBE) on mammalian isolated vascular
smooth muscles. We hypothesised that if SBE possesses anti-
hypertensive effects, this would justify its folkloric use in the
management of hypertension. If, however, SBE induces contrac-
tile effects on vascular smooth muscles, it would be contraindi-
cated in hypertensive patients.
Methods
Experimental protocols and procedures used in this study were
approved by the Animal Ethics Committee of the University of
KwaZulu-Natal and conformed to the
Guide to the Care and Use
of Animals in Research and Teaching
, published by the Animal
Ethics Committee of the University of KwaZulu-Natal, Durban,
South Africa.
Fresh leaves of
S birrea
were collected from an open
grassland field on the Westville campus of the University of
KwaZulu-Natal, Durban. Identification and authentication of the
plant material were done by the taxonomist/curator of the Botany
Department of Pharmacology, School of Pharmacy and
Pharmacology, Faculty of Health Sciences, University of
KwaZulu-Natal, Durban, South Africa
TARIRO MAWOZA, MSc
JOHN AO OJEWOLE, BPharm, MPharm, PhD
PETER MO OWIRA, PhD,
